ThreadLocal源码

public T get() {
        // 获取当前线程
        Thread t = Thread.currentThread();
        // 获取当前线程获取ThreadLocalMap对象
        ThreadLocalMap map = getMap(t);
        if (map != null) {
            // 根据threadLocal对象从map中获取Entry对象
            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;
    }

    private T setInitialValue() {
        T value = initialValue();
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null) {
            map.set(this, value);
        } else {
            createMap(t, value);
        }
        if (this instanceof TerminatingThreadLocal) {
            TerminatingThreadLocal.register((TerminatingThreadLocal<?>) this);
        }
        return value;
    }

    void createMap(Thread t, T firstValue) {
        t.threadLocals = new ThreadLocalMap(this, firstValue);
    }


    static class ThreadLocalMap {
        static class Entry extends WeakReference<ThreadLocal<?>> {
            Object value;

            Entry(ThreadLocal<?> k, Object v) {
                super(k);
                value = v;
            }
        }
    }