Lock和读写锁ReadWriteLock和缓存实例

1：lock和synchronized对比

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(){@Overridepublic void run() {while(true){try {Thread.sleep(10);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}outputer.output("zhangxiaoxiang");}}}).start();new Thread(new Runnable(){@Overridepublic void run() {while(true){try {Thread.sleep(10);} catch (InterruptedException e) {// TODO Auto-generated catch blocke.printStackTrace();}outputer.output("lihuoming");}}}).start();}static class Outputer{Lock lock = new ReentrantLock();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{lock.unlock();}}public synchronized void output2(String name){int len = name.length();for(int i=0;i<len;i++){System.out.print(name.charAt(i));}System.out.println();}public static synchronized void output3(String name){int len = name.length();for(int i=0;i<len;i++){System.out.print(name.charAt(i));}System.out.println();}}}

2.读写锁：ReadWriteLock

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，只能有一个线程能写该数据，但可以有多个线程同时读该数据。ReadWriteLock rwl = new ReentrantReadWriteLock();public void get(){rwl.readLock().lock();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();}}public void put(Object data){rwl.writeLock().lock();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();}}}

3.用读写锁实现一个简单缓存机制

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){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";//实际失去queryDB();}}finally{rwl.writeLock().unlock();}rwl.readLock().lock();}}finally{rwl.readLock().unlock();}return value;}}