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Thursday, 27 March 2014

Servlet – HTTP Servlet Response

In this tutorials we are going to see about Http Servlet response.This tutorial written based on Servlet 3.0.
HttpServletResponse Extends the ServletResponse interface to provide HTTP-specific functionality in sending a response. For example, it has methods to access HTTP headers and cookies.
The servlet container creates an HttpServletResponse object and passes it as an argument to the servlet's service methods (doGet, doPost, etc).
When web browser send http request to web server, it will send Http response back to browser. Normally response consist of headers, document, blank line.
Methods available in Http Servlet Response
S.No
Methods with Description
1 void addCookie(Cookie cookie)
Adds the specified cookie to the response. This method can be called multiple times to set more than one cookie.
2 boolean containsHeader(String name)
Returns a boolean indicating whether the named response header has already been set.
3 String encodeURL(String url)
Encodes the specified URL by including the session ID in it, or, if encoding is not needed, returns the URL unchanged. The implementation of this method includes the logic to determine whether the session ID needs to be encoded in the URL. For example, if the browser supports cookies, or session tracking is turned off, URL encoding is unnecessary.
For robust session tracking, all URLs emitted by a servlet should be run through this method. Otherwise, URL rewriting cannot be used with browsers which do not support cookies. 
4 String encodeRedirectURL(String url)
Encodes the specified URL for use in the sendRedirect method or, if encoding is not needed, returns the URL unchanged. The implementation of this method includes the logic to determine whether the session ID needs to be encoded in the URL. Because the rules for making this determination can differ from those used to decide whether to encode a normal link, this method is separated from the encodeURL method.
All URLs sent to the HttpServletResponse.sendRedirect method should be run through this method. Otherwise, URL rewriting cannot be used with browsers which do not support cookies.
5 String encodeUrl(String url)
Deprecated. As of version 2.1, use encodeURL(String url) instead
6 String encodeRedirectUrl(String url)
Deprecated. As of version 2.1, use encodeRedirectURL(String url) instead
7 void sendError(int sc, String msg)
Sends an error response to the client using the specified status and clears the buffer. The server defaults to creating the response to look like an HTML-formatted server error page containing the specified message, setting the content type to "text/html". The server will preserve cookies and may clear or update any headers needed to serve the error page as a valid response. If an error-page declaration has been made for the web application corresponding to the status code passed in, it will be served back in preference to the suggested msg parameter and the msg parameter will be ignored.
If the response has already been committed, this method throws an IllegalStateException. After using this method, the response should be considered to be committed and should not be written to.
8 void sendError(int sc)
Sends an error response to the client using the specified status code and clears the buffer. The server will preserve cookies and may clear or update any headers needed to serve the error page as a valid response. If an error-page declaration has been made for the web application corresponding to the status code passed in, it will be served back the error page
If the response has already been committed, this method throws an IllegalStateException. After using this method, the response should be considered to be committed and should not be written to
9 void sendRedirect(String location)
Sends a temporary redirect response to the client using the specified redirect location URL and clears the buffer. The buffer will be replaced with the data set by this method. Calling this method sets the status code to SC_FOUND 302 (Found). This method can accept relative URLs;the servlet container must convert the relative URL to an absolute URL before sending the response to the client. If the location is relative without a leading '/' the container interprets it as relative to the current request URI. If the location is relative with a leading '/' the container interprets it as relative to the servlet container root.
