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 */ 017package org.apache.commons.vfs2.util; 018 019import java.lang.ref.WeakReference; 020 021import org.apache.commons.vfs2.FileChangeEvent; 022import org.apache.commons.vfs2.FileListener; 023import org.apache.commons.vfs2.FileName; 024import org.apache.commons.vfs2.FileObject; 025import org.apache.commons.vfs2.FileSystem; 026 027/** 028 * Wrap a listener with a WeakReference. 029 * 030 * @since 2.0 031 */ 032public class WeakRefFileListener implements FileListener { 033 private final FileSystem fs; 034 private final FileName name; 035 private final WeakReference<FileListener> listener; 036 037 protected WeakRefFileListener(final FileObject file, final FileListener listener) { 038 this.fs = file.getFileSystem(); 039 this.name = file.getName(); 040 this.listener = new WeakReference<>(listener); 041 } 042 043 /** 044 * This will install the {@code listener} at the given {@code file}. 045 * 046 * @param file The FileObject to listen on. 047 * @param listener The FileListener 048 */ 049 public static void installListener(final FileObject file, final FileListener listener) { 050 final WeakRefFileListener weakListener = new WeakRefFileListener(file, listener); 051 052 file.getFileSystem().addListener(file, new WeakRefFileListener(file, weakListener)); 053 } 054 055 /** 056 * returns the wrapped listener. If it is gone, the WeakRefFileListener wrapper will remove itself from the list of 057 * listeners. 058 * 059 * @return The FileListener. 060 * @throws Exception if an error occurs. 061 */ 062 protected FileListener getListener() throws Exception { 063 final FileListener listener = this.listener.get(); 064 if (listener == null) { 065 final FileObject file = fs.resolveFile(name); 066 file.getFileSystem().removeListener(file, this); 067 } 068 return listener; 069 } 070 071 /** 072 * Called when a file is created. 073 * 074 * @param event The FileChangeEvent. 075 * @throws Exception if an error occurs. 076 */ 077 @Override 078 public void fileCreated(final FileChangeEvent event) throws Exception { 079 final FileListener listener = getListener(); 080 if (listener == null) { 081 return; 082 } 083 listener.fileCreated(event); 084 } 085 086 /** 087 * Called when a file is deleted. 088 * 089 * @param event The FileChangeEvent. 090 * @throws Exception if an error occurs. 091 */ 092 @Override 093 public void fileDeleted(final FileChangeEvent event) throws Exception { 094 final FileListener listener = getListener(); 095 if (listener == null) { 096 return; 097 } 098 listener.fileDeleted(event); 099 } 100 101 /** 102 * Called when a file is changed. 103 * <p> 104 * This will only happen if you monitor the file using {@link org.apache.commons.vfs2.FileMonitor}. 105 * 106 * @param event The FileChangeEvent. 107 * @throws Exception if an error occurs. 108 */ 109 @Override 110 public void fileChanged(final FileChangeEvent event) throws Exception { 111 final FileListener listener = getListener(); 112 if (listener == null) { 113 return; 114 } 115 listener.fileChanged(event); 116 } 117}