diff --git a/spring-beans/src/main/java/org/springframework/beans/support/PropertyComparator.java b/spring-beans/src/main/java/org/springframework/beans/support/PropertyComparator.java
index 0c33bd276e0c..9a9a7d8f30d1 100644
--- a/spring-beans/src/main/java/org/springframework/beans/support/PropertyComparator.java
+++ b/spring-beans/src/main/java/org/springframework/beans/support/PropertyComparator.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.
@@ -19,6 +19,7 @@
 import java.util.Arrays;
 import java.util.Comparator;
 import java.util.List;
+import java.util.Locale;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -77,8 +78,8 @@ public int compare(T o1, T o2) {
 		Object v1 = getPropertyValue(o1);
 		Object v2 = getPropertyValue(o2);
 		if (this.sortDefinition.isIgnoreCase() && (v1 instanceof String text1) && (v2 instanceof String text2)) {
-			v1 = text1.toLowerCase();
-			v2 = text2.toLowerCase();
+			v1 = text1.toLowerCase(Locale.ROOT);
+			v2 = text2.toLowerCase(Locale.ROOT);
 		}
 
 		int result;
diff --git a/spring-context-support/src/main/java/org/springframework/scheduling/quartz/LocalDataSourceJobStore.java b/spring-context-support/src/main/java/org/springframework/scheduling/quartz/LocalDataSourceJobStore.java
index f6042bee9347..f01a9162b731 100644
--- a/spring-context-support/src/main/java/org/springframework/scheduling/quartz/LocalDataSourceJobStore.java
+++ b/spring-context-support/src/main/java/org/springframework/scheduling/quartz/LocalDataSourceJobStore.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 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.
@@ -19,6 +19,7 @@
 import java.sql.Connection;
 import java.sql.DatabaseMetaData;
 import java.sql.SQLException;
+import java.util.Locale;
 
 import javax.sql.DataSource;
 
@@ -155,7 +156,7 @@ public void initialize() {
 			String productName = JdbcUtils.extractDatabaseMetaData(this.dataSource,
 					DatabaseMetaData::getDatabaseProductName);
 			productName = JdbcUtils.commonDatabaseName(productName);
-			if (productName != null && productName.toLowerCase().contains("hsql")) {
+			if (productName != null && productName.toLowerCase(Locale.ROOT).contains("hsql")) {
 				setUseDBLocks(false);
 				setLockHandler(new SimpleSemaphore());
 			}
diff --git a/spring-context/src/main/java/org/springframework/format/datetime/standard/MonthFormatter.java b/spring-context/src/main/java/org/springframework/format/datetime/standard/MonthFormatter.java
index abae18df61cb..a6c56fbe9354 100644
--- a/spring-context/src/main/java/org/springframework/format/datetime/standard/MonthFormatter.java
+++ b/spring-context/src/main/java/org/springframework/format/datetime/standard/MonthFormatter.java
@@ -34,7 +34,7 @@ class MonthFormatter implements Formatter<Month> {
 
 	@Override
 	public Month parse(String text, Locale locale) throws ParseException {
-		return Month.valueOf(text.toUpperCase());
+		return Month.valueOf(text.toUpperCase(Locale.ROOT));
 	}
 
 	@Override
diff --git a/spring-context/src/main/java/org/springframework/scheduling/support/CronField.java b/spring-context/src/main/java/org/springframework/scheduling/support/CronField.java
index 3124cc25b5e5..e1702c9a548b 100644
--- a/spring-context/src/main/java/org/springframework/scheduling/support/CronField.java
+++ b/spring-context/src/main/java/org/springframework/scheduling/support/CronField.java
@@ -21,6 +21,7 @@
 import java.time.temporal.ChronoUnit;
 import java.time.temporal.Temporal;
 import java.time.temporal.ValueRange;
+import java.util.Locale;
 import java.util.function.BiFunction;
 
 import org.springframework.lang.Nullable;
@@ -143,7 +144,7 @@ private static CronField parseList(String value, Type type, BiFunction<String, T
 	}
 
