/*
* Copyright 2002-2009 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.core;
import java.sql.ResultSet;
import java.sql.ResultSetMetaData;
import java.sql.SQLException;
import org.springframework.dao.TypeMismatchDataAccessException;
import org.springframework.jdbc.IncorrectResultSetColumnCountException;
import org.springframework.jdbc.support.JdbcUtils;
import org.springframework.util.NumberUtils;
/**
* {@link RowMapper} implementation that converts a single column into a single
* result value per row. Expects to operate on a <code>java.sql.ResultSet</code>
* that just contains a single column.
*
* <p>The type of the result value for each row can be specified. The value
* for the single column will be extracted from the <code>ResultSet</code>
* and converted into the specified target type.
*
* @author Juergen Hoeller
* @since 1.2
* @see JdbcTemplate#queryForList(String, Class)
* @see JdbcTemplate#queryForObject(String, Class)
*/
public class SingleColumnRowMapper<T> implements RowMapper<T> {
private Class<T> requiredType;
/**
* Create a new SingleColumnRowMapper.
* @see #setRequiredType
*/
public SingleColumnRowMapper() {
}
/**
* Create a new SingleColumnRowMapper.
* @param requiredType the type that each result object is expected to match
*/
public SingleColumnRowMapper(Class<T> requiredType) {
this.requiredType = requiredType;
}
/**
* Set the type that each result object is expected to match.
* <p>If not specified, the column value will be exposed as
* returned by the JDBC driver.
*/
public void setRequiredType(Class<T> requiredType) {
this.requiredType = requiredType;
}
/**
* Extract a value for the single column in the current row.
* <p>Validates that there is only one column selected,
* then delegates to <code>getColumnValue()</code> and also
* <code>convertValueToRequiredType</code>, if necessary.
* @see java.sql.ResultSetMetaData#getColumnCount()
* @see #getColumnValue(java.sql.ResultSet, int, Class)
* @see #convertValueToRequiredType(Object, Class)
*/
@SuppressWarnings("unchecked")
public T mapRow(ResultSet rs, int rowNum) throws SQLException {
// Validate column count.
ResultSetMetaData rsmd = rs.getMetaData();
int nrOfColumns = rsmd.getColumnCount();
if (nrOfColumns != 1) {
throw new IncorrectResultSetColumnCountException(1, nrOfColumns);
}
// Extract column value from JDBC ResultSet.
Object result = getColumnValue(rs, 1, this.requiredType);
if (result != null && this.requiredType != null && !this.requiredType.isInstance(result)) {
// Extracted value does not match already: try to convert it.
try {
return (T) convertValueToRequiredType(result, this.requiredType);
}
catch (IllegalArgumentException ex) {
throw new TypeMismatchDataAccessException(
"Type mismatch affecting row number " + rowNum + " and column type '" +
rsmd.getColumnTypeName(1) + "': " + ex.getMessage());
}
}
return (T) result;
}
/**
* Retrieve a JDBC object value for the specified column.
* <p>The default implementation calls
* {@link JdbcUtils#getResultSetValue(java.sql.ResultSet, int, Class)}.
* If no required type has been specified, this method delegates to
* <code>getColumnValue(rs, index)</code>, which basically calls
* <code>ResultSet.getObject(index)</code> but applies some additional
* default conversion to appropriate value types.
* @param rs is the ResultSet holding the data
* @param index is the column index
* @param requiredType the type that each result object is expected to match
* (or <code>null</code> if none specified)
* @return the Object value
* @throws SQLException in case of extraction failure
* @see org.springframework.jdbc.support.JdbcUtils#getResultSetValue(java.sql.ResultSet, int, Class)
* @see #getColumnValue(java.sql.ResultSet, int)
*/
protected Object getColumnValue(ResultSet rs, int index, Class requiredType) throws SQLException {
if (requiredType != null) {
return JdbcUtils.getResultSetValue(rs, index, requiredType);
}
else {
// No required type specified -> perform default extraction.
return getColumnValue(rs, index);
}
}
/**
* Retrieve a JDBC object value for the specified column, using the most
* appropriate value type. Called if no required type has been specified.
* <p>The default implementation delegates to <code>JdbcUtils.getResultSetValue()</code>,
* which uses the <code>ResultSet.getObject(index)</code> method. Additionally,
* it includes a "hack" to get around Oracle returning a non-standard object for
* their TIMESTAMP datatype. See the <code>JdbcUtils#getResultSetValue()</code>
* javadoc for details.
* @param rs is the ResultSet holding the data
* @param index is the column index
* @return the Object value
* @throws SQLException in case of extraction failure
* @see org.springframework.jdbc.support.JdbcUtils#getResultSetValue(java.sql.ResultSet, int)
*/
protected Object getColumnValue(ResultSet rs, int index) throws SQLException {
return JdbcUtils.getResultSetValue(rs, index);
}
/**
* Convert the given column value to the specified required type.
* Only called if the extracted column value does not match already.
* <p>If the required type is String, the value will simply get stringified
* via <code>toString()</code>. In case of a Number, the value will be
* converted into a Number, either through number conversion or through
* String parsing (depending on the value type).
* @param value the column value as extracted from <code>getColumnValue()</code>
* (never <code>null</code>)
* @param requiredType the type that each result object is expected to match
* (never <code>null</code>)
* @return the converted value
* @see #getColumnValue(java.sql.ResultSet, int, Class)
*/
@SuppressWarnings("unchecked")
protected Object convertValueToRequiredType(Object value, Class requiredType) {
if (String.class.equals(requiredType)) {
return value.toString();
}
else if (Number.class.isAssignableFrom(requiredType)) {
if (value instanceof Number) {
// Convert original Number to target Number class.
return NumberUtils.convertNumberToTargetClass(((Number) value), requiredType);
}
else {
// Convert stringified value to target Number class.
return NumberUtils.parseNumber(value.toString(), requiredType);
}
}
else {
throw new IllegalArgumentException(
"Value [" + value + "] is of type [" + value.getClass().getName() +
"] and cannot be converted to required type [" + requiredType.getName() + "]");
}
}
}