String path = "/tmp";
    // 获取当前OS平台下的文件系统监控器
    WatchService watcher = FileSystems.getDefault().newWatchService();
    //将监控器注册给指定的文件节点,该方法会让监控器线程就绪并运行，调用完后监控器就开始监控

    /* 文件变化枚举类型
     * ENTRY_CREATE：创建
     * ENTRY_DELETE：删除
     * ENTRY_MODIFY：修改
     */
    Paths.get(path).register(watcher,
        StandardWatchEventKinds.ENTRY_CREATE,
        StandardWatchEventKinds.ENTRY_DELETE,
        StandardWatchEventKinds.ENTRY_MODIFY);

    while (true) {
        WatchKey key = watcher.take();
        // 获得WatchKey（监控池）中的具体监控信息,
        // !!! 一个文件变化动作可能会引发一系列的事件，因此WatchKey中保存着一个事件列表List<WatchEvent<?>> list
        for (WatchEvent<?> event: key.pollEvents()) {

            System.out.println(event.context() + " comes to " + event.kind());
        }
        // 完成一次监控就需要重置监控器一次.
        boolean valid = key.reset(); 
        if (!valid) {
            break;
        }
    }
// ---------- output --------------
// tmp.log comes to ENTRY_DELETE

// server端
public class SocketServer {
  public static void main(String[] args) throws Exception {
    ServerSocket server = new ServerSocket(8080);
    
    // 阻塞等待连接
    Socket socket = server.accept();

    // 从socket中获取输入流，并建立缓冲区进行读取
    InputStream inputStream = socket.getInputStream();
    byte[] bytes = new byte[1024];
    int len;
    StringBuilder sb = new StringBuilder();
    while ((len = inputStream.read(bytes)) != -1) {
      sb.append(new String(bytes, 0, len,"UTF-8"));
    }
    System.out.println("Received: " + sb);
    OutputStream outputStream = socket.getOutputStream();
    outputStream.write("hello client".getBytes("UTF-8"));
    outputStream.flush();

    // 关闭流&连接
    inputStream.close();
    outputStream.close();
    socket.close();
    server.close();
  }
}
// client 端
public class SocketClient {
  public static void main(String args[]) throws Exception {
    Socket socket = new Socket("127.0.0.1", 8080);
    // 建立连接后获得输出流
    OutputStream outputStream = socket.getOutputStream();
    String message="hello server";
    outputStream.write(message.getBytes("UTF-8"));
    //通知server消息发送完成
    socket.shutdownOutput();
    
    // 读取消息
    InputStream inputStream = socket.getInputStream();
    byte[] bytes = new byte[1024];
    int len;
    StringBuilder sb = new StringBuilder();
    while ((len = inputStream.read(bytes)) != -1) {
      sb.append(new String(bytes, 0, len,"UTF-8"));
    }
    System.out.println("Received: " + sb);

    // 关闭流&连接
    inputStream.close();
    outputStream.close();
    socket.close();
  }
}