实现ThreadLocal

public class MyThreadLocal<T> {

    Map<Thread,T> container = Collections.synchronizedMap(new HashMap<Thread, T>());

    public T get(){
        Thread t = Thread.currentThread();
        T value = container.get(t);
        if(null == value&&     !container.containsKey(t)){
            value = initialValue();
            container.put(t,value);
        }
        return value;
    }

    public void set(T value){
        container.put(Thread.currentThread(),value);
    }

    public void remove(){
        container.remove(Thread.currentThread());
    }

    protected T initialValue(){
        return null;
    }

}