If the response has already been committed, this method throws an IllegalStateException. After using this method, the response should be considered to be committed and should not be written to.
10 void setDateHeader(java.lang.String name, long date)
Sets a response header with the given name and date-value. The date is specified in terms of milliseconds since the epoch. If the header had already been set, the new value overwrites the previous one. The containsHeader method can be used to test for the presence of a header before setting its value.
11 void addDateHeader(java.lang.String name,long date)
Adds a response header with the given name and date-value. The date is specified in terms of milliseconds since the epoch. This method allows response headers to have multiple values.
12 void setHeader(java.lang.String name, java.lang.String value)
Sets a response header with the given name and value. If the header had already been set, the new value overwrites the previous one. The containsHeader method can be used to test for the presence of a header before setting its value.
13 void addHeader(String name,String value)
Adds a response header with the given name and value. This method allows response headers to have multiple values.
14 void setIntHeader(java.lang.String name,int value)
Sets a response header with the given name and integer value. If the header had already been set, the new value overwrites the previous one. The containsHeader method can be used to test for the presence of a header before setting its value.
15 void addIntHeader(java.lang.String name,int value)
Adds a response header with the given name and integer value. This method allows response headers to have multiple values.
16 void setStatus(int sc)
Sets the status code for this response.
This method is used to set the return status code when there is no error (for example, for the SC_OK or SC_MOVED_TEMPORARILY status codes).
If this method is used to set an error code, then the container's error page mechanism will not be triggered. If there is an error and the caller wishes to invoke an error page defined in the web application, then sendError(int, java.lang.String) must be used instead.
This method preserves any cookies and other response headers.
Valid status codes are those in the 2XX, 3XX, 4XX, and 5XX ranges. Other status codes are treated as container specific.
17 void setStatus(int sc,String sm)
Deprecated. As of version 2.1, due to ambiguous meaning of the message parameter. To set a status code use setStatus(int), to send an error with a description use sendError(int, String). Sets the status code and message for this response.
18 int getStatus()
Gets the current status code of this response.
19 String getHeader(String name)
Gets the value of the response header with the given name.
If a response header with the given name exists and contains multiple values, the value that was added first will be returned.
This method considers only response headers set or added via setHeader(String, String), addHeader(String, String), setDateHeader(String, long), addDateHeader(String, long), setIntHeader(String, int), or addIntHeader(String, int), respectively.
20 java.util.Collection<String> getHeaders(String name)
Gets the values of the response header with the given name.
This method considers only response headers set or added via setHeader(String, String), addHeader(String, String), setDateHeader(String, long), addDateHeader(String, long), setIntHeader(String, int), or addIntHeader(String, int), respectively.
Any changes to the returned Collection must not affect this HttpServletResponse.
21 java.util.Collection<String> getHeaderNames()
Gets the names of the headers of this response.
This method considers only response headers set or added via setHeader(String, String), addHeader(String, String), setDateHeader(String, long), addDateHeader(String, long), setIntHeader(String, int), or addIntHeader(String, int), respectively.
Any changes to the returned Collection must not affect this HttpServletResponse.

