https://openjdk.java.net/ 
/*
 * Copyright (c) 1995, 2017, Oracle and/or its affiliates. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
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 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
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 * questions.
 */

package java.net;

import java.io.IOException;
import java.io.InputStream;
import java.io.OutputStream;
import java.security.PrivilegedAction;
import java.util.Hashtable;
import java.util.concurrent.ConcurrentHashMap;
import java.util.Date;
import java.util.Iterator;
import java.util.Locale;
import java.util.Objects;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;
import java.util.StringTokenizer;
import java.util.Collections;
import java.util.Map;
import java.util.List;
import java.security.Permission;
import java.security.AccessController;
import sun.security.util.SecurityConstants;
import sun.net.www.MessageHeader;
import sun.security.action.GetPropertyAction;


The abstract class URLConnection is the superclass of all classes that represent a communications link between the application and a URL. Instances of this class can be used both to read from and to write to the resource referenced by the URL. 

In general, creating a connection to a URL is a multistep process:

    

  1. The connection object is created by invoking the openConnection method on a URL. 
  2. The setup parameters and general request properties are manipulated.

  3. The actual connection to the remote object is made, using the connect method. 
  4. The remote object becomes available. The header fields and the contents
    of the remote object can be accessed.




The setup parameters are modified using the following methods:

    
  
  • setAllowUserInteraction 
  • setDoInput 
  • setDoOutput 
  • setIfModifiedSince 
  • setUseCaches 



and the general request properties are modified using the method:

    
  
  • setRequestProperty 


 Default values for the AllowUserInteraction and UseCaches parameters can be set using the methods setDefaultAllowUserInteraction and setDefaultUseCaches. 
 Each of the above set methods has a corresponding get method to retrieve the value of the parameter or general request property. The specific parameters and general request properties that are applicable are protocol specific. 

The following methods are used to access the header fields and
the contents after the connection is made to the remote object:

    
  
  • getContent 
  • getHeaderField 
  • getInputStream 
  • getOutputStream 



Certain header fields are accessed frequently. The methods:

    
  
  • getContentEncoding 
  • getContentLength 
  • getContentType 
  • getDate 
  • getExpiration 
  • getLastModified 


 provide convenient access to these fields. The getContentType method is used by the getContent method to determine the type of the remote object; subclasses may find it convenient to override the getContentType method. 
 In the common case, all of the pre-connection parameters and general request properties can be ignored: the pre-connection parameters and request properties default to sensible values. For most clients of this interface, there are only two interesting methods: getInputStream and getContent, which are mirrored in the URL class by convenience methods. 
 More information on the request properties and header fields of an http connection can be found at: 
http://www.ietf.org/rfc/rfc2616.txt

 Invoking the close() methods on the InputStream or OutputStream of an URLConnection after a request may free network resources associated with this instance, unless particular protocol specifications specify different behaviours for it. 
Author: James Gosling
See Also:
Since:  1.0
/**
 * The abstract class {@code URLConnection} is the superclass
 * of all classes that represent a communications link between the
 * application and a URL. Instances of this class can be used both to
 * read from and to write to the resource referenced by the URL.
 *
 * <p>
 * In general, creating a connection to a URL is a multistep process:
 * <ol>
 * <li>The connection object is created by invoking the
 *     {@link URL#openConnection() openConnection} method on a URL.
 * <li>The setup parameters and general request properties are manipulated.
 * <li>The actual connection to the remote object is made, using the
 *    {@link #connect() connect} method.
 * <li>The remote object becomes available. The header fields and the contents
 *     of the remote object can be accessed.
 * </ol>
 * <p>
 * The setup parameters are modified using the following methods:
 * <ul>
 *   <li>{@code setAllowUserInteraction}
 *   <li>{@code setDoInput}
 *   <li>{@code setDoOutput}
 *   <li>{@code setIfModifiedSince}
 *   <li>{@code setUseCaches}
 * </ul>
 * <p>
 * and the general request properties are modified using the method:
 * <ul>
 *   <li>{@code setRequestProperty}
 * </ul>
 * <p>
 * Default values for the {@code AllowUserInteraction} and
 * {@code UseCaches} parameters can be set using the methods
 * {@code setDefaultAllowUserInteraction} and
 * {@code setDefaultUseCaches}.
 * <p>
 * Each of the above {@code set} methods has a corresponding
 * {@code get} method to retrieve the value of the parameter or
 * general request property. The specific parameters and general
 * request properties that are applicable are protocol specific.
 * <p>
 * The following methods are used to access the header fields and
 * the contents after the connection is made to the remote object:
 * <ul>
 *   <li>{@code getContent}
 *   <li>{@code getHeaderField}
 *   <li>{@code getInputStream}
 *   <li>{@code getOutputStream}
 * </ul>
 * <p>
 * Certain header fields are accessed frequently. The methods:
 * <ul>
 *   <li>{@code getContentEncoding}
 *   <li>{@code getContentLength}
 *   <li>{@code getContentType}
 *   <li>{@code getDate}
 *   <li>{@code getExpiration}
 *   <li>{@code getLastModified}
 * </ul>
 * <p>
 * provide convenient access to these fields. The
 * {@code getContentType} method is used by the
 * {@code getContent} method to determine the type of the remote
 * object; subclasses may find it convenient to override the
 * {@code getContentType} method.
 * <p>
 * In the common case, all of the pre-connection parameters and
 * general request properties can be ignored: the pre-connection
 * parameters and request properties default to sensible values. For
 * most clients of this interface, there are only two interesting
 * methods: {@code getInputStream} and {@code getContent},
 * which are mirrored in the {@code URL} class by convenience methods.
 * <p>
 * More information on the request properties and header fields of
 * an {@code http} connection can be found at:
 * <blockquote><pre>
 * <a href="http://www.ietf.org/rfc/rfc2616.txt">http://www.ietf.org/rfc/rfc2616.txt</a>
 * </pre></blockquote>
 *
 * Invoking the {@code close()} methods on the {@code InputStream} or {@code OutputStream} of an
 * {@code URLConnection} after a request may free network resources associated with this
 * instance, unless particular protocol specifications specify different behaviours
 * for it.
 *
 * @author  James Gosling
 * @see     java.net.URL#openConnection()
 * @see     java.net.URLConnection#connect()
 * @see     java.net.URLConnection#getContent()
 * @see     java.net.URLConnection#getContentEncoding()
 * @see     java.net.URLConnection#getContentLength()
 * @see     java.net.URLConnection#getContentType()
 * @see     java.net.URLConnection#getDate()
 * @see     java.net.URLConnection#getExpiration()
 * @see     java.net.URLConnection#getHeaderField(int)
 * @see     java.net.URLConnection#getHeaderField(java.lang.String)
 * @see     java.net.URLConnection#getInputStream()
 * @see     java.net.URLConnection#getLastModified()
 * @see     java.net.URLConnection#getOutputStream()
 * @see     java.net.URLConnection#setAllowUserInteraction(boolean)
 * @see     java.net.URLConnection#setDefaultUseCaches(boolean)
 * @see     java.net.URLConnection#setDoInput(boolean)
 * @see     java.net.URLConnection#setDoOutput(boolean)
 * @see     java.net.URLConnection#setIfModifiedSince(long)
 * @see     java.net.URLConnection#setRequestProperty(java.lang.String, java.lang.String)
 * @see     java.net.URLConnection#setUseCaches(boolean)
 * @since   1.0
 */
public abstract class URLConnection {

   
The URL represents the remote object on the World Wide Web to
which this connection is opened.

 The value of this field can be accessed by the getURL method. 
 The default value of this variable is the value of the URL argument in the URLConnection constructor. 
See Also:
/**
     * The URL represents the remote object on the World Wide Web to
     * which this connection is opened.
     * <p>
     * The value of this field can be accessed by the
     * {@code getURL} method.
     * <p>
     * The default value of this variable is the value of the URL
     * argument in the {@code URLConnection} constructor.
     *
     * @see     java.net.URLConnection#getURL()
     * @see     java.net.URLConnection#url
     */
    protected URL url;

   
This variable is set by the setDoInput method. Its value is returned by the getDoInput method. 
 A URL connection can be used for input and/or output. Setting the doInput flag to true indicates that the application intends to read data from the URL connection. 
 The default value of this field is true. 
See Also:
/**
     * This variable is set by the {@code setDoInput} method. Its
     * value is returned by the {@code getDoInput} method.
     * <p>
     * A URL connection can be used for input and/or output. Setting the
     * {@code doInput} flag to {@code true} indicates that
     * the application intends to read data from the URL connection.
     * <p>
     * The default value of this field is {@code true}.
     *
     * @see     java.net.URLConnection#getDoInput()
     * @see     java.net.URLConnection#setDoInput(boolean)
     */
    protected boolean doInput = true;

   
This variable is set by the setDoOutput method. Its value is returned by the getDoOutput method. 
 A URL connection can be used for input and/or output. Setting the doOutput flag to true indicates that the application intends to write data to the URL connection. 
 The default value of this field is false. 
See Also:
/**
     * This variable is set by the {@code setDoOutput} method. Its
     * value is returned by the {@code getDoOutput} method.
     * <p>
     * A URL connection can be used for input and/or output. Setting the
     * {@code doOutput} flag to {@code true} indicates
     * that the application intends to write data to the URL connection.
     * <p>
     * The default value of this field is {@code false}.
     *
     * @see     java.net.URLConnection#getDoOutput()
     * @see     java.net.URLConnection#setDoOutput(boolean)
     */
    protected boolean doOutput = false;

    private static boolean defaultAllowUserInteraction = false;

