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 org.apache.hadoop.classification.InterfaceAudience;
023    
024    import javax.servlet.Filter;
025    import javax.servlet.FilterChain;
026    import javax.servlet.FilterConfig;
027    import javax.servlet.ServletException;
028    import javax.servlet.ServletRequest;
029    import javax.servlet.ServletResponse;
030    import java.io.IOException;
031    import java.net.InetAddress;
032    
033    /**
034     * Filter that resolves the requester hostname.
035     */
036    @InterfaceAudience.Private
037    public class HostnameFilter implements Filter {
038      static final ThreadLocal<String> HOSTNAME_TL = new ThreadLocal<String>();
039    
040      /**
041       * Initializes the filter.
042       * <p/>
043       * This implementation is a NOP.
044       *
045       * @param config filter configuration.
046       *
047       * @throws ServletException thrown if the filter could not be initialized.
048       */
049      @Override
050      public void init(FilterConfig config) throws ServletException {
051      }
052    
053      /**
054       * Resolves the requester hostname and delegates the request to the chain.
055       * <p/>
056       * The requester hostname is available via the {@link #get} method.
057       *
058       * @param request servlet request.
059       * @param response servlet response.
060       * @param chain filter chain.
061       *
062       * @throws IOException thrown if an IO error occurrs.
063       * @throws ServletException thrown if a servet error occurrs.
064       */
065      @Override
066      public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
067        throws IOException, ServletException {
068        try {
069          String hostname = InetAddress.getByName(request.getRemoteAddr()).getCanonicalHostName();
070          HOSTNAME_TL.set(hostname);
071          chain.doFilter(request, response);
072        } finally {
073          HOSTNAME_TL.remove();
074        }
075      }
076    
077      /**
078       * Returns the requester hostname.
079       *
080       * @return the requester hostname.
081       */
082      public static String get() {
083        return HOSTNAME_TL.get();
084      }
085    
086      /**
087       * Destroys the filter.
088       * <p/>
089       * This implementation is a NOP.
090       */
091      @Override
092      public void destroy() {
093      }
094    }