/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You 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 or
 * implicitly. The priority order for specifying the response body is:
 * <ol>
 * <li>explicitly per request using {@link #setCharacterEncoding} and
 *    {@link #setContentType}</li>
 * <li>implicitly per request using {@link #setLocale}</li>
 * <li>per web application via the deployment descriptor or
 *     {@link ServletContext#setRequestCharacterEncoding(String)}</li>
 * <li>container default via vendor specific configuration</li>
 * <li>ISO-8859-1</li>
 * </ol>
 * 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.
 *
 * @see ServletOutputStream
 */
public interface ServletResponse {

    /**
     * Returns the name of the character encoding (MIME charset) used for the
     * body sent in this response.
     * The charset for the MIME body response can be specified explicitly or
     * implicitly. The priority order for specifying the response body is:
     * <ol>
     * <li>explicitly per request using {@link #setCharacterEncoding} and
     *    {@link #setContentType}</li>
     * <li>implicitly per request using {@link #setLocale}</li>
     * <li>per web application via the deployment descriptor or
     *     {@link ServletContext#setRequestCharacterEncoding(String)}</li>
     * <li>container default via vendor specific configuration</li>
     * <li>ISO-8859-1</li>
     * </ol>
     * Calls made to {@link #setCharacterEncoding}, {@link #setContentType} or
     * {@link #setLocale} 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>
     */
    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}, 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
     */
    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.
     *
     * @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
     */
    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.
     *
     * @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
     */
    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 character encoding has already
     * been set by container default, ServletContext default,
     * {@link #setContentType} or {@link #setLocale}, this method overrides it.
     * 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 #setLocale
     * @since Servlet 2.4
     */
    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
     */
    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 length
     *            an integer specifying the length of the content being returned
     *            to the client; sets the Content-Length header
     *
     * @since Servlet 3.1
     */
    void setContentLengthLong(long length);

    /**
     * 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
     */
    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
     */
    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
     */
    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.
     *
     * @throws IOException if an I/O occurs during the flushing of the response
     *
     * @see #setBufferSize
     * @see #getBufferSize
     * @see #isCommitted
     * @see #reset
     */
    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
     */
    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
     */
    boolean isCommitted();

    /**
     * Clears any data that exists in the buffer as well as the status code and
     * headers. 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
     */
    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
     */
    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.
     *
     * @return The locale specified for this response using the
     *          {@link #setLocale} method. If no locale has been specified, the
     *          container's default locale is returned.
     *
     * @see #setLocale
     */
    Locale getLocale();

}