   
If true, this URL is being examined in a context in which it makes sense to allow user interactions such as popping up an authentication dialog. If false, then no user interaction is allowed. 
 The value of this field can be set by the setAllowUserInteraction method. Its value is returned by the getAllowUserInteraction method. Its default value is the value of the argument in the last invocation of the setDefaultAllowUserInteraction method. 
See Also:
/**
     * If {@code true}, this {@code URL} is being examined in
     * a context in which it makes sense to allow user interactions such
     * as popping up an authentication dialog. If {@code false},
     * then no user interaction is allowed.
     * <p>
     * The value of this field can be set by the
     * {@code setAllowUserInteraction} method.
     * Its value is returned by the
     * {@code getAllowUserInteraction} method.
     * Its default value is the value of the argument in the last invocation
     * of the {@code setDefaultAllowUserInteraction} method.
     *
     * @see     java.net.URLConnection#getAllowUserInteraction()
     * @see     java.net.URLConnection#setAllowUserInteraction(boolean)
     * @see     java.net.URLConnection#setDefaultAllowUserInteraction(boolean)
     */
    protected boolean allowUserInteraction = defaultAllowUserInteraction;

    private static volatile boolean defaultUseCaches = true;

   
If true, the protocol is allowed to use caching whenever it can. If false, the protocol must always try to get a fresh copy of the object. 
 This field is set by the setUseCaches method. Its value is returned by the getUseCaches method. 
 Its default value is the value given in the last invocation of the setDefaultUseCaches method. 
 The default setting may be overridden per protocol with setDefaultUseCaches(String, boolean). 
See Also:
/**
     * If {@code true}, the protocol is allowed to use caching
     * whenever it can. If {@code false}, the protocol must always
     * try to get a fresh copy of the object.
     * <p>
     * This field is set by the {@code setUseCaches} method. Its
     * value is returned by the {@code getUseCaches} method.
     * <p>
     * Its default value is the value given in the last invocation of the
     * {@code setDefaultUseCaches} method.
     * <p>
     * The default setting may be overridden per protocol with
     * {@link #setDefaultUseCaches(String,boolean)}.
     *
     * @see     java.net.URLConnection#setUseCaches(boolean)
     * @see     java.net.URLConnection#getUseCaches()
     * @see     java.net.URLConnection#setDefaultUseCaches(boolean)
     */
    protected boolean useCaches;

    private static final ConcurrentHashMap<String,Boolean> defaultCaching =
        new ConcurrentHashMap<>();

   
Some protocols support skipping the fetching of the object unless
the object has been modified more recently than a certain time.


A nonzero value gives a time as the number of milliseconds since
January 1, 1970, GMT. The object is fetched only if it has been
modified more recently than that time.

 This variable is set by the setIfModifiedSince method. Its value is returned by the getIfModifiedSince method. 
 The default value of this field is 0, indicating that the fetching must always occur. 
See Also:
/**
     * Some protocols support skipping the fetching of the object unless
     * the object has been modified more recently than a certain time.
     * <p>
     * A nonzero value gives a time as the number of milliseconds since
     * January 1, 1970, GMT. The object is fetched only if it has been
     * modified more recently than that time.
     * <p>
     * This variable is set by the {@code setIfModifiedSince}
     * method. Its value is returned by the
     * {@code getIfModifiedSince} method.
     * <p>
     * The default value of this field is {@code 0}, indicating
     * that the fetching must always occur.
     *
     * @see     java.net.URLConnection#getIfModifiedSince()
     * @see     java.net.URLConnection#setIfModifiedSince(long)
     */
    protected long ifModifiedSince = 0;

   
If false, this connection object has not created a communications link to the specified URL. If true, the communications link has been established. 
/**
     * If {@code false}, this connection object has not created a
     * communications link to the specified URL. If {@code true},
     * the communications link has been established.
     */
    protected boolean connected = false;

    
Since:1.5
/**
     * @since 1.5
     */
    private int connectTimeout;
    private int readTimeout;

    
Since:1.6
/**
     * @since 1.6
     */
    private MessageHeader requests;

   
Since:  1.1
/**
    * @since   1.1
    */
    private static volatile FileNameMap fileNameMap;

    
Loads filename map (a mimetable) from a data file. It will
first try to load the user-specific table, defined
by "content.types.user.table" property. If that fails,
it tries to load the default built-in table.

See Also:
Returns:the FileNameMap
Since:1.2
/**
     * Loads filename map (a mimetable) from a data file. It will
     * first try to load the user-specific table, defined
     * by &quot;content.types.user.table&quot; property. If that fails,
     * it tries to load the default built-in table.
     *
     * @return the FileNameMap
     * @since 1.2
     * @see #setFileNameMap(java.net.FileNameMap)
     */
    public static FileNameMap getFileNameMap() {
        FileNameMap map = fileNameMap;

        if (map == null) {
            fileNameMap = map = new FileNameMap() {
                private FileNameMap internalMap =
                    sun.net.www.MimeTable.loadTable();

                public String getContentTypeFor(String fileName) {
                    return internalMap.getContentTypeFor(fileName);
                }
            };
        }

        return map;
    }

    
Sets the FileNameMap.

 If there is a security manager, this method first calls the security manager's checkSetFactory method to ensure the operation is allowed. This could result in a SecurityException. 
Params:
  • map – the FileNameMap to be set
Throws:
  • SecurityException –  if a security manager exists and its checkSetFactory method doesn't allow the operation.
See Also:
Since:1.2
/**
     * Sets the FileNameMap.
     * <p>
     * If there is a security manager, this method first calls
     * the security manager's {@code checkSetFactory} method
     * to ensure the operation is allowed.
     * This could result in a SecurityException.
     *
     * @param map the FileNameMap to be set
     * @exception  SecurityException  if a security manager exists and its
     *             {@code checkSetFactory} method doesn't allow the operation.
     * @see        SecurityManager#checkSetFactory
     * @see #getFileNameMap()
     * @since 1.2
     */
    public static void setFileNameMap(FileNameMap map) {
        SecurityManager sm = System.getSecurityManager();
        if (sm != null) sm.checkSetFactory();
        fileNameMap = map;
    }

    
Opens a communications link to the resource referenced by this
URL, if such a connection has not already been established.

 If the connect method is called when the connection has already been opened (indicated by the connected field having the value true), the call is ignored. 

URLConnection objects go through two phases: first they are
created, then they are connected.  After being created, and
before being connected, various options can be specified
(e.g., doInput and UseCaches).  After connecting, it is an
error to try to set them.  Operations that depend on being
connected, like getContentLength, will implicitly perform the
connection, if necessary.

Throws:
See Also:
/**
     * Opens a communications link to the resource referenced by this
     * URL, if such a connection has not already been established.
     * <p>
     * If the {@code connect} method is called when the connection
     * has already been opened (indicated by the {@code connected}
     * field having the value {@code true}), the call is ignored.
     * <p>
     * URLConnection objects go through two phases: first they are
     * created, then they are connected.  After being created, and
     * before being connected, various options can be specified
     * (e.g., doInput and UseCaches).  After connecting, it is an
     * error to try to set them.  Operations that depend on being
     * connected, like getContentLength, will implicitly perform the
     * connection, if necessary.
     *
     * @throws SocketTimeoutException if the timeout expires before
     *               the connection can be established
     * @exception  IOException  if an I/O error occurs while opening the
     *               connection.
     * @see java.net.URLConnection#connected
     * @see #getConnectTimeout()
     * @see #setConnectTimeout(int)
     */
    public abstract void connect() throws IOException;

    
Sets a specified timeout value, in milliseconds, to be used
when opening a communications link to the resource referenced
by this URLConnection.  If the timeout expires before the
connection can be established, a
java.net.SocketTimeoutException is raised. A timeout of zero is
interpreted as an infinite timeout.

 Some non-standard implementation of this method may ignore
the specified timeout. To see the connect timeout set, please
call getConnectTimeout().

Params:
  • timeout – an int that specifies the connect timeout value in milliseconds
Throws:
See Also:
Since:1.5
/**
     * Sets a specified timeout value, in milliseconds, to be used
     * when opening a communications link to the resource referenced
     * by this URLConnection.  If the timeout expires before the
     * connection can be established, a
     * java.net.SocketTimeoutException is raised. A timeout of zero is
     * interpreted as an infinite timeout.

     * <p> Some non-standard implementation of this method may ignore
     * the specified timeout. To see the connect timeout set, please
     * call getConnectTimeout().
     *
     * @param timeout an {@code int} that specifies the connect
     *               timeout value in milliseconds
     * @throws IllegalArgumentException if the timeout parameter is negative
     *
     * @see #getConnectTimeout()
     * @see #connect()
     * @since 1.5
     */
    public void setConnectTimeout(int timeout) {
        if (timeout < 0) {
            throw new IllegalArgumentException("timeout can not be negative");
        }
        connectTimeout = timeout;
    }

    
Returns setting for connect timeout.


0 return implies that the option is disabled
(i.e., timeout of infinity).

See Also:
Returns:an int that indicates the connect timeout value in milliseconds
Since:1.5
/**
     * Returns setting for connect timeout.
     * <p>
     * 0 return implies that the option is disabled
     * (i.e., timeout of infinity).
     *
     * @return an {@code int} that indicates the connect timeout
     *         value in milliseconds
     * @see #setConnectTimeout(int)
     * @see #connect()
     * @since 1.5
     */
    public int getConnectTimeout() {
        return connectTimeout;
    }

    
Sets the read timeout to a specified timeout, in
milliseconds. A non-zero value specifies the timeout when
reading from Input stream when a connection is established to a
resource. If the timeout expires before there is data available
for read, a java.net.SocketTimeoutException is raised. A
timeout of zero is interpreted as an infinite timeout.

 Some non-standard implementation of this method ignores the
specified timeout. To see the read timeout set, please call
getReadTimeout().

Params:
  • timeout – an int that specifies the timeout value to be used in milliseconds
Throws:
See Also:
Since:1.5
/**
     * Sets the read timeout to a specified timeout, in
     * milliseconds. A non-zero value specifies the timeout when
     * reading from Input stream when a connection is established to a
     * resource. If the timeout expires before there is data available
     * for read, a java.net.SocketTimeoutException is raised. A
     * timeout of zero is interpreted as an infinite timeout.
     *
     *<p> Some non-standard implementation of this method ignores the
     * specified timeout. To see the read timeout set, please call
     * getReadTimeout().
     *
     * @param timeout an {@code int} that specifies the timeout
     * value to be used in milliseconds
     * @throws IllegalArgumentException if the timeout parameter is negative
     *
     * @see #getReadTimeout()
     * @see InputStream#read()
     * @since 1.5
     */
    public void setReadTimeout(int timeout) {
        if (timeout < 0) {
            throw new IllegalArgumentException("timeout can not be negative");
        }
        readTimeout = timeout;
    }

    
Returns setting for read timeout. 0 return implies that the
option is disabled (i.e., timeout of infinity).

