12.Java5读写锁技术的妙用

 1 import java.util.Random;
 2 import java.util.concurrent.locks.ReadWriteLock;
 3 import java.util.concurrent.locks.ReentrantReadWriteLock;
 4 /**
 5  *
 6  * @author LiTaiQing
 7  *
 8  */
 9 public class ReadWriteLockTest {
10     public static void main(String[] args){
11         final Queue3 q3 = new Queue3();
12
13         for (int i = 0; i < 3; i++) {
14             new Thread(){
15                 @Override
16                 public void run(){
17                     while(true){
18                         q3.get();
19                     }
20                 }
21             }.start();
22
23             new Thread(){
24                 @Override
25                 public void run() {
26                     q3.put(new Random().nextInt(10000));
27                 };
28             }.start();
29
30         }
31
32     }
33
34 }
35 class Queue3{
36     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。
37     //读写锁-实现类ReentrantReadWriteLock
38     ReadWriteLock rwl = new ReentrantReadWriteLock();
39     public void get(){
40         rwl.readLock().lock();
41         try {
42             System.out.println(Thread.currentThread().getName() + " be ready to read data!");
43             Thread.sleep((long)(Math.random()*1000));
44             System.out.println(Thread.currentThread().getName() + "have read data :" + data);
45         } catch (InterruptedException e) {
46             e.printStackTrace();
47         }finally{
48             rwl.readLock().unlock();
49         }
50     }
51     public void put(Object data){
52         rwl.writeLock().lock();
53         try {
54             System.out.println(Thread.currentThread().getName() + " be ready to write data!");
55             Thread.sleep((long)(Math.random()*1000));
56             this.data = data;
57             System.out.println(Thread.currentThread().getName() + " have write data: " + data);
58         } catch (InterruptedException e) {
59             e.printStackTrace();
60         }finally{
61             rwl.writeLock().unlock();
62         }
63     }
64 }

 1 import java.util.HashMap;
 2 import java.util.Map;
 3 import java.util.concurrent.locks.ReadWriteLock;
 4 import java.util.concurrent.locks.ReentrantReadWriteLock;
 5 /**
 6  * 面试题，写一个缓存系统
 7  * @author LiTaiQing
 8  *
 9  */
10 public class CacheDemo {
11
12     private Map<String,Object> cache = new HashMap<String,Object>();
13
14     public static void main(String[] args) {
15
16     }
17     /**
18      *    读写锁的应用
19      */
20     private ReadWriteLock rwl = new ReentrantReadWriteLock();
21     public Object getData(String key){
22         rwl.readLock().lock();
23         Object value = null;
24         try{
25             value =    cache.get(key);
26             if(value == null){
27                 rwl.readLock().unlock();
28                 rwl.writeLock().lock();
29                 try{
30                     if(value == null){
31                         value = "abc";//实际是去queryDB();
32                     }
33                 }finally{
34                     rwl.writeLock().unlock();
35                 }
36                 rwl.readLock().lock();
37             }
38         }finally{
39             rwl.readLock().unlock();
40         }
41         return value;
42     }
43
44 }