001    /*
002     * Licensed to the Apache Software Foundation (ASF) under one or more
003     * contributor license agreements.  See the NOTICE file distributed with
004     * this work for additional information regarding copyright ownership.
005     * The ASF licenses this file to You under the Apache License, Version 2.0
006     * (the "License"); you may not use this file except in compliance with
007     * the License.  You may obtain a copy of the License at
008     *
009     *      http://www.apache.org/licenses/LICENSE-2.0
010     *
011     * Unless required by applicable law or agreed to in writing, software
012     * distributed under the License is distributed on an "AS IS" BASIS,
013     * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
014     * See the License for the specific language governing permissions and
015     * limitations under the License.
016     */
017    package org.apache.commons.dbutils.handlers;
018    
019    import java.sql.ResultSet;
020    import java.sql.SQLException;
021    
022    import org.apache.commons.dbutils.ResultSetHandler;
023    
024    /**
025     * <code>ResultSetHandler</code> implementation that converts one
026     * <code>ResultSet</code> column into an Object. This class is thread safe.
027     * 
028     * @see org.apache.commons.dbutils.ResultSetHandler
029     */
030    public class ScalarHandler implements ResultSetHandler {
031    
032        /**
033         * The column number to retrieve.
034         */
035        private final int columnIndex;
036    
037        /**
038         * The column name to retrieve.  Either columnName or columnIndex
039         * will be used but never both.
040         */
041        private final String columnName;
042    
043        /** 
044         * Creates a new instance of ScalarHandler.  The first column will
045         * be returned from <code>handle()</code>.
046         */
047        public ScalarHandler() {
048            this(1, null);
049        }
050    
051        /** 
052         * Creates a new instance of ScalarHandler.
053         * 
054         * @param columnIndex The index of the column to retrieve from the 
055         * <code>ResultSet</code>.
056         */
057        public ScalarHandler(int columnIndex) {
058            this(columnIndex, null);
059        }
060    
061        /** 
062         * Creates a new instance of ScalarHandler.
063         * 
064         * @param columnName The name of the column to retrieve from the 
065         * <code>ResultSet</code>.
066         */
067        public ScalarHandler(String columnName) {
068            this(1, columnName);
069        }
070    
071        // Helper constructor
072        private ScalarHandler(int columnIndex, String columnName){
073            this.columnIndex = columnIndex;
074            this.columnName = columnName;        
075        }
076    
077        /**
078         * Returns one <code>ResultSet</code> column as an object via the
079         * <code>ResultSet.getObject()</code> method that performs type 
080         * conversions.
081         * 
082         * @return The column or <code>null</code> if there are no rows in
083         * the <code>ResultSet</code>.
084         * 
085         * @throws SQLException if a database access error occurs
086         * 
087         * @see org.apache.commons.dbutils.ResultSetHandler#handle(java.sql.ResultSet)
088         */
089        public Object handle(ResultSet rs) throws SQLException {
090    
091            if (rs.next()) {
092                if (this.columnName == null) {
093                    return rs.getObject(this.columnIndex);
094                } else {
095                    return rs.getObject(this.columnName);
096                }
097    
098            } else {
099                return null;
100            }
101        }
102    }