ThreadLocalStack


1   package com.tonbeller.wcf.controller;
2   
3   import java.util.Stack  ;
4   
5   /**
6    * Maintains a stack in a ThreadLocal. If the stack is empty, the ThreadLocal is cleared,
7    * so there is no memory leak.
8    * <p/>
9    * Implementation note: its not necessary to synchronize because every Thread
10   * uses its own instance of the java.util.Stack. 
11   * 
12   * @author av
13   * @since Sep 12, 2005
14   */
15  class ThreadLocalStack {
16    ThreadLocal   tl = new ThreadLocal  ();
17  
18    public void push(Object   obj) {
19      Stack   stack = (Stack  ) tl.get();
20      if (stack == null) {
21        stack = new Stack  ();
22        tl.set(stack);
23      }
24      stack.push(obj);
25    }
26  
27    /**
28     * @param failIfEmpty if true, an EmptyThreadLocalStackException is thrown
29     * when called on an empty stack. If false, null is returned for an empty stack.
30     */
31    public Object   peek(boolean failIfEmpty) throws EmptyThreadLocalStackException {
32      Stack   stack = (Stack  ) tl.get();
33      if (stack == null || stack.isEmpty()) {
34        if (failIfEmpty)
35          throw new EmptyThreadLocalStackException();
36        return null;
37      }
38      return stack.peek();
39    }
40  
41  
42    public void pop() {
43      Stack   stack = (Stack  ) tl.get();
44      if (stack == null || stack.isEmpty())
45        throw new EmptyThreadLocalStackException();
46      stack.pop();
47      if (stack.isEmpty())
48        tl.set(null);
49    }
50  
51  }
52

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