Classes in this File | Line Coverage | Branch Coverage | Complexity | ||||
AnonymousPersistentField |
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| 1.5555555555555556;1.556 |
1 | package org.apache.ojb.broker.metadata.fieldaccess; | |
2 | ||
3 | /* Copyright 2003-2005 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 | ||
18 | import java.util.Map; | |
19 | ||
20 | import org.apache.commons.collections.map.ReferenceIdentityMap; | |
21 | import org.apache.ojb.broker.metadata.MetadataException; | |
22 | ||
23 | /** | |
24 | * This class handle an anonymous persistent fiels for 1-1 association, | |
25 | * and ojbConcreteClass | |
26 | * @author Houar TINE | |
27 | * @version $Id: AnonymousPersistentField.java,v 1.1 2007-08-24 22:17:35 ewestfal Exp $ | |
28 | */ | |
29 | public class AnonymousPersistentField implements PersistentField | |
30 | { | |
31 | private static final long serialVersionUID = 3989863424358352941L; | |
32 | ||
33 | private transient Map fkCache; | |
34 | private String fieldname; | |
35 | ||
36 | public AnonymousPersistentField(String fieldname) | |
37 | { | |
38 | this.fieldname = fieldname; | |
39 | } | |
40 | ||
41 | public synchronized void set(Object obj, Object value) throws MetadataException | |
42 | { | |
43 | putToFieldCache(obj, value); | |
44 | } | |
45 | ||
46 | public synchronized Object get(Object anObject) throws MetadataException | |
47 | { | |
48 | return getFromFieldCache(anObject); | |
49 | } | |
50 | ||
51 | /* | |
52 | Use ReferenceIdentityMap (with weak key and hard value setting) instead of | |
53 | WeakHashMap to hold anonymous field values. Here is an snip of the mail from Andy Malakov: | |
54 | <snip> | |
55 | I found that usage of database identity in Java produces quite interesting problem in OJB: | |
56 | In my application all persistent Java objects use database identity instead of Java reference identity | |
57 | (i.e. Persistable.equals() is redefined so that two persistent objects are the same if they have the same | |
58 | primary key and top-level class). | |
59 | ||
60 | In OJB, for each field declared in repository there is dedicated instance of AnonymousPersistentField that stores | |
61 | object-to-field-value mapping in WeakHashMap (in fkCache attribute). Despite usage of cache | |
62 | (ObjectCachePerBrokerImpl in my case) it is possible that identical DB objects will end up as different | |
63 | Java objects during retrieval of complex objects. | |
64 | ||
65 | Now imagine what happens when two identical instances are retrieved: | |
66 | 1) | |
67 | When first instance is retrieved it stores its foreign keys in AnonymousPersistentField.fkCache under instance's | |
68 | identity. (happens in RowReaderDefaultImpl.buildWithReflection()) | |
69 | 2) | |
70 | When second object is retrieved and stored in fkCache, first instance is probably still cached | |
71 | [WeakHashMap entries are cleaned up only during GC]. Since keys are identical WeakHashMap only updates entry | |
72 | value and DOES NOT update entry key. | |
73 | 3) | |
74 | If Full GC happens after that moment it will dispose fcCache entry if the FIRST reference becomes | |
75 | soft-referenced only. | |
76 | </snip> | |
77 | */ | |
78 | protected void putToFieldCache(Object key, Object value) | |
79 | { | |
80 | if (key != null) | |
81 | { | |
82 | if (fkCache == null) | |
83 | { | |
84 | fkCache = new ReferenceIdentityMap (ReferenceIdentityMap.WEAK, ReferenceIdentityMap.HARD, true); | |
85 | } | |
86 | if (value != null) | |
87 | fkCache.put(key, value); | |
88 | else | |
89 | fkCache.remove (key); | |
90 | } | |
91 | } | |
92 | ||
93 | protected Object getFromFieldCache(Object key) | |
94 | { | |
95 | return (key != null && fkCache != null) ? fkCache.get(key) : null; | |
96 | } | |
97 | ||
98 | /** | |
99 | * Always returns <tt>null</tt>. | |
100 | * @see PersistentField#getDeclaringClass() | |
101 | */ | |
102 | public Class getDeclaringClass() | |
103 | { | |
104 | return null; | |
105 | } | |
106 | ||
107 | /** | |
108 | * @see PersistentField#getName() | |
109 | */ | |
110 | public String getName() | |
111 | { | |
112 | return fieldname; | |
113 | } | |
114 | ||
115 | /** | |
116 | * Always returns <tt>null</tt>. | |
117 | * @see PersistentField#getType() | |
118 | */ | |
119 | public Class getType() | |
120 | { | |
121 | return null; | |
122 | } | |
123 | ||
124 | /** | |
125 | * Returns <tt>false</tt>. | |
126 | * @see PersistentField#usesAccessorsAndMutators() | |
127 | */ | |
128 | public boolean usesAccessorsAndMutators() | |
129 | { | |
130 | return false; | |
131 | } | |
132 | } |