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,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 *
 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
 * or visit www.oracle.com if you need additional information or have any
 * questions.
 */

package java.net;

import java.io.IOException;
import java.io.InputStream;
import java.net.spi.URLStreamHandlerProvider;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.util.Hashtable;
import java.io.InvalidObjectException;
import java.io.ObjectStreamException;
import java.io.ObjectStreamField;
import java.io.ObjectInputStream.GetField;
import java.util.Iterator;
import java.util.Locale;
import java.util.NoSuchElementException;
import java.util.ServiceConfigurationError;
import java.util.ServiceLoader;

import jdk.internal.misc.JavaNetURLAccess;
import jdk.internal.misc.SharedSecrets;
import sun.security.util.SecurityConstants;
import sun.security.action.GetPropertyAction;


Class URL represents a Uniform Resource Locator, a pointer to a "resource" on the World Wide Web. A resource can be something as simple as a file or a directory, or it can be a reference to a more complicated object, such as a query to a database or to a search engine. More information on the types of URLs and their formats can be found at: 
Types of URL


In general, a URL can be broken into several parts. Consider the
following example:

    http://www.example.com/docs/resource1.html



 The URL above indicates that the protocol to use is http (HyperText Transfer Protocol) and that the information resides on a host machine named www.example.com. The information on that host machine is named /docs/resource1.html. The exact meaning of this name on the host machine is both protocol dependent and host dependent. The information normally resides in a file, but it could be generated on the fly. This component of the URL is called the path component.

 A URL can optionally specify a "port", which is the port number to which the TCP connection is made on the remote host machine. If the port is not specified, the default port for the protocol is used instead. For example, the default port for http is 80. An alternative port could be specified as: 
    http://www.example.com:1080/docs/resource1.html



 The syntax of URL is defined by RFC 2396: Uniform
Resource Identifiers (URI): Generic Syntax, amended by RFC 2732: Format for
Literal IPv6 Addresses in URLs. The Literal IPv6 address format
also supports scope_ids. The syntax and usage of scope_ids is described
here.


A URL may have appended to it a "fragment", also known
as a "ref" or a "reference". The fragment is indicated by the sharp
sign character "#" followed by more characters. For example,

    http://java.sun.com/index.html#chapter1



 This fragment is not technically part of the URL. Rather, it indicates that after the specified resource is retrieved, the application is specifically interested in that part of the document that has the tag chapter1 attached to it. The meaning of a tag is resource specific. 

An application can also specify a "relative URL",
which contains only enough information to reach the resource
relative to another URL. Relative URLs are frequently used within
HTML pages. For example, if the contents of the URL:

    http://java.sun.com/index.html


contained within it the relative URL:

    FAQ.html


it would be a shorthand for:

    http://java.sun.com/FAQ.html




The relative URL need not specify all the components of a URL. If
the protocol, host name, or port number is missing, the value is
inherited from the fully specified URL. The file component must be
specified. The optional fragment is not inherited.


The URL class does not itself encode or decode any URL components
according to the escaping mechanism defined in RFC2396. It is the
responsibility of the caller to encode any fields, which need to be
escaped prior to calling URL, and also to decode any escaped fields,
that are returned from URL. Furthermore, because URL has no knowledge
of URL escaping, it does not recognise equivalence between the encoded
or decoded form of the same URL. For example, the two URLs:


    http://foo.com/hello world/ and http://foo.com/hello%20world

would be considered not equal to each other.

 Note, the URI class does perform escaping of its component fields in certain circumstances. The recommended way to manage the encoding and decoding of URLs is to use URI, and to convert between these two classes using toURI() and URI.toURL(). 
 The URLEncoder and URLDecoder classes can also be used, but only for HTML form encoding, which is not the same as the encoding scheme defined in RFC2396. 
Author: James Gosling
Since:1.0
/**
 * Class {@code URL} represents a Uniform Resource
 * Locator, a pointer to a "resource" on the World
 * Wide Web. A resource can be something as simple as a file or a
 * directory, or it can be a reference to a more complicated object,
 * such as a query to a database or to a search engine. More
 * information on the types of URLs and their formats can be found at:
 * <a href=
 * "http://web.archive.org/web/20051219043731/http://archive.ncsa.uiuc.edu/SDG/Software/Mosaic/Demo/url-primer.html">
 * <i>Types of URL</i></a>
 * <p>
 * In general, a URL can be broken into several parts. Consider the
 * following example:
 * <blockquote><pre>
 *     http://www.example.com/docs/resource1.html
 * </pre></blockquote>
 * <p>
 * The URL above indicates that the protocol to use is
 * {@code http} (HyperText Transfer Protocol) and that the
 * information resides on a host machine named
 * {@code www.example.com}. The information on that host
 * machine is named {@code /docs/resource1.html}. The exact
 * meaning of this name on the host machine is both protocol
 * dependent and host dependent. The information normally resides in
 * a file, but it could be generated on the fly. This component of
 * the URL is called the <i>path</i> component.
 * <p>
 * A URL can optionally specify a "port", which is the
 * port number to which the TCP connection is made on the remote host
 * machine. If the port is not specified, the default port for
 * the protocol is used instead. For example, the default port for
 * {@code http} is {@code 80}. An alternative port could be
 * specified as:
 * <blockquote><pre>
 *     http://www.example.com:1080/docs/resource1.html
 * </pre></blockquote>
 * <p>
 * The syntax of {@code URL} is defined by  <a
 * href="http://www.ietf.org/rfc/rfc2396.txt"><i>RFC&nbsp;2396: Uniform
 * Resource Identifiers (URI): Generic Syntax</i></a>, amended by <a
 * href="http://www.ietf.org/rfc/rfc2732.txt"><i>RFC&nbsp;2732: Format for
 * Literal IPv6 Addresses in URLs</i></a>. The Literal IPv6 address format
 * also supports scope_ids. The syntax and usage of scope_ids is described
 * <a href="Inet6Address.html#scoped">here</a>.
 * <p>
 * A URL may have appended to it a "fragment", also known
 * as a "ref" or a "reference". The fragment is indicated by the sharp
 * sign character "#" followed by more characters. For example,
 * <blockquote><pre>
 *     http://java.sun.com/index.html#chapter1
 * </pre></blockquote>
 * <p>
 * This fragment is not technically part of the URL. Rather, it
 * indicates that after the specified resource is retrieved, the
 * application is specifically interested in that part of the
 * document that has the tag {@code chapter1} attached to it. The
 * meaning of a tag is resource specific.
 * <p>
 * An application can also specify a "relative URL",
 * which contains only enough information to reach the resource
 * relative to another URL. Relative URLs are frequently used within
 * HTML pages. For example, if the contents of the URL:
 * <blockquote><pre>
 *     http://java.sun.com/index.html
 * </pre></blockquote>
 * contained within it the relative URL:
 * <blockquote><pre>
 *     FAQ.html
 * </pre></blockquote>
 * it would be a shorthand for:
 * <blockquote><pre>
 *     http://java.sun.com/FAQ.html
 * </pre></blockquote>
 * <p>
 * The relative URL need not specify all the components of a URL. If
 * the protocol, host name, or port number is missing, the value is
 * inherited from the fully specified URL. The file component must be
 * specified. The optional fragment is not inherited.
 * <p>
 * The URL class does not itself encode or decode any URL components
 * according to the escaping mechanism defined in RFC2396. It is the
 * responsibility of the caller to encode any fields, which need to be
 * escaped prior to calling URL, and also to decode any escaped fields,
 * that are returned from URL. Furthermore, because URL has no knowledge
 * of URL escaping, it does not recognise equivalence between the encoded
 * or decoded form of the same URL. For example, the two URLs:<br>
 * <pre>    http://foo.com/hello world/ and http://foo.com/hello%20world</pre>
 * would be considered not equal to each other.
 * <p>
 * Note, the {@link java.net.URI} class does perform escaping of its
 * component fields in certain circumstances. The recommended way
 * to manage the encoding and decoding of URLs is to use {@link java.net.URI},
 * and to convert between these two classes using {@link #toURI()} and
 * {@link URI#toURL()}.
 * <p>
 * The {@link URLEncoder} and {@link URLDecoder} classes can also be
 * used, but only for HTML form encoding, which is not the same
 * as the encoding scheme defined in RFC2396.
 *
 * @author  James Gosling
 * @since 1.0
 */
public final class URL implements java.io.Serializable {

    static final String BUILTIN_HANDLERS_PREFIX = "sun.net.www.protocol";
    static final long serialVersionUID = -7627629688361524110L;

    
The property which specifies the package prefix list to be scanned
for protocol handlers.  The value of this property (if any) should
be a vertical bar delimited list of package names to search through
for a protocol handler to load.  The policy of this class is that
all protocol handlers will be in a class called .Handler,
and each package in the list is examined in turn for a matching
handler.  If none are found (or the property is not specified), the
default package prefix, sun.net.www.protocol, is used.  The search
proceeds from the first package in the list to the last and stops
when a match is found.

