Java tutorial
/* * Licensed to the Apache Software Foundation (ASF) under one or more * contributor license agreements. See the NOTICE file distributed with * this work for additional information regarding copyright ownership. * The ASF licenses this file to You under the Apache License, Version 2.0 * (the "License"); you may not use this file except in compliance with * the License. You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.apache.commons.dbutils.handlers; import java.sql.ResultSet; import java.sql.SQLException; import org.apache.commons.dbutils.ResultSetHandler; /** * <code>ResultSetHandler</code> implementation that converts one * <code>ResultSet</code> column into an Object. This class is thread safe. * * @param <T> The type of the scalar * @see org.apache.commons.dbutils.ResultSetHandler */ public class ScalarHandler<T> implements ResultSetHandler<T> { /** * The column number to retrieve. */ private final int columnIndex; /** * The column name to retrieve. Either columnName or columnIndex * will be used but never both. */ private final String columnName; /** * Creates a new instance of ScalarHandler. The first column will * be returned from <code>handle()</code>. */ public ScalarHandler() { this(1, null); } /** * Creates a new instance of ScalarHandler. * * @param columnIndex The index of the column to retrieve from the * <code>ResultSet</code>. */ public ScalarHandler(int columnIndex) { this(columnIndex, null); } /** * Creates a new instance of ScalarHandler. * * @param columnName The name of the column to retrieve from the * <code>ResultSet</code>. */ public ScalarHandler(String columnName) { this(1, columnName); } /** Helper constructor * @param columnIndex The index of the column to retrieve from the * <code>ResultSet</code>. * @param columnName The name of the column to retrieve from the * <code>ResultSet</code>. */ private ScalarHandler(int columnIndex, String columnName) { this.columnIndex = columnIndex; this.columnName = columnName; } /** * Returns one <code>ResultSet</code> column as an object via the * <code>ResultSet.getObject()</code> method that performs type * conversions. * @param rs <code>ResultSet</code> to process. * @return The column or <code>null</code> if there are no rows in * the <code>ResultSet</code>. * * @throws SQLException if a database access error occurs * @throws ClassCastException if the class datatype does not match the column type * * @see org.apache.commons.dbutils.ResultSetHandler#handle(java.sql.ResultSet) */ // We assume that the user has picked the correct type to match the column // so getObject will return the appropriate type and the cast will succeed. @SuppressWarnings("unchecked") @Override public T handle(ResultSet rs) throws SQLException { if (rs.next()) { if (this.columnName == null) { return (T) rs.getObject(this.columnIndex); } else { return (T) rs.getObject(this.columnName); } } else { return null; } } }