/*
 * Copyright (c) 1997-2018 Oracle and/or its affiliates. All rights reserved.
 * Copyright 2004 The Apache Software Foundation
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *     http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package javax.servlet;

import java.io.*;
import java.util.*;

Defines an object to provide client request information to a servlet.  The
servlet container creates a ServletRequest object and passes
it as an argument to the servlet's service method.
A ServletRequest object provides data including
parameter name and values, attributes, and an input stream.
Interfaces that extend ServletRequest can provide additional protocol-specific data (for example, HTTP data is provided by HttpServletRequest. 
Author:
Various
See Also:
HttpServletRequest/**
 * Defines an object to provide client request information to a servlet.  The
 * servlet container creates a <code>ServletRequest</code> object and passes
 * it as an argument to the servlet's <code>service</code> method.
 *
 * <p>A <code>ServletRequest</code> object provides data including
 * parameter name and values, attributes, and an input stream.
 * Interfaces that extend <code>ServletRequest</code> can provide
 * additional protocol-specific data (for example, HTTP data is
 * provided by {@link javax.servlet.http.HttpServletRequest}.
 * 
 * @author Various
 *
 * @see javax.servlet.http.HttpServletRequest
 *
 */
public interface ServletRequest {

    
Returns the value of the named attribute as an Object,
or null if no attribute of the given name exists. 
 Attributes can be set two ways.  The servlet container may set
attributes to make available custom information about a request.
For example, for requests made using HTTPS, the attribute
javax.servlet.request.X509Certificate can be used to retrieve information on the certificate of the client. Attributes can also be set programatically using setAttribute. This allows information to be embedded into a request before a RequestDispatcher call. 
Attribute names should follow the same conventions as package
names. This specification reserves names matching java.*,
javax.*, and sun.*. 
Params:
name – a String specifying the name of the attribute
Returns:
an Object containing the value of the attribute,
or null if the attribute does not exist/**
     * Returns the value of the named attribute as an <code>Object</code>,
     * or <code>null</code> if no attribute of the given name exists. 
     *
     * <p> Attributes can be set two ways.  The servlet container may set
     * attributes to make available custom information about a request.
     * For example, for requests made using HTTPS, the attribute
     * <code>javax.servlet.request.X509Certificate</code> can be used to
     * retrieve information on the certificate of the client.  Attributes
     * can also be set programatically using 
     * {@link ServletRequest#setAttribute}.  This allows information to be
     * embedded into a request before a {@link RequestDispatcher} call.
     *
     * <p>Attribute names should follow the same conventions as package
     * names. This specification reserves names matching <code>java.*</code>,
     * <code>javax.*</code>, and <code>sun.*</code>. 
     *
     * @param name a <code>String</code> specifying the name of the attribute
     *
     * @return an <code>Object</code> containing the value of the attribute,
     * or <code>null</code> if the attribute does not exist
     */
    public Object getAttribute(String name);
    
    
Returns an Enumeration containing the
names of the attributes available to this request. 
This method returns an empty Enumeration
if the request has no attributes available to it.
Returns:
an Enumeration of strings containing the names 
of the request's attributes/**
     * Returns an <code>Enumeration</code> containing the
     * names of the attributes available to this request. 
     * This method returns an empty <code>Enumeration</code>
     * if the request has no attributes available to it.
     * 
     * @return an <code>Enumeration</code> of strings containing the names 
     * of the request's attributes
     */
    public Enumeration<String> getAttributeNames();
    
    
Returns the name of the character encoding used in the body of this
request. This method returns null if no request encoding character encoding has been specified. The following methods for specifying the request character encoding are consulted, in decreasing order of priority: per request, per web app (using ServletContext.setRequestCharacterEncoding, deployment descriptor), and per container (for all web applications deployed in that container, using vendor specific configuration). 
Returns:
a String containing the name of the character
encoding, or null if the request does not specify a
character encoding/**
     * Returns the name of the character encoding used in the body of this
     * request. This method returns <code>null</code> if no request encoding
     * character encoding has been specified. The following methods for
     * specifying the request character encoding are consulted, in decreasing
     * order of priority: per request, per web app (using
     * {@link ServletContext#setRequestCharacterEncoding}, deployment
     * descriptor), and per container (for all web applications deployed in 
     * that container, using vendor specific configuration).
     * 
     * @return a <code>String</code> containing the name of the character
     * encoding, or <code>null</code> if the request does not specify a
     * character encoding
     */
    public String getCharacterEncoding();

    
Overrides the name of the character encoding used in the body of this
request. This method must be called prior to reading request parameters
or reading input using getReader(). Otherwise, it has no effect.
Params:
env – String containing the name of
the character encoding.
Throws:
UnsupportedEncodingException – if this ServletRequest is still
in a state where a character encoding may be set,
but the specified encoding is invalid/**
     * Overrides the name of the character encoding used in the body of this
     * request. This method must be called prior to reading request parameters
     * or reading input using getReader(). Otherwise, it has no effect.
     * 
     * @param env <code>String</code> containing the name of
     * the character encoding.
     *
     * @throws UnsupportedEncodingException if this ServletRequest is still
     * in a state where a character encoding may be set,
     * but the specified encoding is invalid
     */
    public void setCharacterEncoding(String env) throws UnsupportedEncodingException;

