JdbcClient holds ConversionService for queries with mapped classes

Closes gh-33467

Author: jhoeller

Diff for: spring-jdbc/src/main/java/org/springframework/jdbc/core/SingleColumnRowMapper.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -70,6 +70,19 @@ public SingleColumnRowMapper(Class<T> requiredType) {
 		}
 	}
 
+	/**
+	 * Create a new {@code SingleColumnRowMapper}.
+	 * @param requiredType the type that each result object is expected to match
+	 * @param conversionService a {@link ConversionService} for converting a fetched value
+	 * @since 7.0
+	 */
+	public SingleColumnRowMapper(Class<T> requiredType, @Nullable ConversionService conversionService) {
+		if (requiredType != Object.class) {
+			setRequiredType(requiredType);
+		}
+		setConversionService(conversionService);
+	}
+
 
 	/**
 	 * Set the type that each result object is expected to match.
@@ -84,12 +97,13 @@ public void setRequiredType(Class<T> requiredType) {
 	 * Set a {@link ConversionService} for converting a fetched value.
 	 * <p>Default is the {@link DefaultConversionService}.
 	 * @since 5.0.4
-	 * @see DefaultConversionService#getSharedInstance
+	 * @see DefaultConversionService#getSharedInstance()
 	 */
 	public void setConversionService(@Nullable ConversionService conversionService) {
 		this.conversionService = conversionService;
 	}
 
+
 	/**
 	 * Extract a value for the single column in the current row.
 	 * <p>Validates that there is only one column selected,

Diff for: spring-jdbc/src/main/java/org/springframework/jdbc/core/simple/DefaultJdbcClient.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -28,6 +28,8 @@
 import org.jspecify.annotations.Nullable;
 
 import org.springframework.beans.BeanUtils;
+import org.springframework.core.convert.ConversionService;
+import org.springframework.core.convert.support.DefaultConversionService;
 import org.springframework.jdbc.core.JdbcOperations;
 import org.springframework.jdbc.core.JdbcTemplate;
 import org.springframework.jdbc.core.PreparedStatementCreator;
@@ -64,24 +66,25 @@ final class DefaultJdbcClient implements JdbcClient {
 
 	private final NamedParameterJdbcOperations namedParamOps;
 
+	private final ConversionService conversionService;
+
 	private final Map<Class<?>, RowMapper<?>> rowMapperCache = new ConcurrentHashMap<>();
 
 
 	public DefaultJdbcClient(DataSource dataSource) {
-		this.classicOps = new JdbcTemplate(dataSource);
-		this.namedParamOps = new NamedParameterJdbcTemplate(this.classicOps);
+		this(new JdbcTemplate(dataSource));
 	}
 
 	public DefaultJdbcClient(JdbcOperations jdbcTemplate) {
-		Assert.notNull(jdbcTemplate, "JdbcTemplate must not be null");
-		this.classicOps = jdbcTemplate;
-		this.namedParamOps = new NamedParameterJdbcTemplate(jdbcTemplate);
+		this(new NamedParameterJdbcTemplate(jdbcTemplate), null);
 	}
 
-	public DefaultJdbcClient(NamedParameterJdbcOperations jdbcTemplate) {
+	public DefaultJdbcClient(NamedParameterJdbcOperations jdbcTemplate, @Nullable ConversionService conversionService) {
 		Assert.notNull(jdbcTemplate, "JdbcTemplate must not be null");
 		this.classicOps = jdbcTemplate.getJdbcOperations();
 		this.namedParamOps = jdbcTemplate;
+		this.conversionService =
+				(conversionService != null ? conversionService : DefaultConversionService.getSharedInstance());
 	}
 
 
@@ -201,8 +204,9 @@ public ResultQuerySpec query() {
 		@Override
 		public <T> MappedQuerySpec<T> query(Class<T> mappedClass) {
 			RowMapper<?> rowMapper = rowMapperCache.computeIfAbsent(mappedClass, key ->
-					BeanUtils.isSimpleProperty(mappedClass) ? new SingleColumnRowMapper<>(mappedClass) :
-							new SimplePropertyRowMapper<>(mappedClass));
+					BeanUtils.isSimpleProperty(mappedClass) ?
+							new SingleColumnRowMapper<>(mappedClass, conversionService) :
+							new SimplePropertyRowMapper<>(mappedClass, conversionService));
 			return query((RowMapper<T>) rowMapper);
 		}
 

