content: /*
   *
   *  * 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.
   *
   */
  
  package org.apache.ambari.server.configuration;
  
  import java.io.File;
  import java.util.function.Consumer;
  
  import org.apache.log4j.helpers.FileWatchdog;
  import org.slf4j.Logger;
  import org.slf4j.LoggerFactory;
  
  /**
   * Watchdog that notifies a listener on a file content change.
   */
  public class SingleFileWatch {
    private static final Logger LOG = LoggerFactory.getLogger(SingleFileWatch.class);
    private final File file;
    private final FileWatchdog watchdog;
    private final Consumer<File> changeListener;
    private volatile boolean started = false;
  
    /**
     * @param file to be watched
     * @param changeListener to be notified if the file content changes
     */
    public SingleFileWatch(File file, Consumer<File> changeListener) {
      this.file = file;
      this.changeListener = changeListener;
      this.watchdog = createWatchDog();
    }
  
    private FileWatchdog createWatchDog() {
      FileWatchdog fileWatch = new FileWatchdog(file.getAbsolutePath()) {
        @Override
        protected void doOnChange() {
          if (started) {
            notifyListener();
          }
        }
      };
      fileWatch.setDelay(1000);
      fileWatch.setDaemon(true);
      fileWatch.setName("FileWatchdog:" + file.getName());
      return fileWatch;
    }
  
    private void notifyListener() {
      LOG.info("{} changed. Sending notification.", file);
      try {
        changeListener.accept(file);
      } catch (Exception e) {
        LOG.warn("Error while notifying " + this + " listener", e);
      }
    }
  
    /**
     * Start the watch service in the background
     */
    public void start() {
      LOG.info("Starting " + this);
      started = true;
      watchdog.start();
    }
  
    /**
     * Stop the watch service
     */
    public void stop() {
      LOG.info("Stopping " + this);
      started = false;
      watchdog.interrupt();
    }
  
    @Override
    public String toString() {
      return "SingleFileWatcher:" + file.getName();
    }
  }
  