理解ThreadLocal

跟以前的文章一样，还是先来一个例子。

public class ThreadLocalDemo implements Runnable {

    //创建线程局部变量studentLocal，在后面你会发现用来保存Student对象    private final static ThreadLocal<Student> studentLocal = new ThreadLocal<Student> ();     public static void main(String[] agrs) {        ThreadLocalDemo td = new ThreadLocalDemo();        Thread t1 = new Thread(td, "a");        Thread t2 = new Thread(td, "b");        t1.start();        t2.start();    }     public void run() {        accessStudent();    }     /**     * 示例业务方法，用来测试     */    public void accessStudent() {        //获取当前线程的名字        String currentThreadName = Thread.currentThread().getName();        System.out.println(currentThreadName + " is running!");        //产生一个随机数并打印        Random random = new Random();        int age = random.nextInt(100);        System.out.println("thread " + currentThreadName + " set age to:" + age);        //获取一个Student对象，并将随机数年龄插入到对象属性中        Student student = getStudent();        student.setAge(age);        System.out.println("thread " + currentThreadName + " first read age is:" + student.getAge());        try {            Thread.sleep(500);        }        catch (InterruptedException ex) {            ex.printStackTrace();        }        System.out.println("thread " + currentThreadName + " second read age is:" + student.getAge());    }     protected Student getStudent() {        //获取本地线程变量并强制转换为Student类型        Student student = (Student) studentLocal.get();        //线程首次执行此方法的时候，studentLocal.get()肯定为null        if (student == null) {            //创建一个Student对象，并保存到本地线程变量studentLocal中            student = new Student();            studentLocal.set(student);        }        return student;    }}

 

 

public class Student {    private int age = 0;   //年龄     public int getAge() {        return this.age;    }     public void setAge(int age) {        this.age = age;    }}

  结果：

 

 

 写道

a is running!
b is running!
thread b set age to:35
thread a set age to:69
thread b first read age is:35
thread a first read age is:69
thread a second read age is:69
thread b second read age is:35

 

   结论：ThreadLocal用于解决线程之间数据隔离问题。Synchronized使用同步的方式解决数据的共享。