利用readwritelock简单模拟实现多线程下cache的系统

 1 package cn.lyy.hibernate.many2one;
 2 
 3 import java.util.HashMap;
 4 import java.util.Map;
 5 import java.util.concurrent.locks.ReadWriteLock;
 6 import java.util.concurrent.locks.ReentrantReadWriteLock;
 7 
 8 public class MultiCacheDemo {
 9 
10     private Map<String, Object> cache = new HashMap<String,Object>();
11     public static void main(String args[]){
12         
13     }
14     
15     private ReadWriteLock rwl = new ReentrantReadWriteLock();
16     public Object getData(String key){
17         rwl.readLock().lock();
18         Object value = null;
19         try{
20             value = cache.get(key);
21             if(value == null){
22                 rwl.readLock().unlock();
23                 rwl.writeLock().lock();
24                 try{
25                     //因为如果同时又多个线程在读数据的话，可能会同时发现value
26                     //为空，所以应该再在这里加一个if语句判断value是否为空
27                     if(value == null){
28                         
29                     value = "aaaa";  //实际是去queryDB();
30                     
31                     }
32                 }finally{
33                     rwl.writeLock().unlock();
34                 }
35                 rwl.readLock().lock();
36             }
37         }finally{
38             rwl.readLock().unlock();
39         }
40         return value;
41     }
42 }