线程学习笔记【5】--ThreadLocal应用

基本的ThreadLocal使用

public class ThreadLocalTest {

static ThreadLocal tl=new ThreadLocal();
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() {
              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();
        }
    }
static class A{  //静态类相当于一个外部类
        public void 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;
private int age;
public String getName() {
return name;
    }
public void setName(String name) {
this.name = name;
    }
public int getAge() {
return age;
    }
public void 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(){}
public static 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。
    public static 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;
private int age;
public String getName() {
return name;
    }
public void setName(String name) {
this.name = name;
    }
public int getAge() {
return age;
    }
public void 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();
		}
	}