KeyedHandler类源码

/* * 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 java.util.HashMap;import java.util.Map;import org.apache.commons.dbutils.ResultSetHandler;import org.apache.commons.dbutils.RowProcessor;/** * <p> * <code>ResultSetHandler</code> implementation that returns a Map of Maps. * <code>ResultSet</code> rows are converted into Maps which are then stored * in a Map under the given key.  Although this implementation uses Maps to  * store row contents, subclasses are encouraged to override the  * <code>createRow()</code> method to convert the rows into any kind of object. * </p> * <p> * If you had a Person table with a primary key column called ID, you could  * retrieve rows from the table like this: * <pre> * ResultSetHandler h = new KeyedHandler("id"); * Map found = (Map) queryRunner.query("select id, name, age from person", h); * Map jane = (Map) found.get(new Long(1)); // jane's id is 1 * String janesName = (String) jane.get("name"); * Integer janesAge = (Integer) jane.get("age"); * </pre> * Note that the "id" passed to KeyedHandler and "name" and "age" passed to the * returned Map's get() method can be in any case.  The data types returned for * name and age are dependent upon how your JDBC driver converts SQL column  * types from the Person table into Java types.   * </p> * <p> * To avoid these type issues you could subclass KeyedHandler and override  * <code>createRow()</code> to store rows in Java bean instances (ie. a * Person class). * </p> * <p>This class is thread safe.</p> *  * @see org.apache.commons.dbutils.ResultSetHandler * @since DbUtils 1.1 */public class KeyedHandler implements ResultSetHandler {    /**     * The RowProcessor implementation to use when converting rows     * into Objects.     */    protected RowProcessor convert = ArrayHandler.ROW_PROCESSOR;    /**     * The column index to retrieve key values from.  Defaults to 1.     */    protected int columnIndex = 1;    /**     * The column name to retrieve key values from.  Either columnName or      * columnIndex will be used but never both.     */    protected String columnName = null;    /**      * Creates a new instance of KeyedHandler.  The value of the first column      * of each row will be a key in the Map.     */    public KeyedHandler() {        super();    }    /**     * Creates a new instance of KeyedHandler.  The value of the first column      * of each row will be a key in the Map.     *     * @param convert The <code>RowProcessor</code> implementation     * to use when converting rows into Maps     */    public KeyedHandler(RowProcessor convert) {        super();        this.convert = convert;    }    /**      * Creates a new instance of KeyedHandler.     *      * @param columnIndex The values to use as keys in the Map are      * retrieved from the column at this index.     */    public KeyedHandler(int columnIndex) {        super();        this.columnIndex = columnIndex;    }    /**      * Creates a new instance of KeyedHandler.     *      * @param columnName The values to use as keys in the Map are      * retrieved from the column with this name.     */    public KeyedHandler(String columnName) {        super();        this.columnName = columnName;    }    /**     * Convert each row's columns into a Map and store then      * in a <code>Map</code> under <code>ResultSet.getObject(key)</code> key.     *      * @return A <code>Map</code> of Maps, never <code>null</code>.      * @throws SQLException if a database access error occurs     * @see org.apache.commons.dbutils.ResultSetHandler#handle(java.sql.ResultSet)     */    public Object handle(ResultSet rs) throws SQLException {        Map result = createMap();        while (rs.next()) {            result.put(createKey(rs), createRow(rs));        }        return result;    }    /**     * This factory method is called by <code>handle()</code> to create the Map     * to store records in.  This implementation returns a <code>HashMap</code>     * instance.     *     * @return Map to store records in     */    protected Map createMap() {        return new HashMap();    }    /**     * This factory method is called by <code>handle()</code> to retrieve the     * key value from the current <code>ResultSet</code> row.  This      * implementation returns <code>ResultSet.getObject()</code> for the      * configured key column name or index.      * @param rs ResultSet to create a key from     * @return Object from the configured key column name/index     * @throws SQLException if a database access error occurs     */    protected Object createKey(ResultSet rs) throws SQLException {        return (columnName == null) ? rs.getObject(columnIndex) : rs                .getObject(columnName);    }    /**     * This factory method is called by <code>handle()</code> to store the     * current <code>ResultSet</code> row in some object. This      * implementation returns a <code>Map</code> with case insensitive column     * names as keys.  Calls to <code>map.get("COL")</code> and      * <code>map.get("col")</code> return the same value.     * @param rs ResultSet to create a row from     * @return Object typed Map containing column names to values     * @throws SQLException if a database access error occurs     */    protected Object createRow(ResultSet rs) throws SQLException {        return this.convert.toMap(rs);    }}