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    import javax.servlet.Filter;
021    import javax.servlet.FilterChain;
022    import javax.servlet.FilterConfig;
023    import javax.servlet.ServletContext;
024    import javax.servlet.ServletException;
025    import javax.servlet.ServletRequest;
026    import javax.servlet.ServletResponse;
027    
028    import org.apache.logging.log4j.Logger;
029    import org.apache.logging.log4j.status.StatusLogger;
030    
031    /**
032     * This is responsible for the following:
033     * <ul>
034     *     <li>Clearing the logger context when the application has finished starting up.</li>
035     *     <li>Setting the logger context before processing a request and clearing it after processing a request.</li>
036     *     <li>Setting the logger context when the application is starting to shut down.</li>
037     * </ul>
038     * This filter is a once-per-request filter. It is capable of filtering all the different types of requests
039     * (standard, asynchronous, error, etc.) but will not apply processing if the filter matches multiple times on the same
040     * logical request.
041     */
042    public class Log4jServletFilter implements Filter {
043    
044        private static final Logger LOGGER = StatusLogger.getLogger();
045    
046        static final String ALREADY_FILTERED_ATTRIBUTE = Log4jServletFilter.class.getName() + ".FILTERED";
047    
048        private ServletContext servletContext;
049        private Log4jWebLifeCycle initializer;
050    
051        @Override
052        public void init(final FilterConfig filterConfig) throws ServletException {
053            this.servletContext = filterConfig.getServletContext();
054            LOGGER.debug("Log4jServletFilter initialized.");
055    
056            this.initializer = WebLoggerContextUtils.getWebLifeCycle(this.servletContext);
057            this.initializer.clearLoggerContext(); // the application is mostly finished starting up now
058        }
059    
060        @Override
061        public void doFilter(final ServletRequest request, final ServletResponse response, final FilterChain chain)
062                throws IOException, ServletException {
063            if (request.getAttribute(ALREADY_FILTERED_ATTRIBUTE) != null) {
064                chain.doFilter(request, response);
065            } else {
066                request.setAttribute(ALREADY_FILTERED_ATTRIBUTE, Boolean.TRUE);
067    
068                try {
069                    this.initializer.setLoggerContext();
070    
071                    chain.doFilter(request, response);
072                } finally {
073                    this.initializer.clearLoggerContext();
074                }
075            }
076        }
077    
078        @Override
079        public void destroy() {
080            if (this.servletContext == null || this.initializer == null) {
081                throw new IllegalStateException("Filter destroyed before it was initialized.");
082            }
083            LOGGER.debug("Log4jServletFilter destroyed.");
084    
085            this.initializer.setLoggerContext(); // the application is just now starting to shut down
086        }
087    }