实战十二：threadlocal 使用

　ThreadLocal是如何做到为每一个线程维护变量的副本的呢？其实实现的思路很简单：在ThreadLocal类中有一个Map，用于存储每一个线程的变量副本，Map中元素的键为线程对象，而值对应线程的变量副本。我们自己就可以提供一个简单的实现版本

 

 

public class TestThreadLocal {

 

ThreadLocal<String> myLocal = new ThreadLocal<String>();

 

String myName;

 

public String getName() {

return myName;

}

 

public void setName(String name) {

myName = name;

}

 

public static void main(String[] args) throws InterruptedException {

TestThreadLocal ooo = new TestThreadLocal();

Thread[] threadArray = new Thread[10];

for (int i = 0; i < 10; i++) {

 

Thread thi = new Thread(new ThreadWithoutThreadLocal(ooo), "thread" + i);

threadArray[i] = thi;

}

 

for (Thread th : threadArray) {

th.start();

}

 

Thread.sleep(3000);

System.out.println("-----------------------------------------------------------------");

 

for (int i = 0; i < 10; i++) {

 

Thread thi = new Thread(new ThreadWithThreadLocal(ooo), "thread" + i);

threadArray[i] = thi;

}

 

for (Thread th : threadArray) {

th.start();

}

}

 

}

 

class ThreadWithoutThreadLocal implements Runnable {

public TestThreadLocal ooo;

 

public ThreadWithoutThreadLocal(TestThreadLocal o) {

ooo = o;

}

 

@Override

public void run() {

String localName = Thread.currentThread().getName();

ooo.setName(localName);

ooo.myLocal.set(localName);

// it will be mess up if multi thread running

// result like this

// ThreadName =======thread1 but it's actual name thread1

// ThreadName =======thread2 but it's actual name thread2

// ThreadName =======thread1 but it's actual name thread0

// ThreadName =======thread4 but it's actual name thread4

// ThreadName =======thread3 but it's actual name thread3

// ThreadName =======thread7 but it's actual name thread7

// ThreadName =======thread6 but it's actual name thread6

// ThreadName =======thread5 but it's actual name thread5

// ThreadName =======thread8 but it's actual name thread8

// ThreadName =======thread9 but it's actual name thread9

System.out.println(

"ThreadName =======" + ooo.getName() + " but it's actual name  " + Thread.currentThread().getName());

 

}

 

}

 

class ThreadWithThreadLocal implements Runnable {

public TestThreadLocal ooo;

 

public ThreadWithThreadLocal(TestThreadLocal o) {

ooo = o;

}

 

@Override

public void run() {

String localName = Thread.currentThread().getName();

ooo.myLocal.set(Thread.currentThread().getName());

 

// ThreadName======thread0 but it's actual name thread0

// ThreadName======thread2 but it's actual name thread2

// ThreadName======thread1 but it's actual name thread1

// ThreadName======thread3 but it's actual name thread3

// ThreadName======thread5 but it's actual name thread5

// ThreadName======thread4 but it's actual name thread4

// ThreadName======thread8 but it's actual name thread8

// ThreadName======thread6 but it's actual name thread6

// ThreadName======thread9 but it's actual name thread9

// ThreadName======thread7 but it's actual name thread7

 

System.out.println("ThreadName======" + ooo.myLocal.get() + " but it's actual name  " + localName);

 

}

 

 

}