 	private static String replaceOrdinals(String value, String[] list) {
-		value = value.toUpperCase();
+		value = value.toUpperCase(Locale.ROOT);
 		for (int i = 0; i < list.length; i++) {
 			String replacement = Integer.toString(i + 1);
 			value = StringUtils.replace(value, list[i], replacement);
diff --git a/spring-core-test/src/main/java/org/springframework/aot/agent/InvocationsRecorderClassVisitor.java b/spring-core-test/src/main/java/org/springframework/aot/agent/InvocationsRecorderClassVisitor.java
index 32cb0ddc0a43..4e7daa8f4119 100644
--- a/spring-core-test/src/main/java/org/springframework/aot/agent/InvocationsRecorderClassVisitor.java
+++ b/spring-core-test/src/main/java/org/springframework/aot/agent/InvocationsRecorderClassVisitor.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 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.
@@ -17,6 +17,7 @@
 package org.springframework.aot.agent;
 
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.Set;
 
 import org.springframework.asm.ClassVisitor;
@@ -40,6 +41,7 @@ class InvocationsRecorderClassVisitor extends ClassVisitor implements Opcodes {
 
 	private final ClassWriter classWriter;
 
+
 	public InvocationsRecorderClassVisitor() {
 		this(new ClassWriter(ClassWriter.COMPUTE_MAXS));
 	}
@@ -49,6 +51,7 @@ private InvocationsRecorderClassVisitor(ClassWriter classWriter) {
 		this.classWriter = classWriter;
 	}
 
+
 	public boolean isTransformed() {
 		return this.isTransformed;
 	}
@@ -64,6 +67,7 @@ public MethodVisitor visitMethod(int access, String name, String descriptor, Str
 		return new InvocationsRecorderMethodVisitor(mv);
 	}
 
+
 	@SuppressWarnings("deprecation")
 	class InvocationsRecorderMethodVisitor extends MethodVisitor implements Opcodes {
 
@@ -83,7 +87,6 @@ public InvocationsRecorderMethodVisitor(MethodVisitor mv) {
 			super(SpringAsmInfo.ASM_VERSION, mv);
 		}
 
-
 		@Override
 		public void visitMethodInsn(int opcode, String owner, String name, String descriptor, boolean isInterface) {
 			if (isOpcodeSupported(opcode) && shouldRecordMethodCall(owner, name)) {
@@ -116,7 +119,6 @@ public void visitInvokeDynamicInsn(String name, String descriptor, Handle bootst
 			super.visitInvokeDynamicInsn(name, descriptor, bootstrapMethodHandle, bootstrapMethodArguments);
 		}
 
-
 		private boolean shouldRecordMethodCall(String owner, String method) {
 			String methodReference = owner + "#" + method;
 			return instrumentedMethods.contains(methodReference);
@@ -124,13 +126,12 @@ private boolean shouldRecordMethodCall(String owner, String method) {
 
 		private String rewriteMethodName(String owner, String methodName) {
 			int classIndex = owner.lastIndexOf('/');
-			return owner.substring(classIndex + 1).toLowerCase() + methodName;
+			return owner.substring(classIndex + 1).toLowerCase(Locale.ROOT) + methodName;
 		}
 
 		private String rewriteDescriptor(int opcode, String owner, String name, String descriptor) {
 			return (opcode == Opcodes.INVOKESTATIC || opcode == Opcodes.H_INVOKESTATIC) ? descriptor : "(L" + owner + ";" + descriptor.substring(1);
 		}
-
 	}
 
 }
diff --git a/spring-core/src/main/java/org/springframework/core/convert/support/StringToBooleanConverter.java b/spring-core/src/main/java/org/springframework/core/convert/support/StringToBooleanConverter.java
index e54534705f7f..694e85b87683 100644
--- a/spring-core/src/main/java/org/springframework/core/convert/support/StringToBooleanConverter.java
+++ b/spring-core/src/main/java/org/springframework/core/convert/support/StringToBooleanConverter.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2022 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.core.convert.support;
 
