Merge branch '6.1.x'

framework-docs/src/main/java/org/springframework/docs/integration/observability/config/conventions/CustomServerRequestObservationConvention.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.
@@ -16,6 +16,8 @@
 
 package org.springframework.docs.integration.observability.config.conventions;
 
+import java.util.Locale;
+
 import io.micrometer.common.KeyValue;
 import io.micrometer.common.KeyValues;
 
@@ -34,7 +36,7 @@ public class CustomServerRequestObservationConvention implements ServerRequestOb
 	@Override
 	public String getContextualName(ServerRequestObservationContext context) {
 		// will be used for the trace name
-		return "http " + context.getCarrier().getMethod().toLowerCase();
+		return "http " + context.getCarrier().getMethod().toLowerCase(Locale.ROOT);
 	}
 
 	@Override

spring-context/src/main/java/org/springframework/validation/DataBinder.java

@@ -27,6 +27,7 @@ import java.util.Collections;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Optional;
 import java.util.Set;
@@ -570,7 +571,8 @@ public class DataBinder implements PropertyEditorRegistry, TypeConverter {
 		else {
 			String[] fieldPatterns = new String[disallowedFields.length];
 			for (int i = 0; i < fieldPatterns.length; i++) {
-				fieldPatterns[i] = PropertyAccessorUtils.canonicalPropertyName(disallowedFields[i]).toLowerCase();
+				String field = PropertyAccessorUtils.canonicalPropertyName(disallowedFields[i]);
+				fieldPatterns[i] = field.toLowerCase(Locale.ROOT);
 			}
 			this.disallowedFields = fieldPatterns;
 		}
@@ -1248,7 +1250,7 @@ public class DataBinder implements PropertyEditorRegistry, TypeConverter {
 		String[] allowed = getAllowedFields();
 		String[] disallowed = getDisallowedFields();
 		return ((ObjectUtils.isEmpty(allowed) || PatternMatchUtils.simpleMatch(allowed, field)) &&
-				(ObjectUtils.isEmpty(disallowed) || !PatternMatchUtils.simpleMatch(disallowed, field.toLowerCase())));
+				(ObjectUtils.isEmpty(disallowed) || !PatternMatchUtils.simpleMatch(disallowed, field.toLowerCase(Locale.ROOT))));
 	}
 
 	/**

spring-core/src/main/java/org/springframework/util/MimeType.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.
@@ -181,10 +181,10 @@ public class MimeType implements Comparable<MimeType>, Serializable {
 		Assert.hasLength(subtype, "'subtype' must not be empty");
 		checkToken(type);
 		checkToken(subtype);
-		this.type = type.toLowerCase(Locale.ENGLISH);
+		this.type = type.toLowerCase(Locale.ROOT);
-		this.subtype = subtype.toLowerCase(Locale.ENGLISH);
+		this.subtype = subtype.toLowerCase(Locale.ROOT);
 		if (!CollectionUtils.isEmpty(parameters)) {
-			Map<String, String> map = new LinkedCaseInsensitiveMap<>(parameters.size(), Locale.ENGLISH);
+			Map<String, String> map = new LinkedCaseInsensitiveMap<>(parameters.size(), Locale.ROOT);
 			parameters.forEach((parameter, value) -> {
 				checkParameters(parameter, value);
 				map.put(parameter, value);

spring-test/src/main/java/org/springframework/mock/web/MockHttpServletRequest.java

@@ -412,7 +412,8 @@ public class MockHttpServletRequest implements HttpServletRequest {
 	private void updateContentTypeHeader() {
 		if (StringUtils.hasLength(this.contentType)) {
 			String value = this.contentType;
-			if (StringUtils.hasLength(this.characterEncoding) && !this.contentType.toLowerCase().contains(CHARSET_PREFIX)) {
+			if (StringUtils.hasLength(this.characterEncoding) &&
+					!this.contentType.toLowerCase(Locale.ROOT).contains(CHARSET_PREFIX)) {
 				value += ';' + CHARSET_PREFIX + this.characterEncoding;
 			}
 			doAddHeaderValue(HttpHeaders.CONTENT_TYPE, value, true);
@@ -490,7 +491,7 @@ public class MockHttpServletRequest implements HttpServletRequest {
 			}
 			catch (IllegalArgumentException ex) {
 				// Try to get charset value anyway
-				contentType = contentType.toLowerCase();
+				contentType = contentType.toLowerCase(Locale.ROOT);
 				int charsetIndex = contentType.indexOf(CHARSET_PREFIX);
 				if (charsetIndex != -1) {
 					this.characterEncoding = contentType.substring(charsetIndex + CHARSET_PREFIX.length());