Diff for: spring-jdbc/src/main/java/org/springframework/jdbc/core/simple/JdbcClient.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2024 the original author or authors.
+ * Copyright 2002-2025 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.
@@ -28,6 +28,7 @@
 
 import org.jspecify.annotations.Nullable;
 
+import org.springframework.core.convert.ConversionService;
 import org.springframework.dao.support.DataAccessUtils;
 import org.springframework.jdbc.core.JdbcOperations;
 import org.springframework.jdbc.core.ResultSetExtractor;
@@ -107,7 +108,22 @@ static JdbcClient create(JdbcOperations jdbcTemplate) {
 	 * @param jdbcTemplate the delegate to perform operations on
 	 */
 	static JdbcClient create(NamedParameterJdbcOperations jdbcTemplate) {
-		return new DefaultJdbcClient(jdbcTemplate);
+		return new DefaultJdbcClient(jdbcTemplate, null);
+	}
+
+	/**
+	 * Create a {@code JdbcClient} for the given {@link NamedParameterJdbcOperations} delegate,
+	 * typically an {@link org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate}.
+	 * <p>Use this factory method to reuse existing {@code NamedParameterJdbcTemplate}
+	 * configuration, including its underlying {@code JdbcTemplate} and {@code DataSource},
+	 * along with a custom {@link ConversionService} for queries with mapped classes.
+	 * @param jdbcTemplate the delegate to perform operations on
+	 * @param conversionService a {@link ConversionService} for converting fetched JDBC values
+	 * to mapped classes in {@link StatementSpec#query(Class)}
+	 * @since 7.0
+	 */
+	static JdbcClient create(NamedParameterJdbcOperations jdbcTemplate, ConversionService conversionService) {
+		return new DefaultJdbcClient(jdbcTemplate, conversionService);
 	}
 
 

Diff for: spring-jdbc/src/test/java/org/springframework/jdbc/core/simple/JdbcClientQueryTests.java

@@ -16,10 +16,12 @@
 
 package org.springframework.jdbc.core.simple;
 
+import java.math.BigInteger;
 import java.sql.Connection;
 import java.sql.PreparedStatement;
 import java.sql.ResultSet;
 import java.sql.ResultSetMetaData;
+import java.sql.SQLFeatureNotSupportedException;
 import java.sql.Types;
 import java.util.ArrayList;
 import java.util.Arrays;
@@ -33,6 +35,11 @@
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import org.springframework.core.convert.converter.Converter;
+import org.springframework.core.convert.support.GenericConversionService;
+import org.springframework.jdbc.core.namedparam.NamedParameterJdbcTemplate;
+import org.springframework.util.NumberUtils;
+
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
 import static org.mockito.ArgumentMatchers.anyString;
@@ -593,13 +600,22 @@ void queryForMappedRecordWithNamedParam() throws Exception {
 	@Test
 	void queryForMappedFieldHolderWithNamedParam() throws Exception {
 		given(resultSet.next()).willReturn(true, false);
-		given(resultSet.getInt(1)).willReturn(22);
-
+		given(resultSet.getObject(1, BigInteger.class)).willThrow(new SQLFeatureNotSupportedException());
+		given(resultSet.getObject(1)).willReturn("big22");
+
+		GenericConversionService conversionService = new GenericConversionService();
+		conversionService.addConverter(new Converter<String, BigInteger>() {  // explicit for generics
+			@Override
+			public BigInteger convert(String source) {
+				return NumberUtils.parseNumber(source.substring(3), BigInteger.class);
+			}
+		});
+		client = JdbcClient.create(new NamedParameterJdbcTemplate(dataSource), conversionService);
 		AgeFieldHolder value = client.sql("SELECT AGE FROM CUSTMR WHERE ID = :id")
 				.param("id", 3)
 				.query(AgeFieldHolder.class).single();
 
-		assertThat(value.age).isEqualTo(22);
+		assertThat(value.age).isEqualTo(BigInteger.valueOf(22));
 		verify(connection).prepareStatement("SELECT AGE FROM CUSTMR WHERE ID = ?");
 		verify(preparedStatement).setObject(1, 3);
 		verify(resultSet).close();
@@ -656,7 +672,7 @@ record AgeRecord(int age) {
 
 	static class AgeFieldHolder {
 
-		public int age;
+		public BigInteger age;
 	}
 
 }