    
Returns the length, in bytes, of the request body and made available by
the input stream, or -1 if the length is not known ir is greater than
Integer.MAX_VALUE. For HTTP servlets,
same as the value of the CGI variable CONTENT_LENGTH.
Returns:
an integer containing the length of the request body or -1 if
the length is not known or is greater than Integer.MAX_VALUE./**
     * Returns the length, in bytes, of the request body and made available by
     * the input stream, or -1 if the length is not known ir is greater than
     * Integer.MAX_VALUE. For HTTP servlets,
     * same as the value of the CGI variable CONTENT_LENGTH.
     *
     * @return an integer containing the length of the request body or -1 if
     * the length is not known or is greater than Integer.MAX_VALUE.
     */
    public int getContentLength();
    
    
Returns the length, in bytes, of the request body and made available by
the input stream, or -1 if the length is not known. For HTTP servlets,
same as the value of the CGI variable CONTENT_LENGTH.
Returns:
a long containing the length of the request body or -1L if
the length is not known
Since:
Servlet 3.1/**
     * Returns the length, in bytes, of the request body and made available by
     * the input stream, or -1 if the length is not known. For HTTP servlets,
     * same as the value of the CGI variable CONTENT_LENGTH.
     *
     * @return a long containing the length of the request body or -1L if
     * the length is not known
     *
     * @since Servlet 3.1
     */
    public long getContentLengthLong();
    
    
Returns the MIME type of the body of the request, or 
null if the type is not known. For HTTP servlets, 
same as the value of the CGI variable CONTENT_TYPE.
Returns:
a String containing the name of the MIME type
of the request, or null if the type is not known/**
     * Returns the MIME type of the body of the request, or 
     * <code>null</code> if the type is not known. For HTTP servlets, 
     * same as the value of the CGI variable CONTENT_TYPE.
     *
     * @return a <code>String</code> containing the name of the MIME type
     * of the request, or null if the type is not known
     */
    public String getContentType();
    
    
Retrieves the body of the request as binary data using a ServletInputStream. Either this method or getReader may be called to read the body, not both. 
Throws:
IllegalStateException – if the getReader method has already been called for this request
IOException – if an input or output exception occurred
Returns:
a ServletInputStream object containing the body of the request/**
     * Retrieves the body of the request as binary data using
     * a {@link ServletInputStream}.  Either this method or 
     * {@link #getReader} may be called to read the body, not both.
     *
     * @return a {@link ServletInputStream} object containing
     * the body of the request
     *
     * @exception IllegalStateException if the {@link #getReader} method
     * has already been called for this request
     *
     * @exception IOException if an input or output exception occurred
     */
    public ServletInputStream getInputStream() throws IOException; 
     
    
Returns the value of a request parameter as a String,
or null if the parameter does not exist. Request parameters
are extra information sent with the request.  For HTTP servlets,
parameters are contained in the query string or posted form data.
You should only use this method when you are sure the parameter has only one value. If the parameter might have more than one value, use getParameterValues. 
If you use this method with a multivalued
parameter, the value returned is equal to the first value
in the array returned by getParameterValues.
If the parameter data was sent in the request body, such as occurs with an HTTP POST request, then reading the body directly via getInputStream or getReader can interfere with the execution of this method. 
Params:
name – a String specifying the name of the parameter
See Also:
getParameterValues
Returns:
a String representing the single value of
the parameter/**
     * Returns the value of a request parameter as a <code>String</code>,
     * or <code>null</code> if the parameter does not exist. Request parameters
     * are extra information sent with the request.  For HTTP servlets,
     * parameters are contained in the query string or posted form data.
     *
     * <p>You should only use this method when you are sure the
     * parameter has only one value. If the parameter might have
     * more than one value, use {@link #getParameterValues}.
     *
     * <p>If you use this method with a multivalued
     * parameter, the value returned is equal to the first value
     * in the array returned by <code>getParameterValues</code>.
     *
     * <p>If the parameter data was sent in the request body, such as occurs
     * with an HTTP POST request, then reading the body directly via {@link
     * #getInputStream} or {@link #getReader} can interfere
     * with the execution of this method.
     *
     * @param name a <code>String</code> specifying the name of the parameter
     *
     * @return a <code>String</code> representing the single value of
     * the parameter
     *
     * @see #getParameterValues
     */
    public String getParameter(String name);
    
