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Java > Open Source Codes > org > apache > ojb > broker > accesslayer > PkEnumeration


1 package org.apache.ojb.broker.accesslayer;
2
3 /* Copyright 2002-2005 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.lang.reflect.Constructor JavaDoc;
19 import java.sql.SQLException JavaDoc;
20 import java.util.Enumeration JavaDoc;
21 import java.util.NoSuchElementException JavaDoc;
22
23 import org.apache.ojb.broker.Identity;
24 import org.apache.ojb.broker.PersistenceBroker;
25 import org.apache.ojb.broker.PersistenceBrokerException;
26 import org.apache.ojb.broker.PersistenceBrokerSQLException;
27 import org.apache.ojb.broker.metadata.ClassDescriptor;
28 import org.apache.ojb.broker.metadata.FieldDescriptor;
29 import org.apache.ojb.broker.query.Query;
30 import org.apache.ojb.broker.util.ConstructorHelper;
31 import org.apache.ojb.broker.util.logging.LoggerFactory;
32
33 /**
34  * this class can be used to create enumerations of PrimaryKey objects.
35  * This is interesting for EJB finder methods
36  * in BMP entity beans which must return such enumerations.
37  * @author Thomas Mahler
38  * @version $Id: PkEnumeration.java,v 1.17.2.3 2005/12/21 22:22:59 tomdz Exp $
39  */
40 public class PkEnumeration implements Enumeration JavaDoc
41 {
42     static final long serialVersionUID = -834955711995869884L;
43     protected boolean hasCalledCheck = false;
44     protected boolean hasNext = false;
45
46     protected PersistenceBroker broker;
47
48     /**
49      * The underlying jdbc resultset produced by select statement
50      */
51     protected ResultSetAndStatement resultSetAndStatment;
52
53     /**
54      * descriptor for the class of which items are to be found
55      */
56     protected ClassDescriptor classDescriptor;
57
58     /**
59      * the Constructor that is needed to build the PrimaryKey Objects
60      */
61     protected Constructor JavaDoc constructor;
62
63     /**
64      * PkEnumeration constructor.
65      * @param query the SELECT statement gerating the underlying resultset
66      * @param cld classDescriptor of the target entity class (say Article)
67      * @param primaryKeyClass the entity classes PrimaryKey class (say ArticleKey).
68      * this key-class MUST have a constructor with one argument of type org.apache.ojb.broker.Identity !
69      */
70     public PkEnumeration(Query query, ClassDescriptor cld, Class JavaDoc primaryKeyClass, PersistenceBroker broker)
71     {
72         this.resultSetAndStatment = broker.serviceJdbcAccess().executeQuery(query, cld);
73         this.classDescriptor = cld;
74         this.broker = broker;
75         // get a contructor object that can be used to build instances of class primaryKeyClass
76 try
77         {
78             Class JavaDoc[] argArray = {Identity.class};
79             this.constructor = primaryKeyClass.getConstructor(argArray);
80         }
81         catch (NoSuchMethodException JavaDoc e)
82         {
83             LoggerFactory.getDefaultLogger().error(primaryKeyClass.getName()
84                     + " must implement a Constructor with one argument of type org.apache.ojb.broker.Identity");
85             throw new PersistenceBrokerException(e);
86         }
87         catch (SecurityException JavaDoc e)
88         {
89             LoggerFactory.getDefaultLogger().error(e);
90             throw new PersistenceBrokerException(e);
91         }
92     }
93
94     /**
95      * returns an Identity object representing the current resultset row
96      */
97     private Identity getIdentityFromResultSet()
98     {
99
100         try
101         {
102             // 1. get an empty instance of the target class
103 Constructor JavaDoc con = classDescriptor.getZeroArgumentConstructor();
104             Object JavaDoc obj = ConstructorHelper.instantiate(con);
105
106             // 2. fill only primary key values from Resultset
107 Object JavaDoc colValue;
108             FieldDescriptor fld;
109             FieldDescriptor[] pkfields = classDescriptor.getPkFields();
110             for (int i = 0; i < pkfields.length; i++)
111             {
112                 fld = pkfields[i];
113                 colValue = fld.getJdbcType().getObjectFromColumn(resultSetAndStatment.m_rs, fld.getColumnName());
114                 fld.getPersistentField().set(obj, colValue);
115             }
116             // 3. return the representing identity object
117 return broker.serviceIdentity().buildIdentity(classDescriptor, obj);
118         }
119         catch (SQLException JavaDoc e)
120         {
121             throw new PersistenceBrokerSQLException("Error reading object from column", e);
122         }
123         catch (Exception JavaDoc e)
124         {
125             throw new PersistenceBrokerException("Error reading Identity from result set", e);
126         }
127     }
128
129     /**
130      * Tests if this enumeration contains more elements.
131      * @return <code>true</code> if and only if this enumeration object
132      * contains at least one more element to provide;
133      * <code>false</code> otherwise.
134      */
135     public boolean hasMoreElements()
136     {
137         try
138         {
139             if (!hasCalledCheck)
140             {
141                 hasCalledCheck = true;
142                 hasNext = resultSetAndStatment.m_rs.next();
143             }
144         }
145         catch (SQLException JavaDoc e)
146         {
147             LoggerFactory.getDefaultLogger().error(e);
148             //releaseDbResources();
149 hasNext = false;
150         }
151         finally
152         {
153             if(!hasNext)
154             {
155                 releaseDbResources();
156             }
157         }
158         return hasNext;
159     }
160
161     private void releaseDbResources()
162     {
163         resultSetAndStatment.close();
164         resultSetAndStatment = null;
165     }
166
167     /**
168      * Returns the next element of this enumeration if this enumeration
169      * object has at least one more element to provide.
170      * @return the next element of this enumeration.
171      * @exception NoSuchElementException if no more elements exist.
172      */
173     public Object JavaDoc nextElement()
174     {
175         try
176         {
177             if (!hasCalledCheck)
178             {
179                 hasMoreElements();
180             }
181             hasCalledCheck = false;
182             if (hasNext)
183             {
184                 Identity oid = getIdentityFromResultSet();
185                 Identity[] args = {oid};
186                 return this.constructor.newInstance(args);
187             }
188             else
189                 throw new NoSuchElementException JavaDoc();
190         }
191         catch (Exception JavaDoc ex)
192         {
193             LoggerFactory.getDefaultLogger().error(ex);
194             throw new NoSuchElementException JavaDoc();
195         }
196     }
197
198     /**
199      * protection just in case someone leaks.
200      */
201     protected void finalize()
202     {
203         if(resultSetAndStatment != null)
204         {
205             LoggerFactory.getDefaultLogger().error("["+PkEnumeration.class.getName()+"] Found unclosed resources while finalize");
206             releaseDbResources();
207         }
208     }
209 }
210
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