spring-test/src/main/java/org/springframework/mock/web/MockHttpServletResponse.java

@@ -226,7 +226,7 @@ public class MockHttpServletResponse implements HttpServletResponse {
 				}
 				catch (Exception ignored) {
 					String value = this.contentType;
-					int charsetIndex = value.toLowerCase().indexOf(CHARSET_PREFIX);
+					int charsetIndex = value.toLowerCase(Locale.ROOT).indexOf(CHARSET_PREFIX);
 					if (charsetIndex != -1) {
 						value = value.substring(0, charsetIndex).trim();
 						if (value.endsWith(";")) {
@@ -246,7 +246,7 @@ public class MockHttpServletResponse implements HttpServletResponse {
 	private void updateContentTypePropertyAndHeader() {
 		if (this.contentType != null) {
 			String value = this.contentType;
-			if (this.characterEncodingSet && !value.toLowerCase().contains(CHARSET_PREFIX)) {
+			if (this.characterEncodingSet && !value.toLowerCase(Locale.ROOT).contains(CHARSET_PREFIX)) {
 				value += ';' + CHARSET_PREFIX + getCharacterEncoding();
 				this.contentType = value;
 			}
@@ -358,7 +358,7 @@ public class MockHttpServletResponse implements HttpServletResponse {
 			}
 			catch (Exception ex) {
 				// Try to get charset value anyway
-				int charsetIndex = contentType.toLowerCase().indexOf(CHARSET_PREFIX);
+				int charsetIndex = contentType.toLowerCase(Locale.ROOT).indexOf(CHARSET_PREFIX);
 				if (charsetIndex != -1) {
 					setExplicitCharacterEncoding(contentType.substring(charsetIndex + CHARSET_PREFIX.length()));
 				}

spring-web/src/main/java/org/springframework/http/HttpHeaders.java

@@ -391,7 +391,7 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 	 */
 	public static final HttpHeaders EMPTY = new ReadOnlyHttpHeaders(new LinkedMultiValueMap<>());
 
-	private static final DecimalFormatSymbols DECIMAL_FORMAT_SYMBOLS = new DecimalFormatSymbols(Locale.ENGLISH);
+	private static final DecimalFormatSymbols DECIMAL_FORMAT_SYMBOLS = new DecimalFormatSymbols(Locale.ROOT);
 
 	private static final ZoneId GMT = ZoneId.of("GMT");
 
@@ -421,7 +421,7 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 	 * <p>This is the common constructor, using a case-insensitive map structure.
 	 */
 	public HttpHeaders() {
-		this(CollectionUtils.toMultiValueMap(new LinkedCaseInsensitiveMap<>(8, Locale.ENGLISH)));
+		this(CollectionUtils.toMultiValueMap(new LinkedCaseInsensitiveMap<>(8, Locale.ROOT)));
 	}
 
 	/**
@@ -717,7 +717,7 @@ public class HttpHeaders implements MultiValueMap<String, String>, Serializable
 	public void setAcceptCharset(List<Charset> acceptableCharsets) {
 		StringJoiner joiner = new StringJoiner(", ");
 		for (Charset charset : acceptableCharsets) {
-			joiner.add(charset.name().toLowerCase(Locale.ENGLISH));
+			joiner.add(charset.name().toLowerCase(Locale.ROOT));
 		}
 		set(ACCEPT_CHARSET, joiner.toString());
 	}

