http://www.jboss.org/jboss-servlet-api_4.0_spec: The Java Servlet 4.0 API classes (JBoss by Red Hat) 
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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 ServletResponse object and
passes it as an argument to the servlet's service method.

To send binary data in a MIME body response, use the ServletOutputStream returned by getOutputStream. To send character data, use the PrintWriter object returned by getWriter. To mix binary and text data, for example, to create a multipart response, use a ServletOutputStream and manage the character sections
manually.

The charset for the MIME body response can be specified explicitly using any of the following techniques: per request, per web-app (using 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 setCharacterEncoding and setContentType methods, or implicitly using the setLocale method. Explicit specifications take precedence over implicit specifications. If no charset is explicitly specified, ISO-8859-1 will be used. The setCharacterEncoding,
setContentType, or setLocale method must
be called before getWriter and before committing
the response for the character encoding to be used.

See the Internet RFCs such as 

RFC 2045 for more information on MIME. Protocols such as SMTP
and HTTP define profiles of MIME, and those standards
are still evolving.

Author:Various
See Also:
/**
 * 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 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 setCharacterEncoding and setContentType methods, or implicitly using the setLocale(java.util.Locale) method. Explicit specifications take precedence over implicit specifications. Calls made to these methods after getWriter has been
called or after the response has been committed have no
effect on the character encoding. If no character encoding
has been specified, ISO-8859-1 is returned.

See RFC 2047 (http://www.ietf.org/rfc/rfc2047.txt)
for more information about character encoding and MIME.

Returns:a String specifying the name of
the character encoding, for example, UTF-8
/**
     * 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 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 getCharacterEncoding or 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. 
Returns:a String specifying the content type,
for example, text/html; charset=UTF-8, or null
Since:Servlet 2.4
/**
     * 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 ServletOutputStream suitable for writing binary data in the response. The servlet container does not encode the binary data. 
 Calling flush() on the ServletOutputStream commits the response. Either this method or getWriter may be called to write the body, not both, except when reset has been called. 
Throws:
See Also:
Returns:a ServletOutputStream for writing binary data
/**
     * 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 PrintWriter object that
can send character text to the client.
The PrintWriter uses the character encoding returned by getCharacterEncoding. If the response's character encoding has not been specified as described in getCharacterEncoding
(i.e., the method just returns the default value 
ISO-8859-1), getWriter
updates it to ISO-8859-1.

Calling flush() on the PrintWriter
commits the response.

Either this method or getOutputStream may be called to write the body, not both, except when reset has been called. 
Throws:
See Also:
Returns:a PrintWriter object that 
can return character data to the client
/**
     * 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 ServletContext.setResponseCharacterEncoding, deployment descriptor, or using the setContentType() or setLocale() methods, the value set in this method overrides any of those values. Calling setContentType with the String
of text/html and calling
this method with the String of UTF-8
is equivalent with calling
setContentType with the String of
text/html; charset=UTF-8.

This method can be called repeatedly to change the character
encoding.
This method has no effect if it is called after
getWriter has been
called or after the response has been committed.

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 Content-Type
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.

Params:
  • charset – a String specifying only the character set
defined by IANA Character Sets
(http://www.iana.org/assignments/character-sets)
See Also:
Since:Servlet 2.4
/**
     * 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.

Params:
  • len – an integer specifying the length of the 
content being returned to the client; sets the Content-Length header
/**
     * 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.

Params:
  • len – a long specifying the length of the 
content being returned to the client; sets the Content-Length header
Since:Servlet 3.1
/**
     * 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, text/html;charset=UTF-8.
The response's character encoding is only set from the given
content type if this method is called before getWriter
is called.

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 getWriter
has been called or after the response has been committed.

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 Content-Type header is used.

Params:
  • type – a String specifying the MIME 
type of the content
See Also:
/**
     * 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 getBufferSize.

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.

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 
IllegalStateException.

Params:
  • size – the preferred buffer size
Throws:
See Also:
/**
     * 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.

See Also:
Returns:the actual buffer size used
/**
     * 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.

Throws:
  • IOException – if the act of flushing the buffer cannot be
completed.
See Also:
/**
     * 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 
IllegalStateException.

See Also:
Since:Servlet 2.3
/**
     * 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.

See Also:
Returns: a boolean indicating if the response has been
committed
/**
     * 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 getWriter or getOutputStream is also cleared. It is legal, for instance, to call getWriter, reset and then getOutputStream. If getWriter or 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 IllegalStateException.

Throws:
See Also:
/**
     * 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 setContentType or setCharacterEncoding, getWriter hasn't
been called yet, and the response hasn't been committed yet.
If the deployment descriptor contains a 
locale-encoding-mapping-list 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.

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 setContentType has been called with a charset specification, after setCharacterEncoding has been called, after getWriter has been called, or after the response
has been committed.

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 Content-Language header,
the character encoding as part of the Content-Type
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.

Params:
  • loc – the locale of the response
See Also:
/**
     * 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 setLocale method. Calls made to setLocale after the response is committed
have no effect. If no locale has been specified,
the container's default locale is returned.

See Also:
Returns:the Locale for this response.
/**
     * 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();

}