001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements. See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache license, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License. You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the license for the specific language governing permissions and
015     * limitations under the license.
016     */
017    package org.apache.logging.log4j.web;
018    
019    import java.io.IOException;
020    
021    import javax.servlet.Filter;
022    import javax.servlet.FilterChain;
023    import javax.servlet.FilterConfig;
024    import javax.servlet.ServletContext;
025    import javax.servlet.ServletException;
026    import javax.servlet.ServletRequest;
027    import javax.servlet.ServletResponse;
028    
029    /**
030     * This is responsible for the following:
031     * <ul>
032     *     <li>Clearing the logger context when the application has finished starting up.</li>
033     *     <li>Setting the logger context before processing a request and clearing it after processing a request.</li>
034     *     <li>Setting the logger context when the application is starting to shut down.</li>
035     * </ul>
036     * This filter is a once-per-request filter. It is capable of filtering all the different types of requests
037     * (standard, asynchronous, error, etc.) but will not apply processing if the filter matches multiple times on the same
038     * logical request.
039     */
040    public class Log4jServletFilter implements Filter {
041    
042        static final String ALREADY_FILTERED_ATTRIBUTE = Log4jServletFilter.class.getName() + ".FILTERED";
043    
044        private ServletContext servletContext;
045        private Log4jWebLifeCycle initializer;
046    
047        @Override
048        public void init(final FilterConfig filterConfig) throws ServletException {
049            this.servletContext = filterConfig.getServletContext();
050            this.servletContext.log("Log4jServletFilter initialized.");
051    
052            this.initializer = Log4jWebInitializerImpl.getLog4jWebInitializer(this.servletContext);
053            this.initializer.clearLoggerContext(); // the application is mostly finished starting up now
054        }
055    
056        @Override
057        public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain)
058                throws IOException, ServletException {
059            if (request.getAttribute(ALREADY_FILTERED_ATTRIBUTE) != null) {
060                chain.doFilter(request, response);
061            } else {
062                request.setAttribute(ALREADY_FILTERED_ATTRIBUTE, true);
063    
064                try {
065                    this.initializer.setLoggerContext();
066    
067                    chain.doFilter(request, response);
068                } finally {
069                    this.initializer.clearLoggerContext();
070                }
071            }
072        }
073    
074        @Override
075        public void destroy() {
076            if (this.servletContext == null || this.initializer == null) {
077                throw new IllegalStateException("Filter destroyed before it was initialized.");
078            }
079            this.servletContext.log("Log4jServletFilter destroyed.");
080    
081            this.initializer.setLoggerContext(); // the application is just now starting to shut down
082        }
083    }