之前项目中经常会碰到线程共享数据的场景,简单总结下:
1、通常情况会用java.lang.ThreadLocal来实现线程范围的共享变量,线程内共享,线程外独立;
2、ThreadLocal的作用和目的:用于实现线程内的数据共享,即对于相同的程序代码,多个模块在同一个线程中运行时要共享一份数据,而在另外线程中运行时又共享另外一份数据。
应用场景:订单处理、银行转账;
3、demo
package cn.cloudBy.concurrent; import java.util.Random; /** * @description:different modules(different classes or methods) share data in one thread * @author: sunyan * @time: 2016年1月7日 上午9:30:33 */ public class ThreadLocalTest { public static void main(String[] args) { for (int i = 0; i < 2; i++) { new Thread(new Runnable() { public void run() { int data = new Random().nextInt(); System.out.println(Thread.currentThread().getName()+ "put data:"+data); MyThreadScopeData.getThreadInstance().setName("name" + data); MyThreadScopeData.getThreadInstance().setAge(data); new A().get(); new B().get(); } }).start(); } } //moduleA static class A { public void get() { MyThreadScopeData myData = MyThreadScopeData.getThreadInstance(); System.out.println("A from " + Thread.currentThread().getName() + " getMyData: " + myData.getName() + "," + myData.getAge()); } } //module B static class B { public void get() { MyThreadScopeData myData = MyThreadScopeData.getThreadInstance(); System.out.println("B from " + Thread.currentThread().getName() + " getMyData: " + myData.getName() + "," + myData.getAge()); } } } //data class class MyThreadScopeData { private String name; private int age; public String getName() { return name; } public void setName(String name) { this.name = name; } public int getAge() { return age; } public void setAge(int age) { this.age = age; } private MyThreadScopeData() { } private static ThreadLocal<MyThreadScopeData> map=new ThreadLocal<MyThreadScopeData>(); public static MyThreadScopeData getThreadInstance() { MyThreadScopeData instance = map.get(); if (instance == null) { instance = new MyThreadScopeData(); map.set(instance); } return instance; } }
4、每个线程调用全局ThreadLocal对象的set方法,就相当于往其内部的map中增加一条记录,key分别是各自的线程,value是各自的set方法传进去的值。在线程结束时可以调用ThreadLocal.clear()方法,这样会更快释放内存,不调用也可以,因为线程结束后也可以自动释放相关的ThreadLocal变量(gc)。