ThreadLocal详解

ThnreadLocal是一个本地线程副本变量工具类。主要用于将私有线程和该线程存放的副本对象做一个映射，各个线程之间的变量互不干扰，在高并发场景下，可以实现无状态的调用，特别适用于各个线程依赖不通的变量值完成操作的场景。
首先ThreadLocalMap 是Thread中的一个副本变量，ThreadLocalMap 为ThreadLocal中的静态类

public class Thread implements Runnable {
    /* ThreadLocal values pertaining to this thread. This map is maintained
     * by the ThreabdLocal class. */
    ThreadLocal.ThreadLocalMap threadLocals = null;
    /*
     * InheritableThreadLocal values pertaining to this thread. This map is
     * maintained by the InheritableThreadLocal class.
     */
    ThreadLocal.Threa dLocalMap inheritableThreadLocals = null;
}

public class ThreadLocal<T> {
  static class ThreadLocalMap {
      static class Entry extends WeakReference<ThreadLocal<?>> {
            Object value;
            Entry(ThreadLocal<?> k, Object v) {
                super(k);
                value = v;
            }
        }
        private Entry[] table;
  }
}

t中保存一个弱引用Entry数组，Entry作为ThreadLocal的包装类，当ThreadLoca