Java中是否有线程组局部变量？

我将在本地线程中存储一个值持有者，并将其初始化为同一组所有线程的相同值持有者。

 public class ThreadGroupLocal<T> extends ThreadLocal<ValueHolder> {     private static class ValueHolder {         public Object value;     }     // Weak & Concurrent would be even the better, but Java API wont offer that :(     private static ConcurrentMap<ThreadGroup, ValueHolder> map = new ConcurrentHashMap<ThreadGroup, ValueHolder>;     private static ValueHolder valueHolderForThread(Thread t) {         map.putIfAbsent(t.getThreadGroup(), new ValueHolder());         return map.get(t.getThreadGroup());     }     @Override      protected ValueHolder initialValue() {         return valueHolderForThread(Thread.currentThread());     }     public T getValue() { (T) get().value; }     public void setValue(T value) { get().value = value; } }

然后使用

 ThreadGroupLocal<String> groupLocal = new ThreadGroupLocal<String>(); groupLocal.setValue("foo"); //... String foo = groupLocal.getValue();

确实（期望初始化）的执行与本地线程完全一样。