See Also:
Returns:an int that indicates the read timeout value in milliseconds
Since:1.5
/**
     * Returns setting for read timeout. 0 return implies that the
     * option is disabled (i.e., timeout of infinity).
     *
     * @return an {@code int} that indicates the read timeout
     *         value in milliseconds
     *
     * @see #setReadTimeout(int)
     * @see InputStream#read()
     * @since 1.5
     */
    public int getReadTimeout() {
        return readTimeout;
    }

    
Constructs a URL connection to the specified URL. A connection to
the object referenced by the URL is not created.

Params:
  • url –   the specified URL.
/**
     * Constructs a URL connection to the specified URL. A connection to
     * the object referenced by the URL is not created.
     *
     * @param   url   the specified URL.
     */
    protected URLConnection(URL url) {
        this.url = url;
        if (url == null) {
            this.useCaches = defaultUseCaches;
        } else {
            this.useCaches = getDefaultUseCaches(url.getProtocol());
        }
    }

    
Returns the value of this URLConnection's URL field. 
See Also:
Returns: the value of this URLConnection's URL field.
/**
     * Returns the value of this {@code URLConnection}'s {@code URL}
     * field.
     *
     * @return  the value of this {@code URLConnection}'s {@code URL}
     *          field.
     * @see     java.net.URLConnection#url
     */
    public URL getURL() {
        return url;
    }

    
Returns the value of the content-length header field. 

Note: getContentLengthLong() should be preferred over this method, since it returns a long instead and is therefore more portable.


Returns: the content length of the resource that this connection's URL references, -1 if the content length is not known, or if the content length is greater than Integer.MAX_VALUE.
/**
     * Returns the value of the {@code content-length} header field.
     * <P>
     * <B>Note</B>: {@link #getContentLengthLong() getContentLengthLong()}
     * should be preferred over this method, since it returns a {@code long}
     * instead and is therefore more portable.</P>
     *
     * @return  the content length of the resource that this connection's URL
     *          references, {@code -1} if the content length is not known,
     *          or if the content length is greater than Integer.MAX_VALUE.
     */
    public int getContentLength() {
        long l = getContentLengthLong();
        if (l > Integer.MAX_VALUE)
            return -1;
        return (int) l;
    }

    
Returns the value of the content-length header field as a long. 
Returns: the content length of the resource that this connection's URL references, or -1 if the content length is not known.
Since:1.7
/**
     * Returns the value of the {@code content-length} header field as a
     * long.
     *
     * @return  the content length of the resource that this connection's URL
     *          references, or {@code -1} if the content length is
     *          not known.
     * @since 1.7
     */
    public long getContentLengthLong() {
        return getHeaderFieldLong("content-length", -1);
    }

    
Returns the value of the content-type header field. 
See Also:
Returns: the content type of the resource that the URL references, or null if not known.
/**
     * Returns the value of the {@code content-type} header field.
     *
     * @return  the content type of the resource that the URL references,
     *          or {@code null} if not known.
     * @see     java.net.URLConnection#getHeaderField(java.lang.String)
     */
    public String getContentType() {
        return getHeaderField("content-type");
    }

    
Returns the value of the content-encoding header field. 
See Also:
Returns: the content encoding of the resource that the URL references, or null if not known.
/**
     * Returns the value of the {@code content-encoding} header field.
     *
     * @return  the content encoding of the resource that the URL references,
     *          or {@code null} if not known.
     * @see     java.net.URLConnection#getHeaderField(java.lang.String)
     */
    public String getContentEncoding() {
        return getHeaderField("content-encoding");
    }

    
Returns the value of the expires header field. 
See Also:
Returns: the expiration date of the resource that this URL references,
         or 0 if not known. The value is the number of milliseconds since
         January 1, 1970 GMT.
/**
     * Returns the value of the {@code expires} header field.
     *
     * @return  the expiration date of the resource that this URL references,
     *          or 0 if not known. The value is the number of milliseconds since
     *          January 1, 1970 GMT.
     * @see     java.net.URLConnection#getHeaderField(java.lang.String)
     */
    public long getExpiration() {
        return getHeaderFieldDate("expires", 0);
    }

    
Returns the value of the date header field. 
See Also:
Returns: the sending date of the resource that the URL references, or 0 if not known. The value returned is the number of milliseconds since January 1, 1970 GMT.
/**
     * Returns the value of the {@code date} header field.
     *
     * @return  the sending date of the resource that the URL references,
     *          or {@code 0} if not known. The value returned is the
     *          number of milliseconds since January 1, 1970 GMT.
     * @see     java.net.URLConnection#getHeaderField(java.lang.String)
     */
    public long getDate() {
        return getHeaderFieldDate("date", 0);
    }

    
Returns the value of the last-modified header field. The result is the number of milliseconds since January 1, 1970 GMT. 
See Also:
Returns: the date the resource referenced by this URLConnection was last modified, or 0 if not known.
/**
     * Returns the value of the {@code last-modified} header field.
     * The result is the number of milliseconds since January 1, 1970 GMT.
     *
     * @return  the date the resource referenced by this
     *          {@code URLConnection} was last modified, or 0 if not known.
     * @see     java.net.URLConnection#getHeaderField(java.lang.String)
     */
    public long getLastModified() {
        return getHeaderFieldDate("last-modified", 0);
    }

    
Returns the value of the named header field.


If called on a connection that sets the same header multiple times
with possibly different values, only the last value is returned.

Params:
  • name –   the name of a header field.
Returns: the value of the named header field, or null if there is no such field in the header.
/**
     * Returns the value of the named header field.
     * <p>
     * If called on a connection that sets the same header multiple times
     * with possibly different values, only the last value is returned.
     *
     *
     * @param   name   the name of a header field.
     * @return  the value of the named header field, or {@code null}
     *          if there is no such field in the header.
     */
    public String getHeaderField(String name) {
        return null;
    }

    
Returns an unmodifiable Map of the header fields.
The Map keys are Strings that represent the
response-header field names. Each Map value is an
unmodifiable List of Strings that represents
the corresponding field values.

Returns:a Map of header fields
Since:1.4
/**
     * Returns an unmodifiable Map of the header fields.
     * The Map keys are Strings that represent the
     * response-header field names. Each Map value is an
     * unmodifiable List of Strings that represents
     * the corresponding field values.
     *
     * @return a Map of header fields
     * @since 1.4
     */
    public Map<String,List<String>> getHeaderFields() {
        return Collections.emptyMap();
    }

    
Returns the value of the named field parsed as a number.

 This form of getHeaderField exists because some connection types (e.g., http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing. 
Params:
  • name –      the name of the header field.
  • Default –   the default value.
Returns: the value of the named field, parsed as an integer. The Default value is returned if the field is missing or malformed.
/**
     * Returns the value of the named field parsed as a number.
     * <p>
     * This form of {@code getHeaderField} exists because some
     * connection types (e.g., {@code http-ng}) have pre-parsed
     * headers. Classes for that connection type can override this method
     * and short-circuit the parsing.
     *
     * @param   name      the name of the header field.
     * @param   Default   the default value.
     * @return  the value of the named field, parsed as an integer. The
     *          {@code Default} value is returned if the field is
     *          missing or malformed.
     */
    public int getHeaderFieldInt(String name, int Default) {
        String value = getHeaderField(name);
        try {
            return Integer.parseInt(value);
        } catch (Exception e) { }
        return Default;
    }

    
Returns the value of the named field parsed as a number.

 This form of getHeaderField exists because some connection types (e.g., http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing. 
Params:
  • name –      the name of the header field.
  • Default –   the default value.
Returns: the value of the named field, parsed as a long. The Default value is returned if the field is missing or malformed.
Since:1.7
/**
     * Returns the value of the named field parsed as a number.
     * <p>
     * This form of {@code getHeaderField} exists because some
     * connection types (e.g., {@code http-ng}) have pre-parsed
     * headers. Classes for that connection type can override this method
     * and short-circuit the parsing.
     *
     * @param   name      the name of the header field.
     * @param   Default   the default value.
     * @return  the value of the named field, parsed as a long. The
     *          {@code Default} value is returned if the field is
     *          missing or malformed.
     * @since 1.7
     */
    public long getHeaderFieldLong(String name, long Default) {
        String value = getHeaderField(name);
        try {
            return Long.parseLong(value);
        } catch (Exception e) { }
        return Default;
    }

    
Returns the value of the named field parsed as date.
The result is the number of milliseconds since January 1, 1970 GMT
represented by the named field.

