ReentrantReadWriteLock

独占锁（写锁）一次只能被一个线程占有
共享锁（读锁）多个线程可以同时占有

public class LockTest {
    public static void main(String[] args) throws InterruptedException {
        CacheDemo cacheDemo = new CacheDemo();
        // 写入
        for (int i = 0; i < 5; i++) {
            final int temp = i;
            new Thread(()->{
                cacheDemo.put(temp + "", temp + "");
            }, String.valueOf(i)).start();
        }
        // 读取
        for (int i = 0; i < 5; i++) {
            final int temp = i;
            new Thread(()->{
                cacheDemo.get(temp + "");
            }, String.valueOf(i)).start();
        }
    }
}
class CacheDemo {
    private volatile Map<String, Object> map = new HashMap<>();
    // 读写锁
    private ReadWriteLock readWriteLock = new ReentrantReadWriteLock();
    public void put(String key, Object value) {
        // 加写锁
        readWriteLock.writeLock().lock();
        try {
            System.out.println("写入：" + Thread.currentThread().getName());
            map.put(key, value);
            System.out.println("写完：" + Thread.currentThread().getName());
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readWriteLock.writeLock().unlock();
        }
    }
    public void get(String key) {
        readWriteLock.readLock().lock();
        try {
            System.out.println("读取：" + Thread.currentThread().getName());
            map.get(key);
            System.out.println("读完：" + Thread.currentThread().getName());
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            readWriteLock.readLock().unlock();
        }
    }
}