Package jakarta.servlet

Interface ServletResponse

All Known Subinterfaces:
HttpServletResponse
All Known Implementing Classes:
HttpServletResponseWrapper, ServletResponseWrapper
public interface ServletResponse
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(java.lang.String), 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(String), setCharacterEncoding(Charset) and setContentType(java.lang.String) methods, or implicitly using the setLocale(java.util.Locale) 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:

  • Method Summary

    Modifier and Type
    Method
    Description
    void
    flushBuffer()
    Forces any content in the buffer to be written to the client.
    int
    getBufferSize()
    Returns the actual buffer size used for the response.
    String
    getCharacterEncoding()
    Returns the name of the character encoding (MIME charset) used for the body sent in this response.
    String
    getContentType()
    Returns the content type used for the MIME body sent in this response.
    Locale
    getLocale()
    Returns the locale specified for this response using the setLocale(java.util.Locale) method.
    ServletOutputStream
    getOutputStream()
    Returns a ServletOutputStream suitable for writing binary data in the response.
    PrintWriter
    getWriter()
    Returns a PrintWriter object that can send character text to the client.
    boolean
    isCommitted()
    Returns a boolean indicating if the response has been committed.
    void
    reset()
    Clears any data that exists in the buffer as well as the status code, headers.
    void
    resetBuffer()
    Clears the content of the underlying buffer in the response without clearing headers or status code.
    void
    setBufferSize(int size)
    Sets the preferred buffer size for the body of the response.
    void
    setCharacterEncoding(String encoding)
    Sets the character encoding (MIME charset) of the response being sent to the client, for example, to UTF-8.
    default void
    setCharacterEncoding(Charset encoding)
    Sets the character encoding (MIME charset) of the response being sent to the client, for example, to UTF-8.
    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.
    void
    setContentLengthLong(long len)
    Sets the length of the content body in the response In HTTP servlets, this method sets the HTTP Content-Length header.
    void
    setContentType(String type)
    Sets the content type of the response being sent to the client, if the response has not been committed yet.
    void
    setLocale(Locale loc)
    Sets the locale of the response, if the response has not been committed yet.

  • Method Details

    • getCharacterEncoding

      String getCharacterEncoding()
      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(java.lang.String), 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(String), setCharacterEncoding(Charset) and setContentType(java.lang.String) 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

    • getContentType

      String getContentType()
      Returns the content type used for the MIME body sent in this response. The content type proper must have been specified using setContentType(java.lang.String) 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

    • getOutputStream

      ServletOutputStream getOutputStream() throws IOException
      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.

      Returns:
      a ServletOutputStream for writing binary data
      Throws:
      IllegalStateException - if the getWriter method has been called on this response
      IOException - if an input or output exception occurred
      See Also:

    • getWriter

      PrintWriter getWriter() 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.

      Returns:
      a PrintWriter object that can return character data to the client
      Throws:
      UnsupportedEncodingException - if the character encoding returned by getCharacterEncoding cannot be used
      IllegalStateException - if the getOutputStream method has already been called for this response object
      IOException - if an input or output exception occurred
      See Also:

    • setCharacterEncoding

      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 ServletContext.setResponseCharacterEncoding(java.lang.String), the deployment descriptor, or using the setCharacterEncoding(Charset), setContentType(java.lang.String) or setLocale(java.util.Locale) methods, the value set in this method overrides all of those values. Calling setContentType(java.lang.String) with the String of text/html and calling this method with the String of UTF-8 is equivalent to calling setContentType(java.lang.String) 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.

      If calling this method has an effect (as per the previous paragraph), calling this method with null clears any character encoding set via a previous call to this method, setCharacterEncoding(Charset), setContentType(java.lang.String) or setLocale(java.util.Locale) but does not affect any default character encoding configured via ServletContext.setResponseCharacterEncoding(java.lang.String) or the deployment descriptor.

      If this method is called with an invalid or unrecognised character encoding, then a subsequent call to getWriter() will throw a UnsupportedEncodingException. Content for an unknown encoding can be sent with the ServletOutputStream returned from getOutputStream().

      Containers may choose to log calls to this method that use an invalid or unrecognised character encoding.

