/*
* Copyright 2002-2018 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;
import org.springframework.lang.Nullable;
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, Thomas Risberg, Jean-Pierre Pawlak Type parameters: - <T> – the result type
See Also:
/**
* 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
* @param <T> the result type
* @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.
/**
* Constructor to allow use as a JavaBean.
*/
public MappingSqlQueryWithParameters() {
}
Convenient constructor with DataSource and SQL string.
Params: - ds – the DataSource to use to get connections
- sql – the SQL to run
/**
* Convenient constructor with DataSource and SQL string.
* @param ds the DataSource to use to get connections
* @param sql the 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.
/**
* Implementation of protected abstract method. This invokes the subclass's
* implementation of the mapRow() method.
*/
@Override
protected RowMapper<T> newRowMapper(@Nullable Object[] parameters, @Nullable 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.
Params: - rs – the ResultSet we're working through
- rowNum – row number (from 0) we're up to
- parameters – to the query (passed to the execute() method). Subclasses are rarely interested in these. It can be
null if there are no parameters. - context – passed to the execute() method. It can be
null if no contextual information is need.
Throws: - SQLException – if there's an error extracting data.
Subclasses can simply not catch SQLExceptions, relying on the
framework to clean up.
Returns: an object of the result type
/**
* Subclasses must implement this method to convert each row
* of the ResultSet into an object of the result type.
* @param rs the 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.
*/
@Nullable
protected abstract T mapRow(ResultSet rs, int rowNum, @Nullable Object[] parameters, @Nullable Map<?, ?> context)
throws SQLException;
Implementation of RowMapper that calls the enclosing class's mapRow method for each row. /**
* Implementation of RowMapper that calls the enclosing
* class's {@code mapRow} method for each row.
*/
protected class RowMapperImpl implements RowMapper<T> {
@Nullable
private final Object[] params;
@Nullable
private final Map<?, ?> context;
Use an array results. More efficient if we know how many results to expect.
/**
* Use an array results. More efficient if we know how many results to expect.
*/
public RowMapperImpl(@Nullable Object[] parameters, @Nullable Map<?, ?> context) {
this.params = parameters;
this.context = context;
}
@Override
@Nullable
public T mapRow(ResultSet rs, int rowNum) throws SQLException {
return MappingSqlQueryWithParameters.this.mapRow(rs, rowNum, this.params, this.context);
}
}
}