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1   /* Copyright 2004, 2005 Acegi Technology Pty Limited
2    *
3    * Licensed under the Apache License, Version 2.0 (the "License");
4    * you may not use this file except in compliance with the License.
5    * You may obtain a copy of the License at
6    *
7    *     http://www.apache.org/licenses/LICENSE-2.0
8    *
9    * Unless required by applicable law or agreed to in writing, software
10   * distributed under the License is distributed on an "AS IS" BASIS,
11   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
12   * See the License for the specific language governing permissions and
13   * limitations under the License.
14   */
15  
16  package org.acegisecurity.context;
17  
18  import org.springframework.util.Assert;
19  
20  
21  /***
22   * Associates a given {@link SecurityContext} with the current execution
23   * thread and any new threads the current execution thread may spawn.
24   * 
25   * <p>
26   * To guarantee that {@link #getContext()} never returns <code>null</code>, this
27   * class defaults to returning <code>SecurityContextImpl</code> if no
28   * <code>SecurityContext</code> has ever been associated with the current
29   * thread of execution. Despite this behaviour, in general another class will
30   * select the concrete <code>SecurityContext</code> implementation to use and
31   * expressly set an instance of that implementation against the
32   * <code>SecurityContextHolder</code>.
33   * </p>
34   *
35   * @author Ben Alex
36   * @version $Id: SecurityContextHolder.java,v 1.4 2005/11/17 00:55:49 benalex Exp $
37   *
38   * @see java.lang.ThreadLocal
39   * @see org.acegisecurity.context.HttpSessionContextIntegrationFilter
40   */
41  public class SecurityContextHolder {
42      //~ Static fields/initializers =============================================
43  
44      private static ThreadLocal contextHolder = new ThreadLocal();
45  
46      //~ Methods ================================================================
47  
48      /***
49       * Associates a new <code>SecurityContext</code> with the current thread of
50       * execution.
51       *
52       * @param context the new <code>SecurityContext</code> (may not be
53       *        <code>null</code>)
54       */
55      public static void setContext(SecurityContext context) {
56          Assert.notNull(context,
57              "Only non-null SecurityContext instances are permitted");
58          contextHolder.set(context);
59      }
60  
61      /***
62       * Obtains the <code>SecurityContext</code> associated with the current
63       * thread of execution. If no <code>SecurityContext</code> has been
64       * associated with the current thread of execution, a new instance of
65       * {@link SecurityContextImpl} is associated with the current thread and
66       * then returned.
67       *
68       * @return the current <code>SecurityContext</code> (guaranteed to never be
69       *         <code>null</code>)
70       */
71      public static SecurityContext getContext() {
72          if (contextHolder.get() == null) {
73              contextHolder.set(new SecurityContextImpl());
74          }
75  
76          return (SecurityContext) contextHolder.get();
77      }
78  }