      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.

      Parameters:
      encoding - a String specifying only the character set defined by IANA Character Sets (http://www.iana.org/assignments/character-sets) or null
      Since:
      Servlet 2.4
      See Also:

    • setCharacterEncoding

      default void setCharacterEncoding(Charset 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 ServletContext.setResponseCharacterEncoding(java.lang.String), the deployment descriptor, or using the setCharacterEncoding(String), setContentType(java.lang.String) or setLocale(java.util.Locale) methods, the value set in this method overrides all of those values. Calling setContentType(java.lang.String) with the String of text/html and calling this method with StandardCharsets.UTF_8 is equivalent to calling setContentType(java.lang.String) 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.

      If calling this method has an effect (as per the previous paragraph), calling this method with null clears any character encoding set via a previous call to this method, setCharacterEncoding(String), setContentType(java.lang.String) or setLocale(java.util.Locale) but does not affect any default character encoding configured via ServletContext.setResponseCharacterEncoding(java.lang.String) or the deployment descriptor.

      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.

      Implementations are strongly encouraged to override this default method and provide a more efficient implementation.

      Parameters:
      encoding - a Charset instance representing the encoding to use or null
      Since:
      Servlet 6.1
      See Also:

    • setContentLength

      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.

      This method may be called repeatedly to change the content length. This method has no effect if called after the response has been committed.

      Parameters:
      len - an integer specifying the length of the content being returned to the client; sets the Content-Length header

    • setContentLengthLong

      void setContentLengthLong(long len)
      Sets the length of the content body in the response In HTTP servlets, this method sets the HTTP Content-Length header.

      This method may be called repeatedly to change the content length. This method has no effect if called after the response has been committed.

      Parameters:
      len - a long specifying the length of the content being returned to the client; sets the Content-Length header
      Since:
      Servlet 3.1

    • setContentType

      void setContentType(String type)
      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.

      If calling this method has an effect (as per the previous paragraph), calling this method with 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, setCharacterEncoding(String), setCharacterEncoding(Charset) or setLocale(java.util.Locale) but does not affect any default character encoding configured via ServletContext.setResponseCharacterEncoding(java.lang.String) or the deployment descriptor.

      If this method is called with an invalid or unrecognised character encoding, then a subsequent call to getWriter() will throw a UnsupportedEncodingException. Content for an unknown encoding can be sent with the ServletOutputStream returned from getOutputStream().

      Containers may choose to log calls to this method that use an invalid or unrecognised character encoding.

      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.

      Parameters:
      type - a String specifying the MIME type of the content or null
      See Also:

    • setBufferSize

      void setBufferSize(int size)
      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.

      Parameters:
      size - the preferred buffer size
      Throws:
      IllegalStateException - if this method is called after content has been written
      See Also:

    • getBufferSize

      int getBufferSize()
      Returns the actual buffer size used for the response. If no buffering is used, this method returns 0.
      Returns:
      the actual buffer size used
      See Also:

    • flushBuffer

      void flushBuffer() throws IOException
      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:

    • resetBuffer

      void resetBuffer()
      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.
      Since:
      Servlet 2.3
      See Also:

    • isCommitted

      boolean isCommitted()
      Returns a boolean indicating if the response has been committed. A committed response has already had its status code and headers written.
      Returns:
      a boolean indicating if the response has been committed
      See Also:

    • reset

      void reset()
      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:
      IllegalStateException - if the response has already been committed
      See Also:

    • setLocale

      void setLocale(Locale loc)
      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(java.lang.String), setCharacterEncoding(String) or setCharacterEncoding(Charset), 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(java.lang.String) has been called with a charset specification, after setCharacterEncoding(String) has been called, after setCharacterEncoding(Charset) has been called, after getWriter has been called, or after the response has been committed.

      If calling this method has an effect on the locale (as per the previous paragraph), calling this method with 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 null clears the previously set character encoding.

      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.

      Parameters:
      loc - the locale of the response or {code @null}
      See Also:

    • getLocale

      Locale getLocale()
      Returns the locale specified for this response using the setLocale(java.util.Locale) 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.
      Returns:
      the Locale for this response.
      See Also: