java并发编程--ThreadLocal的用法和分析

ThreadLocal这个类，理解起来比较简单，但是使用时，还是需要一些技巧的，简单介绍如下：

 

例子1：threadLocal变量一般用法

 

 package concurrent.thread;

 /**
  * 技巧：
  *      1.在当前线程里执行threadLocal.set(value) 相当于 currentThread.threadLocalMap.set(threadLocal,value)。
  *          即：每个线程均含有一个threadLocalMap变量，该变量由ThreadLocal维护。
  *      2.ThreadLocal变量一般使用private static修饰。
  */
 public class ThreadLocalDemo_step0 {

     private static ThreadLocal<String> myData = new ThreadLocal<String>();

     public static void main(String[] args) {
         Thread t1 = new Thread(new Runnable(){
             public void run() {
                 System.out.println("Thread " + Thread.currentThread().getName() + "[begin] has " + myData.get());
                 myData.set("t1");
                 System.out.println("Thread " + Thread.currentThread().getName() + "[end] has " + myData.get());
             }
         });
         Thread t2 = new Thread(new Runnable(){
             public void run() {
                 System.out.println("Thread " + Thread.currentThread().getName() + "[begin] has " + myData.get());
                 myData.set("t2");
                 System.out.println("Thread " + Thread.currentThread().getName() + "[end] has " + myData.get());
             }
         });
         t1.start();
         t2.start();
     }
 }

 

 

例子2：threadLocal变量的简单封装用法（重要）

 

 package concurrent.thread;

 /**
  * 技巧：
  *      3.如果希望线程局部变量初始化其它值，那么需要自己实现ThreadLocal的子类并重写initialValue()方法，
  *      通常使用一个内部匿名类对ThreadLocal进行子类化.比如下面的例子，SerialNum类为每一个类分配一个序号：
  */
 public class ThreadLocalDemo_step1 {

     public static void main(String[] args) {
         Thread t1 = new Thread(new Runnable(){
             public void run() {
                 System.out.println("Thread " + Thread.currentThread().getName() + " has " + SerialNum.get());
             }
         });
         Thread t2 = new Thread(new Runnable(){
             public void run() {
                 System.out.println("Thread " + Thread.currentThread().getName() + " has " + SerialNum.get());
             }
         });
         t1.start();
         t2.start();
     }

     //技巧：对threadLocal变量进行简单封装，可以简化多线程操作
     static class SerialNum {
          // The next serial number to be assigned
          private static int nextSerialNum = 0;

          private static ThreadLocal serialNum = new ThreadLocal() {
              protected synchronized Object initialValue() {
                  return new Integer(nextSerialNum++);
              }
          };

          public static int get() {
              return ((Integer) (serialNum.get())).intValue();
          }
      }


 }

 

 

 

参考文献：

 

http://my.oschina.net/ITBoy/blog/17190 java类ThreadLocal的理解

http://www.iteye.com/topic/103804 正确理解ThreadLocal

原文http://suo.iteye.com/blog/1342393