ServletResponse.java

/*
 * Copyright (c) 1997, 2023 Oracle and/or its affiliates and others.
 * 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 jakarta.servlet;

import java.io.IOException;
import java.io.PrintWriter;
import java.io.UnsupportedEncodingException;
import java.nio.charset.Charset;
import java.nio.charset.StandardCharsets;
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(String)},
 * {@link #setCharacterEncoding(Charset)} 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(String)}, {@link #setCharacterEncoding(Charset)} 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 {@link ServletContext#setResponseCharacterEncoding}, the
     * deployment descriptor, or using the {@link #setCharacterEncoding(Charset)}, {@link #setContentType} or
     * {@link #setLocale} methods, the value set in this method overrides all 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 to calling {@link #setContentType} 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>
     * If calling this method has an effect (as per the previous paragraph), calling this method with {@code null} clears
     * any character encoding set via a previous call to this method, {@link #setCharacterEncoding(Charset)},
     * {@link #setContentType} or {@link #setLocale} but does not affect any default character encoding configured via
     * {@link ServletContext#setResponseCharacterEncoding} or the deployment descriptor.
     * <p>
     * If this method is called with an invalid or unrecognised character encoding, then a subsequent call to
     * {@link #getWriter()} will throw a {@link UnsupportedEncodingException}. Content for an unknown encoding can be sent
     * with the {@link ServletOutputStream} returned from {@link #getOutputStream()}.
     * <p>
     * Containers may choose to log calls to this method that use an invalid or unrecognised character encoding.
     * <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 encoding a String specifying only the character set defined by IANA Character Sets
     * (http://www.iana.org/assignments/character-sets) or {@code null}
     *
     * @see #setCharacterEncoding(Charset)
     * @see #setContentType
     * @see #setLocale
     *
     * @since Servlet 2.4
     */
    public void setCharacterEncoding(String encoding);

    /**
     * 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 {@link ServletContext#setResponseCharacterEncoding}, the
     * deployment descriptor, or using the {@link #setCharacterEncoding(String)}, {@link #setContentType} or
     * {@link #setLocale} methods, the value set in this method overrides all of those values. Calling
     * {@link #setContentType} with the <code>String</code> of <code>text/html</code> and calling this method with
     * {@link StandardCharsets#UTF_8} is equivalent to calling {@link #setContentType} 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>
     * If calling this method has an effect (as per the previous paragraph), calling this method with {@code null} clears
     * any character encoding set via a previous call to this method, {@link #setCharacterEncoding(String)},
     * {@link #setContentType} or {@link #setLocale} but does not affect any default character encoding configured via
     * {@link ServletContext#setResponseCharacterEncoding} or the deployment descriptor.
     * <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.
     * <p>
     * Implementations are strongly encouraged to override this default method and provide a more efficient implementation.
     *
     * @param encoding a Charset instance representing the encoding to use or {@code null}
     *
     * @see #setCharacterEncoding(String)
     * @see #setContentType
     * @see #setLocale
     *
     * @since Servlet 6.1
     */
    default public void setCharacterEncoding(Charset encoding) {
        setCharacterEncoding(encoding.name());
    }

    /**
     * Sets the length of the content body in the response In HTTP servlets, this method sets the HTTP Content-Length
     * header.
     * <p>
     * This method may be called repeatedly to change the content length. This method has no effect if called after the
     * response has been committed.
     *
     * @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.
     * <p>
     * This method may be called repeatedly to change the content length. This method has no effect if called after the
     * response has been committed.
     *
     * @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
     * {@link #getWriter()} 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>
     * If calling this method has an effect (as per the previous paragraph), calling this method with {@code null} clears
     * any content type set via a previous call to this method and clears any character encoding set via a previous call to
     * this method, {@link #setCharacterEncoding(String)}, {@link #setCharacterEncoding(Charset)} or {@link #setLocale} but
     * does not affect any default character encoding configured via {@link ServletContext#setResponseCharacterEncoding} or
     * the deployment descriptor.
     * <p>
     * If this method is called with an invalid or unrecognised character encoding, then a subsequent call to
     * {@link #getWriter()} will throw a {@link UnsupportedEncodingException}. Content for an unknown encoding can be sent
     * with the {@link ServletOutputStream} returned from {@link #getOutputStream()}.
     * <p>
     * Containers may choose to log calls to this method that use an invalid or unrecognised character encoding.
     * <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 or {@code null}
     *
     * @see #setLocale
     * @see #setCharacterEncoding(String)
     * @see #setCharacterEncoding(Charset)
     * @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}, {@link #setCharacterEncoding(String)} or {@link #setCharacterEncoding(Charset)},
     * <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(String)} has
     * been called, after {@link #setCharacterEncoding(Charset)} has been called, after <code>getWriter</code> has been
     * called, or after the response has been committed.
     * <p>
     * If calling this method has an effect on the locale (as per the previous paragraph), calling this method with
     * {@code null} clears any locale set via a previous call to this method. If calling this method has an effect on the
     * character encoding, calling this method with {@code null} clears the previously set character encoding.
     * <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 or {code @null}
     *
     * @see #getLocale
     * @see #setContentType
     * @see #setCharacterEncoding(String)
     * @see #setCharacterEncoding(Charset)
     */
    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();

}