set方法:

    public void set(T value) {
    	// 获取当前的线程
        Thread t = Thread.currentThread();
        // 将当前的线程传递到getMap(Thread t)中
        ThreadLocalMap map = getMap(t);
        if (map != null)
            map.set(this, value);
        else
            createMap(t, value);
    }

getMap(Thread t)方法:

	ThreadLocalMap getMap(Thread t) {
		// 这里就是隔离的真相了,是放到【当前】线程的 threadLocals 变量中。划重点:【当前】
        return t.threadLocals;
    }

这里出现一个新的对象 ThreadLocalMap，下面看下ThreadLocalMap是做什么用的 

	static class ThreadLocalMap {
		//
        static class Entry extends WeakReference<ThreadLocal<?>> {
            /** The value associated with this ThreadLocal. */
            Object value;

            Entry(ThreadLocal<?> k, Object v) {
            	// k当前ThreadLocal本身
                super(k);
 				// 这里super的super是 Reference 抽象类
                value = v;
            }
        }

        private static final int INITIAL_CAPACITY = 16;

        private Entry[] table;

        private int size = 0;

        private int threshold; // Default to 0

        private void setThreshold(int len) {
            threshold = len * 2 / 3;
        }

        // 这里是 ThreadLocal 存值的方法
        // 这里的key是ThreadLocal自己本身this,value是真正要存储的值
        private void set(ThreadLocal<?> key, Object value) {
			// ThreadLocal基础结构是Entry[]数组
			// 这里虽然是Entry[]数组,但是设置值只是用了一个位置(槽)
            Entry[] tab = table;
 			//将当前ThreadLocal中的table给临时变量
            int len = tab.length;
 			// 当前表的长度
            int i = key.threadLocalHashCode & (len-1);

				

			// 这段代码主要是检测是否已经设置值，如果有值,已经设置了，就覆盖掉
            for (Entry e = tab[i];
                 e != null;
                 e = tab[i = nextIndex(i, len)]) {
                ThreadLocal<?> k = e.get();

                if (k == key) {
                    e.value = value;
                    // 直接结束该方法
                    return;
                }

                if (k == null) {
                    replaceStaleEntry(key, value, i);
                    // 直接结束该方法                    
                    return;
                }
            }

			// 如果之前没有覆盖值,直接赋新值
			// new Entry(key,value)中的key是ThreadLocal自己本身this,value是真正要存储的值
            tab[i] = new Entry(key, value);
            int sz = ++size;
 			// size大小自增
            // 如果超过大小,需要直接rehash,重新计算位置
            if (!cleanSomeSlots(i, sz) && sz >= threshold)
                rehash();
        }

        private void remove(ThreadLocal<?> key) {
            Entry[] tab = table;
            int len = tab.length;
            int i = key.threadLocalHashCode & (len-1);
            // 这段代码和set的一致,这里如果都满足,直接clear掉
            for (Entry e = tab[i];
                 e != null;
                 e = tab[i = nextIndex(i, len)]) {
                if (e.get() == key) {
                	// 这里的e是Reference的子类,因为Entry是继承 WeakReference 类的
                	// WeakReference 类又继承抽象类 Reference
                    e.clear();
                    expungeStaleEntry(i);
                    return;
                }
            }
        }
        
        private boolean cleanSomeSlots(int i, int n) {
            boolean removed = false;
            Entry[] tab = table;
            int len = tab.length;
            do {
                i = nextIndex(i, len);
                Entry e = tab[i];
                if (e != null && e.get() == null) {
                    n = len;
                    removed = true;
                    i = expungeStaleEntry(i);
                }
            } while ( (n >>>= 1) != 0);
            return removed;
        }

        private void rehash() {
            expungeStaleEntries();

            // Use lower threshold for doubling to avoid hysteresis
            if (size >= threshold - threshold / 4)
                resize();
        }

		
		// 重新resize下
        private void resize() {
            Entry[] oldTab = table;
            int oldLen = oldTab.length;
            int newLen = oldLen * 2;
            Entry[] newTab = new Entry[newLen];
            int count = 0;

            for (int j = 0; j < oldLen; ++j) {
                Entry e = oldTab[j];
                if (e != null) {
                    ThreadLocal<?> k = e.get();
                    if (k == null) {
                        e.value = null; // Help the GC
                    } else {
                        int h = k.threadLocalHashCode & (newLen - 1);
                        while (newTab[h] != null)
                            h = nextIndex(h, newLen);
                        newTab[h] = e;
                        count++;
                    }
                }
            }

            setThreshold(newLen);
            size = count;
            table = newTab;
        }


		// 清理旧的Entry
        private void expungeStaleEntries() {
            Entry[] tab = table;
            int len = tab.length;
            for (int j = 0; j < len; j++) {
                Entry e = tab[j];
                if (e != null && e.get() == null)
                    expungeStaleEntry(j);
            }
        }
    }

下面都是ThreadLocal中的对象

private final int threadLocalHashCode = nextHashCode();

// 这里获取原子类的下一个
private static int nextHashCode() {
	return nextHashCode.getAndAdd(HASH_INCREMENT);
}

// 这里采用了原子类
private static AtomicInteger nextHashCode =
 new AtomicInteger();

Reference类中的clear方法:

public void clear() {
	this.referent = null;
}