+import java.util.Locale;
 import java.util.Set;
 
 import org.springframework.core.convert.converter.Converter;
@@ -43,7 +44,7 @@ public Boolean convert(String source) {
 		if (value.isEmpty()) {
 			return null;
 		}
-		value = value.toLowerCase();
+		value = value.toLowerCase(Locale.ROOT);
 		if (trueValues.contains(value)) {
 			return Boolean.TRUE;
 		}
diff --git a/spring-core/src/main/java/org/springframework/core/env/SystemEnvironmentPropertySource.java b/spring-core/src/main/java/org/springframework/core/env/SystemEnvironmentPropertySource.java
index 6b5f2fa36ac5..ebea27125309 100644
--- a/spring-core/src/main/java/org/springframework/core/env/SystemEnvironmentPropertySource.java
+++ b/spring-core/src/main/java/org/springframework/core/env/SystemEnvironmentPropertySource.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2021 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.
@@ -16,6 +16,7 @@
 
 package org.springframework.core.env;
 
+import java.util.Locale;
 import java.util.Map;
 
 import org.springframework.lang.Nullable;
@@ -109,7 +110,7 @@ protected final String resolvePropertyName(String name) {
 		if (resolvedName != null) {
 			return resolvedName;
 		}
-		String uppercasedName = name.toUpperCase();
+		String uppercasedName = name.toUpperCase(Locale.ROOT);
 		if (!name.equals(uppercasedName)) {
 			resolvedName = checkPropertyName(uppercasedName);
 			if (resolvedName != null) {
diff --git a/spring-core/src/main/java/org/springframework/util/ResourceUtils.java b/spring-core/src/main/java/org/springframework/util/ResourceUtils.java
index 02c302752c89..9a2f12f1cdbf 100644
--- a/spring-core/src/main/java/org/springframework/util/ResourceUtils.java
+++ b/spring-core/src/main/java/org/springframework/util/ResourceUtils.java
@@ -24,6 +24,7 @@
 import java.net.URISyntaxException;
 import java.net.URL;
 import java.net.URLConnection;
+import java.util.Locale;
 
 import org.springframework.lang.Nullable;
 
@@ -306,7 +307,7 @@ public static boolean isJarURL(URL url) {
 	 */
 	public static boolean isJarFileURL(URL url) {
 		return (URL_PROTOCOL_FILE.equals(url.getProtocol()) &&
-				url.getPath().toLowerCase().endsWith(JAR_FILE_EXTENSION));
+				url.getPath().toLowerCase(Locale.ROOT).endsWith(JAR_FILE_EXTENSION));
 	}
 
 	/**
diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/SpelParserConfiguration.java b/spring-expression/src/main/java/org/springframework/expression/spel/SpelParserConfiguration.java
index f0430ac2d676..9d5053a0e2df 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/SpelParserConfiguration.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/SpelParserConfiguration.java
@@ -16,6 +16,8 @@
 
 package org.springframework.expression.spel;
 
+import java.util.Locale;
+
 import org.springframework.core.SpringProperties;
 import org.springframework.lang.Nullable;
 
@@ -46,7 +48,7 @@ public class SpelParserConfiguration {
 	static {
 		String compilerMode = SpringProperties.getProperty(SPRING_EXPRESSION_COMPILER_MODE_PROPERTY_NAME);
 		defaultCompilerMode = (compilerMode != null ?
-				SpelCompilerMode.valueOf(compilerMode.toUpperCase()) : SpelCompilerMode.OFF);
+				SpelCompilerMode.valueOf(compilerMode.toUpperCase(Locale.ROOT)) : SpelCompilerMode.OFF);
 	}
 
 
diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/ast/TypeReference.java b/spring-expression/src/main/java/org/springframework/expression/spel/ast/TypeReference.java
index 3effcf1858e0..0085bb6856cb 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/ast/TypeReference.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/ast/TypeReference.java
@@ -17,6 +17,7 @@
 package org.springframework.expression.spel.ast;
 
 import java.lang.reflect.Array;
+import java.util.Locale;
 
