java緩存及讀寫鎖實例應用

package com.thread.demo.lock;

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

/**
* 
* @author Torey
*
*/
public class CacheDemo {
// 創建一個緩存對象
static Map<String, Object> cache = Collections
.synchronizedMap(new HashMap<>());
static ReadWriteLock rwLock = new ReentrantReadWriteLock();

/**
* 定義一個獲取數據的方法
* 
* @param key
* @return
*/
public Object getData(String key) {
// 開啟讀鎖
rwLock.readLock().lock();
Object value = null;
try {
// 獲取到緩沖對象中的數據
value = cache.get(key);
if (value == null) {
// 關閉讀鎖
rwLock.readLock().unlock();
// 開啟 寫鎖
rwLock.writeLock().lock();
try {
value = cache.get(key);
if (value == null) {
System.out.println("從DB獲取數據：" + key);
cache.put(key, key + "_key的值");
value = cache.get(key);
} else {
System.out.println("從緩存讀取：");
value = cache.get(key);
}
} catch (Exception ex) {
ex.printStackTrace();
} finally {
// 釋放寫鎖
rwLock.writeLock().unlock();
}
// 釋放讀鎖
rwLock.readLock().lock();
} else {
System.out.println("從緩存讀取");
value = cache.get(key);
}
} catch (Exception ex) {
ex.printStackTrace();
} finally {
// 關閉讀鎖
rwLock.readLock().unlock();
}
return value;
}

static class CacheRunnable implements Runnable {

@Override
public void run() {
// TODO Auto-generated method stub
for (int i = 0; i < 3; i++) {
System.out.println(Thread.currentThread().getName() + "_" + i+"="+new CacheDemo().getData(Thread.currentThread().getName() + "_" + i));
}
}

}

public static void main(String[] args) {

for (int i = 0; i < 3; i++) {
new Thread(new CacheRunnable(), "線程").start();
}
}
}