    
Returns an Enumeration of String
objects containing the names of the parameters contained
in this request. If the request has 
no parameters, the method returns an empty Enumeration. 
Returns:
an Enumeration of String
objects, each String containing the name of
a request parameter; or an empty Enumeration
if the request has no parameters/**
     *
     * Returns an <code>Enumeration</code> of <code>String</code>
     * objects containing the names of the parameters contained
     * in this request. If the request has 
     * no parameters, the method returns an empty <code>Enumeration</code>. 
     *
     * @return an <code>Enumeration</code> of <code>String</code>
     * objects, each <code>String</code> containing the name of
     * a request parameter; or an empty <code>Enumeration</code>
     * if the request has no parameters
     */
    public Enumeration<String> getParameterNames();
        
    
Returns an array of String objects containing 
all of the values the given request parameter has, or 
null if the parameter does not exist.
If the parameter has a single value, the array has a length
of 1.
Params:
name – a String containing the name of 
the parameter whose value is requested
See Also:
getParameter
Returns:
an array of String objects 
containing the parameter's values/**
     * Returns an array of <code>String</code> objects containing 
     * all of the values the given request parameter has, or 
     * <code>null</code> if the parameter does not exist.
     *
     * <p>If the parameter has a single value, the array has a length
     * of 1.
     *
     * @param name a <code>String</code> containing the name of 
     * the parameter whose value is requested
     *
     * @return an array of <code>String</code> objects 
     * containing the parameter's values
     *
     * @see #getParameter
     */
    public String[] getParameterValues(String name);
 
    
Returns a java.util.Map of the parameters of this request.
Request parameters are extra information sent with the request.
For HTTP servlets, parameters are contained in the query string or
posted form data.
Returns:
an immutable java.util.Map containing parameter names as 
keys and parameter values as map values. The keys in the parameter
map are of type String. The values in the parameter map are of type
String array./**
     * Returns a java.util.Map of the parameters of this request.
     * 
     * <p>Request parameters are extra information sent with the request.
     * For HTTP servlets, parameters are contained in the query string or
     * posted form data.
     *
     * @return an immutable java.util.Map containing parameter names as 
     * keys and parameter values as map values. The keys in the parameter
     * map are of type String. The values in the parameter map are of type
     * String array.
     */
    public Map<String, String[]> getParameterMap();
    
    
Returns the name and version of the protocol the request uses
in the form protocol/majorVersion.minorVersion, for 
example, HTTP/1.1. For HTTP servlets, the value
returned is the same as the value of the CGI variable 
SERVER_PROTOCOL.
Returns:
a String containing the protocol 
name and version number/**
     * Returns the name and version of the protocol the request uses
     * in the form <i>protocol/majorVersion.minorVersion</i>, for 
     * example, HTTP/1.1. For HTTP servlets, the value
     * returned is the same as the value of the CGI variable 
     * <code>SERVER_PROTOCOL</code>.
     *
     * @return a <code>String</code> containing the protocol 
     * name and version number
     */    
    public String getProtocol();
    
    
Returns the name of the scheme used to make this request, 
for example,
http, https, or ftp.
Different schemes have different rules for constructing URLs,
as noted in RFC 1738.
Returns:
a String containing the name 
of the scheme used to make this request/**
     * Returns the name of the scheme used to make this request, 
     * for example,
     * <code>http</code>, <code>https</code>, or <code>ftp</code>.
     * Different schemes have different rules for constructing URLs,
     * as noted in RFC 1738.
     *
     * @return a <code>String</code> containing the name 
     * of the scheme used to make this request
     */
    public String getScheme();
    
    
Returns the host name of the server to which the request was sent.
It is the value of the part before ":" in the Host
header value, if any, or the resolved server name, or the server IP
address.
Returns:
a String containing the name of the server/**
     * Returns the host name of the server to which the request was sent.
     * It is the value of the part before ":" in the <code>Host</code>
     * header value, if any, or the resolved server name, or the server IP
     * address.
     *
     * @return a <code>String</code> containing the name of the server
     */
    public String getServerName();
    
    
Returns the port number to which the request was sent.
It is the value of the part after ":" in the Host
header value, if any, or the server port where the client connection
was accepted on.
Returns:
an integer specifying the port number/**
     * Returns the port number to which the request was sent.
     * It is the value of the part after ":" in the <code>Host</code>
     * header value, if any, or the server port where the client connection
     * was accepted on.
     *
     * @return an integer specifying the port number
     */
    public int getServerPort();
    
    
Retrieves the body of the request as character data using
a BufferedReader. The reader translates the character data according to the character encoding used on the body. Either this method or getInputStream may be called to read the body, not both. 
Throws:
UnsupportedEncodingException –  if the character set encoding
used is not supported and the text cannot be decoded
IllegalStateException – if getInputStream method has been called on this request
IOException – if an input or output exception occurred
See Also:
getInputStream
Returns:
a BufferedReader containing the body of the request/**
     * Retrieves the body of the request as character data using
     * a <code>BufferedReader</code>.  The reader translates the character
     * data according to the character encoding used on the body.
     * Either this method or {@link #getInputStream} may be called to read the
     * body, not both.
     * 
     * @return a <code>BufferedReader</code> containing the body of the request 
     *
     * @exception UnsupportedEncodingException  if the character set encoding
     * used is not supported and the text cannot be decoded
     *
     * @exception IllegalStateException if {@link #getInputStream} method
     * has been called on this request
     *
     * @exception IOException if an input or output exception occurred
     *
     * @see #getInputStream
     */
    public BufferedReader getReader() throws IOException;
    
