ThreadLocal

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

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