Lock

package cn.itcast.heima2;

import java.util.concurrent.locks.Lock;
import java.util.concurrent.locks.ReentrantLock;


public class LockTest {

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		new LockTest().init();
	}
	
	private void init(){
		final Outputer outputer = new Outputer();
		new Thread(new Runnable(){
			@Override
			public void run() {
				while(true){
					try {
						Thread.sleep(10);
					} catch (InterruptedException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
					outputer.output("zhangxiaoxiang");
				}
				
			}
		}).start();
		
		new Thread(new Runnable(){
			@Override
			public void run() {
				while(true){
					try {
						Thread.sleep(10);
					} catch (InterruptedException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
					outputer.output("lihuoming");
				}
				
			}
		}).start();
		
	}

	static class Outputer{
		Lock lock = new ReentrantLock();//TODO 锁
		public void output(String name){
			int len = name.length();
			lock.lock();
			try{
				for(int i=0;i<len;i++){
					System.out.print(name.charAt(i));
				}
				System.out.println();
			}finally{	//todo 保证正常或者非正常退出,都会释放锁
				lock.unlock();
			}
		}

	}
}

读写锁

Lock比Synchronized方式更加面向对象，而且锁本身也是一个对象，两个线程要实现同步互斥的效果，他们必须使用同一个lock对象
读写锁：多个读锁不互斥，读锁和写锁互斥，写锁和写锁互斥。这是由jvm控制的，你只要上相应的锁即可。如果你的代码只读数据，可以很多人读，但不能同时写那就上读锁；如果你的代码修改数据，只能有一个人在写，且不能同时读取，那就上写锁。

package cn.itcast.heima2;

import java.util.Random;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;

public class ReadWriteLockTest {
	public static void main(String[] args) {
		final Queue3 q3 = new Queue3();
		for(int i=0;i<3;i++)
		{
			new Thread(){
				public void run(){
					while(true){
						q3.get();						
					}
				}
				
			}.start();

			new Thread(){
				public void run(){
					while(true){
						q3.put(new Random().nextInt(10000));
					}
				}			
				
			}.start();
		}
		
	}
}

class Queue3{
	private Object data = null;//共享数据,只有一个线程能写该数据,但是多个线程能同时读
	ReadWriteLock rwl = new ReentrantReadWriteLock(); //todo 不能上普通的锁,否则读和写都会互斥
	public void get(){
		rwl.readLock().lock();//todo
		try {
			System.out.println(Thread.currentThread().getName() + " be ready to read data!");
			Thread.sleep((long)(Math.random()*1000));
			System.out.println(Thread.currentThread().getName() + "have read data :" + data);			
		} catch (InterruptedException e) {
			e.printStackTrace();
		}finally{
			rwl.readLock().unlock(); //todo
		}
	}
	
	public void put(Object data){

		rwl.writeLock().lock();	//todo
		try {
			System.out.println(Thread.currentThread().getName() + " be ready to write data!");					
			Thread.sleep((long)(Math.random()*1000));
			this.data = data;		
			System.out.println(Thread.currentThread().getName() + " have write data: " + data);					
		} catch (InterruptedException e) {
			e.printStackTrace();
		}finally{
			rwl.writeLock().unlock(); //todo
		}
		
	
	}
}

读写锁缓存demo

package cn.itcast.heima2;

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

public class CacheDemo {

	private Map<String, Object> cache = new HashMap<String, Object>();
	public static void main(String[] args) {
		// TODO Auto-generated method stub

	}

	private ReadWriteLock rwl = new ReentrantReadWriteLock();
	public  Object getData(String key){    //可以用synchronized但是不推荐
		rwl.readLock().lock();
		Object value = null;
		try{
			value = cache.get(key);
			if(value == null){
				rwl.readLock().unlock();
				rwl.writeLock().lock();
				try{
					if(value==null){
						value = "aaaa";//实际去queryDB
					}
				}finally{
					rwl.writeLock().unlock();
				}
				rwl.readLock().lock();
			}
		}finally{
			rwl.readLock().unlock();
		}
		return value;
	}
}