正确理解ThreadLocal

一般用法：

class Test{

public static ThreadLocal test = new ThreadLocal();

public static String getThreadLocalTest(){

   return test.get();

}

 

public static void setThreadLocalTest(String value){

   test.set(value);

}

}

 

当test.set(value)给ThreadLocal变量值时， 低层方法实现：将当前的ThreadLocal实例做为key, 将值做为value，做为Map， 跟当前线程绑定的， 在代码的其他的地方， 可以直接Test.getThreadLocalTest()，获取当前线程的ThreadLocal为key的值

1、ThreadLocal类中的代码

public void set(T value) {   
        Thread t = Thread.currentThread(); 
        //取得当前线程的ThreadLocal的内部类ThreadLocalMap  
        ThreadLocalMap map = getMap(t);  
	//如果有值， 修改， 如果没有，
        if (map != null)   
            map.set(this, value);   
        else  
            createMap(t, value);   
    } 

    public T get() {   
        Thread t = Thread.currentThread();   
        ThreadLocalMap map = getMap(t);   
        if (map != null)   
            return (T)map.get(this);   
  
        // Maps are constructed lazily.  if the map for this thread   
        // doesn't exist, create it, with this ThreadLocal and its   
        // initial value as its only entry.   
        T value = initialValue();   
        createMap(t, value);   
        return value;   
    } 

    ThreadLocalMap getMap(Thread t) {   
        return t.threadLocals;   
    }  

 

2、Thread类

publicclass Thread implements Runnable { 

...... 

 /* ThreadLocal values pertaining to this thread. This map is maintained 


* by the ThreadLocal class. */

//Thread类中有一个属性是：ThreadLocalMap，与当前线程绑定的值
ThreadLocal.ThreadLocalMap threadLocals = null; 

...... 


} 

  

 

 

 

主题：正确理解ThreadLocal

 

关于ThreadLocal模式的体会