 import org.springframework.asm.MethodVisitor;
 import org.springframework.asm.Type;
@@ -58,7 +59,7 @@ public TypedValue getValueInternal(ExpressionState state) throws EvaluationExcep
 		String typeName = (String) this.children[0].getValueInternal(state).getValue();
 		Assert.state(typeName != null, "No type name");
 		if (!typeName.contains(".") && Character.isLowerCase(typeName.charAt(0))) {
-			TypeCode tc = TypeCode.valueOf(typeName.toUpperCase());
+			TypeCode tc = TypeCode.valueOf(typeName.toUpperCase(Locale.ROOT));
 			if (tc != TypeCode.OBJECT) {
 				// It is a primitive type
 				Class<?> clazz = makeArrayIfNecessary(tc.getType());
diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/standard/InternalSpelExpressionParser.java b/spring-expression/src/main/java/org/springframework/expression/spel/standard/InternalSpelExpressionParser.java
index 8d2c0d2a3ede..c8c341a54375 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/standard/InternalSpelExpressionParser.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/standard/InternalSpelExpressionParser.java
@@ -21,6 +21,7 @@
 import java.util.Collections;
 import java.util.Deque;
 import java.util.List;
+import java.util.Locale;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.concurrent.ConcurrentMap;
 import java.util.regex.Pattern;
@@ -750,7 +751,7 @@ private SpelNodeImpl eatPossiblyQualifiedId() {
 				throw internalException( this.expressionString.length(), SpelMessage.OOD);
 			}
 			throw internalException(node.startPos, SpelMessage.NOT_EXPECTED_TOKEN,
-					"qualified ID", node.getKind().toString().toLowerCase());
+					"qualified ID", node.getKind().toString().toLowerCase(Locale.ROOT));
 		}
 		return new QualifiedIdentifier(qualifiedIdPieces.getFirst().getStartPosition(),
 				qualifiedIdPieces.getLast().getEndPosition(), qualifiedIdPieces.toArray(new SpelNodeImpl[0]));
@@ -942,7 +943,7 @@ private Token eatToken(TokenKind expectedKind) {
 		}
 		if (t.kind != expectedKind) {
 			throw internalException(t.startPos, SpelMessage.NOT_EXPECTED_TOKEN,
-					expectedKind.toString().toLowerCase(), t.getKind().toString().toLowerCase());
+					expectedKind.toString().toLowerCase(Locale.ROOT), t.getKind().toString().toLowerCase(Locale.ROOT));
 		}
 		return t;
 	}
@@ -1038,7 +1039,7 @@ public String toString(@Nullable Token t) {
 		if (t.getKind().hasPayload()) {
 			return t.stringValue();
 		}
-		return t.kind.toString().toLowerCase();
+		return t.kind.toString().toLowerCase(Locale.ROOT);
 	}
 
 	private void checkOperands(Token token, @Nullable SpelNodeImpl left, @Nullable SpelNodeImpl right) {
diff --git a/spring-expression/src/main/java/org/springframework/expression/spel/standard/Tokenizer.java b/spring-expression/src/main/java/org/springframework/expression/spel/standard/Tokenizer.java
index 8d80fc8a3364..379ca5b22250 100644
--- a/spring-expression/src/main/java/org/springframework/expression/spel/standard/Tokenizer.java
+++ b/spring-expression/src/main/java/org/springframework/expression/spel/standard/Tokenizer.java
@@ -19,6 +19,7 @@
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Locale;
 