spring-web/src/main/java/org/springframework/http/MediaTypeFactory.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.
@@ -77,7 +77,7 @@ public final class MediaTypeFactory {
 				String[] tokens = StringUtils.tokenizeToStringArray(line, " \t\n\r\f");
 				MediaType mediaType = MediaType.parseMediaType(tokens[0]);
 				for (int i = 1; i < tokens.length; i++) {
-					String fileExtension = tokens[i].toLowerCase(Locale.ENGLISH);
+					String fileExtension = tokens[i].toLowerCase(Locale.ROOT);
 					result.add(fileExtension, mediaType);
 				}
 			}
@@ -117,7 +117,7 @@ public final class MediaTypeFactory {
 		List<MediaType> mediaTypes = null;
 		String ext = StringUtils.getFilenameExtension(filename);
 		if (ext != null) {
-			mediaTypes = fileExtensionToMediaTypes.get(ext.toLowerCase(Locale.ENGLISH));
+			mediaTypes = fileExtensionToMediaTypes.get(ext.toLowerCase(Locale.ROOT));
 		}
 		return (mediaTypes != null ? mediaTypes : Collections.emptyList());
 	}

spring-web/src/main/java/org/springframework/http/client/JdkClientHttpRequest.java

@@ -28,6 +28,7 @@ import java.net.http.HttpTimeoutException;
 import java.nio.ByteBuffer;
 import java.time.Duration;
 import java.util.Collections;
+import java.util.Locale;
 import java.util.Set;
 import java.util.TreeSet;
 import java.util.concurrent.CancellationException;
@@ -141,7 +142,7 @@ class JdkClientHttpRequest extends AbstractStreamingClientHttpRequest {
 		HttpRequest.Builder builder = HttpRequest.newBuilder().uri(this.uri);
 
 		headers.forEach((headerName, headerValues) -> {
-			if (!DISALLOWED_HEADERS.contains(headerName.toLowerCase())) {
+			if (!DISALLOWED_HEADERS.contains(headerName.toLowerCase(Locale.ROOT))) {
 				for (String headerValue : headerValues) {
 					builder.header(headerName, headerValue);
 				}

spring-web/src/main/java/org/springframework/http/client/JdkClientHttpResponse.java

@@ -57,7 +57,7 @@ class JdkClientHttpResponse implements ClientHttpResponse {
 
 	private static HttpHeaders adaptHeaders(HttpResponse<?> response) {
 		Map<String, List<String>> rawHeaders = response.headers().map();
-		Map<String, List<String>> map = new LinkedCaseInsensitiveMap<>(rawHeaders.size(), Locale.ENGLISH);
+		Map<String, List<String>> map = new LinkedCaseInsensitiveMap<>(rawHeaders.size(), Locale.ROOT);
 		MultiValueMap<String, String> multiValueMap = CollectionUtils.toMultiValueMap(map);
 		multiValueMap.putAll(rawHeaders);
 		return HttpHeaders.readOnlyHttpHeaders(multiValueMap);

spring-web/src/main/java/org/springframework/http/client/observation/DefaultClientRequestObservationConvention.java

@@ -17,6 +17,7 @@
 package org.springframework.http.client.observation;
 
 import java.io.IOException;
+import java.util.Locale;
 import java.util.regex.Pattern;
 
 import io.micrometer.common.KeyValue;
@@ -89,7 +90,7 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 	@Nullable
 	public String getContextualName(ClientRequestObservationContext context) {
 		ClientHttpRequest request = context.getCarrier();
-		return (request != null ? "http " + request.getMethod().name().toLowerCase() : null);
+		return (request != null ? "http " + request.getMethod().name().toLowerCase(Locale.ROOT) : null);
 	}
 
 	@Override

spring-web/src/main/java/org/springframework/http/client/reactive/JdkClientHttpResponse.java

