我們不從把ThreadLocal源碼直接復(fù)制到這里進(jìn)行挨個(gè)分析，我們把使用列出來(lái)北苟，找出突破點(diǎn)進(jìn)行分析

public static final ThreadLocal<String> mThreadLocal = new ThreadLocal<String>() ;
    public static void main(String[] args) {
        //主線程設(shè)置為false
        mThreadLocal.set("小明") ;
        new Thread("therad--1"){
            public void run() {
                mThreadLocal.set("小紅") ;
                System.out.println("thread--1:" + mThreadLocal.get());
            };
        }.start() ;
        new Thread("therad--2"){
            public void run() {
                mThreadLocal.set("小花") ;
                System.out.println("thread--2:" + mThreadLocal.get());
            };
        }.start() ;
        System.out.println("主線程:" + mThreadLocal.get());
    }

執(zhí)行結(jié)果大家肯定知道棘街，各個(gè)線程有自己各個(gè)線程的打印。但是ThreadLocal這個(gè)類型的變量卻是全局的湖饱，如果ThreadLocal與普通變量一樣，那么久違背了多線程訪問(wèn)共享資源原理,所以從set方法作為切入點(diǎn)

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

ThreadLocalMap getMap(Thread t) {
    return t.threadLocals;//ThreadLocal.ThreadLocalMap threadLocals = null;這個(gè)變量是Thread內(nèi)所有
}

也就是說(shuō)對(duì)應(yīng)Thread內(nèi)部有一個(gè)ThreadLocal.ThreadLocalMap杀捻，設(shè)置值是拿到當(dāng)前線程井厌，然后設(shè)置對(duì)應(yīng)的值入map中

private void set(ThreadLocal<?> key, Object value) {
    Entry[] tab = table;
    int len = tab.length;
    int i = key.threadLocalHashCode & (len-1);//得到對(duì)應(yīng)下標(biāo)，每一個(gè)線程都有自己的key致讥，這個(gè)i是一定的
    //遍歷下表然后挨個(gè)進(jìn)行查找對(duì)比
    for (Entry e = tab[i];
         e != null;
         e = tab[i = nextIndex(i, len)]) {
        ThreadLocal<?> k = e.get();
        //覆蓋式操作
        if (k == key) {
            e.value = value;
            return;
        }
        //當(dāng)key為空也就是之前并沒(méi)有這個(gè)元素
        if (k == null) {
            replaceStaleEntry(key, value, i);
            return;
        }
    }
    //生成這個(gè)元素&添加到列表中
    tab[i] = new Entry(key, value);
    int sz = ++size;
    //如果超過(guò)對(duì)應(yīng)size則進(jìn)行rehash操作
    if (!cleanSomeSlots(i, sz) && sz >= threshold)
        rehash();
}

這里需要注意初始容量是16：
private static final int INITIAL_CAPACITY = 16;具體操作是set的時(shí)候如果沒(méi)有創(chuàng)建ThreadLocalMap則進(jìn)行創(chuàng)建構(gòu)造中設(shè)置值

ThreadLocalMap(ThreadLocal<?> firstKey, Object firstValue) {
    table = new Entry[INITIAL_CAPACITY];
    int i = firstKey.threadLocalHashCode & (INITIAL_CAPACITY - 1);
    table[i] = new Entry(firstKey, firstValue);
    size = 1;
    setThreshold(INITIAL_CAPACITY);//16
}

這個(gè)時(shí)候我們就將值放入了對(duì)應(yīng)集合

public T get() {
    Thread t = Thread.currentThread();
    ThreadLocalMap map = getMap(t);//得到對(duì)應(yīng)線程內(nèi)的對(duì)應(yīng)map
    if (map != null) {
        ThreadLocalMap.Entry e = map.getEntry(this);//得到Entry
        if (e != null) {
            @SuppressWarnings("unchecked")
            T result = (T)e.value;
            return result;
        }
    }
    return setInitialValue();//當(dāng)沒(méi)有找到值也就是說(shuō)沒(méi)有設(shè)置值仅仆，然后要找值就進(jìn)行初始化
}