/**
     * The property which specifies the package prefix list to be scanned
     * for protocol handlers.  The value of this property (if any) should
     * be a vertical bar delimited list of package names to search through
     * for a protocol handler to load.  The policy of this class is that
     * all protocol handlers will be in a class called <protocolname>.Handler,
     * and each package in the list is examined in turn for a matching
     * handler.  If none are found (or the property is not specified), the
     * default package prefix, sun.net.www.protocol, is used.  The search
     * proceeds from the first package in the list to the last and stops
     * when a match is found.
     */
    private static final String protocolPathProp = "java.protocol.handler.pkgs";

    
The protocol to use (ftp, http, nntp, ... etc.) .

@serial
/**
     * The protocol to use (ftp, http, nntp, ... etc.) .
     * @serial
     */
    private String protocol;

    
The host name to connect to.

@serial
/**
     * The host name to connect to.
     * @serial
     */
    private String host;

    
The protocol port to connect to.

@serial
/**
     * The protocol port to connect to.
     * @serial
     */
    private int port = -1;

    
The specified file name on that host. file is defined as path[?query] 
@serial
/**
     * The specified file name on that host. {@code file} is
     * defined as {@code path[?query]}
     * @serial
     */
    private String file;

    
The query part of this URL.

/**
     * The query part of this URL.
     */
    private transient String query;

    
The authority part of this URL.

@serial
/**
     * The authority part of this URL.
     * @serial
     */
    private String authority;

    
The path part of this URL.

/**
     * The path part of this URL.
     */
    private transient String path;

    
The userinfo part of this URL.

/**
     * The userinfo part of this URL.
     */
    private transient String userInfo;

    
# reference.

@serial
/**
     * # reference.
     * @serial
     */
    private String ref;

    
The host's IP address, used in equals and hashCode.
Computed on demand. An uninitialized or unknown hostAddress is null.

/**
     * The host's IP address, used in equals and hashCode.
     * Computed on demand. An uninitialized or unknown hostAddress is null.
     */
    transient InetAddress hostAddress;

    
The URLStreamHandler for this URL.

/**
     * The URLStreamHandler for this URL.
     */
    transient URLStreamHandler handler;

    /* Our hash code.
     * @serial
     */
    private int hashCode = -1;

    private transient UrlDeserializedState tempState;

    
Creates a URL object from the specified protocol, host, port number, and file.
 host can be expressed as a host name or a literal IP address. If IPv6 literal address is used, it should be enclosed in square brackets ('[' and ']'), as specified by RFC 2732;
However, the literal IPv6 address format defined in RFC 2373: IP
Version 6 Addressing Architecture is also accepted.
 Specifying a port number of -1 indicates that the URL should use the default port for the protocol.

If this is the first URL object being created with the specified
protocol, a stream protocol handler object, an instance of class URLStreamHandler, is created for that protocol: 
    

  1. If the application has previously set up an instance of URLStreamHandlerFactory as the stream handler factory, then the createURLStreamHandler method of that instance is called with the protocol string as an argument to create the stream protocol handler. 
  2. If no URLStreamHandlerFactory has yet been set up, or if the factory's createURLStreamHandler method returns null, then the 
    ServiceLoader mechanism is used to locate URLStreamHandlerProvider implementations using the system class loader. The order that providers are located is implementation specific, and an implementation is free to cache the located providers. A 
    ServiceConfigurationError, Error or RuntimeException thrown from the createURLStreamHandler, if encountered, will be propagated to the calling thread. The 
    createURLStreamHandler method of each provider, if instantiated, is invoked, with the protocol string, until a provider returns non-null, or all providers have been exhausted. 
  3. If the previous step fails to find a protocol handler, the
    constructor reads the value of the system property:
    
    
        java.protocol.handler.pkgs
    
     If the value of that system property is not null, it is interpreted as a list of packages separated by a vertical slash character '|'. The constructor tries to load the class named: 
    
        <package>.<protocol>.Handler
    
     where <package> is replaced by the name of the package and <protocol> is replaced by the name of the protocol. If this class does not exist, or if the class exists but it is not a subclass of URLStreamHandler, then the next package in the list is tried. 
  4. If the previous step fails to find a protocol handler, then the constructor tries to load a built-in protocol handler. If this class does not exist, or if the class exists but it is not a subclass of URLStreamHandler, then a MalformedURLException is thrown. 


Protocol handlers for the following protocols are guaranteed
to exist on the search path :-

    http, https, file, and jar


Protocol handlers for additional protocols may also be  available.
Some protocol handlers, for example those used for loading platform
classes or classes on the class path, may not be overridden. The details
of such restrictions, and when those restrictions apply (during
initialization of the runtime for example), are implementation specific
and therefore not specified

No validation of the inputs is performed by this constructor.

Params:
  • protocol –   the name of the protocol to use.
  • host –       the name of the host.
  • port –       the port number on the host.
  • file –       the file on the host
Throws:
See Also:
/**
     * Creates a {@code URL} object from the specified
     * {@code protocol}, {@code host}, {@code port}
     * number, and {@code file}.<p>
     *
     * {@code host} can be expressed as a host name or a literal
     * IP address. If IPv6 literal address is used, it should be
     * enclosed in square brackets ({@code '['} and {@code ']'}), as
     * specified by <a
     * href="http://www.ietf.org/rfc/rfc2732.txt">RFC&nbsp;2732</a>;
     * However, the literal IPv6 address format defined in <a
     * href="http://www.ietf.org/rfc/rfc2373.txt"><i>RFC&nbsp;2373: IP
     * Version 6 Addressing Architecture</i></a> is also accepted.<p>
     *
     * Specifying a {@code port} number of {@code -1}
     * indicates that the URL should use the default port for the
     * protocol.<p>
     *
     * If this is the first URL object being created with the specified
     * protocol, a <i>stream protocol handler</i> object, an instance of
     * class {@code URLStreamHandler}, is created for that protocol:
     * <ol>
     * <li>If the application has previously set up an instance of
     *     {@code URLStreamHandlerFactory} as the stream handler factory,
     *     then the {@code createURLStreamHandler} method of that instance
     *     is called with the protocol string as an argument to create the
     *     stream protocol handler.
     * <li>If no {@code URLStreamHandlerFactory} has yet been set up,
     *     or if the factory's {@code createURLStreamHandler} method
     *     returns {@code null}, then the {@linkplain java.util.ServiceLoader
     *     ServiceLoader} mechanism is used to locate {@linkplain
     *     java.net.spi.URLStreamHandlerProvider URLStreamHandlerProvider}
     *     implementations using the system class
     *     loader. The order that providers are located is implementation
     *     specific, and an implementation is free to cache the located
     *     providers. A {@linkplain java.util.ServiceConfigurationError
     *     ServiceConfigurationError}, {@code Error} or {@code RuntimeException}
     *     thrown from the {@code createURLStreamHandler}, if encountered, will
     *     be propagated to the calling thread. The {@code
     *     createURLStreamHandler} method of each provider, if instantiated, is
     *     invoked, with the protocol string, until a provider returns non-null,
     *     or all providers have been exhausted.
     * <li>If the previous step fails to find a protocol handler, the
     *     constructor reads the value of the system property:
     *     <blockquote>{@code
     *         java.protocol.handler.pkgs
     *     }</blockquote>
     *     If the value of that system property is not {@code null},
     *     it is interpreted as a list of packages separated by a vertical
     *     slash character '{@code |}'. The constructor tries to load
     *     the class named:
     *     <blockquote>{@code
     *         <package>.<protocol>.Handler
     *     }</blockquote>
     *     where {@code <package>} is replaced by the name of the package
     *     and {@code <protocol>} is replaced by the name of the protocol.
     *     If this class does not exist, or if the class exists but it is not
     *     a subclass of {@code URLStreamHandler}, then the next package
     *     in the list is tried.
     * <li>If the previous step fails to find a protocol handler, then the
     *     constructor tries to load a built-in protocol handler.
     *     If this class does not exist, or if the class exists but it is not a
     *     subclass of {@code URLStreamHandler}, then a
     *     {@code MalformedURLException} is thrown.
     * </ol>
     *
     * <p>Protocol handlers for the following protocols are guaranteed
     * to exist on the search path :-
     * <blockquote><pre>
     *     http, https, file, and jar
     * </pre></blockquote>
     * Protocol handlers for additional protocols may also be  available.
     * Some protocol handlers, for example those used for loading platform
     * classes or classes on the class path, may not be overridden. The details
     * of such restrictions, and when those restrictions apply (during
     * initialization of the runtime for example), are implementation specific
     * and therefore not specified
     *
     * <p>No validation of the inputs is performed by this constructor.
     *
     * @param      protocol   the name of the protocol to use.
     * @param      host       the name of the host.
     * @param      port       the port number on the host.
     * @param      file       the file on the host
     * @exception  MalformedURLException  if an unknown protocol or the port
     *                  is a negative number other than -1
     * @see        java.lang.System#getProperty(java.lang.String)
     * @see        java.net.URL#setURLStreamHandlerFactory(
     *                  java.net.URLStreamHandlerFactory)
     * @see        java.net.URLStreamHandler
     * @see        java.net.URLStreamHandlerFactory#createURLStreamHandler(
     *                  java.lang.String)
     */
    public URL(String protocol, String host, int port, String file)
        throws MalformedURLException
    {
        this(protocol, host, port, file, null);
    }

    
Creates a URL from the specified protocol name, host name, and file name. The default port for the specified protocol is used. 

