File: HttpServletResponse.java

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/*
 * 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.http;

import java.io.IOException;
import java.util.Collection;
import java.util.Map;
import java.util.function.Supplier;
import javax.servlet.ServletResponse;

/**
 *
 * Extends the {@link ServletResponse} interface to provide HTTP-specific
 * functionality in sending a response.  For example, it has methods
 * to access HTTP headers and cookies.
 *
 * <p>The servlet container creates an <code>HttpServletResponse</code> object
 * and passes it as an argument to the servlet's service methods
 * (<code>doGet</code>, <code>doPost</code>, etc).
 *
 * 
 * @author	Various
 *
 * @see		javax.servlet.ServletResponse
 *
 */
public interface HttpServletResponse extends ServletResponse {

    /**
     * Adds the specified cookie to the response.  This method can be called
     * multiple times to set more than one cookie.
     *
     * @param cookie the Cookie to return to the client
     *
     */
    public void addCookie(Cookie cookie);

    /**
     * Returns a boolean indicating whether the named response header 
     * has already been set.
     * 
     * @param	name	the header name
     * @return		<code>true</code> if the named response header 
     *			has already been set; 
     * 			<code>false</code> otherwise
     */
    public boolean containsHeader(String name);

    /**
     * Encodes the specified URL by including the session ID,
     * or, if encoding is not needed, returns the URL unchanged.
     * The implementation of this method includes the logic to
     * determine whether the session ID needs to be encoded in the URL.
     * For example, if the browser supports cookies, or session
     * tracking is turned off, URL encoding is unnecessary.
     * 
     * <p>For robust session tracking, all URLs emitted by a servlet 
     * should be run through this
     * method.  Otherwise, URL rewriting cannot be used with browsers
     * which do not support cookies.
     *
     * <p>If the URL is relative, it is always relative to the current
     * HttpServletRequest.
     *
     * @param	url	the url to be encoded.
     * @return		the encoded URL if encoding is needed;
     * 			the unchanged URL otherwise.
     * @exception IllegalArgumentException if the url is not valid
     */
    public String encodeURL(String url);

    /**
     * Encodes the specified URL for use in the
     * <code>sendRedirect</code> method or, if encoding is not needed,
     * returns the URL unchanged.  The implementation of this method
     * includes the logic to determine whether the session ID
     * needs to be encoded in the URL.  For example, if the browser supports
     * cookies, or session tracking is turned off, URL encoding is
     * unnecessary.  Because the rules for making this determination can
     * differ from those used to decide whether to
     * encode a normal link, this method is separated from the
     * <code>encodeURL</code> method.
     * 
     * <p>All URLs sent to the <code>HttpServletResponse.sendRedirect</code>
     * method should be run through this method.  Otherwise, URL
     * rewriting cannot be used with browsers which do not support
     * cookies.
     *
     * <p>If the URL is relative, it is always relative to the current
     * HttpServletRequest.
     *
     * @param	url	the url to be encoded.
     * @return		the encoded URL if encoding is needed;
     * 			the unchanged URL otherwise.
     * @exception IllegalArgumentException if the url is not valid
     *
     * @see #sendRedirect
     * @see #encodeUrl
     */
    public String encodeRedirectURL(String url);

    /**
     * @deprecated	As of version 2.1, use encodeURL(String url) instead
     *
     * @param	url	the url to be encoded.
     * @return		the encoded URL if encoding is needed; 
     * 			the unchanged URL otherwise.
     * @exception IllegalArgumentException if the url is not valid
     */
    @Deprecated
    public String encodeUrl(String url);
    
    /**
     * @deprecated	As of version 2.1, use 
     *			encodeRedirectURL(String url) instead
     *
     * @param	url	the url to be encoded.
     * @return		the encoded URL if encoding is needed; 
     * 			the unchanged URL otherwise.
     * @exception IllegalArgumentException if the url is not valid
     */
    @Deprecated
    public String encodeRedirectUrl(String url);

