线程学习笔记【5】--ThreadLocal应用

基本的ThreadLocal使用

publicclass ThreadLocalTest {

    static ThreadLocal tl=new ThreadLocal();
    publicstaticvoid main(String[] args) {

        for(int i=0;i<2;i++){
            new Thread(new Runnable(){
              int data =new Random().nextInt();
              publicvoid run() {
              System.out.println(Thread.currentThread().getName()+"存入的数据是 "+data);
              tl.set(data); //存到了当前线程
new A().getThreadData();
              }
            }).start();
        }
    }
    staticclass A{  //静态类相当于一个外部类
publicvoid getThreadData(){
            System.out.println("data is "+tl.get());
        }
    }
}

结果可能是

Thread-0存入的数据是 1997234255
Thread-1存入的数据是 267171693
data is 1997234255
data is 267171693

通过包装对象非常烂的使用方式

class MyThreadScopeData{
    private String name;
    privateint age;
    public String getName() {
        return name;
    }
    publicvoid setName(String name) {
        this.name = name;
    }
    publicint getAge() {
        return age;
    }
    publicvoid setAge(int age) {
        this.age = age;
    }
}

 

public class ThreadLocalTest {
static ThreadLocal<MyThreadScopeData> myThreadScopeData=
new ThreadLocal<MyThreadScopeData>();
    public static void main(String[] args) {

        for(int i=0;i<2;i++){
            new Thread(new Runnable(){
                int data =new Random().nextInt();
                public void run() {
                  MyThreadScopeData mydata=new MyThreadScopeData();
                  mydata.setName("name is name"+data);
                  mydata.setAge(data);
                  //把对象存入ThreadLocal   这样的做法非常烂！！！！！
                    myThreadScopeData.set(mydata);  
                  new B().showThreadScopeData();
                    
                }
            }).start();
        }
    }
    
    
    static class B{
        public void showThreadScopeData(){
            System.out.println(myThreadScopeData.get().getName());
            System.out.println("age is "+myThreadScopeData.get().getAge());
        }
    }
    
        }

}

 

标准使用方式

/**
 * 单列线程
 * 在线程中范围内任意地方调，得到都是同一个实例对象
 * 把ThreadLocal封装到单列的内部
 */
class ThreadSingle{
    private ThreadSingle(){}
    publicstatic ThreadLocal<ThreadSingle> map=new ThreadLocal<ThreadSingle>();
     //不需要加synchronized，即便有第2个线程进入，但拿到的map.get()是独有的。
publicstatic ThreadSingle getThreadInstance(){  //方法得到是与本线程相关的实例 
        ThreadSingle obj=map.get();
        /**
         * 如果A进入时obj=null，刚创建完还没赋值，此时B线程进入，但B和A没有关系。
         */
        if(obj==null){    
            obj=new ThreadSingle();
            map.set(obj);
        }
        return obj;
    }
    private String name;
    privateint age;
    public String getName() {
        return name;
    }
    publicvoid setName(String name) {
        this.name = name;
    }
    publicint getAge() {
        return age;
    }
    publicvoid setAge(int age) {
        this.age = age;
    }
    
}

 

 

public class ThreadLocalTest {

	public static void main(String[] args) {

		for(int i=0;i<2;i++){
			new Thread(new Runnable(){
				int data =new Random().nextInt();
				public void run() {						
					ThreadSingle.getThreadInstance().setName("name"+data);
					ThreadSingle.getThreadInstance().setAge(data);
					new C().showData();
				}
			}).start();
		}
	}