ThreadLocal

ThreadLocal用于实现线程内数据的共享，即对于相同的代码程序，多个模块在同一个线程中运行时共享一份数据，而在另外线程中运行时又共享另外一份数据
每个线程调用全局ThreadLocal对象的set方法，就相当于往其内部的map中增加一条记录，key分别是各自的线程，value为各自的set方法传进去的值，在线程结束是可以调用ThreadLocal.clear()方法，这样会释放内存，不调用也可以，因为线程结束后也可以自动释放相关ThreadLocal变量。

package Thread02;
import java.util.Random;
public class ThreadLocalScope {
    private static ThreadLocal<Integer> local = new ThreadLocal<Integer>();
    public static void main(String[] args) {
        for (int i = 0; i < 2; i++) {
            new Thread() {
                @Override
                public void run() {
                    int data = new Random().nextInt();
                    System.out.println(Thread.currentThread().getName()
                            + " has put data:" + data);
                    local.set(data);// 把数据放在当前线程
                    new A().get();
                    new B().get();
                }
            }.start();
        }
    }

    static class A {
        public void get() {
            int data = local.get();
            System.out.println("A from " + Thread.currentThread().getName()
                    + "  get data :" + data);
        }
    }

    static class B {
        public void get() {
            int data = local.get();
            System.out.println("B from " + Thread.currentThread().getName()
                    + "  get data :" + data);
        }
    }
}

package Thread02;

import java.util.Random;

public class ThreadLocalScope {
    private static ThreadLocal<Integer> local = new ThreadLocal<Integer>();
    public static void main(String[] args) {
        for (int i = 0; i < 2; i++) {
            new Thread() {
                @Override
                public void run() {
                    int data = new Random().nextInt();
                    System.out.println(Thread.currentThread().getName()
                            + " has put data:" + data);
                    local.set(data);// 把数据放在当前线程
                    MyThreadScopeData.getInstance().setName("name"+data);
                    MyThreadScopeData.getInstance().setAge(data);
                    new A().get();
                    new B().get();
                }
            }.start();
        }
    }
    static class A {
        public void get() {
            int data = local.get();
            System.out.println("A from " + Thread.currentThread().getName()
                    + "  get data :" + data);
            MyThreadScopeData mydata=MyThreadScopeData.getInstance();
            System.out.println("A from " + Thread.currentThread().getName()
                    + "  getMydata :" + mydata.getName()+","+mydata.getAge());
        }
    }

    static class B {
        public void get() {
            int data = local.get();
            System.out.println("B from " + Thread.currentThread().getName()
                    + "  get data :" + data);
            MyThreadScopeData mydata=MyThreadScopeData.getInstance();
            System.out.println("B from " + Thread.currentThread().getName()
                    + "  getMydata :" +mydata.getName()+","+mydata.getAge());
        }
    }
}
class MyThreadScopeData{

    private MyThreadScopeData(){

    }
    public static MyThreadScopeData getInstance(){
        MyThreadScopeData instance=map.get();
        if(instance==null){
            instance=new MyThreadScopeData();
            map.set(instance);
        }
        return instance;
    }
    private static ThreadLocal<MyThreadScopeData> map=new ThreadLocal<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;
    }   
}

Thread-0 has put data:-1724589288
Thread-1 has put data:-1923889218
A from Thread-1  get data :-1923889218
A from Thread-0  get data :-1724589288
A from Thread-1  getMydata :name-1923889218,-1923889218
A from Thread-0  getMydata :name-1724589288,-1724589288
B from Thread-0  get data :-1724589288
B from Thread-1  get data :-1923889218
B from Thread-0  getMydata :name-1724589288,-1724589288
B from Thread-1  getMydata :name-1923889218,-1923889218