This constructor is equivalent to the four-argument
constructor with the only difference of using the
default port for the specified protocol.
No validation of the inputs is performed by this constructor.

Params:
  • protocol –   the name of the protocol to use.
  • host –       the name of the host.
  • file –       the file on the host.
Throws:
See Also:
/**
     * Creates a URL from the specified {@code protocol}
     * name, {@code host} name, and {@code file} name. The
     * default port for the specified protocol is used.
     * <p>
     * This constructor is equivalent to the four-argument
     * constructor with the only difference of using the
     * default port for the specified protocol.
     *
     * No validation of the inputs is performed by this constructor.
     *
     * @param      protocol   the name of the protocol to use.
     * @param      host       the name of the host.
     * @param      file       the file on the host.
     * @exception  MalformedURLException  if an unknown protocol is specified.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *                  int, java.lang.String)
     */
    public URL(String protocol, String host, String file)
            throws MalformedURLException {
        this(protocol, host, -1, file);
    }

    
Creates a URL object from the specified protocol, host, port number, file, and handler. Specifying a port number of -1 indicates that the URL should use the default port for the protocol. Specifying a handler of null indicates that the URL should use a default stream handler for the protocol, as outlined for: java.net.URL#URL(java.lang.String, java.lang.String, int, java.lang.String) 
If the handler is not null and there is a security manager, the security manager's checkPermission method is called with a NetPermission("specifyStreamHandler") permission. This may result in a SecurityException. No validation of the inputs is performed by this constructor. 
Params:
  • protocol –   the name of the protocol to use.
  • host –       the name of the host.
  • port –       the port number on the host.
  • file –       the file on the host
  • handler –    the stream handler for the URL.
Throws:
  • MalformedURLException –  if an unknown protocol or the port
is a negative number other than -1
  • SecurityException –  if a security manager exists and its checkPermission method doesn't allow specifying a stream handler explicitly.
See Also:
/**
     * Creates a {@code URL} object from the specified
     * {@code protocol}, {@code host}, {@code port}
     * number, {@code file}, and {@code handler}. Specifying
     * a {@code port} number of {@code -1} indicates that
     * the URL should use the default port for the protocol. Specifying
     * a {@code handler} of {@code null} indicates that the URL
     * should use a default stream handler for the protocol, as outlined
     * for:
     *     java.net.URL#URL(java.lang.String, java.lang.String, int,
     *                      java.lang.String)
     *
     * <p>If the handler is not null and there is a security manager,
     * the security manager's {@code checkPermission}
     * method is called with a
     * {@code NetPermission("specifyStreamHandler")} permission.
     * This may result in a SecurityException.
     *
     * No validation of the inputs is performed by this constructor.
     *
     * @param      protocol   the name of the protocol to use.
     * @param      host       the name of the host.
     * @param      port       the port number on the host.
     * @param      file       the file on the host
     * @param      handler    the stream handler for the URL.
     * @exception  MalformedURLException  if an unknown protocol or the port
                        is a negative number other than -1
     * @exception  SecurityException
     *        if a security manager exists and its
     *        {@code checkPermission} method doesn't allow
     *        specifying a stream handler explicitly.
     * @see        java.lang.System#getProperty(java.lang.String)
     * @see        java.net.URL#setURLStreamHandlerFactory(
     *                  java.net.URLStreamHandlerFactory)
     * @see        java.net.URLStreamHandler
     * @see        java.net.URLStreamHandlerFactory#createURLStreamHandler(
     *                  java.lang.String)
     * @see        SecurityManager#checkPermission
     * @see        java.net.NetPermission
     */
    public URL(String protocol, String host, int port, String file,
               URLStreamHandler handler) throws MalformedURLException {
        if (handler != null) {
            SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
                // check for permission to specify a handler
                checkSpecifyHandler(sm);
            }
        }

        protocol = protocol.toLowerCase(Locale.ROOT);
        this.protocol = protocol;
        if (host != null) {

            /**
             * if host is a literal IPv6 address,
             * we will make it conform to RFC 2732
             */
            if (host.indexOf(':') >= 0 && !host.startsWith("[")) {
                host = "["+host+"]";
            }
            this.host = host;

            if (port < -1) {
                throw new MalformedURLException("Invalid port number :" +
                                                    port);
            }
            this.port = port;
            authority = (port == -1) ? host : host + ":" + port;
        }

        int index = file.indexOf('#');
        this.ref = index < 0 ? null : file.substring(index + 1);
        file = index < 0 ? file : file.substring(0, index);
        int q = file.lastIndexOf('?');
        if (q != -1) {
            this.query = file.substring(q + 1);
            this.path = file.substring(0, q);
            this.file = path + "?" + query;
        } else {
            this.path = file;
            this.file = path;
        }

        // Note: we don't do validation of the URL here. Too risky to change
        // right now, but worth considering for future reference. -br
        if (handler == null &&
            (handler = getURLStreamHandler(protocol)) == null) {
            throw new MalformedURLException("unknown protocol: " + protocol);
        }
        this.handler = handler;
    }

    
Creates a URL object from the String representation. 
 This constructor is equivalent to a call to the two-argument constructor with a null first argument. 
Params:
  • spec –  the String to parse as a URL.
Throws:
  • MalformedURLException –  if no protocol is specified, or an unknown protocol is found, or spec is null, or the parsed URL fails to comply with the specific syntax of the associated protocol.
See Also:
/**
     * Creates a {@code URL} object from the {@code String}
     * representation.
     * <p>
     * This constructor is equivalent to a call to the two-argument
     * constructor with a {@code null} first argument.
     *
     * @param      spec   the {@code String} to parse as a URL.
     * @exception  MalformedURLException  if no protocol is specified, or an
     *               unknown protocol is found, or {@code spec} is {@code null},
     *               or the parsed URL fails to comply with the specific syntax
     *               of the associated protocol.
     * @see        java.net.URL#URL(java.net.URL, java.lang.String)
     */
    public URL(String spec) throws MalformedURLException {
        this(null, spec);
    }

    
Creates a URL by parsing the given spec within a specified context.
The new URL is created from the given context URL and the spec
argument as described in
RFC2396 "Uniform Resource Identifiers : Generic * Syntax" :

         <scheme>://<authority><path>?<query>#<fragment>


The reference is parsed into the scheme, authority, path, query and
fragment parts. If the path component is empty and the scheme,
authority, and query components are undefined, then the new URL is a
reference to the current document. Otherwise, the fragment and query
parts present in the spec are used in the new URL.


If the scheme component is defined in the given spec and does not match
the scheme of the context, then the new URL is created as an absolute
URL based on the spec alone. Otherwise the scheme component is inherited
from the context URL.


If the authority component is present in the spec then the spec is
treated as absolute and the spec authority and path will replace the
context authority and path. If the authority component is absent in the
spec then the authority of the new URL will be inherited from the
context.


If the spec's path component begins with a slash character
"/" then the
path is treated as absolute and the spec path replaces the context path.


Otherwise, the path is treated as a relative path and is appended to the
context path, as described in RFC2396. Also, in this case,
the path is canonicalized through the removal of directory
changes made by occurrences of ".." and ".".


For a more detailed description of URL parsing, refer to RFC2396.