 import org.springframework.expression.spel.InternalParseException;
 import org.springframework.expression.spel.SpelMessage;
@@ -457,7 +458,7 @@ private void lexIdentifier() {
 		// Check if this is the alternative (textual) representation of an operator (see
 		// ALTERNATIVE_OPERATOR_NAMES).
 		if (subarray.length == 2 || subarray.length == 3) {
-			String asString = new String(subarray).toUpperCase();
+			String asString = new String(subarray).toUpperCase(Locale.ROOT);
 			int idx = Arrays.binarySearch(ALTERNATIVE_OPERATOR_NAMES, asString);
 			if (idx >= 0) {
 				pushOneCharOrTwoCharToken(TokenKind.valueOf(asString), start, subarray);
diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/CallMetaDataContext.java b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/CallMetaDataContext.java
index 6b84ceb1d02e..fdc66aa1c342 100755
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/CallMetaDataContext.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/CallMetaDataContext.java
@@ -385,7 +385,7 @@ protected List<SqlParameter> reconcileParameters(List<SqlParameter> parameters)
 				if (meta.isReturnParameter()) {
 					param = declaredParams.get(getFunctionReturnName());
 					if (param == null && !getOutParameterNames().isEmpty()) {
-						param = declaredParams.get(getOutParameterNames().get(0).toLowerCase());
+						param = declaredParams.get(getOutParameterNames().get(0).toLowerCase(Locale.ROOT));
 					}
 					if (param == null) {
 						throw new InvalidDataAccessApiUsageException(
@@ -488,7 +488,7 @@ public Map<String, Object> matchInParameterValuesWithCallParameters(SqlParameter
 				String parameterName = parameter.getName();
 				String parameterNameToMatch = obtainMetaDataProvider().parameterNameToUse(parameterName);
 				if (parameterNameToMatch != null) {
-					callParameterNames.put(parameterNameToMatch.toLowerCase(), parameterName);
+					callParameterNames.put(parameterNameToMatch.toLowerCase(Locale.ROOT), parameterName);
 				}
 				if (parameterName != null) {
 					if (parameterSource.hasValue(parameterName)) {
@@ -496,7 +496,7 @@ public Map<String, Object> matchInParameterValuesWithCallParameters(SqlParameter
 								SqlParameterSourceUtils.getTypedValue(parameterSource, parameterName));
 					}
 					else {
-						String lowerCaseName = parameterName.toLowerCase();
+						String lowerCaseName = parameterName.toLowerCase(Locale.ROOT);
 						if (parameterSource.hasValue(lowerCaseName)) {
 							matchedParameters.put(parameterName,
 									SqlParameterSourceUtils.getTypedValue(parameterSource, lowerCaseName));
@@ -556,7 +556,7 @@ else if (logger.isInfoEnabled()) {
 				String parameterName = parameter.getName();
 				String parameterNameToMatch = provider.parameterNameToUse(parameterName);
 				if (parameterNameToMatch != null) {
-					callParameterNames.put(parameterNameToMatch.toLowerCase(), parameterName);
+					callParameterNames.put(parameterNameToMatch.toLowerCase(Locale.ROOT), parameterName);
 				}
 			}
 		}
@@ -681,7 +681,7 @@ protected String createParameterBinding(SqlParameter parameter) {
 	}
 
 	private static String lowerCase(@Nullable String paramName) {
-		return (paramName != null ? paramName.toLowerCase() : "");
+		return (paramName != null ? paramName.toLowerCase(Locale.ROOT) : "");
 	}
 
 }
diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/Db2CallMetaDataProvider.java b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/Db2CallMetaDataProvider.java
index 13904c9f340e..66c49564681c 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/Db2CallMetaDataProvider.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/Db2CallMetaDataProvider.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -18,6 +18,7 @@
 
 import java.sql.DatabaseMetaData;
 import java.sql.SQLException;
+import java.util.Locale;
 
 import org.springframework.lang.Nullable;
 
@@ -73,7 +74,7 @@ public String metaDataSchemaNameToUse(@Nullable String schemaName) {
 
 		// Use current user schema if no schema specified...
 		String userName = getUserName();
-		return (userName != null ? userName.toUpperCase() : null);
+		return (userName != null ? userName.toUpperCase(Locale.ROOT) : null);
 	}
 
 }
diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/DerbyCallMetaDataProvider.java b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/DerbyCallMetaDataProvider.java
index 02bbaa629f23..efaa556cf6b3 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/DerbyCallMetaDataProvider.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/DerbyCallMetaDataProvider.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2018 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.
@@ -18,6 +18,7 @@
 
 import java.sql.DatabaseMetaData;
 import java.sql.SQLException;
+import java.util.Locale;
 
 import org.springframework.lang.Nullable;
 
@@ -45,7 +46,7 @@ public String metaDataSchemaNameToUse(@Nullable String schemaName) {
 
 		// Use current user schema if no schema specified...
 		String userName = getUserName();
-		return (userName != null ? userName.toUpperCase() : null);
+		return (userName != null ? userName.toUpperCase(Locale.ROOT) : null);
 	}
 