    
Returns the Internet Protocol (IP) address of the client 
or last proxy that sent the request.
For HTTP servlets, same as the value of the 
CGI variable REMOTE_ADDR.
Returns:
a String containing the 
IP address of the client that sent the request/**
     * Returns the Internet Protocol (IP) address of the client 
     * or last proxy that sent the request.
     * For HTTP servlets, same as the value of the 
     * CGI variable <code>REMOTE_ADDR</code>.
     *
     * @return a <code>String</code> containing the 
     * IP address of the client that sent the request
     */
    public String getRemoteAddr();
    
    
Returns the fully qualified name of the client
or the last proxy that sent the request.
If the engine cannot or chooses not to resolve the hostname 
(to improve performance), this method returns the dotted-string form of 
the IP address. For HTTP servlets, same as the value of the CGI variable 
REMOTE_HOST.
Returns:
a String containing the fully 
qualified name of the client/**
     * Returns the fully qualified name of the client
     * or the last proxy that sent the request.
     * If the engine cannot or chooses not to resolve the hostname 
     * (to improve performance), this method returns the dotted-string form of 
     * the IP address. For HTTP servlets, same as the value of the CGI variable 
     * <code>REMOTE_HOST</code>.
     *
     * @return a <code>String</code> containing the fully 
     * qualified name of the client
     */
    public String getRemoteHost();
    
    
Stores an attribute in this request. Attributes are reset between requests. This method is most often used in conjunction with RequestDispatcher. 
Attribute names should follow the same conventions as
package names. Names beginning with java.*,
javax.*, and com.sun.*, are
reserved for use by Sun Microsystems.

 If the object passed in is null, the effect is the same as calling removeAttribute. 
 It is warned that when the request is dispatched from the
servlet resides in a different web application by
RequestDispatcher, the object set by this method
may not be correctly retrieved in the caller servlet.
Params:
name – a String specifying 
the name of the attribute
o – the Object to be stored/**
     * Stores an attribute in this request.
     * Attributes are reset between requests.  This method is most
     * often used in conjunction with {@link RequestDispatcher}.
     *
     * <p>Attribute names should follow the same conventions as
     * package names. Names beginning with <code>java.*</code>,
     * <code>javax.*</code>, and <code>com.sun.*</code>, are
     * reserved for use by Sun Microsystems.
     *<br> If the object passed in is null, the effect is the same as
     * calling {@link #removeAttribute}.
     * <br> It is warned that when the request is dispatched from the
     * servlet resides in a different web application by
     * <code>RequestDispatcher</code>, the object set by this method
     * may not be correctly retrieved in the caller servlet.
     *
     * @param name a <code>String</code> specifying 
     * the name of the attribute
     *
     * @param o the <code>Object</code> to be stored
     *
     */
    public void setAttribute(String name, Object o);
    
    
Removes an attribute from this request.  This method is not
generally needed as attributes only persist as long as the request
is being handled.
Attribute names should follow the same conventions as
package names. Names beginning with java.*,
javax.*, and com.sun.*, are
reserved for use by Sun Microsystems.
Params:
name – a String specifying 
the name of the attribute to remove/**
     *
     * Removes an attribute from this request.  This method is not
     * generally needed as attributes only persist as long as the request
     * is being handled.
     *
     * <p>Attribute names should follow the same conventions as
     * package names. Names beginning with <code>java.*</code>,
     * <code>javax.*</code>, and <code>com.sun.*</code>, are
     * reserved for use by Sun Microsystems.
     *
     * @param name a <code>String</code> specifying 
     * the name of the attribute to remove
     */
    public void removeAttribute(String name);
    
    
Returns the preferred Locale that the client will 
accept content in, based on the Accept-Language header.
If the client request doesn't provide an Accept-Language header,
this method returns the default locale for the server.
Returns:
the preferred Locale for the client/**
     * Returns the preferred <code>Locale</code> that the client will 
     * accept content in, based on the Accept-Language header.
     * If the client request doesn't provide an Accept-Language header,
     * this method returns the default locale for the server.
     *
     * @return the preferred <code>Locale</code> for the client
     */
    public Locale getLocale();
    