Params:
  • context –   the context in which to parse the specification.
  • spec –  the String to parse as a URL.
Throws:
  • MalformedURLException –  if no protocol is specified, or an unknown protocol is found, or spec is null, or the parsed URL fails to comply with the specific syntax of the associated protocol.
See Also:
/**
     * Creates a URL by parsing the given spec within a specified context.
     *
     * The new URL is created from the given context URL and the spec
     * argument as described in
     * RFC2396 &quot;Uniform Resource Identifiers : Generic * Syntax&quot; :
     * <blockquote><pre>
     *          &lt;scheme&gt;://&lt;authority&gt;&lt;path&gt;?&lt;query&gt;#&lt;fragment&gt;
     * </pre></blockquote>
     * The reference is parsed into the scheme, authority, path, query and
     * fragment parts. If the path component is empty and the scheme,
     * authority, and query components are undefined, then the new URL is a
     * reference to the current document. Otherwise, the fragment and query
     * parts present in the spec are used in the new URL.
     * <p>
     * If the scheme component is defined in the given spec and does not match
     * the scheme of the context, then the new URL is created as an absolute
     * URL based on the spec alone. Otherwise the scheme component is inherited
     * from the context URL.
     * <p>
     * If the authority component is present in the spec then the spec is
     * treated as absolute and the spec authority and path will replace the
     * context authority and path. If the authority component is absent in the
     * spec then the authority of the new URL will be inherited from the
     * context.
     * <p>
     * If the spec's path component begins with a slash character
     * &quot;/&quot; then the
     * path is treated as absolute and the spec path replaces the context path.
     * <p>
     * Otherwise, the path is treated as a relative path and is appended to the
     * context path, as described in RFC2396. Also, in this case,
     * the path is canonicalized through the removal of directory
     * changes made by occurrences of &quot;..&quot; and &quot;.&quot;.
     * <p>
     * For a more detailed description of URL parsing, refer to RFC2396.
     *
     * @param      context   the context in which to parse the specification.
     * @param      spec      the {@code String} to parse as a URL.
     * @exception  MalformedURLException  if no protocol is specified, or an
     *               unknown protocol is found, or {@code spec} is {@code null},
     *               or the parsed URL fails to comply with the specific syntax
     *               of the associated protocol.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *                  int, java.lang.String)
     * @see        java.net.URLStreamHandler
     * @see        java.net.URLStreamHandler#parseURL(java.net.URL,
     *                  java.lang.String, int, int)
     */
    public URL(URL context, String spec) throws MalformedURLException {
        this(context, spec, null);
    }

    
Creates a URL by parsing the given spec with the specified handler
within a specified context. If the handler is null, the parsing
occurs as with the two argument constructor.

Params:
  • context –   the context in which to parse the specification.
  • spec –  the String to parse as a URL.
  • handler –   the stream handler for the URL.
Throws:
  • MalformedURLException –  if no protocol is specified, or an unknown protocol is found, or spec is null, or the parsed URL fails to comply with the specific syntax of the associated protocol.
  • SecurityException –  if a security manager exists and its checkPermission method doesn't allow specifying a stream handler.
See Also:
/**
     * Creates a URL by parsing the given spec with the specified handler
     * within a specified context. If the handler is null, the parsing
     * occurs as with the two argument constructor.
     *
     * @param      context   the context in which to parse the specification.
     * @param      spec      the {@code String} to parse as a URL.
     * @param      handler   the stream handler for the URL.
     * @exception  MalformedURLException  if no protocol is specified, or an
     *               unknown protocol is found, or {@code spec} is {@code null},
     *               or the parsed URL fails to comply with the specific syntax
     *               of the associated protocol.
     * @exception  SecurityException
     *        if a security manager exists and its
     *        {@code checkPermission} method doesn't allow
     *        specifying a stream handler.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *                  int, java.lang.String)
     * @see        java.net.URLStreamHandler
     * @see        java.net.URLStreamHandler#parseURL(java.net.URL,
     *                  java.lang.String, int, int)
     */
    public URL(URL context, String spec, URLStreamHandler handler)
        throws MalformedURLException
    {
        String original = spec;
        int i, limit, c;
        int start = 0;
        String newProtocol = null;
        boolean aRef=false;
        boolean isRelative = false;

        // Check for permission to specify a handler
        if (handler != null) {
            SecurityManager sm = System.getSecurityManager();
            if (sm != null) {
                checkSpecifyHandler(sm);
            }
        }

        try {
            limit = spec.length();
            while ((limit > 0) && (spec.charAt(limit - 1) <= ' ')) {
                limit--;        //eliminate trailing whitespace
            }
            while ((start < limit) && (spec.charAt(start) <= ' ')) {
                start++;        // eliminate leading whitespace
            }

            if (spec.regionMatches(true, start, "url:", 0, 4)) {
                start += 4;
            }
            if (start < spec.length() && spec.charAt(start) == '#') {
                /* we're assuming this is a ref relative to the context URL.
                 * This means protocols cannot start w/ '#', but we must parse
                 * ref URL's like: "hello:there" w/ a ':' in them.
                 */
                aRef=true;
            }
            for (i = start ; !aRef && (i < limit) &&
                     ((c = spec.charAt(i)) != '/') ; i++) {
                if (c == ':') {
                    String s = spec.substring(start, i).toLowerCase(Locale.ROOT);
                    if (isValidProtocol(s)) {
                        newProtocol = s;
                        start = i + 1;
                    }
                    break;
                }
            }

            // Only use our context if the protocols match.
            protocol = newProtocol;
            if ((context != null) && ((newProtocol == null) ||
                            newProtocol.equalsIgnoreCase(context.protocol))) {
                // inherit the protocol handler from the context
                // if not specified to the constructor
                if (handler == null) {
                    handler = context.handler;
                }

                // If the context is a hierarchical URL scheme and the spec
                // contains a matching scheme then maintain backwards
                // compatibility and treat it as if the spec didn't contain
                // the scheme; see 5.2.3 of RFC2396
                if (context.path != null && context.path.startsWith("/"))
                    newProtocol = null;

                if (newProtocol == null) {
                    protocol = context.protocol;
                    authority = context.authority;
                    userInfo = context.userInfo;
                    host = context.host;
                    port = context.port;
                    file = context.file;
                    path = context.path;
                    isRelative = true;
                }
            }

            if (protocol == null) {
                throw new MalformedURLException("no protocol: "+original);
            }

            // Get the protocol handler if not specified or the protocol
            // of the context could not be used
            if (handler == null &&
                (handler = getURLStreamHandler(protocol)) == null) {
                throw new MalformedURLException("unknown protocol: "+protocol);
            }

            this.handler = handler;

            i = spec.indexOf('#', start);
            if (i >= 0) {
                ref = spec.substring(i + 1, limit);
                limit = i;
            }

            /*
             * Handle special case inheritance of query and fragment
             * implied by RFC2396 section 5.2.2.
             */
            if (isRelative && start == limit) {
                query = context.query;
                if (ref == null) {
                    ref = context.ref;
                }
            }

            handler.parseURL(this, spec, start, limit);

        } catch(MalformedURLException e) {
            throw e;
        } catch(Exception e) {
            MalformedURLException exception = new MalformedURLException(e.getMessage());
            exception.initCause(e);
            throw exception;
        }
    }

    
Creates a URL from a URI, as if by invoking uri.toURL(). 
See Also:
/**
     * Creates a URL from a URI, as if by invoking {@code uri.toURL()}.
     *
     * @see java.net.URI#toURL()
     */
    static URL fromURI(URI uri) throws MalformedURLException {
        if (!uri.isAbsolute()) {
            throw new IllegalArgumentException("URI is not absolute");
        }
        String protocol = uri.getScheme();

        // In general we need to go via Handler.parseURL, but for the jrt
        // protocol we enforce that the Handler is not overrideable and can
        // optimize URI to URL conversion.
        //
        // Case-sensitive comparison for performance; malformed protocols will
        // be handled correctly by the slow path.
        if (protocol.equals("jrt") && !uri.isOpaque()
                && uri.getRawFragment() == null) {

            String query = uri.getRawQuery();
            String path = uri.getRawPath();
            String file = (query == null) ? path : path + "?" + query;

            // URL represent undefined host as empty string while URI use null
            String host = uri.getHost();
            if (host == null) {
                host = "";
            }

            int port = uri.getPort();

            return new URL("jrt", host, port, file, null);
        } else {
            return new URL((URL)null, uri.toString(), null);
        }
    }

    /*
     * Returns true if specified string is a valid protocol name.
     */
    private boolean isValidProtocol(String protocol) {
        int len = protocol.length();
        if (len < 1)
            return false;
        char c = protocol.charAt(0);
        if (!Character.isLetter(c))
            return false;
        for (int i = 1; i < len; i++) {
            c = protocol.charAt(i);
            if (!Character.isLetterOrDigit(c) && c != '.' && c != '+' &&
                c != '-') {
                return false;
            }
        }
        return true;
    }

    /*
     * Checks for permission to specify a stream handler.
     */
    private void checkSpecifyHandler(SecurityManager sm) {
        sm.checkPermission(SecurityConstants.SPECIFY_HANDLER_PERMISSION);
    }

    
Sets the fields of the URL. This is not a public method so that
only URLStreamHandlers can modify URL fields. URLs are
otherwise constant.