    /**
     * <p>Sends an error response to the client using the specified
     * status and clears the buffer.  The server defaults to creating
     * the response to look like an HTML-formatted server error page
     * containing the specified message, setting the content type to
     * "text/html".  The caller is <strong>not</strong> responsible for
     * escaping or re-encoding the message to ensure it is safe with
     * respect to the current response encoding and content type.  This
     * aspect of safety is the responsibility of the container, as it is
     * generating the error page containing the message.  The server
     * will preserve cookies and may clear or update any headers needed
     * to serve the error page as a valid response.</p>
     *
     * <p>If an error-page declaration has been made for the web
     * application corresponding to the status code passed in, it will
     * be served back in preference to the suggested msg parameter and
     * the msg parameter will be ignored.</p>
     *
     * <p>If the response has already been committed, this method throws 
     * an IllegalStateException.
     * After using this method, the response should be considered
     * to be committed and should not be written to.
     *
     * @param	sc	the error status code
     * @param	msg	the descriptive message
     * @exception	IOException	If an input or output exception occurs
     * @exception	IllegalStateException	If the response was committed
     */
    public void sendError(int sc, String msg) throws IOException;

    /**
     * Sends an error response to the client using the specified status
     * code and clears the buffer.
     * 
     * The server will preserve cookies and may clear or
     * update any headers needed to serve the error page as a valid response.
     *
     * If an error-page declaration has been made for the web application
     * corresponding to the status code passed in, it will be served back
     * the error page
     * 
     * <p>If the response has already been committed, this method throws 
     * an IllegalStateException.
     * After using this method, the response should be considered
     * to be committed and should not be written to.
     *
     * @param	sc	the error status code
     * @exception	IOException	If an input or output exception occurs
     * @exception	IllegalStateException	If the response was committed
     *						before this method call
     */
    public void sendError(int sc) throws IOException;

    /**
     * Sends a temporary redirect response to the client using the
     * specified redirect location URL and clears the buffer. The buffer will
     * be replaced with the data set by this method. Calling this method sets the
     * status code to {@link #SC_FOUND} 302 (Found).
     * This method can accept relative URLs;the servlet container must convert
     * the relative URL to an absolute URL
     * before sending the response to the client. If the location is relative 
     * without a leading '/' the container interprets it as relative to
     * the current request URI. If the location is relative with a leading
     * '/' the container interprets it as relative to the servlet container root.
     * If the location is relative with two leading '/' the container interprets
     * it as a network-path reference (see
     * <a href="http://www.ietf.org/rfc/rfc3986.txt">
     * RFC 3986: Uniform Resource Identifier (URI): Generic Syntax</a>, section 4.2
     * &quot;Relative Reference&quot;).
     *
     * <p>If the response has already been committed, this method throws 
     * an IllegalStateException.
     * After using this method, the response should be considered
     * to be committed and should not be written to.
     *
     * @param		location	the redirect location URL
     * @exception	IOException	If an input or output exception occurs
     * @exception	IllegalStateException	If the response was committed or
     *              if a partial URL is given and cannot be converted into a valid URL
     */
    public void sendRedirect(String location) throws IOException;
    
    /**
     * 
     * Sets a response header with the given name and
     * date-value.  The date is specified in terms of
     * milliseconds since the epoch.  If the header had already
     * been set, the new value overwrites the previous one.  The
     * <code>containsHeader</code> method can be used to test for the
     * presence of a header before setting its value.
     * 
     * @param	name	the name of the header to set
     * @param	date	the assigned date value
     * 
     * @see #containsHeader
     * @see #addDateHeader
     */
    public void setDateHeader(String name, long date);
    
    /**
     * 
     * Adds a response header with the given name and
     * date-value.  The date is specified in terms of
     * milliseconds since the epoch.  This method allows response headers 
     * to have multiple values.
     * 
     * @param	name	the name of the header to set
     * @param	date	the additional date value
     * 
     * @see #setDateHeader
     */
    public void addDateHeader(String name, long date);
    
    /**
     *
     * Sets a response header with the given name and value.
     * If the header had already been set, the new value overwrites the
     * previous one.  The <code>containsHeader</code> method can be
     * used to test for the presence of a header before setting its
     * value.
     * 
     * @param	name	the name of the header
     * @param	value	the header value  If it contains octet string,
     *		it should be encoded according to RFC 2047
     *		(http://www.ietf.org/rfc/rfc2047.txt)
     *
     * @see #containsHeader
     * @see #addHeader
     */
    public void setHeader(String name, String value);
    
    /**
     * Adds a response header with the given name and value.
     * This method allows response headers to have multiple values.
     * 
     * @param	name	the name of the header
     * @param	value	the additional header value   If it contains
     *		octet string, it should be encoded
     *		according to RFC 2047
     *		(http://www.ietf.org/rfc/rfc2047.txt)
     *
     * @see #setHeader
     */
    public void addHeader(String name, String value);