 }
diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/GenericCallMetaDataProvider.java b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/GenericCallMetaDataProvider.java
index 36383fefc578..5eb124b063f6 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/GenericCallMetaDataProvider.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/GenericCallMetaDataProvider.java
@@ -22,6 +22,7 @@
 import java.sql.Types;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -284,10 +285,10 @@ private String identifierNameToUse(@Nullable String identifierName) {
 			return null;
 		}
 		else if (isStoresUpperCaseIdentifiers()) {
-			return identifierName.toUpperCase();
+			return identifierName.toUpperCase(Locale.ROOT);
 		}
 		else if (isStoresLowerCaseIdentifiers()) {
-			return identifierName.toLowerCase();
+			return identifierName.toLowerCase(Locale.ROOT);
 		}
 		else {
 			return identifierName;
diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/GenericTableMetaDataProvider.java b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/GenericTableMetaDataProvider.java
index 6269c0d91ae8..b5e65f418b9b 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/GenericTableMetaDataProvider.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/GenericTableMetaDataProvider.java
@@ -24,6 +24,7 @@
 import java.util.Arrays;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 
 import org.apache.commons.logging.Log;
@@ -214,10 +215,10 @@ private String identifierNameToUse(@Nullable String identifierName) {
 			return null;
 		}
 		else if (isStoresUpperCaseIdentifiers()) {
-			return identifierName.toUpperCase();
+			return identifierName.toUpperCase(Locale.ROOT);
 		}
 		else if (isStoresLowerCaseIdentifiers()) {
-			return identifierName.toLowerCase();
+			return identifierName.toLowerCase(Locale.ROOT);
 		}
 		else {
 			return identifierName;
@@ -326,10 +327,10 @@ private void locateTableAndProcessMetaData(DatabaseMetaData databaseMetaData,
 				TableMetaData tmd = new TableMetaData(tables.getString("TABLE_CAT"),
 						tables.getString("TABLE_SCHEM"), tables.getString("TABLE_NAME"));
 				if (tmd.schemaName() == null) {
-					tableMeta.put(this.userName != null ? this.userName.toUpperCase() : "", tmd);
+					tableMeta.put(this.userName != null ? this.userName.toUpperCase(Locale.ROOT) : "", tmd);
 				}
 				else {
-					tableMeta.put(tmd.schemaName().toUpperCase(), tmd);
+					tableMeta.put(tmd.schemaName().toUpperCase(Locale.ROOT), tmd);
 				}
 			}
 		}
@@ -356,7 +357,7 @@ private TableMetaData findTableMetaData(@Nullable String schemaName, @Nullable S
 			Map<String, TableMetaData> tableMeta) {
 
 		if (schemaName != null) {
-			TableMetaData tmd = tableMeta.get(schemaName.toUpperCase());
+			TableMetaData tmd = tableMeta.get(schemaName.toUpperCase(Locale.ROOT));
 			if (tmd == null) {
 				throw new DataAccessResourceFailureException("Unable to locate table meta-data for '" +
 						tableName + "' in the '" + schemaName + "' schema");
@@ -369,7 +370,7 @@ else if (tableMeta.size() == 1) {
 		else {
 			TableMetaData tmd = tableMeta.get(getDefaultSchema());
 			if (tmd == null) {
-				tmd = tableMeta.get(this.userName != null ? this.userName.toUpperCase() : "");
+				tmd = tableMeta.get(this.userName != null ? this.userName.toUpperCase(Locale.ROOT) : "");
 			}
 			if (tmd == null) {
 				tmd = tableMeta.get("PUBLIC");
diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/TableMetaDataContext.java b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/TableMetaDataContext.java
index 577a0093d8e9..5b655509783e 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/TableMetaDataContext.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/core/metadata/TableMetaDataContext.java
@@ -20,6 +20,7 @@
 import java.util.Collections;
 import java.util.LinkedHashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 
@@ -217,11 +218,11 @@ protected List<String> reconcileColumnsToUse(List<String> declaredColumns, Strin
 		}
 		Set<String> keys = new LinkedHashSet<>(generatedKeyNames.length);
 		for (String key : generatedKeyNames) {
-			keys.add(key.toUpperCase());
+			keys.add(key.toUpperCase(Locale.ROOT));
 		}
 		List<String> columns = new ArrayList<>();
 		for (TableParameterMetaData meta : obtainMetaDataProvider().getTableParameterMetaData()) {
-			if (!keys.contains(meta.getParameterName().toUpperCase())) {
+			if (!keys.contains(meta.getParameterName().toUpperCase(Locale.ROOT))) {
 				columns.add(meta.getParameterName());
 			}
 		}
@@ -243,7 +244,7 @@ public List<Object> matchInParameterValuesWithInsertColumns(SqlParameterSource p
 				values.add(SqlParameterSourceUtils.getTypedValue(parameterSource, column));
 			}
 			else {
-				String lowerCaseName = column.toLowerCase();
+				String lowerCaseName = column.toLowerCase(Locale.ROOT);
 				if (parameterSource.hasValue(lowerCaseName)) {
 					values.add(SqlParameterSourceUtils.getTypedValue(parameterSource, lowerCaseName));
 				}
@@ -276,7 +277,7 @@ public List<Object> matchInParameterValuesWithInsertColumns(Map<String, ?> inPar
 		for (String column : this.tableColumns) {
 			Object value = inParameters.get(column);
 			if (value == null) {
-				value = inParameters.get(column.toLowerCase());
+				value = inParameters.get(column.toLowerCase(Locale.ROOT));
 				if (value == null) {
 					for (Map.Entry<String, ?> entry : inParameters.entrySet()) {
 						if (column.equalsIgnoreCase(entry.getKey())) {
@@ -298,7 +299,7 @@ public List<Object> matchInParameterValuesWithInsertColumns(Map<String, ?> inPar
 	public String createInsertString(String... generatedKeyNames) {
 		Set<String> keys = new LinkedHashSet<>(generatedKeyNames.length);
 		for (String key : generatedKeyNames) {
-			keys.add(key.toUpperCase());
+			keys.add(key.toUpperCase(Locale.ROOT));
 		}
 