Params:
  • protocol – the name of the protocol to use
  • host – the name of the host
  • port – the port number on the host
  • file – the file on the host
  • ref – the internal reference in the URL
/**
     * Sets the fields of the URL. This is not a public method so that
     * only URLStreamHandlers can modify URL fields. URLs are
     * otherwise constant.
     *
     * @param protocol the name of the protocol to use
     * @param host the name of the host
       @param port the port number on the host
     * @param file the file on the host
     * @param ref the internal reference in the URL
     */
    void set(String protocol, String host, int port,
             String file, String ref) {
        synchronized (this) {
            this.protocol = protocol;
            this.host = host;
            authority = port == -1 ? host : host + ":" + port;
            this.port = port;
            this.file = file;
            this.ref = ref;
            /* This is very important. We must recompute this after the
             * URL has been changed. */
            hashCode = -1;
            hostAddress = null;
            int q = file.lastIndexOf('?');
            if (q != -1) {
                query = file.substring(q+1);
                path = file.substring(0, q);
            } else
                path = file;
        }
    }

    
Sets the specified 8 fields of the URL. This is not a public method so
that only URLStreamHandlers can modify URL fields. URLs are otherwise
constant.

Params:
  • protocol – the name of the protocol to use
  • host – the name of the host
  • port – the port number on the host
  • authority – the authority part for the url
  • userInfo – the username and password
  • path – the file on the host
  • ref – the internal reference in the URL
  • query – the query part of this URL
Since:1.3
/**
     * Sets the specified 8 fields of the URL. This is not a public method so
     * that only URLStreamHandlers can modify URL fields. URLs are otherwise
     * constant.
     *
     * @param protocol the name of the protocol to use
     * @param host the name of the host
     * @param port the port number on the host
     * @param authority the authority part for the url
     * @param userInfo the username and password
     * @param path the file on the host
     * @param ref the internal reference in the URL
     * @param query the query part of this URL
     * @since 1.3
     */
    void set(String protocol, String host, int port,
             String authority, String userInfo, String path,
             String query, String ref) {
        synchronized (this) {
            this.protocol = protocol;
            this.host = host;
            this.port = port;
            this.file = query == null ? path : path + "?" + query;
            this.userInfo = userInfo;
            this.path = path;
            this.ref = ref;
            /* This is very important. We must recompute this after the
             * URL has been changed. */
            hashCode = -1;
            hostAddress = null;
            this.query = query;
            this.authority = authority;
        }
    }

    
Gets the query part of this URL. 
Returns: the query part of this URL, or null if one does not exist
Since:1.3
/**
     * Gets the query part of this {@code URL}.
     *
     * @return  the query part of this {@code URL},
     * or <CODE>null</CODE> if one does not exist
     * @since 1.3
     */
    public String getQuery() {
        return query;
    }

    
Gets the path part of this URL. 
Returns: the path part of this URL, or an empty string if one does not exist
Since:1.3
/**
     * Gets the path part of this {@code URL}.
     *
     * @return  the path part of this {@code URL}, or an
     * empty string if one does not exist
     * @since 1.3
     */
    public String getPath() {
        return path;
    }

    
Gets the userInfo part of this URL. 
Returns: the userInfo part of this URL, or null if one does not exist
Since:1.3
/**
     * Gets the userInfo part of this {@code URL}.
     *
     * @return  the userInfo part of this {@code URL}, or
     * <CODE>null</CODE> if one does not exist
     * @since 1.3
     */
    public String getUserInfo() {
        return userInfo;
    }

    
Gets the authority part of this URL. 
Returns: the authority part of this URL
Since:1.3
/**
     * Gets the authority part of this {@code URL}.
     *
     * @return  the authority part of this {@code URL}
     * @since 1.3
     */
    public String getAuthority() {
        return authority;
    }

    
Gets the port number of this URL. 
Returns: the port number, or -1 if the port is not set
/**
     * Gets the port number of this {@code URL}.
     *
     * @return  the port number, or -1 if the port is not set
     */
    public int getPort() {
        return port;
    }

    
Gets the default port number of the protocol associated with this URL. If the URL scheme or the URLStreamHandler for the URL do not define a default port number, then -1 is returned. 
Returns: the port number
Since:1.4
/**
     * Gets the default port number of the protocol associated
     * with this {@code URL}. If the URL scheme or the URLStreamHandler
     * for the URL do not define a default port number,
     * then -1 is returned.
     *
     * @return  the port number
     * @since 1.4
     */
    public int getDefaultPort() {
        return handler.getDefaultPort();
    }

    
Gets the protocol name of this URL. 
Returns: the protocol of this URL.
/**
     * Gets the protocol name of this {@code URL}.
     *
     * @return  the protocol of this {@code URL}.
     */
    public String getProtocol() {
        return protocol;
    }

    
Gets the host name of this URL, if applicable. The format of the host conforms to RFC 2732, i.e. for a literal IPv6 address, this method will return the IPv6 address enclosed in square brackets ('[' and ']'). 
Returns: the host name of this URL.
/**
     * Gets the host name of this {@code URL}, if applicable.
     * The format of the host conforms to RFC 2732, i.e. for a
     * literal IPv6 address, this method will return the IPv6 address
     * enclosed in square brackets ({@code '['} and {@code ']'}).
     *
     * @return  the host name of this {@code URL}.
     */
    public String getHost() {
        return host;
    }

    
Gets the file name of this URL. The returned file portion will be the same as getPath(), plus the concatenation of
the value of getQuery(), if any. If there is
no query portion, this method and getPath() will
return identical results.

Returns: the file name of this URL, or an empty string if one does not exist
/**
     * Gets the file name of this {@code URL}.
     * The returned file portion will be
     * the same as <CODE>getPath()</CODE>, plus the concatenation of
     * the value of <CODE>getQuery()</CODE>, if any. If there is
     * no query portion, this method and <CODE>getPath()</CODE> will
     * return identical results.
     *
     * @return  the file name of this {@code URL},
     * or an empty string if one does not exist
     */
    public String getFile() {
        return file;
    }

    
Gets the anchor (also known as the "reference") of this URL. 
Returns: the anchor (also known as the "reference") of this URL, or null if one does not exist
/**
     * Gets the anchor (also known as the "reference") of this
     * {@code URL}.
     *
     * @return  the anchor (also known as the "reference") of this
     *          {@code URL}, or <CODE>null</CODE> if one does not exist
     */
    public String getRef() {
        return ref;
    }

    
Compares this URL for equality with another object.
 If the given object is not a URL then this method immediately returns false.

Two URL objects are equal if they have the same protocol, reference
equivalent hosts, have the same port number on the host, and the same
file and fragment of the file.

Two hosts are considered equivalent if both host names can be resolved
into the same IP addresses; else if either host name can't be
resolved, the host names must be equal without regard to case; or both
host names equal to null.

Since hosts comparison requires name resolution, this operation is a
blocking operation. 
 Note: The defined behavior for equals is known to be inconsistent with virtual hosting in HTTP. 
Params:
  • obj –   the URL to compare against.
Returns: true if the objects are the same; false otherwise.
/**
     * Compares this URL for equality with another object.<p>
     *
     * If the given object is not a URL then this method immediately returns
     * {@code false}.<p>
     *
     * Two URL objects are equal if they have the same protocol, reference
     * equivalent hosts, have the same port number on the host, and the same
     * file and fragment of the file.<p>
     *
     * Two hosts are considered equivalent if both host names can be resolved
     * into the same IP addresses; else if either host name can't be
     * resolved, the host names must be equal without regard to case; or both
     * host names equal to null.<p>
     *
     * Since hosts comparison requires name resolution, this operation is a
     * blocking operation. <p>
     *
     * Note: The defined behavior for {@code equals} is known to
     * be inconsistent with virtual hosting in HTTP.
     *
     * @param   obj   the URL to compare against.
     * @return  {@code true} if the objects are the same;
     *          {@code false} otherwise.
     */
    public boolean equals(Object obj) {
        if (!(obj instanceof URL))
            return false;
        URL u2 = (URL)obj;

        return handler.equals(this, u2);
    }

    
Creates an integer suitable for hash table indexing.