    
Returns an Enumeration of Locale objects
indicating, in decreasing order starting with the preferred locale, the
locales that are acceptable to the client based on the Accept-Language
header.
If the client request doesn't provide an Accept-Language header,
this method returns an Enumeration containing one 
Locale, the default locale for the server.
Returns:
an Enumeration of preferred 
Locale objects for the client/**
     * Returns an <code>Enumeration</code> of <code>Locale</code> objects
     * indicating, in decreasing order starting with the preferred locale, the
     * locales that are acceptable to the client based on the Accept-Language
     * header.
     * If the client request doesn't provide an Accept-Language header,
     * this method returns an <code>Enumeration</code> containing one 
     * <code>Locale</code>, the default locale for the server.
     *
     * @return an <code>Enumeration</code> of preferred 
     * <code>Locale</code> objects for the client
     */
    public Enumeration<Locale> getLocales();
    
    
Returns a boolean indicating whether this request was made using a
secure channel, such as HTTPS.
Returns:
a boolean indicating if the request was made using a
secure channel/**
     *
     * Returns a boolean indicating whether this request was made using a
     * secure channel, such as HTTPS.
     *
     * @return a boolean indicating if the request was made using a
     * secure channel
     */
    public boolean isSecure();
    
    
Returns a RequestDispatcher object that acts as a wrapper for the resource located at the given path. A RequestDispatcher object can be used to forward
a request to the resource or to include the resource in a response.
The resource can be dynamic or static.
The pathname specified may be relative, although it cannot extend
outside the current servlet context.  If the path begins with 
a "/" it is interpreted as relative to the current context root.  
This method returns null if the servlet container
cannot return a RequestDispatcher.
The difference between this method and ServletContext.getRequestDispatcher is that this method can take a relative path. 
Params:
path – a String specifying the pathname
to the resource. If it is relative, it must be
relative against the current servlet.
See Also:
RequestDispatcher
ServletContext.getRequestDispatcher
Returns:
a RequestDispatcher object that acts as a
wrapper for the resource at the specified path,
or null if the servlet container cannot
return a RequestDispatcher/**
     *
     * Returns a {@link RequestDispatcher} object that acts as a wrapper for
     * the resource located at the given path.  
     * A <code>RequestDispatcher</code> object can be used to forward
     * a request to the resource or to include the resource in a response.
     * The resource can be dynamic or static.
     *
     * <p>The pathname specified may be relative, although it cannot extend
     * outside the current servlet context.  If the path begins with 
     * a "/" it is interpreted as relative to the current context root.  
     * This method returns <code>null</code> if the servlet container
     * cannot return a <code>RequestDispatcher</code>.
     *
     * <p>The difference between this method and {@link
     * ServletContext#getRequestDispatcher} is that this method can take a
     * relative path.
     *
     * @param path a <code>String</code> specifying the pathname
     * to the resource. If it is relative, it must be
     * relative against the current servlet.
     *
     * @return a <code>RequestDispatcher</code> object that acts as a
     * wrapper for the resource at the specified path,
     * or <code>null</code> if the servlet container cannot
     * return a <code>RequestDispatcher</code>
     *
     * @see RequestDispatcher
     * @see ServletContext#getRequestDispatcher
     */
    public RequestDispatcher getRequestDispatcher(String path);
    
    
Params:
path – the path for which the real path is to be returned.
Returns:
the real path, or null if the
translation cannot be performed.
Deprecated:
 As of Version 2.1 of the Java Servlet API, use ServletContext.getRealPath instead./**
     * @param path the path for which the real path is to be returned.

     * @return the <i>real</i> path, or <tt>null</tt> if the
     * translation cannot be performed.

     * @deprecated  As of Version 2.1 of the Java Servlet API,
     *    use {@link ServletContext#getRealPath} instead.
     */
    public String getRealPath(String path);
    
    
Returns the Internet Protocol (IP) source port of the client
or last proxy that sent the request.
Returns:
an integer specifying the port number
Since:
Servlet 2.4/**
     * Returns the Internet Protocol (IP) source port of the client
     * or last proxy that sent the request.
     *
     * @return an integer specifying the port number
     *
     * @since Servlet 2.4
     */    
    public int getRemotePort();

    
Returns the host name of the Internet Protocol (IP) interface on
which the request was received.
Returns:
a String containing the host
        name of the IP on which the request was received.
Since:
Servlet 2.4/**
     * Returns the host name of the Internet Protocol (IP) interface on
     * which the request was received.
     *
     * @return a <code>String</code> containing the host
     *         name of the IP on which the request was received.
     *
     * @since Servlet 2.4
     */
    public String getLocalName();

    
Returns the Internet Protocol (IP) address of the interface on
which the request  was received.
Returns:
a String containing the
IP address on which the request was received.
Since:
Servlet 2.4/**
     * Returns the Internet Protocol (IP) address of the interface on
     * which the request  was received.
     *
     * @return a <code>String</code> containing the
     * IP address on which the request was received. 
     *
     * @since Servlet 2.4
     */       
    public String getLocalAddr();

    
Returns the Internet Protocol (IP) port number of the interface
on which the request was received.
Returns:
an integer specifying the port number
Since:
Servlet 2.4/**
     * Returns the Internet Protocol (IP) port number of the interface
     * on which the request was received.
     *
     * @return an integer specifying the port number
     *
     * @since Servlet 2.4
     */
    public int getLocalPort();