    /**
     * Sets a response header with the given name and
     * integer value.  If the header had already been set, the new value
     * overwrites the previous one.  The <code>containsHeader</code>
     * method can be used to test for the presence of a header before
     * setting its value.
     *
     * @param	name	the name of the header
     * @param	value	the assigned integer value
     *
     * @see #containsHeader
     * @see #addIntHeader
     */
    public void setIntHeader(String name, int value);

    /**
     * Adds a response header with the given name and
     * integer value.  This method allows response headers to have multiple
     * values.
     *
     * @param	name	the name of the header
     * @param	value	the assigned integer value
     *
     * @see #setIntHeader
     */
    public void addIntHeader(String name, int value);

    /**
     * Sets the status code for this response. 
     *
     * <p>This method is used to set the return status code when there is
     * no error (for example, for the SC_OK or SC_MOVED_TEMPORARILY status
     * codes).
     *
     * <p>If this method is used to set an error code, then the container's
     * error page mechanism will not be triggered. If there is an error and
     * the caller wishes to invoke an error page defined in the web
     * application, then {@link #sendError} must be used instead.
     *
     * <p>This method preserves any cookies and other response headers. 
     *
     * <p>Valid status codes are those in the 2XX, 3XX, 4XX, and 5XX ranges.
     * Other status codes are treated as container specific.
     *
     * @param	sc	the status code
     *
     * @see #sendError
     */
    public void setStatus(int sc);
  

    /**
     * @deprecated As of version 2.1, due to ambiguous meaning of the 
     * message parameter. To set a status code 
     * use <code>setStatus(int)</code>, to send an error with a description
     * use <code>sendError(int, String)</code>.
     *
     * Sets the status code and message for this response.
     * 
     * @param	sc	the status code
     * @param	sm	the status message
     */
    @Deprecated
    public void setStatus(int sc, String sm);

    /**
     * Gets the current status code of this response.
     *
     * @return the current status code of this response
     *
     * @since Servlet 3.0
     */
    default public int getStatus() { return -1; }

    /**
     * Gets the value of the response header with the given name.
     * 
     * <p>If a response header with the given name exists and contains
     * multiple values, the value that was added first will be returned.
     *
     * <p>This method considers only response headers set or added via
     * {@link #setHeader}, {@link #addHeader}, {@link #setDateHeader},
     * {@link #addDateHeader}, {@link #setIntHeader}, or
     * {@link #addIntHeader}, respectively.
     *
     * @param name the name of the response header whose value to return
     *
     * @return the value of the response header with the given name,
     * or <tt>null</tt> if no header with the given name has been set
     * on this response
     *
     * @since Servlet 3.0
     */
    default public String getHeader(String name) { return null; }

    /**
     * Gets the values of the response header with the given name.
     *
     * <p>This method considers only response headers set or added via
     * {@link #setHeader}, {@link #addHeader}, {@link #setDateHeader},
     * {@link #addDateHeader}, {@link #setIntHeader}, or
     * {@link #addIntHeader}, respectively.
     *
     * <p>Any changes to the returned <code>Collection</code> must not 
     * affect this <code>HttpServletResponse</code>.
     *
     * @param name the name of the response header whose values to return
     *
     * @return a (possibly empty) <code>Collection</code> of the values
     * of the response header with the given name
     *
     * @since Servlet 3.0
     */			
    default public Collection<String> getHeaders(String name) { return null; }
    
    /**
     * Gets the names of the headers of this response.
     *
     * <p>This method considers only response headers set or added via
     * {@link #setHeader}, {@link #addHeader}, {@link #setDateHeader},
     * {@link #addDateHeader}, {@link #setIntHeader}, or
     * {@link #addIntHeader}, respectively.
     *
     * <p>Any changes to the returned <code>Collection</code> must not 
     * affect this <code>HttpServletResponse</code>.
     *
     * @return a (possibly empty) <code>Collection</code> of the names
     * of the headers of this response
     *
     * @since Servlet 3.0
     */
    default public Collection<String> getHeaderNames() { return null; }