 This form of getHeaderField exists because some connection types (e.g., http-ng) have pre-parsed headers. Classes for that connection type can override this method and short-circuit the parsing. 
Params:
  • name –     the name of the header field.
  • Default –   a default value.
Returns: the value of the field, parsed as a date. The value of the Default argument is returned if the field is missing or malformed.
/**
     * Returns the value of the named field parsed as date.
     * The result is the number of milliseconds since January 1, 1970 GMT
     * represented by the named field.
     * <p>
     * This form of {@code getHeaderField} exists because some
     * connection types (e.g., {@code http-ng}) have pre-parsed
     * headers. Classes for that connection type can override this method
     * and short-circuit the parsing.
     *
     * @param   name     the name of the header field.
     * @param   Default   a default value.
     * @return  the value of the field, parsed as a date. The value of the
     *          {@code Default} argument is returned if the field is
     *          missing or malformed.
     */
    @SuppressWarnings("deprecation")
    public long getHeaderFieldDate(String name, long Default) {
        String value = getHeaderField(name);
        try {
            return Date.parse(value);
        } catch (Exception e) { }
        return Default;
    }

    
Returns the key for the nth header field. It returns null if there are fewer than n+1 fields. 
Params:
  • n –  an index, where n>=0
Returns: the key for the nth header field, or null if there are fewer than n+1 fields.
/**
     * Returns the key for the {@code n}<sup>th</sup> header field.
     * It returns {@code null} if there are fewer than {@code n+1} fields.
     *
     * @param   n   an index, where {@code n>=0}
     * @return  the key for the {@code n}<sup>th</sup> header field,
     *          or {@code null} if there are fewer than {@code n+1}
     *          fields.
     */
    public String getHeaderFieldKey(int n) {
        return null;
    }

    
Returns the value for the nth header field. It returns null if there are fewer than n+1fields. 
 This method can be used in conjunction with the getHeaderFieldKey method to iterate through all the headers in the message. 
Params:
  • n –  an index, where n>=0
See Also:
Returns: the value of the nth header field or null if there are fewer than n+1 fields
/**
     * Returns the value for the {@code n}<sup>th</sup> header field.
     * It returns {@code null} if there are fewer than
     * {@code n+1}fields.
     * <p>
     * This method can be used in conjunction with the
     * {@link #getHeaderFieldKey(int) getHeaderFieldKey} method to iterate through all
     * the headers in the message.
     *
     * @param   n   an index, where {@code n>=0}
     * @return  the value of the {@code n}<sup>th</sup> header field
     *          or {@code null} if there are fewer than {@code n+1} fields
     * @see     java.net.URLConnection#getHeaderFieldKey(int)
     */
    public String getHeaderField(int n) {
        return null;
    }

    
Retrieves the contents of this URL connection.

 This method first determines the content type of the object by calling the getContentType method. If this is the first time that the application has seen that specific content type, a content handler for that content type is created. 
 This is done as follows:

    

  1. If the application has set up a content handler factory instance using the setContentHandlerFactory method, the createContentHandler method of that instance is called with the content type as an argument; the result is a content handler for that content type. 
  2. If no ContentHandlerFactory has yet been set up, or if the factory's createContentHandler method returns null, then the 
    ServiceLoader mechanism is used to locate ContentHandlerFactory implementations using the system class loader. The order that factories are located is implementation specific, and an implementation is free to cache the located factories. A 
    ServiceConfigurationError, Error or RuntimeException thrown from the createContentHandler, if encountered, will be propagated to the calling thread. The 
    createContentHandler method of each factory, if instantiated, is invoked, with the content type, until a factory returns non-null, or all factories have been exhausted. 
  3. Failing that, this method tries to load a content handler class as defined by ContentHandler. If the class does not exist, or is not a subclass of 
    ContentHandler, then an UnknownServiceException is thrown. 


Throws:
See Also:
Returns: the object fetched. The instanceof operator should be used to determine the specific kind of object returned.
/**
     * Retrieves the contents of this URL connection.
     * <p>
     * This method first determines the content type of the object by
     * calling the {@code getContentType} method. If this is
     * the first time that the application has seen that specific content
     * type, a content handler for that content type is created.
     * <p> This is done as follows:
     * <ol>
     * <li>If the application has set up a content handler factory instance
     *     using the {@code setContentHandlerFactory} method, the
     *     {@code createContentHandler} method of that instance is called
     *     with the content type as an argument; the result is a content
     *     handler for that content type.
     * <li>If no {@code ContentHandlerFactory} has yet been set up,
     *     or if the factory's {@code createContentHandler} method
     *     returns {@code null}, then the {@linkplain java.util.ServiceLoader
     *     ServiceLoader} mechanism is used to locate {@linkplain
     *     java.net.ContentHandlerFactory ContentHandlerFactory}
     *     implementations using the system class
     *     loader. The order that factories are located is implementation
     *     specific, and an implementation is free to cache the located
     *     factories. A {@linkplain java.util.ServiceConfigurationError
     *     ServiceConfigurationError}, {@code Error} or {@code RuntimeException}
     *     thrown from the {@code createContentHandler}, if encountered, will
     *     be propagated to the calling thread. The {@code
     *     createContentHandler} method of each factory, if instantiated, is
     *     invoked, with the content type, until a factory returns non-null,
     *     or all factories have been exhausted.
     * <li>Failing that, this method tries to load a content handler
     *     class as defined by {@link java.net.ContentHandler ContentHandler}.
     *     If the class does not exist, or is not a subclass of {@code
     *     ContentHandler}, then an {@code UnknownServiceException} is thrown.
     * </ol>
     *
     * @return     the object fetched. The {@code instanceof} operator
     *               should be used to determine the specific kind of object
     *               returned.
     * @exception  IOException              if an I/O error occurs while
     *               getting the content.
     * @exception  UnknownServiceException  if the protocol does not support
     *               the content type.
     * @see        java.net.ContentHandlerFactory#createContentHandler(java.lang.String)
     * @see        java.net.URLConnection#getContentType()
     * @see        java.net.URLConnection#setContentHandlerFactory(java.net.ContentHandlerFactory)
     */
    public Object getContent() throws IOException {
        // Must call getInputStream before GetHeaderField gets called
        // so that FileNotFoundException has a chance to be thrown up
        // from here without being caught.
        getInputStream();
        return getContentHandler().getContent(this);
    }

    
Retrieves the contents of this URL connection.

Params:
  • classes – the Class array indicating the requested types
Throws:
See Also:
Returns: the object fetched that is the first match of the type specified in the classes array. null if none of the requested types are supported. The instanceof operator should be used to determine the specific kind of object returned.
Since:1.3
/**
     * Retrieves the contents of this URL connection.
     *
     * @param classes the {@code Class} array
     * indicating the requested types
     * @return     the object fetched that is the first match of the type
     *               specified in the classes array. null if none of
     *               the requested types are supported.
     *               The {@code instanceof} operator should be used to
     *               determine the specific kind of object returned.
     * @exception  IOException              if an I/O error occurs while
     *               getting the content.
     * @exception  UnknownServiceException  if the protocol does not support
     *               the content type.
     * @see        java.net.URLConnection#getContent()
     * @see        java.net.ContentHandlerFactory#createContentHandler(java.lang.String)
     * @see        java.net.URLConnection#getContent(java.lang.Class[])
     * @see        java.net.URLConnection#setContentHandlerFactory(java.net.ContentHandlerFactory)
     * @since 1.3
     */
    public Object getContent(Class<?>[] classes) throws IOException {
        // Must call getInputStream before GetHeaderField gets called
        // so that FileNotFoundException has a chance to be thrown up
        // from here without being caught.
        getInputStream();
        return getContentHandler().getContent(this, classes);
    }

    
Returns a permission object representing the permission necessary to make the connection represented by this object. This method returns null if no permission is required to make the connection. By default, this method returns java.security.AllPermission. Subclasses should override this method and return the permission that best represents the permission required to make a connection to the URL. For example, a URLConnection representing a file: URL would return a java.io.FilePermission object. 
The permission returned may dependent upon the state of the
connection. For example, the permission before connecting may be
different from that after connecting. For example, an HTTP
sever, say foo.com, may redirect the connection to a different
host, say bar.com. Before connecting the permission returned by
the connection will represent the permission needed to connect
to foo.com, while the permission returned after connecting will
be to bar.com.

Permissions are generally used for two purposes: to protect
caches of objects obtained through URLConnections, and to check
the right of a recipient to learn about a particular URL. In
the first case, the permission should be obtained
after the object has been obtained. For example, in an
HTTP connection, this will represent the permission to connect
to the host from which the data was ultimately fetched. In the
second case, the permission should be obtained and tested
before connecting.

Throws:
  • IOException – if the computation of the permission
requires network or file I/O and an exception occurs while
computing it.
Returns:the permission object representing the permission
necessary to make the connection represented by this
URLConnection.
/**
     * Returns a permission object representing the permission
     * necessary to make the connection represented by this
     * object. This method returns null if no permission is
     * required to make the connection. By default, this method
     * returns {@code java.security.AllPermission}. Subclasses
     * should override this method and return the permission
     * that best represents the permission required to make
     * a connection to the URL. For example, a {@code URLConnection}
     * representing a {@code file:} URL would return a
     * {@code java.io.FilePermission} object.
     *
     * <p>The permission returned may dependent upon the state of the
     * connection. For example, the permission before connecting may be
     * different from that after connecting. For example, an HTTP
     * sever, say foo.com, may redirect the connection to a different
     * host, say bar.com. Before connecting the permission returned by
     * the connection will represent the permission needed to connect
     * to foo.com, while the permission returned after connecting will
     * be to bar.com.
     *
     * <p>Permissions are generally used for two purposes: to protect
     * caches of objects obtained through URLConnections, and to check
     * the right of a recipient to learn about a particular URL. In
     * the first case, the permission should be obtained
     * <em>after</em> the object has been obtained. For example, in an
     * HTTP connection, this will represent the permission to connect
     * to the host from which the data was ultimately fetched. In the
     * second case, the permission should be obtained and tested
     * <em>before</em> connecting.
     *
     * @return the permission object representing the permission
     * necessary to make the connection represented by this
     * URLConnection.
     *
     * @exception IOException if the computation of the permission
     * requires network or file I/O and an exception occurs while
     * computing it.
     */
    public Permission getPermission() throws IOException {
        return SecurityConstants.ALL_PERMISSION;
    }

    
Returns an input stream that reads from this open connection.
A SocketTimeoutException can be thrown when reading from the
returned input stream if the read timeout expires before data
is available for read.

Throws:
See Also:
Returns:    an input stream that reads from this open connection.
/**
     * Returns an input stream that reads from this open connection.
     *
     * A SocketTimeoutException can be thrown when reading from the
     * returned input stream if the read timeout expires before data
     * is available for read.
     *
     * @return     an input stream that reads from this open connection.
     * @exception  IOException              if an I/O error occurs while
     *               creating the input stream.
     * @exception  UnknownServiceException  if the protocol does not support
     *               input.
     * @see #setReadTimeout(int)
     * @see #getReadTimeout()
     */
    public InputStream getInputStream() throws IOException {
        throw new UnknownServiceException("protocol doesn't support input");
    }

    
Returns an output stream that writes to this connection.

