查看“︁Java ThreadLocal”︁的源代码

= ThreadLocal原理 =
每个Thread中维护了一个<span class="article-label">ThreadLocal.ThreadLocalMap</span>的对象来存储：
* 这个变量默认是null，会在线程第一次调用get方法的时候初始化。
* 这个map维护了ThreadLocal对象与值的映射。<syntaxhighlight lang="java" inline>map.set(this, value);</syntaxhighlight>

<syntaxhighlight lang="java">
    public T get() {
        Thread t = Thread.currentThread();
        ThreadLocalMap map = getMap(t);
        if (map != null) {
            ThreadLocalMap.Entry e = map.getEntry(this);
            if (e != null) {
                @SuppressWarnings("unchecked")
                T result = (T)e.value;
                return result;
            }
        }
        return setInitialValue();
    }
</syntaxhighlight>

<syntaxhighlight lang="java">

    /* ThreadLocal values pertaining to this thread. This map is maintained
     * by the ThreadLocal class. */
    ThreadLocal.ThreadLocalMap threadLocals = null;

    /*
     * InheritableThreadLocal values pertaining to this thread. This map is
     * maintained by the InheritableThreadLocal class.
     */
    ThreadLocal.ThreadLocalMap inheritableThreadLocals = null;
</syntaxhighlight>

<q>
ThreadLocal instance does not keep but provides the access to thread-specific value using itself as a key.
</q>

= WeakReference =
这个map中的key使用了WeakReference，

<syntaxhighlight lang="java">
static class Entry extends WeakReference<ThreadLocal<?>>
</syntaxhighlight>

[[Category:Concurrency]]