Java可以如何实现文件变动的监听的示例

public class FileUpTest {

  private long lastTime;

  @Test
  public void testFileUpdate() {
    File file = new File("/tmp/alarmConfig");

    // 首先文件的最近一次修改时间戳
    lastTime = file.lastModified();

    // 定时任务，每秒来判断一下文件是否发生变动，即判断lastModified是否改变
    ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(1);
    scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
      @Override
      public void run() {
        if (file.lastModified() > lastTime) {
          System.out.println("file update! time : " + file.lastModified());
          lastTime = file.lastModified();
        }
      }
    },0, 1, TimeUnit.SECONDS);


    try {
      Thread.sleep(1000 * 60);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}

public class FileUpTest {

  private long lastTime;

  private void ttt() {
    throw new NullPointerException();
  }

  @Test
  public void testFileUpdate() {
    File file = new File("/tmp/alarmConfig");

    lastTime = file.lastModified();

    ScheduledExecutorService scheduledExecutorService = Executors.newScheduledThreadPool(1);
    scheduledExecutorService.scheduleAtFixedRate(new Runnable() {
      @Override
      public void run() {
        if (file.lastModified() > lastTime) {
          System.out.println("file update! time : " + file.lastModified());
          lastTime = file.lastModified();
          ttt();
        }
      }
    }, 0, 1, TimeUnit.SECONDS);


    try {
      Thread.sleep(1000 * 60 * 10);
    } catch (InterruptedException e) {
      e.printStackTrace();
    }
  }
}

<dependency>
  <groupId>commons-io</groupId>
  <artifactId>commons-io</artifactId>
  <version>2.6</version>
</dependency>

public class PropertiesConfListenerHelper {

  public static boolean registerConfChangeListener(File file, Function<File, Map<String, AlarmConfig>> func) {
    try {
      // 轮询间隔 5 秒
      long interval = TimeUnit.SECONDS.toMillis(5);


      // 因为监听是以目录为单位进行的，所以这里直接获取文件的根目录
      File dir = file.getParentFile();

      // 创建一个文件观察器用于过滤
      FileAlterationObserver observer = new FileAlterationObserver(dir,
          FileFilterUtils.and(FileFilterUtils.fileFileFilter(),
              FileFilterUtils.nameFileFilter(file.getName())));

      //设置文件变化监听器
      observer.addListener(new MyFileListener(func));
      FileAlterationMonitor monitor = new FileAlterationMonitor(interval, observer);
      monitor.start();

      return true;
    } catch (Exception e) {
      log.error("register properties change listener error! e:{}", e);
      return false;
    }
  }


  static final class MyFileListener extends FileAlterationListenerAdaptor {

    private Function<File, Map<String, AlarmConfig>> func;

    public MyFileListener(Function<File, Map<String, AlarmConfig>> func) {
      this.func = func;
    }

    @Override
    public void onFileChange(File file) {
      Map<String, AlarmConfig> ans = func.apply(file); // 如果加载失败，打印一条日志
      log.warn("PropertiesConfig changed! reload ans: {}", ans);
    }
  }
}

public void run() {
  while(true) {
    if(this.running) {
      Iterator var1 = this.observers.iterator();

      while(var1.hasNext()) {
        FileAlterationObserver observer = (FileAlterationObserver)var1.next();
        observer.checkAndNotify();
      }

      if(this.running) {
        try {
          Thread.sleep(this.interval);
        } catch (InterruptedException var3) {
          ;
        }
        continue;
      }
    }

    return;
  }
}

@Test
public void testFileUpWather() throws IOException {
  // 说明，这里的监听也必须是目录
  Path path = Paths.get("/tmp");
  WatchService watcher = FileSystems.getDefault().newWatchService();
  path.register(watcher, ENTRY_MODIFY);

  new Thread(() -> {
    try {
      while (true) {
        WatchKey key = watcher.take();
        for (WatchEvent<?> event : key.pollEvents()) {
          if (event.kind() == OVERFLOW) {
            //事件可能lost or discarded 
            continue;
          }
          Path fileName = (Path) event.context();
          System.out.println("文件更新: " + fileName);
        }
        if (!key.reset()) { // 重设WatchKey
          break;
        }
      }
    } catch (Exception e) {
      e.printStackTrace();
    }
  }).start();


  try {
    Thread.sleep(1000 * 60 * 10);
  } catch (InterruptedException e) {
    e.printStackTrace();
  }
}