The hash code is based upon all the URL components relevant for URL
comparison. As such, this operation is a blocking operation.

Returns: a hash code for this URL.
/**
     * Creates an integer suitable for hash table indexing.<p>
     *
     * The hash code is based upon all the URL components relevant for URL
     * comparison. As such, this operation is a blocking operation.
     *
     * @return  a hash code for this {@code URL}.
     */
    public synchronized int hashCode() {
        if (hashCode != -1)
            return hashCode;

        hashCode = handler.hashCode(this);
        return hashCode;
    }

    
Compares two URLs, excluding the fragment component.
 Returns true if this URL and the other argument are equal without taking the fragment component into consideration. 
Params:
  • other –  the URL to compare against.
Returns: true if they reference the same remote object; false otherwise.
/**
     * Compares two URLs, excluding the fragment component.<p>
     *
     * Returns {@code true} if this {@code URL} and the
     * {@code other} argument are equal without taking the
     * fragment component into consideration.
     *
     * @param   other   the {@code URL} to compare against.
     * @return  {@code true} if they reference the same remote object;
     *          {@code false} otherwise.
     */
    public boolean sameFile(URL other) {
        return handler.sameFile(this, other);
    }

    
Constructs a string representation of this URL. The string is created by calling the toExternalForm method of the stream protocol handler for this object. 
See Also:
Returns: a string representation of this object.
/**
     * Constructs a string representation of this {@code URL}. The
     * string is created by calling the {@code toExternalForm}
     * method of the stream protocol handler for this object.
     *
     * @return  a string representation of this object.
     * @see     java.net.URL#URL(java.lang.String, java.lang.String, int,
     *                  java.lang.String)
     * @see     java.net.URLStreamHandler#toExternalForm(java.net.URL)
     */
    public String toString() {
        return toExternalForm();
    }

    
Constructs a string representation of this URL. The string is created by calling the toExternalForm method of the stream protocol handler for this object. 
See Also:
Returns: a string representation of this object.
/**
     * Constructs a string representation of this {@code URL}. The
     * string is created by calling the {@code toExternalForm}
     * method of the stream protocol handler for this object.
     *
     * @return  a string representation of this object.
     * @see     java.net.URL#URL(java.lang.String, java.lang.String,
     *                  int, java.lang.String)
     * @see     java.net.URLStreamHandler#toExternalForm(java.net.URL)
     */
    public String toExternalForm() {
        return handler.toExternalForm(this);
    }

    
Returns a URI equivalent to this URL. This method functions in the same way as new URI (this.toString()). 
Note, any URL instance that complies with RFC 2396 can be converted
to a URI. However, some URLs that are not strictly in compliance
can not be converted to a URI.

Throws:
  • URISyntaxException – if this URL is not formatted strictly according to
           to RFC2396 and cannot be converted to a URI.
Returns:   a URI instance equivalent to this URL.
Since:1.5
/**
     * Returns a {@link java.net.URI} equivalent to this URL.
     * This method functions in the same way as {@code new URI (this.toString())}.
     * <p>Note, any URL instance that complies with RFC 2396 can be converted
     * to a URI. However, some URLs that are not strictly in compliance
     * can not be converted to a URI.
     *
     * @exception URISyntaxException if this URL is not formatted strictly according to
     *            to RFC2396 and cannot be converted to a URI.
     *
     * @return    a URI instance equivalent to this URL.
     * @since 1.5
     */
    public URI toURI() throws URISyntaxException {
        return new URI (toString());
    }

    
Returns a URLConnection instance that represents a connection to the remote object referred to by the URL. 
A new instance of URLConnection is created every time when invoking the 
URLStreamHandler.openConnection(URL) method of the protocol handler for this URL.


It should be noted that a URLConnection instance does not establish the actual network connection on creation. This will happen only when calling URLConnection.connect().


If for the URL's protocol (such as HTTP or JAR), there
exists a public, specialized URLConnection subclass belonging
to one of the following packages or one of their subpackages:
java.lang, java.io, java.util, java.net, the connection
returned will be of that subclass. For example, for HTTP an
HttpURLConnection will be returned, and for JAR a
JarURLConnection will be returned.


Throws:
See Also:
Returns: a URLConnection linking to the URL.
/**
     * Returns a {@link java.net.URLConnection URLConnection} instance that
     * represents a connection to the remote object referred to by the
     * {@code URL}.
     *
     * <P>A new instance of {@linkplain java.net.URLConnection URLConnection} is
     * created every time when invoking the
     * {@linkplain java.net.URLStreamHandler#openConnection(URL)
     * URLStreamHandler.openConnection(URL)} method of the protocol handler for
     * this URL.</P>
     *
     * <P>It should be noted that a URLConnection instance does not establish
     * the actual network connection on creation. This will happen only when
     * calling {@linkplain java.net.URLConnection#connect() URLConnection.connect()}.</P>
     *
     * <P>If for the URL's protocol (such as HTTP or JAR), there
     * exists a public, specialized URLConnection subclass belonging
     * to one of the following packages or one of their subpackages:
     * java.lang, java.io, java.util, java.net, the connection
     * returned will be of that subclass. For example, for HTTP an
     * HttpURLConnection will be returned, and for JAR a
     * JarURLConnection will be returned.</P>
     *
     * @return     a {@link java.net.URLConnection URLConnection} linking
     *             to the URL.
     * @exception  IOException  if an I/O exception occurs.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *             int, java.lang.String)
     */
    public URLConnection openConnection() throws java.io.IOException {
        return handler.openConnection(this);
    }

    
Same as openConnection(), except that the connection will be made through the specified proxy; Protocol handlers that do not support proxing will ignore the proxy parameter and make a normal connection. Invoking this method preempts the system's default ProxySelector settings. 
Params:
  • proxy – the Proxy through which this connection
            will be made. If direct connection is desired,
            Proxy.NO_PROXY should be specified.
Throws:
See Also:
Returns: a URLConnection to the URL.
Since:     1.5
/**
     * Same as {@link #openConnection()}, except that the connection will be
     * made through the specified proxy; Protocol handlers that do not
     * support proxing will ignore the proxy parameter and make a
     * normal connection.
     *
     * Invoking this method preempts the system's default
     * {@link java.net.ProxySelector ProxySelector} settings.
     *
     * @param      proxy the Proxy through which this connection
     *             will be made. If direct connection is desired,
     *             Proxy.NO_PROXY should be specified.
     * @return     a {@code URLConnection} to the URL.
     * @exception  IOException  if an I/O exception occurs.
     * @exception  SecurityException if a security manager is present
     *             and the caller doesn't have permission to connect
     *             to the proxy.
     * @exception  IllegalArgumentException will be thrown if proxy is null,
     *             or proxy has the wrong type
     * @exception  UnsupportedOperationException if the subclass that
     *             implements the protocol handler doesn't support
     *             this method.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *             int, java.lang.String)
     * @see        java.net.URLConnection
     * @see        java.net.URLStreamHandler#openConnection(java.net.URL,
     *             java.net.Proxy)
     * @since      1.5
     */
    public URLConnection openConnection(Proxy proxy)
        throws java.io.IOException {
        if (proxy == null) {
            throw new IllegalArgumentException("proxy can not be null");
        }

        // Create a copy of Proxy as a security measure
        Proxy p = proxy == Proxy.NO_PROXY ? Proxy.NO_PROXY : sun.net.ApplicationProxy.create(proxy);
        SecurityManager sm = System.getSecurityManager();
        if (p.type() != Proxy.Type.DIRECT && sm != null) {
            InetSocketAddress epoint = (InetSocketAddress) p.address();
            if (epoint.isUnresolved())
                sm.checkConnect(epoint.getHostName(), epoint.getPort());
            else
                sm.checkConnect(epoint.getAddress().getHostAddress(),
                                epoint.getPort());
        }
        return handler.openConnection(this, p);
    }

    
Opens a connection to this URL and returns an InputStream for reading from that connection. This method is a shorthand for: 
    openConnection().getInputStream()



Throws:
See Also:
Returns:    an input stream for reading from the URL connection.
/**
     * Opens a connection to this {@code URL} and returns an
     * {@code InputStream} for reading from that connection. This
     * method is a shorthand for:
     * <blockquote><pre>
     *     openConnection().getInputStream()
     * </pre></blockquote>
     *
     * @return     an input stream for reading from the URL connection.
     * @exception  IOException  if an I/O exception occurs.
     * @see        java.net.URL#openConnection()
     * @see        java.net.URLConnection#getInputStream()
     */
    public final InputStream openStream() throws java.io.IOException {
        return openConnection().getInputStream();
    }

