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
18 // Contributors: Mathias Bogaert
19
20 package org.apache.log4j.helpers;
21
22 import java.io.File;
23 import org.apache.log4j.helpers.LogLog;
24
25 /**
26 Check every now and then that a certain file has not changed. If it
27 has, then call the {@link #doOnChange} method.
28
29
30 @author Ceki Gülcü
31 @since version 0.9.1 */
32 public abstract class FileWatchdog extends Thread {
33
34 /**
35 The default delay between every file modification check, set to 60
36 seconds. */
37 static final public long DEFAULT_DELAY = 60000;
38 /**
39 The name of the file to observe for changes.
40 */
41 protected String filename;
42
43 /**
44 The delay to observe between every check. By default set {@link
45 #DEFAULT_DELAY}. */
46 protected long delay = DEFAULT_DELAY;
47
48 File file;
49 long lastModif = 0;
50 boolean warnedAlready = false;
51 boolean interrupted = false;
52
53 protected
54 FileWatchdog(String filename) {
55 this.filename = filename;
56 file = new File(filename);
57 setDaemon(true);
58 checkAndConfigure();
59 }
60
61 /**
62 Set the delay to observe between each check of the file changes.
63 */
64 public
65 void setDelay(long delay) {
66 this.delay = delay;
67 }
68
69 abstract
70 protected
71 void doOnChange();
72
73 protected
74 void checkAndConfigure() {
75 boolean fileExists;
76 try {
77 fileExists = file.exists();
78 } catch(SecurityException e) {
79 LogLog.warn("Was not allowed to read check file existance, file:["+
80 filename+"].");
81 interrupted = true; // there is no point in continuing
82 return;
83 }
84
85 if(fileExists) {
86 long l = file.lastModified(); // this can also throw a SecurityException
87 if(l > lastModif) { // however, if we reached this point this
88 lastModif = l; // is very unlikely.
89 doOnChange();
90 warnedAlready = false;
91 }
92 } else {
93 if(!warnedAlready) {
94 LogLog.debug("["+filename+"] does not exist.");
95 warnedAlready = true;
96 }
97 }
98 }
99
100 public
101 void run() {
102 while(!interrupted) {
103 try {
104 Thread.sleep(delay);
105 } catch(InterruptedException e) {
106 // no interruption expected
107 }
108 checkAndConfigure();
109 }
110 }
111 }
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