@@ -68,7 +68,7 @@ class JdkClientHttpResponse extends AbstractClientHttpResponse {
 
 	private static HttpHeaders adaptHeaders(HttpResponse<Flow.Publisher<List<ByteBuffer>>> response) {
 		Map<String, List<String>> rawHeaders = response.headers().map();
-		Map<String, List<String>> map = new LinkedCaseInsensitiveMap<>(rawHeaders.size(), Locale.ENGLISH);
+		Map<String, List<String>> map = new LinkedCaseInsensitiveMap<>(rawHeaders.size(), Locale.ROOT);
 		MultiValueMap<String, String> multiValueMap = CollectionUtils.toMultiValueMap(map);
 		multiValueMap.putAll(rawHeaders);
 		return HttpHeaders.readOnlyHttpHeaders(multiValueMap);

spring-web/src/main/java/org/springframework/http/server/observation/DefaultServerRequestObservationConvention.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.
@@ -16,6 +16,7 @@
 
 package org.springframework.http.server.observation;
 
+import java.util.Locale;
 import java.util.Set;
 import java.util.stream.Collectors;
 import java.util.stream.Stream;
@@ -89,7 +90,7 @@ public class DefaultServerRequestObservationConvention implements ServerRequestO
 
 	@Override
 	public String getContextualName(ServerRequestObservationContext context) {
-		String httpMethod = context.getCarrier().getMethod().toLowerCase();
+		String httpMethod = context.getCarrier().getMethod().toLowerCase(Locale.ROOT);
 		if (context.getPathPattern() != null) {
 			return "http " + httpMethod + " " + context.getPathPattern();
 		}

spring-web/src/main/java/org/springframework/http/server/reactive/ServletServerHttpRequest.java

@@ -112,7 +112,7 @@ class ServletServerHttpRequest extends AbstractServerHttpRequest {
 
 	private static MultiValueMap<String, String> createDefaultHttpHeaders(HttpServletRequest request) {
 		MultiValueMap<String, String> headers =
-				CollectionUtils.toMultiValueMap(new LinkedCaseInsensitiveMap<>(8, Locale.ENGLISH));
+				CollectionUtils.toMultiValueMap(new LinkedCaseInsensitiveMap<>(8, Locale.ROOT));
 		for (Enumeration<?> names = request.getHeaderNames(); names.hasMoreElements(); ) {
 			String name = (String) names.nextElement();
 			for (Enumeration<?> values = request.getHeaders(name); values.hasMoreElements(); ) {

spring-web/src/main/java/org/springframework/http/server/reactive/observation/DefaultServerRequestObservationConvention.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.
@@ -16,6 +16,7 @@
 
 package org.springframework.http.server.reactive.observation;
 
+import java.util.Locale;
 import java.util.Set;
 
 import io.micrometer.common.KeyValue;
@@ -87,7 +88,7 @@ public class DefaultServerRequestObservationConvention implements ServerRequestO
 
 	@Override
 	public String getContextualName(ServerRequestObservationContext context) {
-		String httpMethod = context.getCarrier().getMethod().name().toLowerCase();
+		String httpMethod = context.getCarrier().getMethod().name().toLowerCase(Locale.ROOT);
 		if (context.getPathPattern() != null) {
 			return "http " + httpMethod + " " + context.getPathPattern();
 		}

spring-web/src/main/java/org/springframework/web/accept/ContentNegotiationManagerFactoryBean.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.
@@ -214,7 +214,7 @@ public class ContentNegotiationManagerFactoryBean
 	 * An alternative to {@link #setMediaTypes} for programmatic registrations.
 	 */
 	public void addMediaType(String key, MediaType mediaType) {
-		this.mediaTypes.put(key.toLowerCase(Locale.ENGLISH), mediaType);
+		this.mediaTypes.put(key.toLowerCase(Locale.ROOT), mediaType);
 	}
 
 	/**

spring-web/src/main/java/org/springframework/web/accept/MappingMediaTypeFileExtensionResolver.java

