Java线程与并发库高级应用-线程范围内共享数据ThreadLocal类

abstract：1.线程范围内共享变量　1.1 前奏：使用一个Map来实现线程范围内共享变量　public class ThreadScopeShareData { static Map dataMap = new HashMap

1.线程范围内共享变量

1.1 前奏：

使用一个Map来实现线程范围内共享变量　

public class ThreadScopeShareData { static Map dataMap = new HashMap(); public static void main(String[] args) { for (int i = 0; i < 2; i++) { new Thread(new Runnable() { @Override public void run() { int data = new Random().nextInt(); // 获取一个随机整数 System.out.println(Thread.currentThread().getName() + " put data " + data); dataMap.put(Thread.currentThread(), data); new A().get(); new B().get(); } }).start(); } } static class A { public void get() { System.out.println(Thread.currentThread().getName() + " get data " + dataMap.get(Thread.currentThread())); } } static class B { public void get() { System.out.println(Thread.currentThread().getName() + "get data " + dataMap.get(Thread.currentThread())); } } }

1.2 ThreadLocal类实际上就是一种map

/** * ThreadLocal 类 这里ThreadLocal存放一个变量，如果有多个变量， 可以先将多个变量封装为一个对象 * * @author Administrator * */ public class ThreadLocalTest { static ThreadLocal x = new ThreadLocal<>(); // public static void main(String[] args) { // for (int i = 0; i < 2; i++) { new Thread(new Runnable() { @Override public void run() { int data = new Random().nextInt(); // 获取一个随机整数 System.out.println(Thread.currentThread().getName() + " put data " + data); x.set(data); new A().get(); new B().get(); } }).start(); } } static class A { public void get() { System.out.println(Thread.currentThread().getName() + " get data " + x.get()); } } static class B { public void get() { System.out.println(Thread.currentThread().getName() + "get data " + x.get()); } } }

2.线程范围内共享多个变量，可以将多个变量封装为一个对象

/** * ThreadLocal 类 这里ThreadLocal存放一个变量，如果有多个变量， 可以先将多个变量封装为一个对象 * * @author Administrator * */ public class ThreadLocalTest { static ThreadLocal x = new ThreadLocal<>(); // public static void main(String[] args) { // for (int i = 0; i < 2; i++) { new Thread(new Runnable() { @Override public void run() { int data = new Random().nextInt(); // 获取一个随机整数 System.out.println(Thread.currentThread().getName() + " put data " + data); x.set(data); MyThreadScopeData myData = MyThreadScopeData.getThreadInstance();//获取与线程绑定的对象 myData.setName("name"+data); myData.setAge(data); System.out.println(Thread.currentThread().getName() + " put Object " + "name: "+myData.getName()+","+" age: "+myData.getAge()); new A().get(); new B().get(); } }).start(); } } static class A { public void get() { System.out.println(Thread.currentThread().getName() + " get data " + x.get()); MyThreadScopeData instance = MyThreadScopeData.getThreadInstance(); //直接获取与该线程相关的对象 System.out.println(Thread.currentThread().getName() + " get Object " + "name: "+instance.getName()+","+" age: "+instance.getAge()); } } static class B { public void get() { System.out.println(Thread.currentThread().getName() + "get data " + x.get()); MyThreadScopeData instance = MyThreadScopeData.getThreadInstance(); //直接获取与该线程相关的对象 System.out.println(Thread.currentThread().getName() + " get Object " + "name: "+instance.getName()+","+" age: "+instance.getAge()); } } } // 单例 class MyThreadScopeData { //类的实例是与线程相关的，那么类的设计就交由类自身完成，只要调用自然就是与线程有关的 private static ThreadLocal map = new ThreadLocal<>(); private MyThreadScopeData() { } public static MyThreadScopeData getThreadInstance() { // 线程间是相互独立的，这里不需要考虑同步 MyThreadScopeData instance = map.get(); if (instance == null) { instance = new MyThreadScopeData(); map.set(instance); } return instance; } private String name; private Integer age; /** * @return the name */ public String getName() { return name; } /** * @param name * the name to set */ public void setName(String name) { this.name = name; } /** * @return the age */ public Integer getAge() { return age; } /** * @param age * the age to set */ public void setAge(Integer age) { this.age = age; } }

打印结果

Thread-1 put data -723086824
Thread-0 put data 772514756
Thread-1 put Object name: name-723086824, age: -723086824
Thread-0 put Object name: name772514756, age: 772514756
Thread-0 get data 772514756
Thread-1 get data -723086824
Thread-0 get Object name: name772514756, age: 772514756
Thread-1 get Object name: name-723086824, age: -723086824
Thread-0get data 772514756
Thread-1get data -723086824
Thread-0 get Object name: name772514756, age: 772514756
Thread-1 get Object name: name-723086824, age: -723086824

类的实例是与线程相关的，那么类的设计就交由类自身完成，只要调用自然就是与线程有关的 strust2的主要思想就是这么设计的

参看JAVA API

ThreadLocal有一个 remove()方法

可以移除与该线程相关的变量

remove()
Removes the current thread's value for this thread-local variable.

补充：

　　虚拟机的对应类 Runtime ，中有一个方法 addShutdownHook(Thread hook)

　　addShutdownHook(Thread hook)
　　Registers a new virtual-machine shutdown hook.

　　例如可以写一个发送邮件的线程Thread，当虚拟机挂掉之前会调用传入的Thread，发送一封邮件。

线程中是不是也应该有这种机制，当一个线程挂掉之前可以执行一个之前注册好的事件，或者有一个监听器在监听线程的状态，从而进行回调

在获取到线程挂掉的通知，就可以把该线程相关的变量全部remove获取clear掉