java-ThreadLocal的实现

1.每个线程内部都维护一个ThreadLocalMap。

ThreadLocal.ThreadLocalMap threadLocals = null;

2.

ThreadLocal的set:   

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

set的时候以ThreadLocal为key,放入在线程内部的ThreadLocalMap中。
3.

 <pre name="code" class="java">ThreadLocal的get:

public T get() {
Thread t = Thread.currentThread();
ThreadLocalMap map = getMap(t);
if (map != null) {
ThreadLocalMap.Entry e = map.getEntry(this);
if (e != null)
return (T)e.value;
}
return setInitialValue();
}

get的时候获取线程上的ThreadLocalMap，以 ThreadLocal为key取出value