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 }
