java并发编程中ReentrantLock可重入读写锁

Lock lock = new ReentrantLock();  //实例化锁
//lock.lock(); //上锁
boolean locked = lock.tryLock();  //尝试上锁
if(locked){
  try {
    //被锁定的同步代码块，同时只能被一个线程执行
  }finally {
    lock.unlock(); //放在finally代码块中，保证锁一定会被释放
  }
}

public class TestReadWriteLock {
  //可以同时执行3个线程任务的线程池
  ExecutorService executor = Executors.newFixedThreadPool(3);
  //读写目标，写线程放入数据到map，读线程从map读取数据
  Map<String, String> map = new HashMap<>();
  //读写锁操作对象
  ReadWriteLock lock = new ReentrantReadWriteLock();

  //写操作函数
  public void write(){
    executor.submit(() -> { //线程池提交写操作任务
      lock.writeLock().lock(); //加写锁
      try {
        map.put("key", "val");  //写数据操作
        Thread.sleep(2000);
      } catch (InterruptedException e) {
        e.printStackTrace();
      } finally {
        lock.writeLock().unlock(); //释放写锁
      }
    });
  }

  //读操作函数
  public void read(){
    lock.readLock().lock(); //加读锁
    System.out.println(Thread.currentThread().getName() + "加读锁");
    try {
      System.out.println(map.get("key")); //读数据操作
    } finally {
      lock.readLock().unlock(); //释放读锁
      System.out.println(Thread.currentThread().getName() + "释放读锁");
    }
  }

}

  //测试
  public static void main(String[] args) {
    TestReadWriteLock test = new TestReadWriteLock();
    test.write();  //提交一次写操作任务，写一条数据
    Runnable readTask = test::read;  //线程方法read，实现线程Runnable接口的简便写法
    test.executor.submit(readTask);  //读1次（新读线程）
    test.executor.submit(readTask);  //读2次 (新读线程）
    test.executor.shutdown();
  }