    
Gets the servlet context to which this ServletRequest was last
dispatched.
Returns:
the servlet context to which this ServletRequest was last
dispatched
Since:
Servlet 3.0/**
     * Gets the servlet context to which this ServletRequest was last
     * dispatched.
     *
     * @return the servlet context to which this ServletRequest was last
     * dispatched
     *
     * @since Servlet 3.0
     */
    public ServletContext getServletContext();

    
Puts this request into asynchronous mode, and initializes its AsyncContext with the original (unwrapped) ServletRequest and ServletResponse objects. 
Calling this method will cause committal of the associated response to be delayed until AsyncContext.complete is called on the returned AsyncContext, or the asynchronous operation has timed out. 
Calling AsyncContext.hasOriginalRequestAndResponse() on the returned AsyncContext will return true. Any filters
invoked in the outbound direction after this request was put
into asynchronous mode may use this as an indication that any request
and/or response wrappers that they added during their inbound
invocation need not stay around for the duration of the asynchronous
operation, and therefore any of their associated resources may be
released.
This method clears the list of AsyncListener instances (if any) that were registered with the AsyncContext returned by the previous call to one of the startAsync methods, after calling each AsyncListener at its onStartAsync method. 
Subsequent invocations of this method, or its overloaded 
variant, will return the same AsyncContext instance, reinitialized
as appropriate.
Throws:
IllegalStateException – if this request is within the scope of a filter or servlet that does not support asynchronous operations (that is, isAsyncSupported returns false), or if this method is called again without any asynchronous dispatch (resulting from one of the AsyncContext.dispatch methods), is called outside the scope of any such dispatch, or is called again within the scope of the same dispatch, or if the response has already been closed
See Also:
AsyncContext.dispatch()
Returns:
the (re)initialized AsyncContext
Since:
Servlet 3.0/**
     * Puts this request into asynchronous mode, and initializes its
     * {@link AsyncContext} with the original (unwrapped) ServletRequest
     * and ServletResponse objects.
     *
     * <p>Calling this method will cause committal of the associated
     * response to be delayed until {@link AsyncContext#complete} is
     * called on the returned {@link AsyncContext}, or the asynchronous
     * operation has timed out.
     *
     * <p>Calling {@link AsyncContext#hasOriginalRequestAndResponse()} on
     * the returned AsyncContext will return <code>true</code>. Any filters
     * invoked in the <i>outbound</i> direction after this request was put
     * into asynchronous mode may use this as an indication that any request
     * and/or response wrappers that they added during their <i>inbound</i>
     * invocation need not stay around for the duration of the asynchronous
     * operation, and therefore any of their associated resources may be
     * released.
     *
     * <p>This method clears the list of {@link AsyncListener} instances
     * (if any) that were registered with the AsyncContext returned by the
     * previous call to one of the startAsync methods, after calling each
     * AsyncListener at its {@link AsyncListener#onStartAsync onStartAsync}
     * method.
     *
     * <p>Subsequent invocations of this method, or its overloaded 
     * variant, will return the same AsyncContext instance, reinitialized
     * as appropriate.
     *
     * @return the (re)initialized AsyncContext
     * 
     * @throws IllegalStateException if this request is within the scope of
     * a filter or servlet that does not support asynchronous operations
     * (that is, {@link #isAsyncSupported} returns false),
     * or if this method is called again without any asynchronous dispatch
     * (resulting from one of the {@link AsyncContext#dispatch} methods),
     * is called outside the scope of any such dispatch, or is called again
     * within the scope of the same dispatch, or if the response has
     * already been closed
     *
     * @see AsyncContext#dispatch()
     * @since Servlet 3.0
     */
    public AsyncContext startAsync() throws IllegalStateException;
 
