Java | ThreadLocal学习笔记

ThreadLocal，它可以在一个线程中传递同一个对象

学习链接：使用ThreadLocal - 廖雪峰的官方网站

eg：

public class ThreadLocalDemo {
    public static void main(String[] args) throws InterruptedException {
        Thread t1 = new Thread(new StudentThread("甄嬛",17, 98));
        Thread t2 = new Thread(new StudentThread("夏冬春", 17, 58));
        t1.setName("T0");
        t2.setName("T1");
        t1.start();
        t2.start();
        Thread.sleep(1000);
        System.out.println("测试完成");
    }
}


class Student {
    private String name;
    private int age;
    private int score;

    public Student(String name, int age, int score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    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 int getScore() {
        return score;
    }

    public void setScore(int score) {
        this.score = score;
    }
}


//把ThreadLocal封装在StudentTaske中，实现AutoCloseable接口，可以使用try(source){...}结构
/*因为当前线程执行完相关代码后，很可能会被重新放入线程池中，
如果ThreadLocal没有被清除，该线程执行其他代码时，会把上一次的状态带进去。*/
class StudentTask implements AutoCloseable {
    static final ThreadLocal stu = new ThreadLocal<>();

    //设置一个Student实例关联到ThreadLocal中
    public StudentTask(String name, int age, int score) {
        stu.set(new Student(name, age, score));
    }

    //静态方法包装get()
    public static Student currentStudent() {
        return stu.get();
    }

    //让编译器自动移除与ThreadLocal关联的实例
    @Override
    public void close() {
        stu.remove();
    }
}


class StudentThread implements Runnable {
    private String name;
    private int age;
    private int score;

    public StudentThread(String name, int age, int score) {
        this.name = name;
        this.age = age;
        this.score = score;
    }

    @Override
    public void run() {
        //try(source){...}结构，结束后自动释放与ThreadLocal关联的实例
        //在移除之前，所有方法都可以随时获取到该Student实例
        try (StudentTask task = new StudentTask(this.name, this.age, this.score)) {
            step1();
            step2();
            log();
        }
    }

    void step1() {
        //获取到当前线程局部变量的Student实例
        Student stu = StudentTask.currentStudent();
        System.out.println(Thread.currentThread()+" 步骤一，学生姓名：" + stu.getName());
        System.out.println(Thread.currentThread()+" 步骤1完成");
    }

    void step2() {
        Student stu = StudentTask.currentStudent();
        System.out.println(Thread.currentThread()+" 步骤二，" + stu.getName() + "年龄" + stu.getAge());
        System.out.println(Thread.currentThread()+" 步骤2完成");
    }

    void log() {
        Student stu = StudentTask.currentStudent();
        String grade = stu.getScore() > 60 ? " GOOD!" : " OH NO!";
        System.out.println(Thread.currentThread()+" 步骤三，"+stu.getName() + "的成绩等级为" + grade);
        System.out.println(Thread.currentThread()+" 步骤3完成");
    }
}