    /**
     * Sets the supplier of trailer headers.
     *
     * <p>The trailer header field value is defined as a comma-separated list
     * (see Section 3.2.2 and Section 4.1.2 of RFC 7230).</p>
     *
     * <p>The supplier will be called within the scope of whatever thread/call
     * causes the response content to be completed. Typically this will
     * be any thread calling close() on the output stream or writer.</p>
     *
     * <p>The trailers that run afoul of the provisions of section 4.1.2 of
     * RFC 7230 are ignored.</p>
     *
     * <p>The RFC requires the name of every key that is to be in the
     * supplied Map is included in the comma separated list that is the value
     * of the "Trailer" response header.  The application is responsible for
     * ensuring this requirement is met.  Failure to do so may lead to
     * interoperability failures.</p>
     *
     * @implSpec
     * The default implementation is a no-op.
     *
     * @param supplier the supplier of trailer headers
     *
     * @exception IllegalStateException if it is invoked after the response has
     *         has been committed,
     *         or the trailer is not supported in the request, for instance,
     *         the underlying protocol is HTTP 1.0, or the response is not
     *         in chunked encoding in HTTP 1.1.
     *
     * @since Servlet 4.0
     */
    default public void setTrailerFields(Supplier<Map<String, String>> supplier) {
    }

    /**
     * Gets the supplier of trailer headers.
     *
     * @implSpec
     * The default implememtation return null.
     *
     * @return <code>Supplier</code> of trailer headers
     * 
     * @since Servlet 4.0
     */
    default public Supplier<Map<String, String>> getTrailerFields() {
        return null;
    }


    /*
     * Server status codes; see RFC 2068.
     */

    /**
     * Status code (100) indicating the client can continue.
     */
    public static final int SC_CONTINUE = 100;

    /**
     * Status code (101) indicating the server is switching protocols
     * according to Upgrade header.
     */
    public static final int SC_SWITCHING_PROTOCOLS = 101;

    /**
     * Status code (200) indicating the request succeeded normally.
     */
    public static final int SC_OK = 200;

    /**
     * Status code (201) indicating the request succeeded and created
     * a new resource on the server.
     */
    public static final int SC_CREATED = 201;

    /**
     * Status code (202) indicating that a request was accepted for
     * processing, but was not completed.
     */
    public static final int SC_ACCEPTED = 202;

    /**
     * Status code (203) indicating that the meta information presented
     * by the client did not originate from the server.
     */
    public static final int SC_NON_AUTHORITATIVE_INFORMATION = 203;

    /**
     * Status code (204) indicating that the request succeeded but that
     * there was no new information to return.
     */
    public static final int SC_NO_CONTENT = 204;

    /**
     * Status code (205) indicating that the agent <em>SHOULD</em> reset
     * the document view which caused the request to be sent.
     */
    public static final int SC_RESET_CONTENT = 205;

    /**
     * Status code (206) indicating that the server has fulfilled
     * the partial GET request for the resource.
     */
    public static final int SC_PARTIAL_CONTENT = 206;

    /**
     * Status code (300) indicating that the requested resource
     * corresponds to any one of a set of representations, each with
     * its own specific location.
     */
    public static final int SC_MULTIPLE_CHOICES = 300;

    /**
     * Status code (301) indicating that the resource has permanently
     * moved to a new location, and that future references should use a
     * new URI with their requests.
     */
    public static final int SC_MOVED_PERMANENTLY = 301;

    /**
     * Status code (302) indicating that the resource has temporarily
     * moved to another location, but that future references should
     * still use the original URI to access the resource.
     *
     * This definition is being retained for backwards compatibility.
     * SC_FOUND is now the preferred definition.
     */
    public static final int SC_MOVED_TEMPORARILY = 302;

    /**
    * Status code (302) indicating that the resource reside
    * temporarily under a different URI. Since the redirection might
    * be altered on occasion, the client should continue to use the
    * Request-URI for future requests.(HTTP/1.1) To represent the
    * status code (302), it is recommended to use this variable.
    */
    public static final int SC_FOUND = 302;

    /**
     * Status code (303) indicating that the response to the request
     * can be found under a different URI.
     */
    public static final int SC_SEE_OTHER = 303;

    /**
     * Status code (304) indicating that a conditional GET operation
     * found that the resource was available and not modified.
     */
    public static final int SC_NOT_MODIFIED = 304;

    /**
     * Status code (305) indicating that the requested resource
     * <em>MUST</em> be accessed through the proxy given by the
     * <code><em>Location</em></code> field.
     */
    public static final int SC_USE_PROXY = 305;

     /**
     * Status code (307) indicating that the requested resource 
     * resides temporarily under a different URI. The temporary URI
     * <em>SHOULD</em> be given by the <code><em>Location</em></code> 
     * field in the response.
     */
    public static final int SC_TEMPORARY_REDIRECT = 307;

    /**
     * Status code (400) indicating the request sent by the client was
     * syntactically incorrect.
     */
    public static final int SC_BAD_REQUEST = 400;

