    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 */
    017package org.apache.commons.dbutils.handlers;
    018
    019import java.sql.ResultSet;
    020import java.sql.SQLException;
    021
    022import org.apache.commons.dbutils.ResultSetHandler;
    023
    024/**
    025 * {@code ResultSetHandler} implementation that converts one
    026 * {@code ResultSet} column into an Object. This class is thread safe.
    027 *
    028 * @param <T> The type of the scalar
    029 * @see org.apache.commons.dbutils.ResultSetHandler
    030 */
    031public class ScalarHandler<T> implements ResultSetHandler<T> {
    032
    033    /**
    034     * The column number to retrieve.
    035     */
    036    private final int columnIndex;
    037
    038    /**
    039     * The column name to retrieve.  Either columnName or columnIndex
    040     * will be used but never both.
    041     */
    042    private final String columnName;
    043
    044    /**
    045     * Creates a new instance of ScalarHandler.  The first column will
    046     * be returned from {@code handle()}.
    047     */
    048    public ScalarHandler() {
    049        this(1, null);
    050    }
    051
    052    /**
    053     * Creates a new instance of ScalarHandler.
    054     *
    055     * @param columnIndex The index of the column to retrieve from the
    056     * {@code ResultSet}.
    057     */
    058    public ScalarHandler(final int columnIndex) {
    059        this(columnIndex, null);
    060    }
    061
    062    /** Helper constructor
    063     * @param columnIndex The index of the column to retrieve from the
    064     * {@code ResultSet}.
    065     * @param columnName The name of the column to retrieve from the
    066     * {@code ResultSet}.
    067     */
    068    private ScalarHandler(final int columnIndex, final String columnName) {
    069        this.columnIndex = columnIndex;
    070        this.columnName = columnName;
    071    }
    072
    073    /**
    074     * Creates a new instance of ScalarHandler.
    075     *
    076     * @param columnName The name of the column to retrieve from the
    077     * {@code ResultSet}.
    078     */
    079    public ScalarHandler(final String columnName) {
    080        this(1, columnName);
    081    }
    082
    083    /**
    084     * Returns one {@code ResultSet} column as an object via the
    085     * {@code ResultSet.getObject()} method that performs type
    086     * conversions.
    087     * @param resultSet {@code ResultSet} to process.
    088     * @return The column or {@code null} if there are no rows in
    089     * the {@code ResultSet}.
    090     *
    091     * @throws SQLException if a database access error occurs
    092     * @throws ClassCastException if the class datatype does not match the column type
    093     *
    094     * @see org.apache.commons.dbutils.ResultSetHandler#handle(java.sql.ResultSet)
    095     */
    096    // We assume that the user has picked the correct type to match the column
    097    // so getObject will return the appropriate type and the cast will succeed.
    098    @SuppressWarnings("unchecked")
    099    @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}