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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *   http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing,
13   * software distributed under the License is distributed on an
14   * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
15   * KIND, either express or implied.  See the License for the
16   * specific language governing permissions and limitations
17   * under the License.
18   */
19  package org.apache.myfaces.orchestra.conversation.spring;
20  
21  import org.springframework.orm.jpa.EntityManagerHolder;
22  import org.springframework.transaction.support.TransactionSynchronizationManager;
23  
24  import javax.persistence.EntityManager;
25  import javax.persistence.EntityManagerFactory;
26  import javax.persistence.FlushModeType;
27  import java.util.Stack;
28  
29  /**
30   * A factory for PersistenceContext objects which integrates with Spring's JPA
31   * support.
32   * <p>
33   * When a bean is invoked which is associated with a conversation, but the conversation
34   * does not yet have a PersistenceContext, then this factory is used to create a
35   * PersistenceContext.
36   * <p>
37   * The returned object knows how to configure itself as the "current persistence context"
38   * within Spring when a method on that bean is invoked, and how to restore the earlier
39   * "current persistence context" after the method returns.
40   */
41  public class JpaPersistenceContextFactory implements PersistenceContextFactory
42  {
43      private EntityManagerFactory entityManagerFactory;
44  
45      public PersistenceContext create()
46      {
47          final EntityManager em = entityManagerFactory.createEntityManager();
48          em.setFlushMode(FlushModeType.COMMIT);
49  
50          return new PersistenceContext()
51          {
52              private final Stack bindings = new Stack();
53  
54              // Store the current EntityManagerHolder on a stack, then install our own as the
55              // current EntityManagerHolder. Storing the old one allows us to restore it when
56              // this context is "unbound".
57              //
58              // Orchestra calls bind every time a method is invoked on a bean which has
59              // a conversation with a persistence context. The unbind is invoked when the
60              // invoked method on that bean returns.
61              //
62              // When a bean has a property that has been annotated as @PersistenceContext,
63              // Spring injects a proxy that looks up the "current" persistence context whenever
64              // a method is invoked on it. Because Orchestra has called persistencecontext.bind
65              // when the bean was first entered, and this object's bind method has installed
66              // itself as the "current" spring persistence context object, the bean sees the
67              // persistence context that is associated with its conversation.
68              //
69              // TODO: what happens when a bean invokes a method on itself? Does bind get called
70              // again? If so, then this implementation is inefficient as it will push itself
71              // onto the stack over and over again. This could be optimised by checking whether
72              // this is the current context, and if so just incrementing a counter rather than
73              // pushing onto a stack...
74              public void bind()
75              {
76                  synchronized(bindings)
77                  {
78                      EntityManagerHolder current = (EntityManagerHolder)
79                          TransactionSynchronizationManager.getResource(entityManagerFactory);
80  
81                      if (current != null)
82                      {
83                          TransactionSynchronizationManager.unbindResource(entityManagerFactory);
84                      }
85  
86                      bindings.push(current);
87  
88                      TransactionSynchronizationManager.bindResource(entityManagerFactory,
89                          new EntityManagerHolder(em));
90                  }
91              }
92  
93              public void unbind()
94              {
95                  synchronized(bindings)
96                  {
97                      if (TransactionSynchronizationManager.hasResource(entityManagerFactory))
98                      {
99                          TransactionSynchronizationManager.unbindResource(entityManagerFactory);
100                     }
101 
102                     Object holder = null;
103                     if (bindings.size() > 0)
104                     {
105                         holder = bindings.pop();
106                     }
107                     if (holder != null)
108                     {
109                         TransactionSynchronizationManager.bindResource(entityManagerFactory,
110                             holder);
111                     }
112                 }
113             }
114 
115             public void close()
116             {
117                 em.close();
118             }
119         };
120     }
121 
122     public EntityManagerFactory getEntityManagerFactory()
123     {
124         return entityManagerFactory;
125     }
126 
127     public void setEntityManagerFactory(EntityManagerFactory entityManagerFactory)
128     {
129         this.entityManagerFactory = entityManagerFactory;
130     }
131 }