Java中讀寫鎖有個接口java.util.concurrent.locks.ReadWriteLock，也有具體的實現ReentrantReadWriteLock，詳細的API可以查看JavaAPI文檔。
下面這個例子是在文例子的基礎上，將普通鎖改為讀寫鎖，並添加賬戶余額查詢的功能，代碼如下：
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.locks.ReadWriteLock;
import java.util.concurrent.locks.ReentrantReadWriteLock;
/**
* Java線程：鎖
*
* @author leizhimin 2009-11-5 10:57:29
*/
public class Test {
public static void main(String[] args) {
//創建並發訪問的賬戶
MyCount myCount = new MyCount("95599200901215522", 10000);
//創建一個鎖對象
ReadWriteLock lock = new ReentrantReadWriteLock(false);
//創建一個線程池
ExecutorService pool = Executors.newFixedThreadPool(2);
//創建一些並發訪問用戶，一個信用卡，存的存，取的取，好熱鬧啊
User u1 = new User("張三", myCount, -4000, lock, false);
User u2 = new User("張三他爹", myCount, 6000, lock, false);
User u3 = new User("張三他弟", myCount, -8000, lock, false);
User u4 = new User("張三", myCount, 800, lock, false);
User u5 = new User("張三他爹", myCount, 0, lock, true);
//在線程池中執行各個用戶的操作
pool.execute(u1);
pool.execute(u2);
pool.execute(u3);
pool.execute(u4);
pool.execute(u5);
//關閉線程池
pool.shutdown();
}
}
/**
* 信用卡的用戶
*/
class User implements Runnable {
private String name; //用戶名
private MyCount myCount; //所要操作的賬戶
private int iocash; //操作的金額，當然有正負之分了
private ReadWriteLock myLock; //執行操作所需的鎖對象
private boolean ischeck; //是否查詢
User(String name, MyCount myCount, int iocash, ReadWriteLock myLock, boolean ischeck) {
this.name = name;
this.myCount = myCount;
this.iocash = iocash;
this.myLock = myLock;
this.ischeck = ischeck;
}
public void run() {
if (ischeck) {
//獲取讀鎖
myLock.readLock().lock();
System.out.println("讀：" + name + "正在查詢" + myCount + "賬戶，當前金額為" + myCount.getCash());
//釋放讀鎖
myLock.readLock().unlock();
} else {
//獲取寫鎖
myLock.writeLock().lock();
//執行現金業務
System.out.println("寫：" + name + "正在操作" + myCount + "賬戶，金額為" + iocash + "，當前金額為" + myCount.getCash());
myCount.setCash(myCount.getCash() + iocash);
System.out.println("寫：" + name + "操作" + myCount + "賬戶成功，金額為" + iocash + "，當前金額為" + myCount.getCash());
//釋放寫鎖
myLock.writeLock().unlock();
}
}
}
/**
* 信用卡賬戶，可隨意透支
*/
class MyCount {
private String oid; //賬號
private int cash; //賬戶余額
MyCount(String oid, int cash) {
this.oid = oid;
this.cash = cash;
}
public String getOid() {
return oid;
}
public void setOid(String oid) {
this.oid = oid;
}
public int getCash() {
return cash;
}
public void setCash(int cash) {
this.cash = cash;
}
@Override
public String toString() {
return "MyCount{" +
"oid='" + oid + '\'' +
", cash=" + cash +
'}';
}
}
寫：張三正在操作MyCount{oid='95599200901215522', cash=10000}賬戶，金額為-4000，當前金額為10000
寫：張三操作MyCount{oid='95599200901215522', cash=6000}賬戶成功，金額為-4000，當前金額為6000
寫：張三他弟正在操作MyCount{oid='95599200901215522', cash=6000}賬戶，金額為-8000，當前金額為6000
寫：張三他弟操作MyCount{oid='95599200901215522', cash=-2000}賬戶成功，金額為-8000，當前金額為-2000
寫：張三正在操作MyCount{oid='95599200901215522', cash=-2000}賬戶，金額為800，當前金額為-2000
寫：張三操作MyCount{oid='95599200901215522', cash=-1200}賬戶成功，金額為800，當前金額為-1200
讀：張三他爹正在查詢MyCount{oid='95599200901215522', cash=-1200}賬戶，當前金額為-1200
寫：張三他爹正在操作MyCount{oid='95599200901215522', cash=-1200}賬戶，金額為6000，當前金額為-1200
寫：張三他爹操作MyCount{oid='95599200901215522', cash=4800}賬戶成功，金額為6000，當前金額為4800
Process finished with exit code 0
在實際開發中，最好在能用讀寫鎖的情況下使用讀寫鎖，而不要用普通鎖，以求更好的性能。
此出處：http://lavasoft.blog.51cto.com/62575/222433