@@ -57,7 +57,7 @@ public class MappingMediaTypeFileExtensionResolver implements MediaTypeFileExten
 		if (mediaTypes != null) {
 			Set<String> allFileExtensions = CollectionUtils.newHashSet(mediaTypes.size());
 			mediaTypes.forEach((extension, mediaType) -> {
-				String lowerCaseExtension = extension.toLowerCase(Locale.ENGLISH);
+				String lowerCaseExtension = extension.toLowerCase(Locale.ROOT);
 				this.mediaTypes.put(lowerCaseExtension, mediaType);
 				addFileExtension(mediaType, lowerCaseExtension);
 				allFileExtensions.add(lowerCaseExtension);
@@ -109,7 +109,7 @@ public class MappingMediaTypeFileExtensionResolver implements MediaTypeFileExten
 	 */
 	@Nullable
 	protected MediaType lookupMediaType(String extension) {
-		return this.mediaTypes.get(extension.toLowerCase(Locale.ENGLISH));
+		return this.mediaTypes.get(extension.toLowerCase(Locale.ROOT));
 	}
 
 }

spring-web/src/main/java/org/springframework/web/accept/PathExtensionContentNegotiationStrategy.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.
@@ -99,7 +99,7 @@ public class PathExtensionContentNegotiationStrategy extends AbstractMappingCont
 		// Ignore LOOKUP_PATH attribute, use our own "fixed" UrlPathHelper with decoding off
 		String path = this.urlPathHelper.getLookupPathForRequest(request);
 		String extension = UriUtils.extractFileExtension(path);
-		return (StringUtils.hasText(extension) ? extension.toLowerCase(Locale.ENGLISH) : null);
+		return (StringUtils.hasText(extension) ? extension.toLowerCase(Locale.ROOT) : null);
 	}
 
 	/**

spring-web/src/main/java/org/springframework/web/client/RestClientResponseException.java

@@ -105,7 +105,7 @@ public class RestClientResponseException extends RestClientException {
 	private static HttpHeaders copyHeaders(@Nullable HttpHeaders headers) {
 		if (headers != null) {
 			MultiValueMap<String, String> result =
-					CollectionUtils.toMultiValueMap(new LinkedCaseInsensitiveMap<>(headers.size(), Locale.ENGLISH));
+					CollectionUtils.toMultiValueMap(new LinkedCaseInsensitiveMap<>(headers.size(), Locale.ROOT));
 			headers.forEach((name, values) -> values.forEach(value -> result.add(name, value)));
 			return HttpHeaders.readOnlyHttpHeaders(result);
 		}

spring-web/src/main/java/org/springframework/web/filter/ForwardedHeaderFilter.java

@@ -82,7 +82,7 @@ public class ForwardedHeaderFilter extends OncePerRequestFilter {
 	private static final Log logger = LogFactory.getLog(ForwardedHeaderFilter.class);
 
 	private static final Set<String> FORWARDED_HEADER_NAMES =
-			Collections.newSetFromMap(new LinkedCaseInsensitiveMap<>(10, Locale.ENGLISH));
+			Collections.newSetFromMap(new LinkedCaseInsensitiveMap<>(10, Locale.ROOT));
 
 	static {
 		FORWARDED_HEADER_NAMES.add("Forwarded");
@@ -204,7 +204,7 @@ public class ForwardedHeaderFilter extends OncePerRequestFilter {
 		}
 
 		private static Set<String> headerNames(HttpServletRequest request) {
-			Set<String> headerNames = Collections.newSetFromMap(new LinkedCaseInsensitiveMap<>(Locale.ENGLISH));
+			Set<String> headerNames = Collections.newSetFromMap(new LinkedCaseInsensitiveMap<>(Locale.ROOT));
 			Enumeration<String> names = request.getHeaderNames();
 			while (names.hasMoreElements()) {
 				String name = names.nextElement();

spring-web/src/main/java/org/springframework/web/filter/HiddenHttpMethodFilter.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.
@@ -81,7 +81,7 @@ public class HiddenHttpMethodFilter extends OncePerRequestFilter {
 		if ("POST".equals(request.getMethod()) && request.getAttribute(WebUtils.ERROR_EXCEPTION_ATTRIBUTE) == null) {
 			String paramValue = request.getParameter(this.methodParam);
 			if (StringUtils.hasLength(paramValue)) {
-				String method = paramValue.toUpperCase(Locale.ENGLISH);
+				String method = paramValue.toUpperCase(Locale.ROOT);
 				if (ALLOWED_METHODS.contains(method)) {
 					requestToUse = new HttpMethodRequestWrapper(request, method);
 				}

