File: ServletResponse.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;

import java.io.IOException;
import java.io.PrintWriter;
import java.util.Locale;


/**
 * Defines an object to assist a servlet in sending a response to the client.
 * The servlet container creates a <code>ServletResponse</code> object and
 * passes it as an argument to the servlet's <code>service</code> method.
 *
 * <p>To send binary data in a MIME body response, use
 * the {@link ServletOutputStream} returned by {@link #getOutputStream}.
 * To send character data, use the <code>PrintWriter</code> object 
 * returned by {@link #getWriter}. To mix binary and text data,
 * for example, to create a multipart response, use a
 * <code>ServletOutputStream</code> and manage the character sections
 * manually.
 *
 * <p>The charset for the MIME body response can be specified explicitly
 * using any of the following techniques: 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).
 * If multiple of the preceding techniques have been employed, the priority is
 * the order listed.
 * For per request, the charset for the response can be specified explicitly
 * using the {@link #setCharacterEncoding} and {@link #setContentType} methods,
 * or implicitly using the {@link #setLocale} method.
 * Explicit specifications take precedence over implicit specifications.
 * If no charset is explicitly specified, ISO-8859-1 will be used.
 * The <code>setCharacterEncoding</code>,
 * <code>setContentType</code>, or <code>setLocale</code> method must
 * be called before <code>getWriter</code> and before committing
 * the response for the character encoding to be used.
 * 
 * <p>See the Internet RFCs such as 
 * <a href="http://www.ietf.org/rfc/rfc2045.txt">
 * RFC 2045</a> for more information on MIME. Protocols such as SMTP
 * and HTTP define profiles of MIME, and those standards
 * are still evolving.
 *
 * @author Various
 *
 * @see ServletOutputStream
 */
 
public interface ServletResponse {
    
    /**
     * Returns the name of the character encoding (MIME charset)
     * used for the body sent in this response.
     * The following methods for specifying the response character encoding are
     * consulted, in decreasing order of priority: per request, perweb-app
     * (using {@link ServletContext#setResponseCharacterEncoding}, deployment
     * descriptor), and per container (for all web applications deployed in
     * that container, using vendor specific configuration).
     * The first one of these methods that yields a result is returned.
     * Per-request, the charset for the response can be specified explicitly
     * using the {@link setCharacterEncoding} and {@link setContentType}
     * methods, or implicitly using the setLocale(java.util.Locale) method.
     * Explicit specifications take precedence over implicit specifications.
     * Calls made to these methods after <code>getWriter</code> has been
     * called or after the response has been committed have no
     * effect on the character encoding. If no character encoding
     * has been specified, <code>ISO-8859-1</code> is returned.
     * <p>See RFC 2047 (http://www.ietf.org/rfc/rfc2047.txt)
     * for more information about character encoding and MIME.
     *
     * @return a <code>String</code> specifying the name of
     * the character encoding, for example, <code>UTF-8</code>
     */
    public String getCharacterEncoding();
    
    /**
     * Returns the content type used for the MIME body
     * sent in this response. The content type proper must
     * have been specified using {@link #setContentType}
     * before the response is committed. If no content type
     * has been specified, this method returns null.
     * If a content type has been specified, and a
     * character encoding has been explicitly or implicitly
     * specified as described in {@link #getCharacterEncoding}
     * or {@link #getWriter} has been called,
     * the charset parameter is included in the string returned.
     * If no character encoding has been specified, the
     * charset parameter is omitted.
     *
     * @return a <code>String</code> specifying the content type,
     * for example, <code>text/html; charset=UTF-8</code>, or null
     *
     * @since Servlet 2.4
     */
    public String getContentType();
    
    

    /**
     * Returns a {@link ServletOutputStream} suitable for writing binary 
     * data in the response. The servlet container does not encode the
     * binary data.  
     *
     * <p> Calling flush() on the ServletOutputStream commits the response.
     *
     * Either this method or {@link #getWriter} may 
     * be called to write the body, not both, except when {@link #reset}
     * has been called.
     *
     * @return a {@link ServletOutputStream} for writing binary data 
     *
     * @exception IllegalStateException if the <code>getWriter</code> method
     * has been called on this response
     *
     * @exception IOException if an input or output exception occurred
     *
     * @see #getWriter
     * @see #reset
     */
    public ServletOutputStream getOutputStream() throws IOException;
    
