javax.servlet.Filter Maven / Gradle / Ivy
/**
*
* Copyright 2003-2004 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.
*/
//
// This source code implements specifications defined by the Java
// Community Process. In order to remain compliant with the specification
// DO NOT add / change / or delete method signatures!
//
package javax.servlet;
import java.io.IOException;
/**
* A filter is an object that performs filtering tasks on either the request to a resource (a servlet or static content), or on the response from a resource, or both.
*
* Filters perform filtering in the doFilter method. Every Filter has access to
* a FilterConfig object from which it can obtain its initialization parameters, a
* reference to the ServletContext which it can use, for example, to load resources
* needed for filtering tasks.
*
* Filters are configured in the deployment descriptor of a web application
*
* Examples that have been identified for this design are
* 1) Authentication Filters
* 2) Logging and Auditing Filters
* 3) Image conversion Filters
* 4) Data compression Filters
* 5) Encryption Filters
* 6) Tokenizing Filters
* 7) Filters that trigger resource access events
* 8) XSL/T filters
* 9) Mime-type chain Filter
*
* @since Servlet 2.3
*
* @version $Rev: 46019 $ $Date: 2004-09-14 04:56:06 -0500 (Tue, 14 Sep 2004) $
*/
public interface Filter {
/**
* Called by the web container to indicate to a filter that it is being placed into
* service. The servlet container calls the init method exactly once after instantiating the
* filter. The init method must complete successfully before the filter is asked to do any
* filtering work.
* The web container cannot place the filter into service if the init method either
* 1.Throws a ServletException
* 2.Does not return within a time period defined by the web container
*/
public void init(FilterConfig filterConfig) throws ServletException;
/**
* The doFilter method of the Filter is called by the container
* each time a request/response pair is passed through the chain due
* to a client request for a resource at the end of the chain. The FilterChain passed in to this
* method allows the Filter to pass on the request and response to the next entity in the
* chain.
* A typical implementation of this method would follow the following pattern:-
* 1. Examine the request
* 2. Optionally wrap the request object with a custom implementation to
* filter content or headers for input filtering
* 3. Optionally wrap the response object with a custom implementation to
* filter content or headers for output filtering
* 4. a) Either invoke the next entity in the chain using the FilterChain object (chain.doFilter()),
* 4. b) or not pass on the request/response pair to the next entity in the filter chain to block the request processing
* 5. Directly set headers on the response after invocation of the next entity in ther filter chain.
*/
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException;
/**
* Called by the web container to indicate to a filter that it is being taken out of service. This
* method is only called once all threads within the filter's doFilter method have exited or after
* a timeout period has passed. After the web container calls this method, it will not call the
* doFilter method again on this instance of the filter.
*
* This method gives the filter an opportunity to clean up any resources that are being held (for
* example, memory, file handles, threads) and make sure that any persistent state is synchronized
* with the filter's current state in memory.
*/
public void destroy();
}