Introduce optionalValue() method on ResultQuerySpec

Closes gh-33560

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2023 the original author or authors.
+ * Copyright 2002-2024 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.
@@ -343,12 +343,26 @@ interface ResultQuerySpec {
 
 		/**
 		 * Retrieve a single value result.
-		 * @return the single row represented as its single column value
+		 * <p>Note: As of 6.2, this will enforce non-null result values
+		 * as originally designed (just accidentally not enforced before).
+		 * (never {@code null})
+		 * @see #optionalValue()
 		 * @see DataAccessUtils#requiredSingleResult(Collection)
 		 */
 		default Object singleValue() {
 			return DataAccessUtils.requiredSingleResult(singleColumn());
 		}
+
+		/**
+		 * Retrieve a single value result, if available, as an {@link Optional} handle.
+		 * @return an Optional handle with the single column value from the single row
+		 * @since 6.2
+		 * @see #singleValue()
+		 * @see DataAccessUtils#optionalResult(Collection)
+		 */
+		default Optional<Object> optionalValue() {
+			return DataAccessUtils.optionalResult(singleColumn());
+		}
 	}
 
 
@@ -384,25 +398,27 @@ default Set<T> set() {
 			return new LinkedHashSet<>(list());
 		}
 
-		/**
-		 * Retrieve a single result, if available, as an {@link Optional} handle.
-		 * @return an Optional handle with a single result object or none
-		 * @see #list()
-		 * @see DataAccessUtils#optionalResult(Collection)
-		 */
-		default Optional<T> optional() {
-			return DataAccessUtils.optionalResult(list());
-		}
-
 		/**
 		 * Retrieve a single result as a required object instance.
+		 * <p>Note: As of 6.2, this will enforce non-null result values
+		 * as originally designed (just accidentally not enforced before).
 		 * @return the single result object (never {@code null})
-		 * @see #list()
+		 * @see #optional()
 		 * @see DataAccessUtils#requiredSingleResult(Collection)
 		 */
 		default T single() {
 			return DataAccessUtils.requiredSingleResult(list());
 		}
+
+		/**
+		 * Retrieve a single result, if available, as an {@link Optional} handle.
+		 * @return an Optional handle with a single result object or none
+		 * @see #single()
+		 * @see DataAccessUtils#optionalResult(Collection)
+		 */
+		default Optional<T> optional() {
+			return DataAccessUtils.optionalResult(list());
+		}
 	}
 
 }

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

@@ -174,6 +174,40 @@ void queryForIntegerWithIndexedParamAndSingleValue() throws Exception {
 		verify(connection).close();
 	}
 
+	@Test
+	void queryForIntegerWithIndexedParamAndOptionalValue() throws Exception {
+		given(resultSet.next()).willReturn(true, false);
+		given(resultSet.getObject(1)).willReturn(22);
+
+		Optional<Object> value = client.sql("SELECT AGE FROM CUSTMR WHERE ID = ?")
+				.param(1, 3)
+				.query().optionalValue();
+
+		assertThat(value.isPresent()).isTrue();
+		assertThat(value.get()).isEqualTo(22);
+		verify(connection).prepareStatement("SELECT AGE FROM CUSTMR WHERE ID = ?");
+		verify(preparedStatement).setObject(1, 3);
+		verify(resultSet).close();
+		verify(preparedStatement).close();
+		verify(connection).close();
+	}
+
+	@Test
+	void queryForIntegerWithIndexedParamAndNonExistingValue() throws Exception {
+		given(resultSet.next()).willReturn(false);
+
+		Optional<Object> value = client.sql("SELECT AGE FROM CUSTMR WHERE ID = ?")
+				.param(1, 3)
+				.query().optionalValue();
+
+		assertThat(value.isPresent()).isFalse();
+		verify(connection).prepareStatement("SELECT AGE FROM CUSTMR WHERE ID = ?");
+		verify(preparedStatement).setObject(1, 3);
+		verify(resultSet).close();
+		verify(preparedStatement).close();
+		verify(connection).close();
+	}
+
 	@Test
 	void queryForIntegerWithIndexedParamAndRowMapper() throws Exception {
 		given(resultSet.next()).willReturn(true, false);