    
Gets the contents of this URL. This method is a shorthand for:

    openConnection().getContent()



Throws:
See Also:
Returns:    the contents of this URL.
/**
     * Gets the contents of this URL. This method is a shorthand for:
     * <blockquote><pre>
     *     openConnection().getContent()
     * </pre></blockquote>
     *
     * @return     the contents of this URL.
     * @exception  IOException  if an I/O exception occurs.
     * @see        java.net.URLConnection#getContent()
     */
    public final Object getContent() throws java.io.IOException {
        return openConnection().getContent();
    }

    
Gets the contents of this URL. This method is a shorthand for:

    openConnection().getContent(classes)



Params:
  • classes – an array of Java types
Throws:
See Also:
Returns:    the content object of this URL that is the first match of
              the types specified in the classes array.
              null if none of the requested types are supported.
Since:1.3
/**
     * Gets the contents of this URL. This method is a shorthand for:
     * <blockquote><pre>
     *     openConnection().getContent(classes)
     * </pre></blockquote>
     *
     * @param classes an array of Java types
     * @return     the content object of this URL that is the first match of
     *               the types specified in the classes array.
     *               null if none of the requested types are supported.
     * @exception  IOException  if an I/O exception occurs.
     * @see        java.net.URLConnection#getContent(Class[])
     * @since 1.3
     */
    public final Object getContent(Class<?>[] classes)
    throws java.io.IOException {
        return openConnection().getContent(classes);
    }

    
The URLStreamHandler factory.

/**
     * The URLStreamHandler factory.
     */
    private static volatile URLStreamHandlerFactory factory;

    
Sets an application's URLStreamHandlerFactory. This method can be called at most once in a given Java Virtual Machine. 
 The URLStreamHandlerFactory instance is used to construct a stream protocol handler from a protocol name. 
 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 application has already set a factory.
  • SecurityException –  if a security manager exists and its checkSetFactory method doesn't allow the operation.
See Also:
/**
     * Sets an application's {@code URLStreamHandlerFactory}.
     * This method can be called at most once in a given Java Virtual
     * Machine.
     *
     *<p> The {@code URLStreamHandlerFactory} instance is used to
     *construct a stream protocol handler from a protocol name.
     *
     * <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 application has already set a factory.
     * @exception  SecurityException  if a security manager exists and its
     *             {@code checkSetFactory} method doesn't allow
     *             the operation.
     * @see        java.net.URL#URL(java.lang.String, java.lang.String,
     *             int, java.lang.String)
     * @see        java.net.URLStreamHandlerFactory
     * @see        SecurityManager#checkSetFactory
     */
    public static void setURLStreamHandlerFactory(URLStreamHandlerFactory fac) {
        synchronized (streamHandlerLock) {
            if (factory != null) {
                throw new Error("factory already defined");
            }
            SecurityManager security = System.getSecurityManager();
            if (security != null) {
                security.checkSetFactory();
            }
            handlers.clear();

            // safe publication of URLStreamHandlerFactory with volatile write
            factory = fac;
        }
    }

    private static final URLStreamHandlerFactory defaultFactory = new DefaultFactory();

    private static class DefaultFactory implements URLStreamHandlerFactory {
        private static String PREFIX = "sun.net.www.protocol";

        public URLStreamHandler createURLStreamHandler(String protocol) {
            String name = PREFIX + "." + protocol + ".Handler";
            try {
                @SuppressWarnings("deprecation")
                Object o = Class.forName(name).newInstance();
                return (URLStreamHandler)o;
            } catch (ClassNotFoundException x) {
                // ignore
            } catch (Exception e) {
                // For compatibility, all Exceptions are ignored.
                // any number of exceptions can get thrown here
            }
            return null;
        }
    }

    private static URLStreamHandler lookupViaProperty(String protocol) {
        String packagePrefixList =
                GetPropertyAction.privilegedGetProperty(protocolPathProp);
        if (packagePrefixList == null) {
            // not set
            return null;
        }

        String[] packagePrefixes = packagePrefixList.split("\\|");
        URLStreamHandler handler = null;
        for (int i=0; handler == null && i<packagePrefixes.length; i++) {
            String packagePrefix = packagePrefixes[i].trim();
            try {
                String clsName = packagePrefix + "." + protocol + ".Handler";
                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();
                    handler = (URLStreamHandler)tmp;
                }
            } catch (Exception e) {
                // any number of exceptions can get thrown here
            }
        }
        return handler;
    }

    private static Iterator<URLStreamHandlerProvider> providers() {
        return new Iterator<>() {

            ClassLoader cl = ClassLoader.getSystemClassLoader();
            ServiceLoader<URLStreamHandlerProvider> sl =
                    ServiceLoader.load(URLStreamHandlerProvider.class, cl);
            Iterator<URLStreamHandlerProvider> i = sl.iterator();

            URLStreamHandlerProvider next = null;

            private boolean getNext() {
                while (next == null) {
                    try {
                        if (!i.hasNext())
                            return false;
                        next = i.next();
                    } catch (ServiceConfigurationError sce) {
                        if (sce.getCause() instanceof SecurityException) {
                            // Ignore security exceptions
                            continue;
                        }
                        throw sce;
                    }
                }
                return true;
            }

            public boolean hasNext() {
                return getNext();
            }

            public URLStreamHandlerProvider next() {
                if (!getNext())
                    throw new NoSuchElementException();
                URLStreamHandlerProvider n = next;
                next = null;
                return n;
            }
        };
    }

    // Thread-local gate to prevent recursive provider lookups
    private static ThreadLocal<Object> gate = new ThreadLocal<>();

    private static URLStreamHandler lookupViaProviders(final String protocol) {
        if (gate.get() != null)
            throw new Error("Circular loading of URL stream handler providers detected");

        gate.set(gate);
        try {
            return AccessController.doPrivileged(
                new PrivilegedAction<>() {
                    public URLStreamHandler run() {
                        Iterator<URLStreamHandlerProvider> itr = providers();
                        while (itr.hasNext()) {
                            URLStreamHandlerProvider f = itr.next();
                            URLStreamHandler h = f.createURLStreamHandler(protocol);
                            if (h != null)
                                return h;
                        }
                        return null;
                    }
                });
        } finally {
            gate.set(null);
        }
    }


    
Non-overrideable protocols: "jrt" and "file"
Character-based comparison for performance reasons; also ensures
case-insensitive comparison in a locale-independent fashion.

/**
     * Non-overrideable protocols: "jrt" and "file"
     *
     * Character-based comparison for performance reasons; also ensures
     * case-insensitive comparison in a locale-independent fashion.
     */
    static boolean isOverrideable(String protocol) {
        if (protocol.length() == 3) {
            if ((Character.toLowerCase(protocol.charAt(0)) == 'j') &&
                    (Character.toLowerCase(protocol.charAt(1)) == 'r') &&
                    (Character.toLowerCase(protocol.charAt(2)) == 't')) {
                return false;
            }
        } else if (protocol.length() == 4) {
            if ((Character.toLowerCase(protocol.charAt(0)) == 'f') &&
                    (Character.toLowerCase(protocol.charAt(1)) == 'i') &&
                    (Character.toLowerCase(protocol.charAt(2)) == 'l') &&
                    (Character.toLowerCase(protocol.charAt(3)) == 'e')) {
                return false;
            }
        }
        return true;
    }

    
A table of protocol handlers.

/**
     * A table of protocol handlers.
     */
    static Hashtable<String,URLStreamHandler> handlers = new Hashtable<>();
    private static final Object streamHandlerLock = new Object();

    
Returns the Stream Handler.

