ResultSetDynaClass


1   /*
2    * Copyright 2001-2004 The Apache Software Foundation.
3    * 
4    * Licensed under the Apache License, Version 2.0 (the "License");
5    * you may not use this file except in compliance with the License.
6    * You may obtain a copy of the License at
7    * 
8    *      http://www.apache.org/licenses/LICENSE-2.0
9    * 
10   * Unless required by applicable law or agreed to in writing, software
11   * distributed under the License is distributed on an "AS IS" BASIS,
12   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13   * See the License for the specific language governing permissions and
14   * limitations under the License.
15   */
16  
17  
18  package org.apache.commons.beanutils;
19  
20  
21  import java.sql.ResultSet  ;
22  import java.sql.SQLException  ;
23  import java.util.HashMap  ;
24  import java.util.Iterator  ;
25  
26  
27  /**
28   * <p>Implementation of <code>DynaClass</code> for DynaBeans that wrap the
29   * <code>java.sql.Row</code> objects of a <code>java.sql.ResultSet</code>.
30   * The normal usage pattern is something like:</p>
31   * <pre>
32   *   ResultSet rs = ...;
33   *   ResultSetDynaClass rsdc = new ResultSetDynaClass(rs);
34   *   Iterator rows = rsdc.iterator();
35   *   while (rows.hasNext())  {
36   *     DynaBean row = (DynaBean) rows.next();
37   *     ... process this row ...
38   *   }
39   *   rs.close();
40   * </pre>
41   *
42   * <p>Each column in the result set will be represented as a DynaBean
43   * property of the corresponding name (optionally forced to lower case
44   * for portability).</p>
45   *
46   * <p><strong>WARNING</strong> - Any {@link DynaBean} instance returned by
47   * this class, or from the <code>Iterator</code> returned by the
48   * <code>iterator()</code> method, is directly linked to the row that the
49   * underlying result set is currently positioned at.  This has the following
50   * implications:</p>
51   * <ul>
52   * <li>Once you retrieve a different {@link DynaBean} instance, you should
53   *     no longer use any previous instance.</li>
54   * <li>Changing the position of the underlying result set will change the
55   *     data that the {@link DynaBean} references.</li>
56   * <li>Once the underlying result set is closed, the {@link DynaBean}
57   *     instance may no longer be used.</li>
58   * </ul>
59   *
60   * <p>Any database data that you wish to utilize outside the context of the
61   * current row of an open result set must be copied.  For example, you could
62   * use the following code to create standalone copies of the information in
63   * a result set:</p>
64   * <pre>
65   *   ArrayList results = new ArrayList(); // To hold copied list
66   *   ResultSetDynaClass rsdc = ...;
67   *   DynaProperty properties[] = rsdc.getDynaProperties();
68   *   BasicDynaClass bdc =
69   *     new BasicDynaClass("foo", BasicDynaBean.class,
70   *                        rsdc.getDynaProperties());
71   *   Iterator rows = rsdc.iterator();
72   *   while (rows.hasNext()) {
73   *     DynaBean oldRow = (DynaBean) rows.next();
74   *     DynaBean newRow = bdc.newInstance();
75   *     PropertyUtils.copyProperties(newRow, oldRow);
76   *     results.add(newRow);
77   *   }
78   * </pre>
79   *
80   * @author Craig R. McClanahan
81   * @version $Revision: 1.15 $ $Date: 2004/02/28 13:18:33 $
82   */
83  
84  public class ResultSetDynaClass extends JDBCDynaClass implements DynaClass {
85  
86  
87      // ----------------------------------------------------------- Constructors
88  
89  
90      /**
91       * <p>Construct a new ResultSetDynaClass for the specified
92       * <code>ResultSet</code>.  The property names corresponding
93       * to column names in the result set will be lower cased.</p>
94       *
95       * @param resultSet The result set to be wrapped
96       *
97       * @exception NullPointerException if <code>resultSet</code>
98       *  is <code>null</code>
99       * @exception SQLException if the metadata for this result set
100      *  cannot be introspected
101      */
102     public ResultSetDynaClass(ResultSet   resultSet) throws SQLException   {
103 
104         this(resultSet, true);
105 
106     }
107 
108 
109     /**
110      * <p>Construct a new ResultSetDynaClass for the specified
111      * <code>ResultSet</code>.  The property names corresponding
112      * to the column names in the result set will be lower cased or not,
113      * depending on the specified <code>lowerCase</code> value.</p>
114      *
115      * <p><strong>WARNING</strong> - If you specify <code>false</code>
116      * for <code>lowerCase</code>, the returned property names will
117      * exactly match the column names returned by your JDBC driver.
118      * Because different drivers might return column names in different
119      * cases, the property names seen by your application will vary
120      * depending on which JDBC driver you are using.</p>
121      *
122      * @param resultSet The result set to be wrapped
123      * @param lowerCase Should property names be lower cased?
124      *
125      * @exception NullPointerException if <code>resultSet</code>
126      *  is <code>null</code>
127      * @exception SQLException if the metadata for this result set
128      *  cannot be introspected
129      */
130     public ResultSetDynaClass(ResultSet   resultSet, boolean lowerCase)
131         throws SQLException   {
132 
133         if (resultSet == null) {
134             throw new NullPointerException  ();
135         }
136         this.resultSet = resultSet;
137         this.lowerCase = lowerCase;
138         introspect(resultSet);
139 
140     }
141 
142 
143     // ----------------------------------------------------- Instance Variables
144 
145 
146     /**
147      * <p>The <code>ResultSet</code> we are wrapping.</p>
148      */
149     protected ResultSet   resultSet = null;
150 
151 
152     // --------------------------------------------------------- Public Methods
153 
154 
155     /**
156      * <p>Return an <code>Iterator</code> of {@link DynaBean} instances for
157      * each row of the wrapped <code>ResultSet</code>, in "forward" order.
158      * Unless the underlying result set supports scrolling, this method
159      * should be called only once.</p>
160      */
161     public Iterator   iterator() {
162 
163         return (new ResultSetIterator(this));
164 
165     }
166 
167 
168     // -------------------------------------------------------- Package Methods
169 
170 
171     /**
172      * <p>Return the result set we are wrapping.</p>
173      */
174     ResultSet   getResultSet() {
175 
176         return (this.resultSet);
177 
178     }
179 
180 
181     // ------------------------------------------------------ Protected Methods
182     
183     /**
184      * <p>Loads the class of the given name which by default uses the class loader used 
185      * to load this library.
186      * Dervations of this class could implement alternative class loading policies such as
187      * using custom ClassLoader or using the Threads's context class loader etc.
188      * </p>
189      */        
190     protected Class   loadClass(String   className) throws SQLException   {
191 
192         try {
193             return getClass().getClassLoader().loadClass(className);
194         } 
195         catch (Exception   e) {
196             throw new SQLException  ("Cannot load column class '" +
197                                    className + "': " + e);
198         }
199     }
200 }
201
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