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/*
* Copyright 2002-2012 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.
*
* <p>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.
*
* <p>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<T> extends SqlQuery<T> {
/**
* 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.
*/
@Override
protected RowMapper<T> 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 {@code null} if there are no parameters.
* @param context passed to the execute() method.
* It can be {@code 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 T mapRow(ResultSet rs, int rowNum, Object[] parameters, Map<?, ?> context)
throws SQLException;
/**
* Implementation of RowMapper that calls the enclosing
* class's {@code mapRow} method for each row.
*/
protected class RowMapperImpl implements RowMapper<T> {
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;
}
@Override
public T mapRow(ResultSet rs, int rowNum) throws SQLException {
return MappingSqlQueryWithParameters.this.mapRow(rs, rowNum, this.params, this.context);
}
}
}
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