    /**
     * Returns a <code>PrintWriter</code> object that
     * can send character text to the client.
     * The <code>PrintWriter</code> uses the character
     * encoding returned by {@link #getCharacterEncoding}.
     * If the response's character encoding has not been
     * specified as described in <code>getCharacterEncoding</code>
     * (i.e., the method just returns the default value 
     * <code>ISO-8859-1</code>), <code>getWriter</code>
     * updates it to <code>ISO-8859-1</code>.
     * <p>Calling flush() on the <code>PrintWriter</code>
     * commits the response.
     * <p>Either this method or {@link #getOutputStream} may be called
     * to write the body, not both, except when {@link #reset}
     * has been called.
     * 
     * @return a <code>PrintWriter</code> object that 
     * can return character data to the client 
     *
     * @exception java.io.UnsupportedEncodingException
     * if the character encoding returned
     * by <code>getCharacterEncoding</code> cannot be used
     *
     * @exception IllegalStateException
     * if the <code>getOutputStream</code>
     * method has already been called for this response object
     *
     * @exception IOException
     * if an input or output exception occurred
     *
     * @see #getOutputStream
     * @see #setCharacterEncoding
     * @see #reset
     */
    public PrintWriter getWriter() throws IOException;
    
    /**
     * Sets the character encoding (MIME charset) of the response
     * being sent to the client, for example, to UTF-8.
     * If the response character encoding has already been set by the
     * {@link ServletContext#setResponseCharacterEncoding},
     * deployment descriptor, or using the setContentType() or setLocale()
     * methods, the value set in this method overrides any of those values.
     * Calling {@link #setContentType} with the <code>String</code>
     * of <code>text/html</code> and calling
     * this method with the <code>String</code> of <code>UTF-8</code>
     * is equivalent with calling
     * <code>setContentType</code> with the <code>String</code> of
     * <code>text/html; charset=UTF-8</code>.
     * <p>This method can be called repeatedly to change the character
     * encoding.
     * This method has no effect if it is called after
     * <code>getWriter</code> has been
     * called or after the response has been committed.
     * <p>Containers must communicate the character encoding used for
     * the servlet response's writer to the client if the protocol
     * provides a way for doing so. In the case of HTTP, the character
     * encoding is communicated as part of the <code>Content-Type</code>
     * header for text media types. Note that the character encoding
     * cannot be communicated via HTTP headers if the servlet does not
     * specify a content type; however, it is still used to encode text
     * written via the servlet response's writer.
     *
     * @param charset a String specifying only the character set
     * defined by IANA Character Sets
     * (http://www.iana.org/assignments/character-sets)
     *
     * @see #setContentType
     * @see #setLocale
     *
     * @since Servlet 2.4
     */
    public void setCharacterEncoding(String charset);
    
    /**
     * Sets the length of the content body in the response
     * In HTTP servlets, this method sets the HTTP Content-Length header.
     *
     * @param len an integer specifying the length of the 
     * content being returned to the client; sets the Content-Length header
     */
    public void setContentLength(int len);
    
    /**
     * Sets the length of the content body in the response
     * In HTTP servlets, this method sets the HTTP Content-Length header.
     *
     * @param len a long specifying the length of the 
     * content being returned to the client; sets the Content-Length header
     *
     * @since Servlet 3.1
     */
    default public void setContentLengthLong(long len) { setContentLength((int) len); }

    /**
     * Sets the content type of the response being sent to
     * the client, if the response has not been committed yet.
     * The given content type may include a character encoding
     * specification, for example, <code>text/html;charset=UTF-8</code>.
     * The response's character encoding is only set from the given
     * content type if this method is called before <code>getWriter</code>
     * is called.
     * <p>This method may be called repeatedly to change content type and
     * character encoding.
     * This method has no effect if called after the response
     * has been committed. It does not set the response's character
     * encoding if it is called after <code>getWriter</code>
     * has been called or after the response has been committed.
     * <p>Containers must communicate the content type and the character
     * encoding used for the servlet response's writer to the client if
     * the protocol provides a way for doing so. In the case of HTTP,
     * the <code>Content-Type</code> header is used.
     *
     * @param type a <code>String</code> specifying the MIME 
     * type of the content
     *
     * @see #setLocale
     * @see #setCharacterEncoding
     * @see #getOutputStream
     * @see #getWriter
     *
     */

    public void setContentType(String type);
    

