diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxy.java b/spring-jdbc/src/main/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxy.java
index 1b4f69c8cc..3244f01e19 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxy.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxy.java
@@ -23,14 +23,15 @@ import java.lang.reflect.Proxy;
 import java.sql.Connection;
 import java.sql.ResultSet;
 import java.sql.SQLException;
+import java.util.Map;
 
 import javax.sql.DataSource;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 
-import org.springframework.core.Constants;
 import org.springframework.lang.Nullable;
+import org.springframework.util.Assert;
 
 /**
  * Proxy for a target DataSource, fetching actual JDBC Connections lazily,
@@ -75,13 +76,22 @@ import org.springframework.lang.Nullable;
  * to retrieve the native JDBC Connection.
  *
  * @author Juergen Hoeller
+ * @author Sam Brannen
  * @since 1.1.4
  * @see DataSourceTransactionManager
  */
 public class LazyConnectionDataSourceProxy extends DelegatingDataSource {
 
-	/** Constants instance for TransactionDefinition. */
-	private static final Constants constants = new Constants(Connection.class);
+	/**
+	 * Map of constant names to constant values for the isolation constants
+	 * defined in {@link java.sql.Connection}.
+	 */
+	static final Map<String, Integer> constants = Map.of(
+			"TRANSACTION_READ_UNCOMMITTED", Connection.TRANSACTION_READ_UNCOMMITTED,
+			"TRANSACTION_READ_COMMITTED", Connection.TRANSACTION_READ_COMMITTED,
+			"TRANSACTION_REPEATABLE_READ", Connection.TRANSACTION_REPEATABLE_READ,
+			"TRANSACTION_SERIALIZABLE", Connection.TRANSACTION_SERIALIZABLE
+		);
 
 	private static final Log logger = LogFactory.getLog(LazyConnectionDataSourceProxy.class);
 
@@ -133,7 +143,10 @@ public class LazyConnectionDataSourceProxy extends DelegatingDataSource {
 	 * @see java.sql.Connection#TRANSACTION_SERIALIZABLE
 	 */
 	public void setDefaultTransactionIsolationName(String constantName) {
-		setDefaultTransactionIsolation(constants.asNumber(constantName).intValue());
+		Assert.hasText(constantName, "'constantName' must not be null or blank");
+		Integer defaultTransactionIsolation = constants.get(constantName);
+		Assert.notNull(defaultTransactionIsolation, "Only transaction isolation constants allowed");
+		this.defaultTransactionIsolation = defaultTransactionIsolation;
 	}
 
 	/**
diff --git a/spring-jdbc/src/test/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxyTests.java b/spring-jdbc/src/test/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxyTests.java
new file mode 100644
index 0000000000..7159752118
--- /dev/null
+++ b/spring-jdbc/src/test/java/org/springframework/jdbc/datasource/LazyConnectionDataSourceProxyTests.java
@@ -0,0 +1,98 @@
+/*
+ * Copyright 2002-2023 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
+ *
+ *      https://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.datasource;
+
+import java.lang.reflect.Field;
+import java.sql.Connection;
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+import java.util.stream.Stream;
+
+import org.junit.jupiter.api.Test;
+
+import org.springframework.util.ReflectionUtils;
+
+import static java.sql.Connection.TRANSACTION_NONE;
+import static java.sql.Connection.TRANSACTION_READ_COMMITTED;
+import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatIllegalArgumentException;
+
+/**
+ * Tests for {@link LazyConnectionDataSourceProxy}.
+ *
+ * @author Sam Brannen
+ * @since 6.1
+ */
+class LazyConnectionDataSourceProxyTests {
+
+	private final LazyConnectionDataSourceProxy proxy = new LazyConnectionDataSourceProxy();
+
+
+	@Test
+	void setDefaultTransactionIsolationNameToUnsupportedValues() {
+		assertThatIllegalArgumentException().isThrownBy(() -> proxy.setDefaultTransactionIsolationName(null));
+		assertThatIllegalArgumentException().isThrownBy(() -> proxy.setDefaultTransactionIsolationName("   "));
+		assertThatIllegalArgumentException().isThrownBy(() -> proxy.setDefaultTransactionIsolationName("bogus"));
+	}
+
+	/**
+	 * Verify that the internal 'constants' map is properly configured for all
+	 * TRANSACTION_ constants defined in {@link java.sql.Connection}.
+	 */
+	@Test
+	void setDefaultTransactionIsolationNameToAllSupportedValues() {
+		Set<Integer> uniqueValues = new HashSet<>();
+		streamIsolationConstants()
+				.forEach(name -> {
+					if ("TRANSACTION_NONE".equals(name)) {
+						assertThatIllegalArgumentException().isThrownBy(() -> proxy.setDefaultTransactionIsolationName(name));
+					}
+					else {
+						proxy.setDefaultTransactionIsolationName(name);
+						Integer defaultTransactionIsolation = proxy.defaultTransactionIsolation();
+						Integer expected = LazyConnectionDataSourceProxy.constants.get(name);
+						assertThat(defaultTransactionIsolation).isEqualTo(expected);
+						uniqueValues.add(defaultTransactionIsolation);
+					}
+				});
+		assertThat(uniqueValues).containsExactlyInAnyOrderElementsOf(LazyConnectionDataSourceProxy.constants.values());
+	}
+
+	@Test
+	void setDefaultTransactionIsolation() {
+		// unsupported values are not checked:
+		proxy.setDefaultTransactionIsolation(-999);
+		assertThat(proxy.defaultTransactionIsolation()).isEqualTo(-999);
+
+		// TRANSACTION_NONE should not be supported, but we currently do not check that.
+		proxy.setDefaultTransactionIsolation(TRANSACTION_NONE);
+		assertThat(proxy.defaultTransactionIsolation()).isEqualTo(TRANSACTION_NONE);
+
+		proxy.setDefaultTransactionIsolation(TRANSACTION_READ_COMMITTED);
+		assertThat(proxy.defaultTransactionIsolation()).isEqualTo(TRANSACTION_READ_COMMITTED);
+	}
+
+
+	private static Stream<String> streamIsolationConstants() {
+		return Arrays.stream(Connection.class.getFields())
+				.filter(ReflectionUtils::isPublicStaticFinal)
+				.map(Field::getName)
+				.filter(name -> name.startsWith("TRANSACTION_"));
+	}
+
+}