jakarta.servlet.Filter Maven / Gradle / Ivy
/*
* Copyright (c) 1997, 2020 Oracle and/or its affiliates and others.
* All rights reserved.
* Copyright 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.
*/
package jakarta.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, and 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:
*
* - Authentication Filters
*
- Logging and Auditing Filters
*
- Image conversion Filters
*
- Data compression Filters
*
- Encryption Filters
*
- Tokenizing Filters
*
- Filters that trigger resource access events
*
- XSL/T filters
*
- Mime-type chain Filter
*
*
* @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.
*
*
*
* The web container cannot place the filter into service if the init method either
*
*
* - Throws a ServletException
*
- Does not return within a time period defined by the web container
*
*
* @implSpec The default implementation takes no action.
*
* @param filterConfig a FilterConfig object containing the filter's configuration and initialization
* parameters
* @throws ServletException if an exception has occurred that interferes with the filter's normal operation
*/
default 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:
*
* - Examine the request
*
- Optionally wrap the request object with a custom implementation to filter content or headers for input filtering
*
- Optionally wrap the response object with a custom implementation to filter content or headers for output
* filtering
*
-
*
* - Either invoke the next entity in the chain using the FilterChain object
* (
chain.doFilter()),
* - or not pass on the request/response pair to the next entity in the filter chain to block the
* request processing
*
* - Directly set headers on the response after invocation of the next entity in the filter chain.
*
*
* @param request the ServletRequest object contains the client's request
* @param response the ServletResponse object contains the filter's response
* @param chain the FilterChain for invoking the next filter or the resource
* @throws IOException if an I/O related error has occurred during the processing
* @throws ServletException if an exception occurs that interferes with the filter's normal operation
*
* @see UnavailableException
*/
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.
*
*
* @implSpec The default implementation takes no action.
*/
default public void destroy() {
}
}