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/*
* 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;
/**
* 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. <br>
* <br>
* Filters perform filtering in the <code>doFilter</code> 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.
* <p>
* Filters are configured in the deployment descriptor of a web application
* <p>
* Examples that have been identified for this design are<br>
* 1) Authentication Filters <br>
* 2) Logging and Auditing Filters <br>
* 3) Image conversion Filters <br>
* 4) Data compression Filters <br>
* 5) Encryption Filters <br>
* 6) Tokenizing Filters <br>
* 7) Filters that trigger resource access events <br>
* 8) XSL/T filters <br>
* 9) Mime-type chain Filter <br>
*
* @since Servlet 2.3
*/
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.
* <p>
* The web container cannot place the filter into service if the init method
* either:
* <ul>
* <li>Throws a ServletException</li>
* <li>Does not return within a time period defined by the web
* container</li>
* </ul>
*
* @param filterConfig The configuration information associated with the
* filter instance being initialised
*
* @throws ServletException if the initialisation fails
*/
public void init(FilterConfig filterConfig) throws ServletException;
/**
* The <code>doFilter</code> 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.
* <p>
* A typical implementation of this method would follow the following
* pattern:- <br>
* 1. Examine the request<br>
* 2. Optionally wrap the request object with a custom implementation to
* filter content or headers for input filtering <br>
* 3. Optionally wrap the response object with a custom implementation to
* filter content or headers for output filtering <br>
* 4. a) <strong>Either</strong> invoke the next entity in the chain using
* the FilterChain object (<code>chain.doFilter()</code>), <br>
* 4. b) <strong>or</strong> not pass on the request/response pair to the
* next entity in the filter chain to block the request processing<br>
* 5. Directly set headers on the response after invocation of the next
* entity in the filter chain.
*
* @param request The request to process
* @param response The response associated with the request
* @param chain Provides access to the next filter in the chain for this
* filter to pass the request and response to for further
* processing
*
* @throws IOException if an I/O error occurs during this filter's
* processing of the request
* @throws ServletException if the processing fails for any other reason
*/
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. <br>
* <br>
*
* 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();
}
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