Throws:
Returns:    an output stream that writes to this connection.
/**
     * Returns an output stream that writes to this connection.
     *
     * @return     an output stream that writes to this connection.
     * @exception  IOException              if an I/O error occurs while
     *               creating the output stream.
     * @exception  UnknownServiceException  if the protocol does not support
     *               output.
     */
    public OutputStream getOutputStream() throws IOException {
        throw new UnknownServiceException("protocol doesn't support output");
    }

    
Returns a String representation of this URL connection. 
Returns: a string representation of this URLConnection.
/**
     * Returns a {@code String} representation of this URL connection.
     *
     * @return  a string representation of this {@code URLConnection}.
     */
    public String toString() {
        return this.getClass().getName() + ":" + url;
    }

    
Sets the value of the doInput field for this URLConnection to the specified value. 

A URL connection can be used for input and/or output.  Set the doInput
flag to true if you intend to use the URL connection for input,
false if not.  The default is true.

Params:
  • doinput –   the new value.
Throws:
See Also:
/**
     * Sets the value of the {@code doInput} field for this
     * {@code URLConnection} to the specified value.
     * <p>
     * A URL connection can be used for input and/or output.  Set the doInput
     * flag to true if you intend to use the URL connection for input,
     * false if not.  The default is true.
     *
     * @param   doinput   the new value.
     * @throws IllegalStateException if already connected
     * @see     java.net.URLConnection#doInput
     * @see #getDoInput()
     */
    public void setDoInput(boolean doinput) {
        checkConnected();
        doInput = doinput;
    }

    
Returns the value of this URLConnection's doInput flag. 
See Also:
Returns: the value of this URLConnection's doInput flag.
/**
     * Returns the value of this {@code URLConnection}'s
     * {@code doInput} flag.
     *
     * @return  the value of this {@code URLConnection}'s
     *          {@code doInput} flag.
     * @see     #setDoInput(boolean)
     */
    public boolean getDoInput() {
        return doInput;
    }

    
Sets the value of the doOutput field for this URLConnection to the specified value. 

A URL connection can be used for input and/or output.  Set the doOutput
flag to true if you intend to use the URL connection for output,
false if not.  The default is false.

Params:
  • dooutput –   the new value.
Throws:
See Also:
/**
     * Sets the value of the {@code doOutput} field for this
     * {@code URLConnection} to the specified value.
     * <p>
     * A URL connection can be used for input and/or output.  Set the doOutput
     * flag to true if you intend to use the URL connection for output,
     * false if not.  The default is false.
     *
     * @param   dooutput   the new value.
     * @throws IllegalStateException if already connected
     * @see #getDoOutput()
     */
    public void setDoOutput(boolean dooutput) {
        checkConnected();
        doOutput = dooutput;
    }

    
Returns the value of this URLConnection's doOutput flag. 
See Also:
Returns: the value of this URLConnection's doOutput flag.
/**
     * Returns the value of this {@code URLConnection}'s
     * {@code doOutput} flag.
     *
     * @return  the value of this {@code URLConnection}'s
     *          {@code doOutput} flag.
     * @see     #setDoOutput(boolean)
     */
    public boolean getDoOutput() {
        return doOutput;
    }

    
Set the value of the allowUserInteraction field of this URLConnection. 
Params:
  • allowuserinteraction –   the new value.
Throws:
See Also:
/**
     * Set the value of the {@code allowUserInteraction} field of
     * this {@code URLConnection}.
     *
     * @param   allowuserinteraction   the new value.
     * @throws IllegalStateException if already connected
     * @see     #getAllowUserInteraction()
     */
    public void setAllowUserInteraction(boolean allowuserinteraction) {
        checkConnected();
        allowUserInteraction = allowuserinteraction;
    }

    
Returns the value of the allowUserInteraction field for this object. 
See Also:
Returns: the value of the allowUserInteraction field for this object.
/**
     * Returns the value of the {@code allowUserInteraction} field for
     * this object.
     *
     * @return  the value of the {@code allowUserInteraction} field for
     *          this object.
     * @see     #setAllowUserInteraction(boolean)
     */
    public boolean getAllowUserInteraction() {
        return allowUserInteraction;
    }

    
Sets the default value of the allowUserInteraction field for all future URLConnection objects to the specified value. 
Params:
  • defaultallowuserinteraction –   the new value.
See Also:
/**
     * Sets the default value of the
     * {@code allowUserInteraction} field for all future
     * {@code URLConnection} objects to the specified value.
     *
     * @param   defaultallowuserinteraction   the new value.
     * @see     #getDefaultAllowUserInteraction()
     */
    public static void setDefaultAllowUserInteraction(boolean defaultallowuserinteraction) {
        defaultAllowUserInteraction = defaultallowuserinteraction;
    }

    
Returns the default value of the allowUserInteraction field. 

This default is "sticky", being a part of the static state of all
URLConnections.  This flag applies to the next, and all following
URLConnections that are created.

See Also:
Returns: the default value of the allowUserInteraction field.
/**
     * Returns the default value of the {@code allowUserInteraction}
     * field.
     * <p>
     * This default is "sticky", being a part of the static state of all
     * URLConnections.  This flag applies to the next, and all following
     * URLConnections that are created.
     *
     * @return  the default value of the {@code allowUserInteraction}
     *          field.
     * @see     #setDefaultAllowUserInteraction(boolean)
     */
    public static boolean getDefaultAllowUserInteraction() {
        return defaultAllowUserInteraction;
    }

    
Sets the value of the useCaches field of this URLConnection to the specified value. 
 Some protocols do caching of documents. Occasionally, it is important to be able to "tunnel through" and ignore the caches (e.g., the "reload" button in a browser). If the UseCaches flag on a connection is true, the connection is allowed to use whatever caches it can. If false, caches are to be ignored. The default value comes from defaultUseCaches, which defaults to true. A default value can also be set per-protocol using setDefaultUseCaches(String, boolean). 
Params:
  • usecaches – a boolean indicating whether or not to allow caching
Throws:
See Also:
/**
     * Sets the value of the {@code useCaches} field of this
     * {@code URLConnection} to the specified value.
     * <p>
     * Some protocols do caching of documents.  Occasionally, it is important
     * to be able to "tunnel through" and ignore the caches (e.g., the
     * "reload" button in a browser).  If the UseCaches flag on a connection
     * is true, the connection is allowed to use whatever caches it can.
     *  If false, caches are to be ignored.
     *  The default value comes from defaultUseCaches, which defaults to
     * true. A default value can also be set per-protocol using
     * {@link #setDefaultUseCaches(String,boolean)}.
     *
     * @param usecaches a {@code boolean} indicating whether
     * or not to allow caching
     * @throws IllegalStateException if already connected
     * @see #getUseCaches()
     */
    public void setUseCaches(boolean usecaches) {
        checkConnected();
        useCaches = usecaches;
    }

    
Returns the value of this URLConnection's useCaches field. 
See Also:
Returns: the value of this URLConnection's useCaches field.
/**
     * Returns the value of this {@code URLConnection}'s
     * {@code useCaches} field.
     *
     * @return  the value of this {@code URLConnection}'s
     *          {@code useCaches} field.
     * @see #setUseCaches(boolean)
     */
    public boolean getUseCaches() {
        return useCaches;
    }

    
Sets the value of the ifModifiedSince field of this URLConnection to the specified value. 
Params:
  • ifmodifiedsince –   the new value.
Throws:
See Also:
/**
     * Sets the value of the {@code ifModifiedSince} field of
     * this {@code URLConnection} to the specified value.
     *
     * @param   ifmodifiedsince   the new value.
     * @throws IllegalStateException if already connected
     * @see     #getIfModifiedSince()
     */
    public void setIfModifiedSince(long ifmodifiedsince) {
        checkConnected();
        ifModifiedSince = ifmodifiedsince;
    }

    
Returns the value of this object's ifModifiedSince field. 
See Also:
Returns: the value of this object's ifModifiedSince field.
/**
     * Returns the value of this object's {@code ifModifiedSince} field.
     *
     * @return  the value of this object's {@code ifModifiedSince} field.
     * @see #setIfModifiedSince(long)
     */
    public long getIfModifiedSince() {
        return ifModifiedSince;
    }

   
Returns the default value of a URLConnection's useCaches flag. 
 This default is "sticky", being a part of the static state of all URLConnections. This flag applies to the next, and all following URLConnections that are created. This default value can be over-ridden per protocol using setDefaultUseCaches(String, boolean) 
See Also:
Returns: the default value of a URLConnection's useCaches flag.
/**
     * Returns the default value of a {@code URLConnection}'s
     * {@code useCaches} flag.
     * <p>
     * This default is "sticky", being a part of the static state of all
     * URLConnections.  This flag applies to the next, and all following
     * URLConnections that are created. This default value can be over-ridden
     * per protocol using {@link #setDefaultUseCaches(String,boolean)}
     *
     * @return  the default value of a {@code URLConnection}'s
     *          {@code useCaches} flag.
     * @see     #setDefaultUseCaches(boolean)
     */
    public boolean getDefaultUseCaches() {
        return defaultUseCaches;
    }

   
Sets the default value of the useCaches field to the specified value. This default value can be over-ridden per protocol using setDefaultUseCaches(String, boolean) 
Params:
  • defaultusecaches –   the new value.
See Also:
/**
     * Sets the default value of the {@code useCaches} field to the
     * specified value. This default value can be over-ridden
     * per protocol using {@link #setDefaultUseCaches(String,boolean)}
     *
     * @param   defaultusecaches   the new value.
     * @see     #getDefaultUseCaches()
     */
    public void setDefaultUseCaches(boolean defaultusecaches) {
        defaultUseCaches = defaultusecaches;
    }

