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/*
 * Copyright 2002-2005 the original author or authors.
 * 
 * Licensed 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.springframework.jdbc.object;

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Map;

import javax.sql.DataSource;

import org.springframework.jdbc.core.RowMapper;

/**
 * Reusable RDBMS query in which concrete subclasses must implement
 * the abstract mapRow(ResultSet, int) method to map each row of
 * the JDBC ResultSet into an object.
 *
 * 

Such manual mapping is usually preferable to "automatic" * mapping using reflection, which can become complex in non-trivial * cases. For example, the present class allows different objects * to be used for different rows (for example, if a subclass is indicated). * It allows computed fields to be set. And there's no need for * ResultSet columns to have the same names as bean properties. * The Pareto Principle in action: going the extra mile to automate * the extraction process makes the framework much more complex * and delivers little real benefit. * *

Subclasses can be constructed providing SQL, parameter types * and a DataSource. SQL will often vary between subclasses. * * @author Rod Johnson * @author Thomas Risberg * @author Jean-Pierre Pawlak * @see org.springframework.jdbc.object.MappingSqlQuery * @see org.springframework.jdbc.object.SqlQuery */ public abstract class MappingSqlQueryWithParameters extends SqlQuery { /** * Constructor to allow use as a JavaBean */ public MappingSqlQueryWithParameters() { } /** * Convenient constructor with DataSource and SQL string. * @param ds DataSource to use to get connections * @param sql SQL to run */ public MappingSqlQueryWithParameters(DataSource ds, String sql) { super(ds, sql); } /** * Implementation of protected abstract method. This invokes the subclass's * implementation of the mapRow() method. */ protected RowMapper newRowMapper(Object[] parameters, Map context) { return new RowMapperImpl(parameters, context); } /** * Subclasses must implement this method to convert each row * of the ResultSet into an object of the result type. * @param rs ResultSet we're working through * @param rowNum row number (from 0) we're up to * @param parameters to the query (passed to the execute() method). * Subclasses are rarely interested in these. * It can be null if there are no parameters. * @param context passed to the execute() method. * It can be null if no contextual information is need. * @return an object of the result type * @throws SQLException if there's an error extracting data. * Subclasses can simply not catch SQLExceptions, relying on the * framework to clean up. */ protected abstract Object mapRow(ResultSet rs, int rowNum, Object[] parameters, Map context) throws SQLException; /** * Implementation of RowMapper that calls the enclosing * class's mapRow method for each row. */ protected class RowMapperImpl implements RowMapper { private final Object[] params; private final Map context; /** * Use an array results. More efficient if we know how many results to expect. */ public RowMapperImpl(Object[] parameters, Map context) { this.params = parameters; this.context = context; } public Object mapRow(ResultSet rs, int rowNum) throws SQLException { return MappingSqlQueryWithParameters.this.mapRow(rs, rowNum, this.params, this.context); } } }





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