Java tutorial
/* * 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 */ public void setContentLengthLong(long 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(); }