   
Sets the default value of the useCaches field for the named protocol to the given value. This value overrides any default setting set by setDefaultUseCaches(boolean) for the given protocol. Successive calls to this method change the setting and affect the default value for all future connections of that protocol. The protocol name is case insensitive. 
Params:
  • protocol – the protocol to set the default for
  • defaultVal – whether caching is enabled by default for the given protocol
Since:9
/**
     * Sets the default value of the {@code useCaches} field for the named
     * protocol to the given value. This value overrides any default setting
     * set by {@link #setDefaultUseCaches(boolean)} for the given protocol.
     * Successive calls to this method change the setting and affect the
     * default value for all future connections of that protocol. The protocol
     * name is case insensitive.
     *
     * @param   protocol the protocol to set the default for
     * @param   defaultVal whether caching is enabled by default for the given protocol
     * @since 9
     */
    public static void setDefaultUseCaches(String protocol, boolean defaultVal) {
        protocol = protocol.toLowerCase(Locale.US);
        defaultCaching.put(protocol, defaultVal);
    }

   
Returns the default value of the useCaches flag for the given protocol. If setDefaultUseCaches(String, boolean) was called for the given protocol, then that value is returned. Otherwise, if setDefaultUseCaches(boolean) was called, then that value is returned. If neither method was called, the return value is true. The protocol name is case insensitive. 
Params:
  • protocol – the protocol whose defaultUseCaches setting is required
Returns: the default value of the useCaches flag for the given protocol.
Since:9
/**
     * Returns the default value of the {@code useCaches} flag for the given protocol. If
     * {@link #setDefaultUseCaches(String,boolean)} was called for the given protocol,
     * then that value is returned. Otherwise, if {@link #setDefaultUseCaches(boolean)}
     * was called, then that value is returned. If neither method was called,
     * the return value is {@code true}. The protocol name is case insensitive.
     *
     * @param protocol the protocol whose defaultUseCaches setting is required
     * @return  the default value of the {@code useCaches} flag for the given protocol.
     * @since 9
     */
    public static boolean getDefaultUseCaches(String protocol) {
        Boolean protoDefault = defaultCaching.get(protocol.toLowerCase(Locale.US));
        if (protoDefault != null) {
            return protoDefault.booleanValue();
        } else {
            return defaultUseCaches;
        }
    }

    
Sets the general request property. If a property with the key already
exists, overwrite its value with the new value.

 NOTE: HTTP requires all request properties which can
legally have multiple instances with the same key
to use a comma-separated list syntax which enables multiple
properties to be appended into a single property.

Params:
  • key –  the keyword by which the request is known (e.g., "Accept").
  • value –   the value associated with it.
Throws:
See Also:
/**
     * Sets the general request property. If a property with the key already
     * exists, overwrite its value with the new value.
     *
     * <p> NOTE: HTTP requires all request properties which can
     * legally have multiple instances with the same key
     * to use a comma-separated list syntax which enables multiple
     * properties to be appended into a single property.
     *
     * @param   key     the keyword by which the request is known
     *                  (e.g., "{@code Accept}").
     * @param   value   the value associated with it.
     * @throws IllegalStateException if already connected
     * @throws NullPointerException if key is {@code null}
     * @see #getRequestProperty(java.lang.String)
     */
    public void setRequestProperty(String key, String value) {
        checkConnected();
        if (key == null)
            throw new NullPointerException ("key is null");

        if (requests == null)
            requests = new MessageHeader();

        requests.set(key, value);
    }

    
Adds a general request property specified by a
key-value pair.  This method will not overwrite
existing values associated with the same key.

Params:
  • key –  the keyword by which the request is known (e.g., "Accept").
  • value –  the value associated with it.
Throws:
See Also:
Since:1.4
/**
     * Adds a general request property specified by a
     * key-value pair.  This method will not overwrite
     * existing values associated with the same key.
     *
     * @param   key     the keyword by which the request is known
     *                  (e.g., "{@code Accept}").
     * @param   value  the value associated with it.
     * @throws IllegalStateException if already connected
     * @throws NullPointerException if key is null
     * @see #getRequestProperties()
     * @since 1.4
     */
    public void addRequestProperty(String key, String value) {
        checkConnected();
        if (key == null)
            throw new NullPointerException ("key is null");

        if (requests == null)
            requests = new MessageHeader();

        requests.add(key, value);
    }


    
Returns the value of the named general request property for this
connection.

Params:
  • key – the keyword by which the request is known (e.g., "Accept").
Throws:
See Also:
Returns: the value of the named general request property for this
          connection. If key is null, then null is returned.
/**
     * Returns the value of the named general request property for this
     * connection.
     *
     * @param key the keyword by which the request is known (e.g., "Accept").
     * @return  the value of the named general request property for this
     *           connection. If key is null, then null is returned.
     * @throws IllegalStateException if already connected
     * @see #setRequestProperty(java.lang.String, java.lang.String)
     */
    public String getRequestProperty(String key) {
        checkConnected();

        if (requests == null)
            return null;

        return requests.findValue(key);
    }

    
Returns an unmodifiable Map of general request
properties for this connection. The Map keys
are Strings that represent the request-header
field names. Each Map value is a unmodifiable List
of Strings that represents the corresponding
field values.

Throws:
Returns: a Map of the general request properties for this connection.
Since:1.4
/**
     * Returns an unmodifiable Map of general request
     * properties for this connection. The Map keys
     * are Strings that represent the request-header
     * field names. Each Map value is a unmodifiable List
     * of Strings that represents the corresponding
     * field values.
     *
     * @return  a Map of the general request properties for this connection.
     * @throws IllegalStateException if already connected
     * @since 1.4
     */
    public Map<String,List<String>> getRequestProperties() {
        checkConnected();

        if (requests == null)
            return Collections.emptyMap();

        return requests.getHeaders(null);
    }

    
Sets the default value of a general request property. When a URLConnection is created, it is initialized with these properties. 
Params:
  • key –  the keyword by which the request is known (e.g., "Accept").
  • value –   the value associated with the key.
See Also:
Deprecated:The instance specific setRequestProperty method
should be used after an appropriate instance of URLConnection
is obtained. Invoking this method will have no effect.
/**
     * Sets the default value of a general request property. When a
     * {@code URLConnection} is created, it is initialized with
     * these properties.
     *
     * @param   key     the keyword by which the request is known
     *                  (e.g., "{@code Accept}").
     * @param   value   the value associated with the key.
     *
     * @see java.net.URLConnection#setRequestProperty(java.lang.String,java.lang.String)
     *
     * @deprecated The instance specific setRequestProperty method
     * should be used after an appropriate instance of URLConnection
     * is obtained. Invoking this method will have no effect.
     *
     * @see #getDefaultRequestProperty(java.lang.String)
     */
    @Deprecated
    public static void setDefaultRequestProperty(String key, String value) {
    }

    
Returns the value of the default request property. Default request
properties are set for every connection.

Params:
  • key – the keyword by which the request is known (e.g., "Accept").
See Also:
Returns: the value of the default request property
for the specified key.
Deprecated:The instance specific getRequestProperty method
should be used after an appropriate instance of URLConnection
is obtained.
/**
     * Returns the value of the default request property. Default request
     * properties are set for every connection.
     *
     * @param key the keyword by which the request is known (e.g., "Accept").
     * @return  the value of the default request property
     * for the specified key.
     *
     * @see java.net.URLConnection#getRequestProperty(java.lang.String)
     *
     * @deprecated The instance specific getRequestProperty method
     * should be used after an appropriate instance of URLConnection
     * is obtained.
     *
     * @see #setDefaultRequestProperty(java.lang.String, java.lang.String)
     */
    @Deprecated
    public static String getDefaultRequestProperty(String key) {
        return null;
    }

    
The ContentHandler factory.

/**
     * The ContentHandler factory.
     */
    private static volatile ContentHandlerFactory factory;

    
Sets the ContentHandlerFactory of an application. It can be called at most once by an application. 
 The ContentHandlerFactory instance is used to construct a content handler from a content type. 
 If there is a security manager, this method first calls the security manager's checkSetFactory method to ensure the operation is allowed. This could result in a SecurityException. 
Params:
  • fac –   the desired factory.
Throws:
  • Error –  if the factory has already been defined.
  • SecurityException –  if a security manager exists and its checkSetFactory method doesn't allow the operation.
See Also:
/**
     * Sets the {@code ContentHandlerFactory} of an
     * application. It can be called at most once by an application.
     * <p>
     * The {@code ContentHandlerFactory} instance is used to
     * construct a content handler from a content type.
     * <p>
     * If there is a security manager, this method first calls
     * the security manager's {@code checkSetFactory} method
     * to ensure the operation is allowed.
     * This could result in a SecurityException.
     *
     * @param      fac   the desired factory.
     * @exception  Error  if the factory has already been defined.
     * @exception  SecurityException  if a security manager exists and its
     *             {@code checkSetFactory} method doesn't allow the operation.
     * @see        java.net.ContentHandlerFactory
     * @see        java.net.URLConnection#getContent()
     * @see        SecurityManager#checkSetFactory
     */
    public static synchronized void setContentHandlerFactory(ContentHandlerFactory fac) {
        if (factory != null) {
            throw new Error("factory already defined");
        }
        SecurityManager security = System.getSecurityManager();
        if (security != null) {
            security.checkSetFactory();
        }
        factory = fac;
    }

    private static final Hashtable<String, ContentHandler> handlers = new Hashtable<>();

    
Gets the Content Handler appropriate for this connection.

