Java多线程-新特征-锁

Java中读写锁有个接口java.util.concurrent.locks.ReadWriteLock，也有具体的实现ReentrantReadWriteLock，详细的API可以查看JavaAPI文档。

下面这个例子是在文例子的基础上，将普通锁改为读写锁，并添加账户余额查询的功能，代码如下：

package cn.thread; import java.util.concurrent.ExecutorService; import java.util.concurrent.Executors; import java.util.concurrent.locks.ReadWriteLock; import java.util.concurrent.locks.ReentrantReadWriteLock; /** * 读写锁 * * @author 林计钦 * @version 1.0 2013-7-25 上午10:33:37 */ public class WriteReadLockTest { public static void main(String[] args) { WriteReadLockTest test = new WriteReadLockTest(); // 创建并发访问的账户 MyCount myCount = test.new MyCount("95599200901215522", 10000); // 创建一个锁对象 ReadWriteLock lock = new ReentrantReadWriteLock(false); // 创建一个线程池 ExecutorService pool = Executors.newFixedThreadPool(2); // 创建一些并发访问用户，一个信用卡，存的存，取的取，好热闹啊 User u1 = test.new User("张三", myCount, -4000, lock, false); User u2 = test.new User("张三他爹", myCount, 6000, lock, false); User u3 = test.new User("张三他弟", myCount, -8000, lock, false); User u4 = test.new User("张三", myCount, 800, lock, false); User u5 = test.new User("张三他爹", myCount, 0, lock, true); // 在线程池中执行各个用户的操作  pool.execute(u1); pool.execute(u2); pool.execute(u3); pool.execute(u4); pool.execute(u5); // 关闭线程池  pool.shutdown(); } /** * 信用卡的用户 */ class User implements Runnable { private String name; // 用户名 private MyCount myCount; // 所要操作的账户 private int iocash; // 操作的金额，当然有正负之分了 private ReadWriteLock myLock; // 执行操作所需的锁对象 private boolean ischeck; // 是否查询  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) { // 获取读锁  myLock.readLock().lock(); System.out.println("读：" + name + "正在查询" + myCount + "账户，当前金额为" + myCount.getCash()); // 释放读锁  myLock.readLock().unlock(); } else { // 获取写锁  myLock.writeLock().lock(); // 执行现金业务 System.out.println("写：" + name + "正在操作" + myCount + "账户，金额为" + iocash + "，当前金额为" + myCount.getCash()); myCount.setCash(myCount.getCash() + iocash); System.out.println("写：" + name + "操作" + myCount + "账户成功，金额为" + iocash + "，当前金额为" + myCount.getCash()); // 释放写锁  myLock.writeLock().unlock(); } } } /** * 信用卡账户，可随意透支 */ class MyCount { private String oid; // 账号 private int cash; // 账户余额  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 + '}'; } } }

写：张三正在操作MyCount{oid='95599200901215522', cash=10000}账户，金额为-4000，当前金额为10000
写：张三操作MyCount{oid='95599200901215522', cash=6000}账户成功，金额为-4000，当前金额为6000 写：张三他爹正在操作MyCount{oid='95599200901215522', cash=6000}账户，金额为6000，当前金额为6000 写：张三他爹操作MyCount{oid='95599200901215522', cash=12000}账户成功，金额为6000，当前金额为12000 写：张三正在操作MyCount{oid='95599200901215522', cash=12000}账户，金额为800，当前金额为12000 写：张三操作MyCount{oid='95599200901215522', cash=12800}账户成功，金额为800，当前金额为12800 写：张三他弟正在操作MyCount{oid='95599200901215522', cash=12800}账户，金额为-8000，当前金额为12800 写：张三他弟操作MyCount{oid='95599200901215522', cash=4800}账户成功，金额为-8000，当前金额为4800 读：张三他爹正在查询MyCount{oid='95599200901215522', cash=4800}账户，当前金额为4800

在实际开发中，最好在能用读写锁的情况下使用读写锁，而不要用普通锁，以求更好的性能。