Fields available in Http Servlet Response
S.No
Fields with Description
1 static final int SC_CONTINUE
Status code (100) indicating the client can continue.
2 static final int SC_SWITCHING_PROTOCOLS
Status code (101) indicating the server is switching protocols according to Upgrade header.
3 static final int SC_OK
Status code (200) indicating the request succeeded normally.
4 static final int SC_CREATED
Status code (201) indicating the request succeeded and created a new resource on the server.
5 static final int SC_ACCEPTED
Status code (202) indicating that a request was accepted for processing, but was not completed.
6 static final int SC_NON_AUTHORITATIVE_INFORMATION
Status code (203) indicating that the meta information presented by the client did not originate from the server.
7 static final int SC_NO_CONTENT
Status code (204) indicating that the request succeeded but that there was no new information to return.
8 static final int SC_RESET_CONTENT
Status code (205) indicating that the agent SHOULD reset the document view which caused the request to be sent.
9 static final int SC_PARTIAL_CONTENT
Status code (206) indicating that the server has fulfilled the partial GET request for the resource.
10 static final int SC_MULTIPLE_CHOICES Status code (300) indicating that the requested resource corresponds to any one of a set of representations, each with its own specific location.
11 static final int SC_MOVED_PERMANENTLY
Status code (301) indicating that the resource has permanently moved to a new location, and that future references should use a new URI with their requests.
12 static final int SC_MOVED_TEMPORARILY
Status code (302) indicating that the resource has temporarily moved to another location, but that future references should still use the original URI to access the resource. This definition is being retained for backwards compatibility. SC_FOUND is now the preferred definition.
13 static final int SC_FOUND
Status code (302) indicating that the resource reside temporarily under a different URI. Since the redirection might be altered on occasion, the client should continue to use the Request-URI for future requests.(HTTP/1.1) To represent the status code (302), it is recommended to use this variable.
14 static final int SC_SEE_OTHER
Status code (303) indicating that the response to the request can be found under a different URI.
15 static final int SC_NOT_MODIFIED
Status code (304) indicating that a conditional GET operation found that the resource was available and not modified.
16 static final int SC_USE_PROXY
Status code (305) indicating that the requested resource MUST be accessed through the proxy given by the Location field.
17 static final int SC_TEMPORARY_REDIRECT
Status code (307) indicating that the requested resource resides temporarily under a different URI. The temporary URI SHOULD be given by the Location field in the response.
18 static final int SC_BAD_REQUEST
Status code (400) indicating the request sent by the client was syntactically incorrect.
19 static final int SC_UNAUTHORIZED
Status code (401) indicating that the request requires HTTP authentication.
20 static final int SC_PAYMENT_REQUIRED
Status code (402) reserved for future use.
21 static final int SC_FORBIDDEN
Status code (403) indicating the server understood the request but refused to fulfill it.
22 static final int SC_NOT_FOUND
Status code (404) indicating that the requested resource is not available.
23 static final int SC_METHOD_NOT_ALLOWED
Status code (405) indicating that the method specified in the Request-Line is not allowed for the resource identified by the Request-URI.
24 static final int SC_NOT_ACCEPTABLE
Status code (406) indicating that the resource identified by the request is only capable of generating response entities which have content characteristics not acceptable according to the accept headers sent in the request.
25 static final int SC_PROXY_AUTHENTICATION_REQUIRED
Status code (407) indicating that the client MUST first authenticate itself with the proxy.
26 static final int SC_REQUEST_TIMEOUT
Status code (408) indicating that the client did not produce a request within the time that the server was prepared to wait.
27 static final int SC_CONFLICT
Status code (409) indicating that the request could not be completed due to a conflict with the current state of the resource.
28 static final int SC_GONE
Status code (410) indicating that the resource is no longer available at the server and no forwarding address is known. This condition SHOULD be considered permanent.
29 static final int SC_LENGTH_REQUIRED
Status code (411) indicating that the request cannot be handled without a defined Content-Length.
30 static final int SC_PRECONDITION_FAILED
Status code (412) indicating that the precondition given in one or more of the request-header fields evaluated to false when it was tested on the server.
31 static final int SC_REQUEST_ENTITY_TOO_LARGE
Status code (413) indicating that the server is refusing to process the request because the request entity is larger than the server is willing or able to process.
32 static final int SC_REQUEST_URI_TOO_LONG
Status code (414) indicating that the server is refusing to service the request because the Request-URI is longer than the server is willing to interpret.
33 static final int SC_UNSUPPORTED_MEDIA_TYPE
Status code (415) indicating that the server is refusing to service the request because the entity of the request is in a format not supported by the requested resource for the requested method.
34 static final int SC_REQUESTED_RANGE_NOT_SATISFIABLE
Status code (416) indicating that the server cannot serve the requested byte range.
35 static final int SC_EXPECTATION_FAILED
Status code (417) indicating that the server could not meet the expectation given in the Expect request header.
36 static final int SC_INTERNAL_SERVER_ERROR
Status code (500) indicating an error inside the HTTP server which prevented it from fulfilling the request.
37 static final int SC_NOT_IMPLEMENTED
Status code (501) indicating the HTTP server does not support the functionality needed to fulfill the request.
38 static final int SC_BAD_GATEWAY
Status code (502) indicating that the HTTP server received an invalid response from a server it consulted when acting as a proxy or gateway.
39 static final int SC_SERVICE_UNAVAILABLE
Status code (503) indicating that the HTTP server is temporarily overloaded, and unable to handle the request.
40 static final int SC_GATEWAY_TIMEOUT
Status code (504) indicating that the server did not receive a timely response from the upstream server while acting as a gateway or proxy.
41 static final int SC_HTTP_VERSION_NOT_SUPPORTED
Status code (505) indicating that the server does not support or refuses to support the HTTP protocol version that was used in the request message.
Annamalai Thangaraj

Annamalai is working as Technical Lead in Leading Telecom company with 5+ years experience in Identity and Access Management , Telecom and Networks, BigData, Java, Spring, Struts, Hibernate, AngularJS, and Enterprise Web Application Development.

Website: Java Tutorials Corner

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Item Reviewed: Servlet – HTTP Servlet Response Rating: 5 Reviewed By: Annamalai Thangaraj