/**
     * Gets the Content Handler appropriate for this connection.
     */
    private ContentHandler getContentHandler() throws UnknownServiceException {
        String contentType = stripOffParameters(getContentType());
        if (contentType == null) {
            throw new UnknownServiceException("no content-type");
        }

        ContentHandler handler = handlers.get(contentType);
        if (handler != null)
            return handler;

        if (factory != null) {
            handler = factory.createContentHandler(contentType);
            if (handler != null)
                return handler;
        }

        handler = lookupContentHandlerViaProvider(contentType);

        if (handler != null) {
            ContentHandler h = handlers.putIfAbsent(contentType, handler);
            return Objects.requireNonNullElse(h, handler);
        }

        try {
            handler = lookupContentHandlerClassFor(contentType);
        } catch (Exception e) {
            e.printStackTrace();
            handler = UnknownContentHandler.INSTANCE;
        }

        assert handler != null;

        ContentHandler h = handlers.putIfAbsent(contentType, handler);
        return Objects.requireNonNullElse(h, handler);
    }

    /*
     * Media types are in the format: type/subtype*(; parameter).
     * For looking up the content handler, we should ignore those
     * parameters.
     */
    private String stripOffParameters(String contentType)
    {
        if (contentType == null)
            return null;
        int index = contentType.indexOf(';');

        if (index > 0)
            return contentType.substring(0, index);
        else
            return contentType;
    }

    private static final String contentClassPrefix = "sun.net.www.content";
    private static final String contentPathProp = "java.content.handler.pkgs";

    
Looks for a content handler in a user-definable set of places. By default it looks in "sun.net.www.content", but users can define a vertical-bar delimited set of class prefixes to search through in addition by defining the "java.content.handler.pkgs" property. The class name must be of the form: 
    {package-prefix}.{major}.{minor}
e.g.
    YoyoDyne.experimental.text.plain



/**
     * Looks for a content handler in a user-definable set of places.
     * By default it looks in {@value #contentClassPrefix}, but users can define
     * a vertical-bar delimited set of class prefixes to search through in
     * addition by defining the {@value #contentPathProp} property.
     * The class name must be of the form:
     * <pre>
     *     {package-prefix}.{major}.{minor}
     * e.g.
     *     YoyoDyne.experimental.text.plain
     * </pre>
     */
    private ContentHandler lookupContentHandlerClassFor(String contentType) {
        String contentHandlerClassName = typeToPackageName(contentType);

        String contentHandlerPkgPrefixes = getContentHandlerPkgPrefixes();

        StringTokenizer packagePrefixIter =
            new StringTokenizer(contentHandlerPkgPrefixes, "|");

        while (packagePrefixIter.hasMoreTokens()) {
            String packagePrefix = packagePrefixIter.nextToken().trim();

            try {
                String clsName = packagePrefix + "." + contentHandlerClassName;
                Class<?> cls = null;
                try {
                    cls = Class.forName(clsName);
                } catch (ClassNotFoundException e) {
                    ClassLoader cl = ClassLoader.getSystemClassLoader();
                    if (cl != null) {
                        cls = cl.loadClass(clsName);
                    }
                }
                if (cls != null) {
                    @SuppressWarnings("deprecation")
                    Object tmp = cls.newInstance();
                    return (ContentHandler) tmp;
                }
            } catch(Exception ignored) { }
        }

        return UnknownContentHandler.INSTANCE;
    }

    private ContentHandler lookupContentHandlerViaProvider(String contentType) {
        return AccessController.doPrivileged(
                new PrivilegedAction<>() {
                    @Override
                    public ContentHandler run() {
                        ClassLoader cl = ClassLoader.getSystemClassLoader();
                        ServiceLoader<ContentHandlerFactory> sl =
                                ServiceLoader.load(ContentHandlerFactory.class, cl);

                        Iterator<ContentHandlerFactory> iterator = sl.iterator();

                        ContentHandler handler = null;
                        while (iterator.hasNext()) {
                            ContentHandlerFactory f;
                            try {
                                f = iterator.next();
                            } catch (ServiceConfigurationError e) {
                                if (e.getCause() instanceof SecurityException) {
                                    continue;
                                }
                                throw e;
                            }
                            handler = f.createContentHandler(contentType);
                            if (handler != null) {
                                break;
                            }
                        }
                        return handler;
                    }
                });
    }

    
Utility function to map a MIME content type into an equivalent
pair of class name components.  For example: "text/html" would
be returned as "text.html"

/**
     * Utility function to map a MIME content type into an equivalent
     * pair of class name components.  For example: "text/html" would
     * be returned as "text.html"
     */
    private String typeToPackageName(String contentType) {
        // make sure we canonicalize the class name: all lower case
        contentType = contentType.toLowerCase();
        int len = contentType.length();
        char nm[] = new char[len];
        contentType.getChars(0, len, nm, 0);
        for (int i = 0; i < len; i++) {
            char c = nm[i];
            if (c == '/') {
                nm[i] = '.';
            } else if (!('A' <= c && c <= 'Z' ||
                       'a' <= c && c <= 'z' ||
                       '0' <= c && c <= '9')) {
                nm[i] = '_';
            }
        }
        return new String(nm);
    }


    
Returns a vertical bar separated list of package prefixes for potential content handlers. Tries to get the java.content.handler.pkgs property to use as a set of package prefixes to search. Whether or not that property has been defined, the "sun.net.www.content" is always the last one on the returned package list. 
/**
     * Returns a vertical bar separated list of package prefixes for potential
     * content handlers.  Tries to get the java.content.handler.pkgs property
     * to use as a set of package prefixes to search.  Whether or not
     * that property has been defined, the {@value #contentClassPrefix}
     * is always the last one on the returned package list.
     */
    private String getContentHandlerPkgPrefixes() {
        String packagePrefixList =
                GetPropertyAction.privilegedGetProperty(contentPathProp, "");

        if (packagePrefixList != "") {
            packagePrefixList += "|";
        }

        return packagePrefixList + contentClassPrefix;
    }

    
Tries to determine the content type of an object, based on the specified "file" component of a URL. This is a convenience method that can be used by subclasses that override the getContentType method. 
Params:
  • fname –   a filename.
See Also:
Returns: a guess as to what the content type of the object is,
         based upon its file name.
/**
     * Tries to determine the content type of an object, based
     * on the specified "file" component of a URL.
     * This is a convenience method that can be used by
     * subclasses that override the {@code getContentType} method.
     *
     * @param   fname   a filename.
     * @return  a guess as to what the content type of the object is,
     *          based upon its file name.
     * @see     java.net.URLConnection#getContentType()
     */
    public static String guessContentTypeFromName(String fname) {
        return getFileNameMap().getContentTypeFor(fname);
    }

    
Tries to determine the type of an input stream based on the characters at the beginning of the input stream. This method can be used by subclasses that override the getContentType method. 
 Ideally, this routine would not be needed. But many http servers return the incorrect content type; in addition, there are many nonstandard extensions. Direct inspection of the bytes to determine the content type is often more accurate than believing the content type claimed by the http server. 
Params:
  • is –   an input stream that supports marks.
Throws:
  • IOException –  if an I/O error occurs while reading the
              input stream.
See Also:
Returns: a guess at the content type, or null if none can be determined.
/**
     * Tries to determine the type of an input stream based on the
     * characters at the beginning of the input stream. This method can
     * be used by subclasses that override the
     * {@code getContentType} method.
     * <p>
     * Ideally, this routine would not be needed. But many
     * {@code http} servers return the incorrect content type; in
     * addition, there are many nonstandard extensions. Direct inspection
     * of the bytes to determine the content type is often more accurate
     * than believing the content type claimed by the {@code http} server.
     *
     * @param      is   an input stream that supports marks.
     * @return     a guess at the content type, or {@code null} if none
     *             can be determined.
     * @exception  IOException  if an I/O error occurs while reading the
     *               input stream.
     * @see        java.io.InputStream#mark(int)
     * @see        java.io.InputStream#markSupported()
     * @see        java.net.URLConnection#getContentType()
     */
    public static String guessContentTypeFromStream(InputStream is)
                        throws IOException {
        // If we can't read ahead safely, just give up on guessing
        if (!is.markSupported())
            return null;

        is.mark(16);
        int c1 = is.read();
        int c2 = is.read();
        int c3 = is.read();
        int c4 = is.read();
        int c5 = is.read();
        int c6 = is.read();
        int c7 = is.read();
        int c8 = is.read();
        int c9 = is.read();
        int c10 = is.read();
        int c11 = is.read();
        int c12 = is.read();
        int c13 = is.read();
        int c14 = is.read();
        int c15 = is.read();
        int c16 = is.read();
        is.reset();

        if (c1 == 0xCA && c2 == 0xFE && c3 == 0xBA && c4 == 0xBE) {
            return "application/java-vm";
        }

        if (c1 == 0xAC && c2 == 0xED) {
            // next two bytes are version number, currently 0x00 0x05
            return "application/x-java-serialized-object";
        }

        if (c1 == '<') {
            if (c2 == '!'
                || ((c2 == 'h' && (c3 == 't' && c4 == 'm' && c5 == 'l' ||
                                   c3 == 'e' && c4 == 'a' && c5 == 'd') ||
                (c2 == 'b' && c3 == 'o' && c4 == 'd' && c5 == 'y'))) ||
                ((c2 == 'H' && (c3 == 'T' && c4 == 'M' && c5 == 'L' ||
                                c3 == 'E' && c4 == 'A' && c5 == 'D') ||
                (c2 == 'B' && c3 == 'O' && c4 == 'D' && c5 == 'Y')))) {
                return "text/html";
            }

            if (c2 == '?' && c3 == 'x' && c4 == 'm' && c5 == 'l' && c6 == ' ') {
                return "application/xml";
            }
        }

        // big and little (identical) endian UTF-8 encodings, with BOM
        if (c1 == 0xef &&  c2 == 0xbb &&  c3 == 0xbf) {
            if (c4 == '<' &&  c5 == '?' &&  c6 == 'x') {
                return "application/xml";
            }
        }

        // big and little endian UTF-16 encodings, with byte order mark
        if (c1 == 0xfe && c2 == 0xff) {
            if (c3 == 0 && c4 == '<' && c5 == 0 && c6 == '?' &&
                c7 == 0 && c8 == 'x') {
                return "application/xml";
            }
        }

        if (c1 == 0xff && c2 == 0xfe) {
            if (c3 == '<' && c4 == 0 && c5 == '?' && c6 == 0 &&
                c7 == 'x' && c8 == 0) {
                return "application/xml";
            }
        }

