1 /*
2 * Licensed to the Apache Software Foundation (ASF) under one or more
3 * contributor license agreements. See the NOTICE file distributed with
4 * this work for additional information regarding copyright ownership.
5 * The ASF licenses this file to You under the Apache License, Version 2.0
6 * (the "License"); you may not use this file except in compliance with
7 * the License. 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 package org.apache.commons.dbutils.handlers;
18
19 import java.sql.ResultSet;
20 import java.sql.SQLException;
21
22 import org.apache.commons.dbutils.ResultSetHandler;
23
24 /**
25 * {@code ResultSetHandler} implementation that converts one
26 * {@code ResultSet} column into an Object. This class is thread safe.
27 *
28 * @param <T> The type of the scalar
29 * @see org.apache.commons.dbutils.ResultSetHandler
30 */
31 public class ScalarHandler<T> implements ResultSetHandler<T> {
32
33 /**
34 * The column number to retrieve.
35 */
36 private final int columnIndex;
37
38 /**
39 * The column name to retrieve. Either columnName or columnIndex
40 * will be used but never both.
41 */
42 private final String columnName;
43
44 /**
45 * Creates a new instance of ScalarHandler. The first column will
46 * be returned from {@code handle()}.
47 */
48 public ScalarHandler() {
49 this(1, null);
50 }
51
52 /**
53 * Creates a new instance of ScalarHandler.
54 *
55 * @param columnIndex The index of the column to retrieve from the
56 * {@code ResultSet}.
57 */
58 public ScalarHandler(final int columnIndex) {
59 this(columnIndex, null);
60 }
61
62 /** Helper constructor
63 * @param columnIndex The index of the column to retrieve from the
64 * {@code ResultSet}.
65 * @param columnName The name of the column to retrieve from the
66 * {@code ResultSet}.
67 */
68 private ScalarHandler(final int columnIndex, final String columnName) {
69 this.columnIndex = columnIndex;
70 this.columnName = columnName;
71 }
72
73 /**
74 * Creates a new instance of ScalarHandler.
75 *
76 * @param columnName The name of the column to retrieve from the
77 * {@code ResultSet}.
78 */
79 public ScalarHandler(final String columnName) {
80 this(1, columnName);
81 }
82
83 /**
84 * Returns one {@code ResultSet} column as an object via the
85 * {@code ResultSet.getObject()} method that performs type
86 * conversions.
87 * @param resultSet {@code ResultSet} to process.
88 * @return The column or {@code null} if there are no rows in
89 * the {@code ResultSet}.
90 *
91 * @throws SQLException if a database access error occurs
92 * @throws ClassCastException if the class datatype does not match the column type
93 *
94 * @see org.apache.commons.dbutils.ResultSetHandler#handle(java.sql.ResultSet)
95 */
96 // We assume that the user has picked the correct type to match the column
97 // so getObject will return the appropriate type and the cast will succeed.
98 @SuppressWarnings("unchecked")
99 @Override
100 public T handle(final ResultSet resultSet) throws SQLException {
101
102 if (resultSet.next()) {
103 if (this.columnName == null) {
104 return (T) resultSet.getObject(this.columnIndex);
105 }
106 return (T) resultSet.getObject(this.columnName);
107 }
108 return null;
109 }
110 }