• ThreadLocal可以用来存储当前线程的一些数据，每一个Thread对象中，都有一个ThreadLocalMap属性，key为ThreadLocal,vaule为Oject数据，ThreadLocal类中有一个静态内部类ThreadLocalMap，由ThreadLocal和value组成一个弱引用的Entry对象

• set的时候，先获取当前线程对象，将当前ThreadLocal作为key，值为value封装成一个ThreadLocalMap，然后设置进去当前线程Thread中的ThreadLocalMap中

  • public void set(T value) {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null)
        map.set(this, value);
        else
        createMap(t, value);
    }
    
    void createMap(Thread t, T firstValue) {
    	t.threadLocals = new ThreadLocalMap(this, firstValue);
    }
    

• get的时候，将当前ThreadLocal对象作为key，从当前Thread对象ThreadLocalMap中的获取到值

  • public T get() {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null) {
            ThreadLocalMap.Entry e = map.getEntry(this);
            if (e != null) {
                @SuppressWarnings("unchecked")
                T result = (T)e.value;
                return result;
            }
        }
        return setInitialValue();
    }
    
    ThreadLocalMap getMap(Thread t) {
        return t.threadLocals;
    }
    

• 内存泄漏的情况

  • 线程池中的线程一般都是重复利用的，那么该线程中的ThreadLocalMap也一直存在，ThreadLocalMap中的ThreadLocal对象也会一直存在并且不断的增加（用完的不会清楚掉），所以可能会泄露。
  • 每次使用完ThreadLocal都要调用remove()方法清除数据
  • 使用private static

• 使用场景

  • public class Person {
        private ThreadLocal<String> name = new ThreadLocal<>();
        private ThreadLocal<String> location = new ThreadLocal<>();
    
        public String getName() {
            return this.name.get();
        }
    
        public  void setName(String name) {
            this.name.set(name);
        }
    
        public  String getLocation() {
            return this.location.get();
        }
    
        public void setLocation(String location) {
            this.location.set(location);
        }
    }
    
    
    vpublic class ThreadUseTest {
    
        public static void main(String[] args) {
            Person person = new Person();
    
            new Thread(new Runnable() {
                @Override
                public void run() {
                    person.setLocation("guangdong");
                    person.setName("johnbarrowman");
                    try {
                        Thread.sleep(3000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(person.getLocation()+ person.getName());
                }
            }).start();
    
            new Thread(new Runnable() {
                @Override
                public void run() {
                    person.setLocation("guangdong1");
                    person.setName("johnbarrowman1");
                    try {
                        Thread.sleep(3000);
                    } catch (InterruptedException e) {
                        e.printStackTrace();
                    }
                    System.out.println(person.getLocation()+ person.getName());
                }
            }).start();
        }
    }
    
    

Q.E.D.