    
Puts this request into asynchronous mode, and initializes its AsyncContext with the given request and response objects. 
The ServletRequest and ServletResponse arguments must be the same instances, or instances of ServletRequestWrapper and ServletResponseWrapper that wrap them, that were passed to the service method of the Servlet or the doFilter method of the Filter, respectively, in whose scope this method is being called. 
Calling this method will cause committal of the associated response to be delayed until AsyncContext.complete is called on the returned AsyncContext, or the asynchronous operation has timed out. 
Calling AsyncContext.hasOriginalRequestAndResponse() on the returned AsyncContext will return false,
unless the passed in ServletRequest and ServletResponse arguments
are the original ones or do not carry any application-provided wrappers.
Any filters invoked in the outbound direction after this
request was put into asynchronous mode may use this as an indication
that some of the request and/or response wrappers that they added
during their inbound invocation may need to stay in place for
the duration of the asynchronous operation, and their associated
resources may not be released.
A ServletRequestWrapper applied during the inbound
invocation of a filter may be released by the outbound
invocation of the filter only if the given servletRequest, which is used to initialize the AsyncContext and will be returned by a call to AsyncContext.getRequest(), does not contain said ServletRequestWrapper. The same holds true for ServletResponseWrapper instances. 
This method clears the list of AsyncListener instances (if any) that were registered with the AsyncContext returned by the previous call to one of the startAsync methods, after calling each AsyncListener at its onStartAsync method. 
Subsequent invocations of this method, or its zero-argument
variant, will return the same AsyncContext instance, reinitialized
as appropriate. If a call to this method is followed by a call to its
zero-argument variant, the specified (and possibly wrapped) request
and response objects will remain locked in on the returned
AsyncContext.
Params:
servletRequest – the ServletRequest used to initialize the
AsyncContext
servletResponse – the ServletResponse used to initialize the
AsyncContext
Throws:
IllegalStateException – if this request is within the scope of a filter or servlet that does not support asynchronous operations (that is, isAsyncSupported returns false), or if this method is called again without any asynchronous dispatch (resulting from one of the AsyncContext.dispatch methods), is called outside the scope of any such dispatch, or is called again within the scope of the same dispatch, or if the response has already been closed
Returns:
the (re)initialized AsyncContext
Since:
Servlet 3.0/**
     * Puts this request into asynchronous mode, and initializes its
     * {@link AsyncContext} with the given request and response objects.
     *
     * <p>The ServletRequest and ServletResponse arguments must be
     * the same instances, or instances of {@link ServletRequestWrapper} and
     * {@link ServletResponseWrapper} that wrap them, that were passed to the
     * {@link Servlet#service service} method of the Servlet or the
     * {@link Filter#doFilter doFilter} method of the Filter, respectively,
     * in whose scope this method is being called.
     *
     * <p>Calling this method will cause committal of the associated
     * response to be delayed until {@link AsyncContext#complete} is
     * called on the returned {@link AsyncContext}, or the asynchronous
     * operation has timed out.
     *
     * <p>Calling {@link AsyncContext#hasOriginalRequestAndResponse()} on
     * the returned AsyncContext will return <code>false</code>,
     * unless the passed in ServletRequest and ServletResponse arguments
     * are the original ones or do not carry any application-provided wrappers.
     * Any filters invoked in the <i>outbound</i> direction after this
     * request was put into asynchronous mode may use this as an indication
     * that some of the request and/or response wrappers that they added
     * during their <i>inbound</i> invocation may need to stay in place for
     * the duration of the asynchronous operation, and their associated
     * resources may not be released.
     * A ServletRequestWrapper applied during the <i>inbound</i>
     * invocation of a filter may be released by the <i>outbound</i>
     * invocation of the filter only if the given <code>servletRequest</code>,
     * which is used to initialize the AsyncContext and will be returned by
     * a call to {@link AsyncContext#getRequest()}, does not contain said
     * ServletRequestWrapper. The same holds true for ServletResponseWrapper
     * instances. 
     *
     * <p>This method clears the list of {@link AsyncListener} instances
     * (if any) that were registered with the AsyncContext returned by the
     * previous call to one of the startAsync methods, after calling each
     * AsyncListener at its {@link AsyncListener#onStartAsync onStartAsync}
     * method.
     *
     * <p>Subsequent invocations of this method, or its zero-argument
     * variant, will return the same AsyncContext instance, reinitialized
     * as appropriate. If a call to this method is followed by a call to its
     * zero-argument variant, the specified (and possibly wrapped) request
     * and response objects will remain <i>locked in</i> on the returned
     * AsyncContext.
     *
     * @param servletRequest the ServletRequest used to initialize the
     * AsyncContext
     * @param servletResponse the ServletResponse used to initialize the
     * AsyncContext
     *
     * @return the (re)initialized AsyncContext
     * 
     * @throws IllegalStateException if this request is within the scope of
     * a filter or servlet that does not support asynchronous operations
     * (that is, {@link #isAsyncSupported} returns false),
     * or if this method is called again without any asynchronous dispatch
     * (resulting from one of the {@link AsyncContext#dispatch} methods),
     * is called outside the scope of any such dispatch, or is called again
     * within the scope of the same dispatch, or if the response has
     * already been closed
     *
     * @since Servlet 3.0
     */
    public AsyncContext startAsync(ServletRequest servletRequest,
                                   ServletResponse servletResponse)
            throws IllegalStateException;
   
