1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. You may obtain a copy of the License at
8 *
9 * http://www.apache.org/licenses/LICENSE-2.0
10 *
11 * Unless required by applicable law or agreed to in writing, software
12 * distributed under the License is distributed on an "AS IS" BASIS,
13 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14 * See the License for the specific language governing permissions and
15 * limitations under the License.
16 */
17 package org.apache.commons.vfs2.util;
18
19 import java.lang.ref.WeakReference;
20
21 import org.apache.commons.vfs2.FileChangeEvent;
22 import org.apache.commons.vfs2.FileListener;
23 import org.apache.commons.vfs2.FileName;
24 import org.apache.commons.vfs2.FileObject;
25 import org.apache.commons.vfs2.FileSystem;
26
27 /**
28 * Wraps a listener with a WeakReference.
29 *
30 * @since 2.0
31 */
32 public class WeakRefFileListener implements FileListener {
33
34 private final FileSystem fs;
35 private final FileName name;
36 private final WeakReference<FileListener> listener;
37
38 protected WeakRefFileListener(final FileObject file, final FileListener listener) {
39 this.fs = file.getFileSystem();
40 this.name = file.getName();
41 this.listener = new WeakReference<>(listener);
42 }
43
44 /**
45 * Installs the {@code listener} at the given {@code file}.
46 *
47 * @param file The FileObject to listen on.
48 * @param listener The FileListener
49 */
50 public static void installListener(final FileObject file, final FileListener listener) {
51 final WeakRefFileListenerener.html#WeakRefFileListener">WeakRefFileListener weakListener = new WeakRefFileListener(file, listener);
52
53 file.getFileSystem().addListener(file, new WeakRefFileListener(file, weakListener));
54 }
55
56 /**
57 * Gets the wrapped listener. If it is gone, the WeakRefFileListener wrapper will remove itself from the list of
58 * listeners.
59 *
60 * @return The FileListener.
61 * @throws Exception if an error occurs.
62 */
63 protected FileListener getListener() throws Exception {
64 final FileListener listener = this.listener.get();
65 if (listener == null) {
66 try (final FileObject fileObject = fs.resolveFile(name)) {
67 fileObject.getFileSystem().removeListener(fileObject, this);
68 }
69 }
70 return listener;
71 }
72
73 /**
74 * Called when a file is created.
75 *
76 * @param event The FileChangeEvent.
77 * @throws Exception if an error occurs.
78 */
79 @Override
80 public void fileCreated(final FileChangeEvent event) throws Exception {
81 final FileListener listener = getListener();
82 if (listener == null) {
83 return;
84 }
85 listener.fileCreated(event);
86 }
87
88 /**
89 * Called when a file is deleted.
90 *
91 * @param event The FileChangeEvent.
92 * @throws Exception if an error occurs.
93 */
94 @Override
95 public void fileDeleted(final FileChangeEvent event) throws Exception {
96 final FileListener listener = getListener();
97 if (listener == null) {
98 return;
99 }
100 listener.fileDeleted(event);
101 }
102
103 /**
104 * Called when a file is changed.
105 * <p>
106 * This will only happen if you monitor the file using {@link org.apache.commons.vfs2.FileMonitor}.
107 * </p>
108 *
109 * @param event The FileChangeEvent.
110 * @throws Exception if an error occurs.
111 */
112 @Override
113 public void fileChanged(final FileChangeEvent event) throws Exception {
114 final FileListener listener = getListener();
115 if (listener == null) {
116 return;
117 }
118 listener.fileChanged(event);
119 }
120 }