/* * 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 Bogaertpackage org.apache.log4j.helpers;import java.io.File;import org.apache.log4j.helpers.LogLog;/**   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) {    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();    }  }}