Tomcat example source code file (Filter.java)

This example Tomcat source code file (Filter.java) is included in the DevDaily.com "Java Source Code Warehouse" project. The intent of this project is to help you "Learn Java by Example" ^TM.

Java - Tomcat tags/keywords

filter, filter, filterchain, filterchain, io, ioexception, servletexception, servletexception, servletrequest, servletrequest, servletresponse

The Tomcat Filter.java source code

/*
* 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>

	* Filters perform filtering in the <code>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.
	** <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. <br>


     	* The web container cannot place the filter into service if the init method either<br>
        * 1.Throws a ServletException <br>
        * 2.Does not return within a time period defined by the web container 
	*/
	public void init(FilterConfig filterConfig) throws ServletException;
	
	
	/**
	* The <code>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.<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 invoke the next entity in the chain using the FilterChain object (chain.doFilter()), 
   
	** 4. b) <strong>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 the 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. <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();


}