        // big and little endian UTF-32 encodings, with BOM
        if (c1 == 0x00 &&  c2 == 0x00 &&  c3 == 0xfe &&  c4 == 0xff) {
            if (c5  == 0 && c6  == 0 && c7  == 0 && c8  == '<' &&
                c9  == 0 && c10 == 0 && c11 == 0 && c12 == '?' &&
                c13 == 0 && c14 == 0 && c15 == 0 && c16 == 'x') {
                return "application/xml";
            }
        }

        if (c1 == 0xff &&  c2 == 0xfe &&  c3 == 0x00 &&  c4 == 0x00) {
            if (c5  == '<' && c6  == 0 && c7  == 0 && c8  == 0 &&
                c9  == '?' && c10 == 0 && c11 == 0 && c12 == 0 &&
                c13 == 'x' && c14 == 0 && c15 == 0 && c16 == 0) {
                return "application/xml";
            }
        }

        if (c1 == 'G' && c2 == 'I' && c3 == 'F' && c4 == '8') {
            return "image/gif";
        }

        if (c1 == '#' && c2 == 'd' && c3 == 'e' && c4 == 'f') {
            return "image/x-bitmap";
        }

        if (c1 == '!' && c2 == ' ' && c3 == 'X' && c4 == 'P' &&
                        c5 == 'M' && c6 == '2') {
            return "image/x-pixmap";
        }

        if (c1 == 137 && c2 == 80 && c3 == 78 &&
                c4 == 71 && c5 == 13 && c6 == 10 &&
                c7 == 26 && c8 == 10) {
            return "image/png";
        }

        if (c1 == 0xFF && c2 == 0xD8 && c3 == 0xFF) {
            if (c4 == 0xE0 || c4 == 0xEE) {
                return "image/jpeg";
            }

            /**
             * File format used by digital cameras to store images.
             * Exif Format can be read by any application supporting
             * JPEG. Exif Spec can be found at:
             * http://www.pima.net/standards/it10/PIMA15740/Exif_2-1.PDF
             */
            if ((c4 == 0xE1) &&
                (c7 == 'E' && c8 == 'x' && c9 == 'i' && c10 =='f' &&
                 c11 == 0)) {
                return "image/jpeg";
            }
        }

        if ((c1 == 0x49 && c2 == 0x49 && c3 == 0x2a && c4 == 0x00)
            || (c1 == 0x4d && c2 == 0x4d && c3 == 0x00 && c4 == 0x2a)) {
            return "image/tiff";
        }

        if (c1 == 0xD0 && c2 == 0xCF && c3 == 0x11 && c4 == 0xE0 &&
            c5 == 0xA1 && c6 == 0xB1 && c7 == 0x1A && c8 == 0xE1) {

            /* Above is signature of Microsoft Structured Storage.
             * Below this, could have tests for various SS entities.
             * For now, just test for FlashPix.
             */
            if (checkfpx(is)) {
                return "image/vnd.fpx";
            }
        }

        if (c1 == 0x2E && c2 == 0x73 && c3 == 0x6E && c4 == 0x64) {
            return "audio/basic";  // .au format, big endian
        }

        if (c1 == 0x64 && c2 == 0x6E && c3 == 0x73 && c4 == 0x2E) {
            return "audio/basic";  // .au format, little endian
        }

        if (c1 == 'R' && c2 == 'I' && c3 == 'F' && c4 == 'F') {
            /* I don't know if this is official but evidence
             * suggests that .wav files start with "RIFF" - brown
             */
            return "audio/x-wav";
        }
        return null;
    }

    
Check for FlashPix image data in InputStream is.  Return true if
the stream has FlashPix data, false otherwise.  Before calling this
method, the stream should have already been checked to be sure it
contains Microsoft Structured Storage data.

/**
     * Check for FlashPix image data in InputStream is.  Return true if
     * the stream has FlashPix data, false otherwise.  Before calling this
     * method, the stream should have already been checked to be sure it
     * contains Microsoft Structured Storage data.
     */
    private static boolean checkfpx(InputStream is) throws IOException {

        /* Test for FlashPix image data in Microsoft Structured Storage format.
         * In general, should do this with calls to an SS implementation.
         * Lacking that, need to dig via offsets to get to the FlashPix
         * ClassID.  Details:
         *
         * Offset to Fpx ClsID from beginning of stream should be:
         *
         * FpxClsidOffset = rootEntryOffset + clsidOffset
         *
         * where: clsidOffset = 0x50.
         *        rootEntryOffset = headerSize + sectorSize*sectDirStart
         *                          + 128*rootEntryDirectory
         *
         *        where:  headerSize = 0x200 (always)
         *                sectorSize = 2 raised to power of uSectorShift,
         *                             which is found in the header at
         *                             offset 0x1E.
         *                sectDirStart = found in the header at offset 0x30.
         *                rootEntryDirectory = in general, should search for
         *                                     directory labelled as root.
         *                                     We will assume value of 0 (i.e.,
         *                                     rootEntry is in first directory)
         */

        // Mark the stream so we can reset it. 0x100 is enough for the first
        // few reads, but the mark will have to be reset and set again once
        // the offset to the root directory entry is computed. That offset
        // can be very large and isn't know until the stream has been read from
        is.mark(0x100);

        // Get the byte ordering located at 0x1E. 0xFE is Intel,
        // 0xFF is other
        long toSkip = (long)0x1C;
        long posn;

        if ((posn = skipForward(is, toSkip)) < toSkip) {
          is.reset();
          return false;
        }

        int c[] = new int[16];
        if (readBytes(c, 2, is) < 0) {
            is.reset();
            return false;
        }

        int byteOrder = c[0];

        posn+=2;
        int uSectorShift;
        if (readBytes(c, 2, is) < 0) {
            is.reset();
            return false;
        }

        if(byteOrder == 0xFE) {
            uSectorShift = c[0];
            uSectorShift += c[1] << 8;
        }
        else {
            uSectorShift = c[0] << 8;
            uSectorShift += c[1];
        }

        posn += 2;
        toSkip = (long)0x30 - posn;
        long skipped = 0;
        if ((skipped = skipForward(is, toSkip)) < toSkip) {
          is.reset();
          return false;
        }
        posn += skipped;

        if (readBytes(c, 4, is) < 0) {
            is.reset();
            return false;
        }

        int sectDirStart;
        if(byteOrder == 0xFE) {
            sectDirStart = c[0];
            sectDirStart += c[1] << 8;
            sectDirStart += c[2] << 16;
            sectDirStart += c[3] << 24;
        } else {
            sectDirStart =  c[0] << 24;
            sectDirStart += c[1] << 16;
            sectDirStart += c[2] << 8;
            sectDirStart += c[3];
        }
        posn += 4;
        is.reset(); // Reset back to the beginning

        toSkip = 0x200L + (long)(1<<uSectorShift)*sectDirStart + 0x50L;

        // Sanity check!
        if (toSkip < 0) {
            return false;
        }

        /*
         * How far can we skip? Is there any performance problem here?
         * This skip can be fairly long, at least 0x4c650 in at least
         * one case. Have to assume that the skip will fit in an int.
         * Leave room to read whole root dir
         */
        is.mark((int)toSkip+0x30);

        if ((skipForward(is, toSkip)) < toSkip) {
            is.reset();
            return false;
        }

        /* should be at beginning of ClassID, which is as follows
         * (in Intel byte order):
         *    00 67 61 56 54 C1 CE 11 85 53 00 AA 00 A1 F9 5B
         *
         * This is stored from Windows as long,short,short,char[8]
         * so for byte order changes, the order only changes for
         * the first 8 bytes in the ClassID.
         *
         * Test against this, ignoring second byte (Intel) since
         * this could change depending on part of Fpx file we have.
         */

        if (readBytes(c, 16, is) < 0) {
            is.reset();
            return false;
        }

        // intel byte order
        if (byteOrder == 0xFE &&
            c[0] == 0x00 && c[2] == 0x61 && c[3] == 0x56 &&
            c[4] == 0x54 && c[5] == 0xC1 && c[6] == 0xCE &&
            c[7] == 0x11 && c[8] == 0x85 && c[9] == 0x53 &&
            c[10]== 0x00 && c[11]== 0xAA && c[12]== 0x00 &&
            c[13]== 0xA1 && c[14]== 0xF9 && c[15]== 0x5B) {
            is.reset();
            return true;
        }

        // non-intel byte order
        else if (c[3] == 0x00 && c[1] == 0x61 && c[0] == 0x56 &&
            c[5] == 0x54 && c[4] == 0xC1 && c[7] == 0xCE &&
            c[6] == 0x11 && c[8] == 0x85 && c[9] == 0x53 &&
            c[10]== 0x00 && c[11]== 0xAA && c[12]== 0x00 &&
            c[13]== 0xA1 && c[14]== 0xF9 && c[15]== 0x5B) {
            is.reset();
            return true;
        }
        is.reset();
        return false;
    }

    
Tries to read the specified number of bytes from the stream
Returns -1, If EOF is reached before len bytes are read, returns 0
otherwise

/**
     * Tries to read the specified number of bytes from the stream
     * Returns -1, If EOF is reached before len bytes are read, returns 0
     * otherwise
     */
    private static int readBytes(int c[], int len, InputStream is)
                throws IOException {

        byte buf[] = new byte[len];
        if (is.read(buf, 0, len) < len) {
            return -1;
        }

        // fill the passed in int array
        for (int i = 0; i < len; i++) {
             c[i] = buf[i] & 0xff;
        }
        return 0;
    }


    
Skips through the specified number of bytes from the stream
until either EOF is reached, or the specified
number of bytes have been skipped

/**
     * Skips through the specified number of bytes from the stream
     * until either EOF is reached, or the specified
     * number of bytes have been skipped
     */
    private static long skipForward(InputStream is, long toSkip)
                throws IOException {

        long eachSkip = 0;
        long skipped = 0;

        while (skipped != toSkip) {
            eachSkip = is.skip(toSkip - skipped);

            // check if EOF is reached
            if (eachSkip <= 0) {
                if (is.read() == -1) {
                    return skipped ;
                } else {
                    skipped++;
                }
            }
            skipped += eachSkip;
        }
        return skipped;
    }

    private void checkConnected() {
        if (connected)
            throw new IllegalStateException("Already connected");
    }
}

class UnknownContentHandler extends ContentHandler {
    static final ContentHandler INSTANCE = new UnknownContentHandler();

    public Object getContent(URLConnection uc) throws IOException {
        return uc.getInputStream();
    }
}