Java tutorial
/* * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS HEADER. * * Copyright (c) 1997-2017 Oracle and/or its affiliates. All rights reserved. * * The contents of this file are subject to the terms of either the GNU * General Public License Version 2 only ("GPL") or the Common Development * and Distribution License("CDDL") (collectively, the "License"). You * may not use this file except in compliance with the License. You can * obtain a copy of the License at * https://oss.oracle.com/licenses/CDDL+GPL-1.1 * or LICENSE.txt. See the License for the specific * language governing permissions and limitations under the License. * * When distributing the software, include this License Header Notice in each * file and include the License file at LICENSE.txt. * * GPL Classpath Exception: * Oracle designates this particular file as subject to the "Classpath" * exception as provided by Oracle in the GPL Version 2 section of the License * file that accompanied this code. * * Modifications: * If applicable, add the following below the License Header, with the fields * enclosed by brackets [] replaced by your own identifying information: * "Portions Copyright [year] [name of copyright owner]" * * Contributor(s): * If you wish your version of this file to be governed by only the CDDL or * only the GPL Version 2, indicate your decision by adding "[Contributor] * elects to include this software in this distribution under the [CDDL or GPL * Version 2] license." If you don't indicate a single choice of license, a * recipient has the option to distribute your version of this file under * either the CDDL, the GPL Version 2 or to extend the choice of license to * its licensees as provided above. However, if you add GPL Version 2 code * and therefore, elected the GPL Version 2 license, then the option applies * only if the new code is made subject to such option by the copyright * holder. */ package javax.servlet.http; import java.io.IOException; import javax.servlet.FilterChain; import javax.servlet.GenericFilter; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; /** * * <p>Provides an abstract class to be subclassed to create * an HTTP filter suitable for a Web site. A subclass of * <code>HttpFilter</code> should override {@link #doFilter(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse, javax.servlet.FilterChain) }.</p> * * <p>Filters typically run on multithreaded servers, * so be aware that a filter must handle concurrent * requests and be careful to synchronize access to shared resources. * Shared resources include in-memory data such as * instance or class variables and external objects * such as files, database connections, and network * connections. * See the * <a href="https://docs.oracle.com/javase/tutorial/essential/concurrency/"> * Java Tutorial on Multithreaded Programming</a> for more * information on handling multiple threads in a Java program. * * @author Various * * @since Servlet 4.0 */ public abstract class HttpFilter extends GenericFilter { /** * <p>Does nothing, because this is an abstract class.</p> * * @since 4.0 */ public HttpFilter() { } /** * * <p>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. There's no need to * override this method.</p> * * <p>The default implementation inspects the incoming {@code req} and {@code res} * objects to determine if they are instances of {@link HttpServletRequest} * and {@link HttpServletResponse}, respectively. If not, a {@link ServletException} is thrown. * Otherwise, the protected {@link #doFilter(javax.servlet.http.HttpServletRequest, javax.servlet.http.HttpServletResponse, javax.servlet.FilterChain)} * method is called.</p> * * @param req a {@link ServletRequest} object that * contains the request the client has made * of the filter * * @param res a {@link ServletResponse} object that * contains the response the filter sends * to the client * * @param chain the <code>FilterChain</code> for invoking the next filter or the resource * * @throws IOException if an input or output error is * detected when the filter handles * the request * * @throws ServletException if the request for the could not be handled or * either parameter is not an instance of the respective {@link HttpServletRequest} * or {@link HttpServletResponse}. * * @since Servlet 4.0 */ @Override public void doFilter(ServletRequest req, ServletResponse res, FilterChain chain) throws IOException, ServletException { if (!(req instanceof HttpServletRequest && res instanceof HttpServletResponse)) { throw new ServletException("non-HTTP request or response"); } this.doFilter((HttpServletRequest) req, (HttpServletResponse) res, chain); } /** * * <p>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> * * <p>The default implementation simply calls {@link FilterChain#doFilter}</p> * * @param req a {@link HttpServletRequest} object that * contains the request the client has made * of the filter * * @param res a {@link HttpServletResponse} object that * contains the response the filter sends * to the client * * @param chain the <code>FilterChain</code> for invoking the next filter or the resource * * @throws IOException if an input or output error is * detected when the filter handles * the request * * @throws ServletException if the request for the could not be handled * * @since Servlet 4.0 */ protected void doFilter(HttpServletRequest req, HttpServletResponse res, FilterChain chain) throws IOException, ServletException { chain.doFilter(req, res); } }