java读写锁，

java读写锁，

/*
 *	Title：ReadWriteLockTest.java<br>
 * 
 */
package testReadWriteLock;

import java.util.HashMap;
import java.util.Map;
import java.util.concurrent.locks.ReentrantReadWriteLock;

/**
 * <br>
 * 
 * @version 1.0
 */
public class ReadWriteLockTest
{
	private ReentrantReadWriteLock readWriteLock = new ReentrantReadWriteLock();
	private Map<String, String> cache = new HashMap<>();

	public String readWriteLockTest(String key)
	{
		String value = null;
		readWriteLock.readLock().lock();
		value = cache.get(key);
		if (value == null)
		{
			readWriteLock.readLock().unlock();
			readWriteLock.writeLock().lock();
			// 获取写锁后再次判断对象是否为null，防止数据重复更新
			value = cache.get(key);
			if (value == null)
			{
				System.out.println(Thread.currentThread().getName());
				value = "123";
				cache.put(key, value);
			}
			// 释放写锁
			readWriteLock.writeLock().unlock();
		}
		else
		{
			readWriteLock.readLock().unlock();
		}
		return value;
	}

	public static void main(String[] args)
	{
		ReadWriteLockTest test = new ReadWriteLockTest();
		for (int i = 0; i < 10; i++)
		{
			new Thread(new Runnable()
			{

				@Override
				public void run()
				{
					System.out.println(Thread.currentThread().getName() + test.readWriteLockTest("1"));

				}
			}).start();
		}
	}
}