java 多线程 ：ThreadLocal 共享变量多线程不同值方案；InheritableThreadLocal变量子线程中自定义值，孙线程可继承

 

ThreadLocal类的使用

变量值的共享可以使用public static变量的形式，所有的线程都是用同一个public static变量。如果想实现每一个线程都有自己的值。该变量可通过ThreadLocal实现

定义：ThreadLocal<T> name = new ThreadLocal<>()；

用法：

• 用法1、变量在线程外定义，在线程执行体内.set()赋值。
• 用法2、变量在定义时设置自动赋值的方法。在对应线程中运行时则自动赋值。

  ThreadLocal<T> name = new ThreadLocal<>(){
      @Override
      protected String initialValue() {
          return <T> t;
      }
  };

取值：.get()

用法1示例：

import javax.management.relation.RelationNotFoundException;

/**
 * @ClassName ThreadLocalExample
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/24.
 */
public class ThreadLocalExample {
    private static ThreadLocal<String> name = new ThreadLocal<>();

    public static void main(String[] args) {
        Runnable r = () -> {
            String threadname = Thread.currentThread().getName();
            /**
             * 线程运行时赋值
             */
            name.set(threadname);
            System.out.println(name.get()); //不同的子线程对应子线程名，本例ABC
        };
        Thread thread = new Thread(r,"A");
        Thread thread2 = new Thread(r,"B");
        Thread thread1 = new Thread(r,"C");
        thread.start();
        thread1.start();
        thread2.start();
        System.out.println(name.get()); //主线程中没有赋值默认为null
    }
}

用法二示例：

/**
 * @ClassName ThreadLocalInitialValue
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/24.
 */
public class ThreadLocalInitialValue {
    /**
     * 定义ThreadLocal变量线程中运行自动初始化值
     */
    private static ThreadLocal<String> name = new ThreadLocal<>(){
        @Override
        protected String initialValue() {
            return Thread.currentThread().getName();
        }
    };
    public static void main(String[] args) {
        Runnable r = new Runnable() {
            @Override
            public void run() {
                System.out.println("我是" + name.get());
            }
        };
        Thread zhangsan = new Thread(r,"张三");
        Thread lisi = new Thread(r,"李四");
        zhangsan.start();
        lisi.start();
        System.out.println("main线程中，我是" + name.get());
    }
}

InheritableThreadLocal子线程中自定义值，孙线程可继承

import java.io.Reader;
import java.sql.SQLOutput;

/**
 * @ClassName ThreadLocalSubThread
 * @projectName: object1
 * @author: Zhangmingda
 * @description： XXX
 * date: 2021/4/24.
 */
public class ThreadLocalSubThread {
    /**
     * 定义变量时，设置自动赋值方法
     */
    private static ThreadLocal<String> name = new InheritableThreadLocal<>(){
        @Override
        protected String initialValue() {
            return Thread.currentThread().getName();
        }
    };

    public static void main(String[] args) {
        Runnable r = () -> {
            System.out.println("我是子线程："+ name.get());//我是子线程：child
            Thread t = new Thread(){
                @Override
                public void run() {
                    System.out.println("我是孙线程，获取子线程变量值："+ name.get());//也是child
                }
            };
            t.start();
        };
        Thread thread = new Thread(r,"child");
        thread.start();
        name.set("主线程"); //主线程中手动赋值
        System.out.println("main线程中 name:" + name.get()); //"主线程"
    }
}