001    /**
002     * Licensed to the Apache Software Foundation (ASF) under one
003     * or more contributor license agreements.  See the NOTICE file
004     * distributed with this work for additional information
005     * regarding copyright ownership.  The ASF licenses this file
006     * to you under the Apache License, Version 2.0 (the
007     * "License"); you may not use this file except in compliance
008     * with the License.  You may obtain a copy of the License at
009     *
010     *     http://www.apache.org/licenses/LICENSE-2.0
011     *
012     * Unless required by applicable law or agreed to in writing, software
013     * distributed under the License is distributed on an "AS IS" BASIS,
014     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015     * See the License for the specific language governing permissions and
016     * limitations under the License.
017     */
018    
019    package org.apache.hadoop.lib.servlet;
020    
021    
022    import javax.servlet.Filter;
023    import javax.servlet.FilterChain;
024    import javax.servlet.FilterConfig;
025    import javax.servlet.ServletException;
026    import javax.servlet.ServletRequest;
027    import javax.servlet.ServletResponse;
028    import java.io.IOException;
029    import java.net.InetAddress;
030    
031    /**
032     * Filter that resolves the requester hostname.
033     */
034    public class HostnameFilter implements Filter {
035      static final ThreadLocal<String> HOSTNAME_TL = new ThreadLocal<String>();
036    
037      /**
038       * Initializes the filter.
039       * <p/>
040       * This implementation is a NOP.
041       *
042       * @param config filter configuration.
043       *
044       * @throws ServletException thrown if the filter could not be initialized.
045       */
046      @Override
047      public void init(FilterConfig config) throws ServletException {
048      }
049    
050      /**
051       * Resolves the requester hostname and delegates the request to the chain.
052       * <p/>
053       * The requester hostname is available via the {@link #get} method.
054       *
055       * @param request servlet request.
056       * @param response servlet response.
057       * @param chain filter chain.
058       *
059       * @throws IOException thrown if an IO error occurrs.
060       * @throws ServletException thrown if a servet error occurrs.
061       */
062      @Override
063      public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
064        throws IOException, ServletException {
065        try {
066          String hostname = InetAddress.getByName(request.getRemoteAddr()).getCanonicalHostName();
067          HOSTNAME_TL.set(hostname);
068          chain.doFilter(request, response);
069        } finally {
070          HOSTNAME_TL.remove();
071        }
072      }
073    
074      /**
075       * Returns the requester hostname.
076       *
077       * @return the requester hostname.
078       */
079      public static String get() {
080        return HOSTNAME_TL.get();
081      }
082    
083      /**
084       * Destroys the filter.
085       * <p/>
086       * This implementation is a NOP.
087       */
088      @Override
089      public void destroy() {
090      }
091    }