 		String identifierQuoteString = (isQuoteIdentifiers() ?
@@ -326,7 +327,7 @@ public String createInsertString(String... generatedKeyNames) {
 		insertStatement.append(" (");
 		int columnCount = 0;
 		for (String columnName : getTableColumns()) {
-			if (!keys.contains(columnName.toUpperCase())) {
+			if (!keys.contains(columnName.toUpperCase(Locale.ROOT))) {
 				columnCount++;
 				if (columnCount > 1) {
 					insertStatement.append(", ");
@@ -366,7 +367,7 @@ public int[] createInsertTypes() {
 		List<TableParameterMetaData> parameters = obtainMetaDataProvider().getTableParameterMetaData();
 		Map<String, TableParameterMetaData> parameterMap = CollectionUtils.newLinkedHashMap(parameters.size());
 		for (TableParameterMetaData tpmd : parameters) {
-			parameterMap.put(tpmd.getParameterName().toUpperCase(), tpmd);
+			parameterMap.put(tpmd.getParameterName().toUpperCase(Locale.ROOT), tpmd);
 		}
 		int typeIndx = 0;
 		for (String column : getTableColumns()) {
@@ -374,7 +375,7 @@ public int[] createInsertTypes() {
 				types[typeIndx] = SqlTypeValue.TYPE_UNKNOWN;
 			}
 			else {
-				TableParameterMetaData tpmd = parameterMap.get(column.toUpperCase());
+				TableParameterMetaData tpmd = parameterMap.get(column.toUpperCase(Locale.ROOT));
 				if (tpmd != null) {
 					types[typeIndx] = tpmd.getSqlType();
 				}
diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/core/namedparam/SqlParameterSourceUtils.java b/spring-jdbc/src/main/java/org/springframework/jdbc/core/namedparam/SqlParameterSourceUtils.java
index 89b3f832dbab..9709561eb286 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/core/namedparam/SqlParameterSourceUtils.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/core/namedparam/SqlParameterSourceUtils.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.
@@ -19,6 +19,7 @@
 import java.util.Arrays;
 import java.util.Collection;
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 
 import org.springframework.jdbc.core.SqlParameterValue;
@@ -115,7 +116,7 @@ public static Map<String, String> extractCaseInsensitiveParameterNames(SqlParame
 		String[] paramNames = parameterSource.getParameterNames();
 		if (paramNames != null) {
 			for (String name : paramNames) {
-				caseInsensitiveParameterNames.put(name.toLowerCase(), name);
+				caseInsensitiveParameterNames.put(name.toLowerCase(Locale.ROOT), name);
 			}
 		}
 		return caseInsensitiveParameterNames;
diff --git a/spring-jdbc/src/main/java/org/springframework/jdbc/core/simple/AbstractJdbcInsert.java b/spring-jdbc/src/main/java/org/springframework/jdbc/core/simple/AbstractJdbcInsert.java
index 979ae771a56f..6b86dbb67390 100644
--- a/spring-jdbc/src/main/java/org/springframework/jdbc/core/simple/AbstractJdbcInsert.java
+++ b/spring-jdbc/src/main/java/org/springframework/jdbc/core/simple/AbstractJdbcInsert.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.
@@ -26,6 +26,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 
 import javax.sql.DataSource;
@@ -490,7 +491,7 @@ private KeyHolder executeInsertAndReturnKeyHolderInternal(List<?> values) {
 			// get generated keys feature. HSQL is one, PostgreSQL is another. Postgres uses a RETURNING
 			// clause while HSQL uses a second query that has to be executed with the same connection.
 
