+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements. See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You under the Apache License, Version 2.0
+ * (the "License"); you may not use this file except in compliance with
+ * the License. You may obtain a copy of the License at
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+// Contributors: Mathias Bogaert
+
+package org.apache.log4j.helpers;
+
+import java.io.File;
+
+/**
+ Check every now and then that a certain file has not changed. If it
+ has, then call the {@link #doOnChange} method.
+
+
+ @author Ceki Gülcü
+ @since version 0.9.1 */
+public abstract class FileWatchdog extends Thread {
+
+ /**
+ The default delay between every file modification check, set to 60
+ seconds. */
+ static final public long DEFAULT_DELAY = 60000;
+ /**
+ The name of the file to observe for changes.
+ */
+ protected String filename;
+
+ /**
+ The delay to observe between every check. By default set {@link
+ #DEFAULT_DELAY}. */
+ protected long delay = DEFAULT_DELAY;
+
+ File file;
+ long lastModif = 0;
+ boolean warnedAlready = false;
+ boolean interrupted = false;
+
+ protected
+ FileWatchdog(String filename) {
+ super("FileWatchdog");
+ this.filename = filename;
+ file = new File(filename);
+ setDaemon(true);
+ checkAndConfigure();
+ }
+
+ /**
+ Set the delay to observe between each check of the file changes.
+ */
+ public
+ void setDelay(long delay) {
+ this.delay = delay;
+ }
+
+ abstract
+ protected
+ void doOnChange();
+
+ protected
+ void checkAndConfigure() {
+ boolean fileExists;
+ try {
+ fileExists = file.exists();
+ } catch(SecurityException e) {
+ LogLog.warn("Was not allowed to read check file existance, file:["+
+ filename+"].");
+ interrupted = true; // there is no point in continuing
+ return;
+ }
+
+ if(fileExists) {
+ long l = file.lastModified(); // this can also throw a SecurityException
+ if(l > lastModif) { // however, if we reached this point this
+ lastModif = l; // is very unlikely.
+ doOnChange();
+ warnedAlready = false;
+ }
+ } else {
+ if(!warnedAlready) {
+ LogLog.debug("["+filename+"] does not exist.");
+ warnedAlready = true;
+ }
+ }
+ }
+
+ public
+ void run() {
+ while(!interrupted) {
+ try {
+ Thread.sleep(delay);
+ } catch(InterruptedException e) {
+ // no interruption expected
+ }
+ checkAndConfigure();
+ }
+ }
+}