    /**
     * Status code (401) indicating that the request requires HTTP
     * authentication.
     */
    public static final int SC_UNAUTHORIZED = 401;

    /**
     * Status code (402) reserved for future use.
     */
    public static final int SC_PAYMENT_REQUIRED = 402;

    /**
     * Status code (403) indicating the server understood the request
     * but refused to fulfill it.
     */
    public static final int SC_FORBIDDEN = 403;

    /**
     * Status code (404) indicating that the requested resource is not
     * available.
     */
    public static final int SC_NOT_FOUND = 404;

    /**
     * Status code (405) indicating that the method specified in the
     * <code><em>Request-Line</em></code> is not allowed for the resource
     * identified by the <code><em>Request-URI</em></code>.
     */
    public static final int SC_METHOD_NOT_ALLOWED = 405;

    /**
     * Status code (406) indicating that the resource identified by the
     * request is only capable of generating response entities which have
     * content characteristics not acceptable according to the accept
     * headers sent in the request.
     */
    public static final int SC_NOT_ACCEPTABLE = 406;

    /**
     * Status code (407) indicating that the client <em>MUST</em> first
     * authenticate itself with the proxy.
     */
    public static final int SC_PROXY_AUTHENTICATION_REQUIRED = 407;

    /**
     * Status code (408) indicating that the client did not produce a
     * request within the time that the server was prepared to wait.
     */
    public static final int SC_REQUEST_TIMEOUT = 408;

    /**
     * Status code (409) indicating that the request could not be
     * completed due to a conflict with the current state of the
     * resource.
     */
    public static final int SC_CONFLICT = 409;

    /**
     * Status code (410) indicating that the resource is no longer
     * available at the server and no forwarding address is known.
     * This condition <em>SHOULD</em> be considered permanent.
     */
    public static final int SC_GONE = 410;

    /**
     * Status code (411) indicating that the request cannot be handled
     * without a defined <code><em>Content-Length</em></code>.
     */
    public static final int SC_LENGTH_REQUIRED = 411;

    /**
     * Status code (412) indicating that the precondition given in one
     * or more of the request-header fields evaluated to false when it
     * was tested on the server.
     */
    public static final int SC_PRECONDITION_FAILED = 412;

    /**
     * Status code (413) indicating that the server is refusing to process
     * the request because the request entity is larger than the server is
     * willing or able to process.
     */
    public static final int SC_REQUEST_ENTITY_TOO_LARGE = 413;

    /**
     * Status code (414) indicating that the server is refusing to service
     * the request because the <code><em>Request-URI</em></code> is longer
     * than the server is willing to interpret.
     */
    public static final int SC_REQUEST_URI_TOO_LONG = 414;

    /**
     * Status code (415) indicating that the server is refusing to service
     * the request because the entity of the request is in a format not
     * supported by the requested resource for the requested method.
     */
    public static final int SC_UNSUPPORTED_MEDIA_TYPE = 415;

    /**
     * Status code (416) indicating that the server cannot serve the
     * requested byte range.
     */
    public static final int SC_REQUESTED_RANGE_NOT_SATISFIABLE = 416;

    /**
     * Status code (417) indicating that the server could not meet the
     * expectation given in the Expect request header.
     */
    public static final int SC_EXPECTATION_FAILED = 417;

    /**
     * Status code (500) indicating an error inside the HTTP server
     * which prevented it from fulfilling the request.
     */
    public static final int SC_INTERNAL_SERVER_ERROR = 500;

    /**
     * Status code (501) indicating the HTTP server does not support
     * the functionality needed to fulfill the request.
     */
    public static final int SC_NOT_IMPLEMENTED = 501;

    /**
     * Status code (502) indicating that the HTTP server received an
     * invalid response from a server it consulted when acting as a
     * proxy or gateway.
     */
    public static final int SC_BAD_GATEWAY = 502;

    /**
     * Status code (503) indicating that the HTTP server is
     * temporarily overloaded, and unable to handle the request.
     */
    public static final int SC_SERVICE_UNAVAILABLE = 503;

    /**
     * Status code (504) indicating that the server did not receive
     * a timely response from the upstream server while acting as
     * a gateway or proxy.
     */
    public static final int SC_GATEWAY_TIMEOUT = 504;

    /**
     * Status code (505) indicating that the server does not support
     * or refuses to support the HTTP protocol version that was used
     * in the request message.
     */
    public static final int SC_HTTP_VERSION_NOT_SUPPORTED = 505;
}