Params:
  • protocol – the protocol to use
/**
     * Returns the Stream Handler.
     * @param protocol the protocol to use
     */
    static URLStreamHandler getURLStreamHandler(String protocol) {

        URLStreamHandler handler = handlers.get(protocol);

        if (handler != null) {
            return handler;
        }

        URLStreamHandlerFactory fac;
        boolean checkedWithFactory = false;

        if (isOverrideable(protocol) && jdk.internal.misc.VM.isBooted()) {
            // Use the factory (if any). Volatile read makes
            // URLStreamHandlerFactory appear fully initialized to current thread.
            fac = factory;
            if (fac != null) {
                handler = fac.createURLStreamHandler(protocol);
                checkedWithFactory = true;
            }

            if (handler == null && !protocol.equalsIgnoreCase("jar")) {
                handler = lookupViaProviders(protocol);
            }

            if (handler == null) {
                handler = lookupViaProperty(protocol);
            }
        }

        synchronized (streamHandlerLock) {
            if (handler == null) {
                // Try the built-in protocol handler
                handler = defaultFactory.createURLStreamHandler(protocol);
            } else {
                URLStreamHandler handler2 = null;

                // Check again with hashtable just in case another
                // thread created a handler since we last checked
                handler2 = handlers.get(protocol);

                if (handler2 != null) {
                    return handler2;
                }

                // Check with factory if another thread set a
                // factory since our last check
                if (!checkedWithFactory && (fac = factory) != null) {
                    handler2 =  fac.createURLStreamHandler(protocol);
                }

                if (handler2 != null) {
                    // The handler from the factory must be given more
                    // importance. Discard the default handler that
                    // this thread created.
                    handler = handler2;
                }
            }

            // Insert this handler into the hashtable
            if (handler != null) {
                handlers.put(protocol, handler);
            }
        }

        return handler;
    }

    
@serialField   protocol String
@serialField   host String
@serialField   port int
@serialField   authority String
@serialField   file String
@serialField   ref String
@serialField   hashCode int
/**
     * @serialField    protocol String
     *
     * @serialField    host String
     *
     * @serialField    port int
     *
     * @serialField    authority String
     *
     * @serialField    file String
     *
     * @serialField    ref String
     *
     * @serialField    hashCode int
     *
     */
    private static final ObjectStreamField[] serialPersistentFields = {
        new ObjectStreamField("protocol", String.class),
        new ObjectStreamField("host", String.class),
        new ObjectStreamField("port", int.class),
        new ObjectStreamField("authority", String.class),
        new ObjectStreamField("file", String.class),
        new ObjectStreamField("ref", String.class),
        new ObjectStreamField("hashCode", int.class), };

    
WriteObject is called to save the state of the URL to an
ObjectOutputStream. The handler is not saved since it is
specific to this system.

@serialDatathe default write object value. When read back in,
the reader must ensure that calling getURLStreamHandler with
the protocol variable returns a valid URLStreamHandler and
throw an IOException if it does not.
/**
     * WriteObject is called to save the state of the URL to an
     * ObjectOutputStream. The handler is not saved since it is
     * specific to this system.
     *
     * @serialData the default write object value. When read back in,
     * the reader must ensure that calling getURLStreamHandler with
     * the protocol variable returns a valid URLStreamHandler and
     * throw an IOException if it does not.
     */
    private synchronized void writeObject(java.io.ObjectOutputStream s)
        throws IOException
    {
        s.defaultWriteObject(); // write the fields
    }

    
readObject is called to restore the state of the URL from the
stream.  It reads the components of the URL and finds the local
stream handler.

/**
     * readObject is called to restore the state of the URL from the
     * stream.  It reads the components of the URL and finds the local
     * stream handler.
     */
    private synchronized void readObject(java.io.ObjectInputStream s)
            throws IOException, ClassNotFoundException {
        GetField gf = s.readFields();
        String protocol = (String)gf.get("protocol", null);
        if (getURLStreamHandler(protocol) == null) {
            throw new IOException("unknown protocol: " + protocol);
        }
        String host = (String)gf.get("host", null);
        int port = gf.get("port", -1);
        String authority = (String)gf.get("authority", null);
        String file = (String)gf.get("file", null);
        String ref = (String)gf.get("ref", null);
        int hashCode = gf.get("hashCode", -1);
        if (authority == null
                && ((host != null && host.length() > 0) || port != -1)) {
            if (host == null)
                host = "";
            authority = (port == -1) ? host : host + ":" + port;
        }
        tempState = new UrlDeserializedState(protocol, host, port, authority,
               file, ref, hashCode);
    }

    
Replaces the de-serialized object with an URL object.

Throws:
Returns:a newly created object from deserialized data
/**
     * Replaces the de-serialized object with an URL object.
     *
     * @return a newly created object from deserialized data
     *
     * @throws ObjectStreamException if a new object replacing this
     * object could not be created
     */

   private Object readResolve() throws ObjectStreamException {

        URLStreamHandler handler = null;
        // already been checked in readObject
        handler = getURLStreamHandler(tempState.getProtocol());

        URL replacementURL = null;
        if (isBuiltinStreamHandler(handler.getClass().getName())) {
            replacementURL = fabricateNewURL();
        } else {
            replacementURL = setDeserializedFields(handler);
        }
        return replacementURL;
    }

    private URL setDeserializedFields(URLStreamHandler handler) {
        URL replacementURL;
        String userInfo = null;
        String protocol = tempState.getProtocol();
        String host = tempState.getHost();
        int port = tempState.getPort();
        String authority = tempState.getAuthority();
        String file = tempState.getFile();
        String ref = tempState.getRef();
        int hashCode = tempState.getHashCode();


        // Construct authority part
        if (authority == null
            && ((host != null && host.length() > 0) || port != -1)) {
            if (host == null)
                host = "";
            authority = (port == -1) ? host : host + ":" + port;

            // Handle hosts with userInfo in them
            int at = host.lastIndexOf('@');
            if (at != -1) {
                userInfo = host.substring(0, at);
                host = host.substring(at+1);
            }
        } else if (authority != null) {
            // Construct user info part
            int ind = authority.indexOf('@');
            if (ind != -1)
                userInfo = authority.substring(0, ind);
        }

        // Construct path and query part
        String path = null;
        String query = null;
        if (file != null) {
            // Fix: only do this if hierarchical?
            int q = file.lastIndexOf('?');
            if (q != -1) {
                query = file.substring(q+1);
                path = file.substring(0, q);
            } else
                path = file;
        }

        // Set the object fields.
        this.protocol = protocol;
        this.host = host;
        this.port = port;
        this.file = file;
        this.authority = authority;
        this.ref = ref;
        this.hashCode = hashCode;
        this.handler = handler;
        this.query = query;
        this.path = path;
        this.userInfo = userInfo;
        replacementURL = this;
        return replacementURL;
    }

    private URL fabricateNewURL()
                throws InvalidObjectException {
        // create URL string from deserialized object
        URL replacementURL = null;
        String urlString = tempState.reconstituteUrlString();

        try {
            replacementURL = new URL(urlString);
        } catch (MalformedURLException mEx) {
            resetState();
            InvalidObjectException invoEx = new InvalidObjectException(
                    "Malformed URL:  " + urlString);
            invoEx.initCause(mEx);
            throw invoEx;
        }
        replacementURL.setSerializedHashCode(tempState.getHashCode());
        resetState();
        return replacementURL;
    }

    private boolean isBuiltinStreamHandler(String handlerClassName) {
        return (handlerClassName.startsWith(BUILTIN_HANDLERS_PREFIX));
    }

    private void resetState() {
        this.protocol = null;
        this.host = null;
        this.port = -1;
        this.file = null;
        this.authority = null;
        this.ref = null;
        this.hashCode = -1;
        this.handler = null;
        this.query = null;
        this.path = null;
        this.userInfo = null;
        this.tempState = null;
    }

    private void setSerializedHashCode(int hc) {
        this.hashCode = hc;
    }

    static {
        SharedSecrets.setJavaNetURLAccess(
                new JavaNetURLAccess() {
                    @Override
                    public URLStreamHandler getHandler(URL u) {
                        return u.handler;
                    }
                }
        );
    }
}

final class UrlDeserializedState {
    private final String protocol;
    private final String host;
    private final int port;
    private final String authority;
    private final String file;
    private final String ref;
    private final int hashCode;

    public UrlDeserializedState(String protocol,
                                String host, int port,
                                String authority, String file,
                                String ref, int hashCode) {
        this.protocol = protocol;
        this.host = host;
        this.port = port;
        this.authority = authority;
        this.file = file;
        this.ref = ref;
        this.hashCode = hashCode;
    }

    String getProtocol() {
        return protocol;
    }

    String getHost() {
        return host;
    }

    String getAuthority () {
        return authority;
    }

    int getPort() {
        return port;
    }

    String getFile () {
        return file;
    }

    String getRef () {
        return ref;
    }

    int getHashCode () {
        return hashCode;
    }

    String reconstituteUrlString() {

        // pre-compute length of StringBuffer
        int len = protocol.length() + 1;
        if (authority != null && authority.length() > 0)
            len += 2 + authority.length();
        if (file != null) {
            len += file.length();
        }
        if (ref != null)
            len += 1 + ref.length();
        StringBuilder result = new StringBuilder(len);
        result.append(protocol);
        result.append(":");
        if (authority != null && authority.length() > 0) {
            result.append("//");
            result.append(authority);
        }
        if (file != null) {
            result.append(file);
        }
        if (ref != null) {
            result.append("#");
            result.append(ref);
        }
        return result.toString();
    }
}