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 import org.apache.hadoop.classification.InterfaceAudience;
022 import org.apache.hadoop.fs.FileSystem;
023 import org.apache.hadoop.lib.service.FileSystemAccess;
024
025 import javax.servlet.Filter;
026 import javax.servlet.FilterChain;
027 import javax.servlet.FilterConfig;
028 import javax.servlet.ServletException;
029 import javax.servlet.ServletRequest;
030 import javax.servlet.ServletResponse;
031 import java.io.IOException;
032
033 /**
034 * The <code>FileSystemReleaseFilter</code> releases back to the
035 * {@link FileSystemAccess} service a <code>FileSystem</code> instance.
036 * <p/>
037 * This filter is useful in situations where a servlet request
038 * is streaming out HDFS data and the corresponding filesystem
039 * instance have to be closed after the streaming completes.
040 */
041 @InterfaceAudience.Private
042 public abstract class FileSystemReleaseFilter implements Filter {
043 private static final ThreadLocal<FileSystem> FILE_SYSTEM_TL = new ThreadLocal<FileSystem>();
044
045 /**
046 * Initializes the filter.
047 * <p/>
048 * This implementation is a NOP.
049 *
050 * @param filterConfig filter configuration.
051 *
052 * @throws ServletException thrown if the filter could not be initialized.
053 */
054 @Override
055 public void init(FilterConfig filterConfig) throws ServletException {
056 }
057
058 /**
059 * It delegates the incoming request to the <code>FilterChain</code>, and
060 * at its completion (in a finally block) releases the filesystem instance
061 * back to the {@link FileSystemAccess} service.
062 *
063 * @param servletRequest servlet request.
064 * @param servletResponse servlet response.
065 * @param filterChain filter chain.
066 *
067 * @throws IOException thrown if an IO error occurrs.
068 * @throws ServletException thrown if a servet error occurrs.
069 */
070 @Override
071 public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain)
072 throws IOException, ServletException {
073 try {
074 filterChain.doFilter(servletRequest, servletResponse);
075 } finally {
076 FileSystem fs = FILE_SYSTEM_TL.get();
077 if (fs != null) {
078 FILE_SYSTEM_TL.remove();
079 getFileSystemAccess().releaseFileSystem(fs);
080 }
081 }
082 }
083
084 /**
085 * Destroys the filter.
086 * <p/>
087 * This implementation is a NOP.
088 */
089 @Override
090 public void destroy() {
091 }
092
093 /**
094 * Static method that sets the <code>FileSystem</code> to release back to
095 * the {@link FileSystemAccess} service on servlet request completion.
096 *
097 * @param fs fileystem instance.
098 */
099 public static void setFileSystem(FileSystem fs) {
100 FILE_SYSTEM_TL.set(fs);
101 }
102
103 /**
104 * Abstract method to be implemetned by concrete implementations of the
105 * filter that return the {@link FileSystemAccess} service to which the filesystem
106 * will be returned to.
107 *
108 * @return the FileSystemAccess service.
109 */
110 protected abstract FileSystemAccess getFileSystemAccess();
111
112 }