Java线程中的ThreadLocal类解读

package org.example.thread;

import org.example.domain.Book;

public class ThreadLocalTest {

    ThreadLocal<Book> localBook = new ThreadLocal<>();

    Book book = new Book();

    public void test() {

        Thread thread = new Thread(new Runnable() {
            @Override
            public void run() {
                localBook.set(book);
                System.out.println(localBook.get());
                localBook.remove();
            }
        });
        thread.start();

        try {
            Thread.sleep(1000);
        } catch (InterruptedException e) {
            throw new RuntimeException(e);
        }
        System.out.println(localBook.get());

        localBook.remove();
    }

    public static void main(String[] arg) {
        ThreadLocalTest localBookTest = new ThreadLocalTest();
        localBookTest.test();
    }
}

    static class ThreadLocalMap {

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

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

        private static final int INITIAL_CAPACITY = 16;

        private Entry[] table;

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

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

    ThreadLocalMap getMap(Thread t) {
        return t.threadLocals;
    }

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

    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();
    }

     public void remove() {
         ThreadLocalMap m = getMap(Thread.currentThread());
         if (m != null) {
             m.remove(this);
         }
     }

        private void remove(ThreadLocal<?> key) {
            Entry[] tab = table;
            int len = tab.length;
            int i = key.threadLocalHashCode & (len-1);
            for (Entry e = tab[i];
                 e != null;
                 e = tab[i = nextIndex(i, len)]) {
                if (e.get() == key) {
                    e.clear();
                    expungeStaleEntry(i);
                    return;
                }
            }
        }