ThreadLocal和InheritableThreadLocal的区别

1、ThreadLocal
主要解决每个线程绑定自己的值，达到线程直接隔离。
1.1如果第一次访问没有设定初始值，返回为null
1.2线程直接的隔离性

//继承ThreadLocal类
public class ThreadLocalExt extends ThreadLocal{
}

//创建两个线程，分别设置自己的值
public class ThreadA extends  Thread{
    @Override
    public void run() {
        for(int i = 0; i < 10; i ++){
            Tools.local.set("A:"+ i);
            System.out.println("A:" + Tools.local.get());
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}
public class ThreadB extends Thread{
    @Override
    public void run() {
        for(int i = 0; i < 10; i ++){
            Tools.local.set("B:"+ i);
            System.out.println("B：" + Tools.local.get());
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

public class Tools {
    public static ThreadLocalExt local = new ThreadLocalExt();
}

程序入口类：
public class Run {
    public static void main(String[] args) throws InterruptedException {
        ThreadA t1 = new ThreadA();
        t1.start();
        ThreadB t2 = new ThreadB();
        t2.start();
    }
}

运行结果

A:A:0
B：B:0
B：B:1
A:A:1
B：B:2
A:A:2
A:A:3
B：B:3
A:A:4
B：B:4
A:A:5
B：B:5
A:A:6
B：B:6
A:A:7
B：B:7
A:A:8
B：B:8
B：B:9
A:A:9

1.3通过重写initialValue方法可以设置初始化值
2、InheriThreadLocalExt
2.1值继承子线程可以从父线程中取得值。

public class InheriThreadLocalExt  extends InheritableThreadLocal{
    @Override
    protected Object initialValue() {
        return new Date().getTime();
    }
}

public class Tools {
    public static  InheriThreadLocalExt local = new InheriThreadLocalExt();
}

public class ThreadA extends  Thread{
    @Override
    public void run() {
        for(int i = 0; i < 10; i ++){
            System.out.println("A:" + Tools.local.get());
            try {
                Thread.sleep(1000);
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }
}

public class Run {
    public static void main(String[] args) throws InterruptedException {
        for(int i = 0; i < 10; i ++){
            System.out.println("Main方法中获取" + Tools.local.get());
        }
        ThreadA t1 = new ThreadA();
        t1.start();
    }
}

运行结果：

Main方法中获取1494859232485
Main方法中获取1494859232485
Main方法中获取1494859232485
Main方法中获取1494859232485
Main方法中获取1494859232485
Main方法中获取1494859232485
Main方法中获取1494859232485
Main方法中获取1494859232485
Main方法中获取1494859232485
Main方法中获取1494859232485
A:1494859232492
A:1494859232492
A:1494859232492
A:1494859232492
A:1494859232492
A:1494859232492
A:1494859232492
A:1494859232492
A:1494859232492
A:1494859232492

2.2注意：子线程取值的时候主线程将值进行更改，子线程读到的还是旧值。