ControlThreadContext


1   package org.apache.beehive.controls.api.context;
2   /*
3    * Copyright 2004 The Apache Software Foundation.
4    *
5    * Licensed under the Apache License, Version 2.0 (the "License");
6    * you may not use this file except in compliance with the License.
7    * You may obtain a copy of the License at
8    * 
9    *     http://www.apache.org/licenses/LICENSE-2.0
10   * 
11   * Unless required by applicable law or agreed to in writing, software
12   * distributed under the License is distributed on an "AS IS" BASIS,
13   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
14   * See the License for the specific language governing permissions and
15   * limitations under the License.
16   *
17   * $Header:$
18   */
19  
20  import java.util.Stack  ;
21  
22  /**
23   * The ControlThreadContext class manages the association between ControlContainerContexts 
24   * and threads of execution.   For a given thread of execution, the beginning and ending of
25   * contexts will always be nested (never interleaved), so each thread will maintain its own 
26   * stack of currently executing contexts.  This can be used to reassociate with the current 
27   * active context.
28   */
29  public class ControlThreadContext
30  {
31      /**
32       * This thread local maintains a per-thread stack of ControlContainerContext instances.
33       */
34      static private ThreadLocal  <Stack  <ControlContainerContext>> _threadContexts = 
35                                              new ThreadLocal  <Stack  <ControlContainerContext>>(); 
36  
37      /**
38       * Returns the active ControlContainerContext for the current thread, or null if no
39       * context is currently active.
40       * @return the current active ControlContainerContext
41       */ 
42      public static ControlContainerContext getContext() 
43      {
44          Stack  <ControlContainerContext> contextStack = _threadContexts.get();
45          if (contextStack == null || contextStack.size() == 0)
46              return null;
47  
48          return contextStack.peek();
49      }
50  
51      /**
52       * Defines the beginning of a new control container execution context.
53       */
54      public static void beginContext(ControlContainerContext context)
55      {
56          Stack  <ControlContainerContext> contextStack = _threadContexts.get();
57          if (contextStack == null)
58          {
59              contextStack = new Stack  <ControlContainerContext>();
60              _threadContexts.set(contextStack);
61          }
62          contextStack.push(context);
63      }
64  
65      /**
66       * Ends the current control container execution context
67       * @throws IllegalStateExeption if there is not current active context or it is not
68       *         the requested context. 
69       */
70      public static void endContext(ControlContainerContext context)
71      {
72          Stack  <ControlContainerContext> contextStack = _threadContexts.get();
73          if (contextStack == null || contextStack.size() == 0)
74              throw new IllegalStateException  ("No context started for current thread");
75  
76          if (contextStack.peek() != context)
77              throw new IllegalStateException  ("Context is not the current active context");
78  
79          contextStack.pop();
80      }
81  }
82
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