    
Checks if this request has been put into asynchronous mode.
A ServletRequest is put into asynchronous mode by calling startAsync or startAsync(ServletRequest, ServletResponse) on it. 
This method returns false if this request was put into asynchronous mode, but has since been dispatched using one of the AsyncContext.dispatch methods or released from asynchronous mode via a call to AsyncContext.complete. 
Returns:
true if this request has been put into asynchronous mode,
false otherwise
Since:
Servlet 3.0/**
     * Checks if this request has been put into asynchronous mode.
     *
     * <p>A ServletRequest is put into asynchronous mode by calling
     * {@link #startAsync} or
     * {@link #startAsync(ServletRequest,ServletResponse)} on it.
     * 
     * <p>This method returns <tt>false</tt> if this request was
     * put into asynchronous mode, but has since been dispatched using
     * one of the {@link AsyncContext#dispatch} methods or released
     * from asynchronous mode via a call to {@link AsyncContext#complete}.
     *
     * @return true if this request has been put into asynchronous mode,
     * false otherwise
     *
     * @since Servlet 3.0
     */
    public boolean isAsyncStarted();

    
Checks if this request supports asynchronous operation.
Asynchronous operation is disabled for this request if this request
is within the scope of a filter or servlet that has not been annotated
or flagged in the deployment descriptor as being able to support
asynchronous handling.
Returns:
true if this request supports asynchronous operation, false
otherwise
Since:
Servlet 3.0/**
     * Checks if this request supports asynchronous operation.
     *
     * <p>Asynchronous operation is disabled for this request if this request
     * is within the scope of a filter or servlet that has not been annotated
     * or flagged in the deployment descriptor as being able to support
     * asynchronous handling.
     *
     * @return true if this request supports asynchronous operation, false
     * otherwise
     *
     * @since Servlet 3.0
     */
    public boolean isAsyncSupported();

    
Gets the AsyncContext that was created or reinitialized by the most recent invocation of startAsync or startAsync(ServletRequest, ServletResponse) on this request. 
Throws:
IllegalStateException – if this request has not been put into asynchronous mode, i.e., if neither startAsync nor startAsync(ServletRequest, ServletResponse) has been called
Returns:
the AsyncContext that was created or reinitialized by the most recent invocation of startAsync or startAsync(ServletRequest, ServletResponse) on this request
Since:
Servlet 3.0/**
     * Gets the AsyncContext that was created or reinitialized by the
     * most recent invocation of {@link #startAsync} or
     * {@link #startAsync(ServletRequest,ServletResponse)} on this request.
     *
     * @return the AsyncContext that was created or reinitialized by the
     * most recent invocation of {@link #startAsync} or
     * {@link #startAsync(ServletRequest,ServletResponse)} on
     * this request 
     *
     * @throws IllegalStateException if this request has not been put 
     * into asynchronous mode, i.e., if neither {@link #startAsync} nor
     * {@link #startAsync(ServletRequest,ServletResponse)} has been called
     *
     * @since Servlet 3.0
     */
    public AsyncContext getAsyncContext();

    
Gets the dispatcher type of this request.
The dispatcher type of a request is used by the container
to select the filters that need to be applied to the request:
Only filters with matching dispatcher type and url patterns will
be applied.
Allowing a filter that has been configured for multiple 
dispatcher types to query a request for its dispatcher type
allows the filter to process the request differently depending on
its dispatcher type.
The initial dispatcher type of a request is defined as
DispatcherType.REQUEST. The dispatcher type of a request dispatched via RequestDispatcher.forward(ServletRequest, ServletResponse) or RequestDispatcher.include(ServletRequest, ServletResponse) is given as DispatcherType.FORWARD or
DispatcherType.INCLUDE, respectively, while the dispatcher type of an asynchronous request dispatched via one of the AsyncContext.dispatch methods is given as DispatcherType.ASYNC. Finally, the dispatcher type of a
request dispatched to an error page by the container's error handling
mechanism is given as DispatcherType.ERROR.
See Also:
DispatcherType
Returns:
the dispatcher type of this request
Since:
Servlet 3.0/**
     * Gets the dispatcher type of this request.
     *
     * <p>The dispatcher type of a request is used by the container
     * to select the filters that need to be applied to the request:
     * Only filters with matching dispatcher type and url patterns will
     * be applied.
     * 
     * <p>Allowing a filter that has been configured for multiple 
     * dispatcher types to query a request for its dispatcher type
     * allows the filter to process the request differently depending on
     * its dispatcher type.
     *
     * <p>The initial dispatcher type of a request is defined as
     * <code>DispatcherType.REQUEST</code>. The dispatcher type of a request
     * dispatched via {@link RequestDispatcher#forward(ServletRequest,
     * ServletResponse)} or {@link RequestDispatcher#include(ServletRequest,
     * ServletResponse)} is given as <code>DispatcherType.FORWARD</code> or
     * <code>DispatcherType.INCLUDE</code>, respectively, while the
     * dispatcher type of an asynchronous request dispatched via
     * one of the {@link AsyncContext#dispatch} methods is given as
     * <code>DispatcherType.ASYNC</code>. Finally, the dispatcher type of a
     * request dispatched to an error page by the container's error handling
     * mechanism is given as <code>DispatcherType.ERROR</code>.
     *
     * @return the dispatcher type of this request
     * 
     * @see DispatcherType
     *
     * @since Servlet 3.0
     */
    public DispatcherType getDispatcherType();

}