-			if (keyQuery.toUpperCase().startsWith("RETURNING")) {
+			if (keyQuery.toUpperCase(Locale.ROOT).startsWith("RETURNING")) {
 				Long key = getJdbcTemplate().queryForObject(
 						getInsertString() + " " + keyQuery, Long.class, values.toArray());
 				Map<String, Object> keys = new HashMap<>(2);
diff --git a/spring-jms/src/main/java/org/springframework/jms/config/JmsListenerContainerParser.java b/spring-jms/src/main/java/org/springframework/jms/config/JmsListenerContainerParser.java
index 39ff7a719a1c..85d075415a9a 100644
--- a/spring-jms/src/main/java/org/springframework/jms/config/JmsListenerContainerParser.java
+++ b/spring-jms/src/main/java/org/springframework/jms/config/JmsListenerContainerParser.java
@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 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.
@@ -16,6 +16,8 @@
 
 package org.springframework.jms.config;
 
+import java.util.Locale;
+
 import jakarta.jms.Session;
 import org.w3c.dom.Element;
 
@@ -155,7 +157,7 @@ protected MutablePropertyValues parseSpecificContainerProperties(Element contain
 				}
 			}
 			else {
-				properties.add("cacheLevelName", "CACHE_" + cache.toUpperCase());
+				properties.add("cacheLevelName", "CACHE_" + cache.toUpperCase(Locale.ROOT));
 			}
 		}
 
diff --git a/spring-test/src/main/java/org/springframework/test/context/NestedTestConfiguration.java b/spring-test/src/main/java/org/springframework/test/context/NestedTestConfiguration.java
index 3686560b7a15..c348ef157665 100644
--- a/spring-test/src/main/java/org/springframework/test/context/NestedTestConfiguration.java
+++ b/spring-test/src/main/java/org/springframework/test/context/NestedTestConfiguration.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.
@@ -22,6 +22,7 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
+import java.util.Locale;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -159,7 +160,7 @@ public static EnclosingConfiguration from(@Nullable String name) {
 				return null;
 			}
 			try {
-				return EnclosingConfiguration.valueOf(name.trim().toUpperCase());
+				return EnclosingConfiguration.valueOf(name.trim().toUpperCase(Locale.ROOT));
 			}
 			catch (IllegalArgumentException ex) {
 				Log logger = LogFactory.getLog(EnclosingConfiguration.class);
@@ -171,7 +172,6 @@ public static EnclosingConfiguration from(@Nullable String name) {
 				return null;
 			}
 		}
-
 	}
 
 }
diff --git a/spring-test/src/main/java/org/springframework/test/context/TestConstructor.java b/spring-test/src/main/java/org/springframework/test/context/TestConstructor.java
index 74ebda799dd9..8997f455b611 100644
--- a/spring-test/src/main/java/org/springframework/test/context/TestConstructor.java
+++ b/spring-test/src/main/java/org/springframework/test/context/TestConstructor.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.
@@ -22,6 +22,7 @@
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
 import java.lang.annotation.Target;
+import java.util.Locale;
 
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
@@ -161,7 +162,7 @@ public static AutowireMode from(@Nullable String name) {
 				return null;
 			}
 			try {
-				return AutowireMode.valueOf(name.trim().toUpperCase());
+				return AutowireMode.valueOf(name.trim().toUpperCase(Locale.ROOT));
 			}
 			catch (IllegalArgumentException ex) {
 				Log logger = LogFactory.getLog(AutowireMode.class);