    /**
     * Sets the preferred buffer size for the body of the response.  
     * The servlet container will use a buffer at least as large as 
     * the size requested.  The actual buffer size used can be found
     * using <code>getBufferSize</code>.
     *
     * <p>A larger buffer allows more content to be written before anything is
     * actually sent, thus providing the servlet with more time to set
     * appropriate status codes and headers.  A smaller buffer decreases 
     * server memory load and allows the client to start receiving data more
     * quickly.
     *
     * <p>This method must be called before any response body content is
     * written; if content has been written or the response object has
     * been committed, this method throws an 
     * <code>IllegalStateException</code>.
     *
     * @param size the preferred buffer size
     *
     * @exception IllegalStateException if this method is called after
     * content has been written
     *
     * @see 		#getBufferSize
     * @see 		#flushBuffer
     * @see 		#isCommitted
     * @see 		#reset
     */
    public void setBufferSize(int size);
   
    /**
     * Returns the actual buffer size used for the response.  If no buffering
     * is used, this method returns 0.
     *
     * @return the actual buffer size used
     *
     * @see #setBufferSize
     * @see #flushBuffer
     * @see #isCommitted
     * @see #reset
     */
    public int getBufferSize();
    
    /**
     * Forces any content in the buffer to be written to the client.  A call
     * to this method automatically commits the response, meaning the status 
     * code and headers will be written.
     *
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #isCommitted
     * @see #reset

     * @throws IOException if the act of flushing the buffer cannot be
     * completed.
     *
     */
    public void flushBuffer() throws IOException;
    
    /**
     * Clears the content of the underlying buffer in the response without
     * clearing headers or status code. If the 
     * response has been committed, this method throws an 
     * <code>IllegalStateException</code>.
     *
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #isCommitted
     * @see #reset
     *
     * @since Servlet 2.3
     */

    public void resetBuffer();
    
    /**
     * Returns a boolean indicating if the response has been
     * committed.  A committed response has already had its status 
     * code and headers written.
     *
     * @return  a boolean indicating if the response has been
     * committed
     *
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #flushBuffer
     * @see #reset
     *
     */
    public boolean isCommitted();
    
    /**
     * Clears any data that exists in the buffer as well as the status code,
     * headers.  The state of calling {@link #getWriter} or
     * {@link #getOutputStream} is also cleared.  It is legal, for instance,
     * to call {@link #getWriter}, {@link #reset} and then
     * {@link #getOutputStream}.  If {@link #getWriter} or
     * {@link #getOutputStream} have been called before this method,
     * then the corrresponding returned Writer or OutputStream will be
     * staled and the behavior of using the stale object is undefined.
     * If the response has been committed, this method throws an 
     * <code>IllegalStateException</code>.
     *
     * @exception IllegalStateException  if the response has already been
     * committed
     *
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #flushBuffer
     * @see #isCommitted
     */
    public void reset();
    
    /**
     * Sets the locale of the response, if the response has not been
     * committed yet. It also sets the response's character encoding
     * appropriately for the locale, if the character encoding has not
     * been explicitly set using {@link #setContentType} or
     * {@link #setCharacterEncoding}, <code>getWriter</code> hasn't
     * been called yet, and the response hasn't been committed yet.
     * If the deployment descriptor contains a 
     * <code>locale-encoding-mapping-list</code> element, and that
     * element provides a mapping for the given locale, that mapping
     * is used. Otherwise, the mapping from locale to character
     * encoding is container dependent.
     * <p>This method may be called repeatedly to change locale and
     * character encoding. The method has no effect if called after the
     * response has been committed. It does not set the response's
     * character encoding if it is called after {@link #setContentType}
     * has been called with a charset specification, after
     * {@link #setCharacterEncoding} has been called, after
     * <code>getWriter</code> has been called, or after the response
     * has been committed.
     * <p>Containers must communicate the locale and the character encoding
     * used for the servlet response's writer to the client if the protocol
     * provides a way for doing so. In the case of HTTP, the locale is
     * communicated via the <code>Content-Language</code> header,
     * the character encoding as part of the <code>Content-Type</code>
     * header for text media types. Note that the character encoding
     * cannot be communicated via HTTP headers if the servlet does not
     * specify a content type; however, it is still used to encode text
     * written via the servlet response's writer.
     * 
     * @param loc the locale of the response
     *
     * @see #getLocale
     * @see #setContentType
     * @see #setCharacterEncoding
     */
    public void setLocale(Locale loc);
    
    /**
     * Returns the locale specified for this response
     * using the {@link #setLocale} method. Calls made to
     * <code>setLocale</code> after the response is committed
     * have no effect. If no locale has been specified,
     * the container's default locale is returned.
     *
     * @return the Locale for this response.
     * 
     * @see #setLocale
     */
    public Locale getLocale();

}