spring-web/src/main/java/org/springframework/web/filter/reactive/HiddenHttpMethodFilter.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.
@@ -88,7 +88,7 @@ public class HiddenHttpMethodFilter implements WebFilter {
 	}
 
 	private ServerWebExchange mapExchange(ServerWebExchange exchange, String methodParamValue) {
-		HttpMethod httpMethod = HttpMethod.valueOf(methodParamValue.toUpperCase(Locale.ENGLISH));
+		HttpMethod httpMethod = HttpMethod.valueOf(methodParamValue.toUpperCase(Locale.ROOT));
 		if (ALLOWED_METHODS.contains(httpMethod)) {
 			return exchange.mutate().request(builder -> builder.method(httpMethod)).build();
 		}

spring-web/src/main/java/org/springframework/web/multipart/support/MultipartResolutionDelegate.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 @@ package org.springframework.web.multipart.support;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Locale;
 
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.Part;
@@ -71,7 +72,7 @@ public final class MultipartResolutionDelegate {
 
 	private static boolean isMultipartContent(HttpServletRequest request) {
 		String contentType = request.getContentType();
-		return (contentType != null && contentType.toLowerCase().startsWith("multipart/"));
+		return (contentType != null && contentType.toLowerCase(Locale.ROOT).startsWith("multipart/"));
 	}
 
 	static MultipartHttpServletRequest asMultipartHttpServletRequest(HttpServletRequest request) {

spring-web/src/main/java/org/springframework/web/multipart/support/StandardMultipartHttpServletRequest.java

@@ -28,6 +28,7 @@ import java.util.Collections;
 import java.util.Enumeration;
 import java.util.LinkedHashMap;
 import java.util.LinkedHashSet;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 
@@ -118,7 +119,7 @@ public class StandardMultipartHttpServletRequest extends AbstractMultipartHttpSe
 		do {
 			String msg = cause.getMessage();
 			if (msg != null) {
-				msg = msg.toLowerCase();
+				msg = msg.toLowerCase(Locale.ROOT);
 				if ((msg.contains("exceed") && (msg.contains("size") || msg.contains("length"))) ||
 						(msg.contains("request") && (msg.contains("big") || msg.contains("large")))) {
 					throw new MaxUploadSizeExceededException(-1, ex);

spring-web/src/main/java/org/springframework/web/server/adapter/ForwardedHeaderTransformer.java

@@ -61,7 +61,7 @@ import org.springframework.web.util.UriComponents;
 public class ForwardedHeaderTransformer implements Function<ServerHttpRequest, ServerHttpRequest> {
 
 	static final Set<String> FORWARDED_HEADER_NAMES =
-			Collections.newSetFromMap(new LinkedCaseInsensitiveMap<>(10, Locale.ENGLISH));
+			Collections.newSetFromMap(new LinkedCaseInsensitiveMap<>(10, Locale.ROOT));
 
 	static {
 		FORWARDED_HEADER_NAMES.add("Forwarded");

spring-web/src/main/java/org/springframework/web/util/DisconnectedClientHelper.java

@@ -16,6 +16,7 @@
 
 package org.springframework.web.util;
 
+import java.util.Locale;
 import java.util.Set;
 
 import org.apache.commons.logging.Log;
@@ -84,7 +85,7 @@ public class DisconnectedClientHelper {
 	public static boolean isClientDisconnectedException(Throwable ex) {
 		String message = NestedExceptionUtils.getMostSpecificCause(ex).getMessage();
 		if (message != null) {
-			String text = message.toLowerCase();
+			String text = message.toLowerCase(Locale.ROOT);
 			for (String phrase : EXCEPTION_PHRASES) {
 				if (text.contains(phrase)) {
 					return true;

spring-web/src/main/java/org/springframework/web/util/UrlPathHelper.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.
@@ -18,6 +18,7 @@ package org.springframework.web.util;
 
 import java.net.URLDecoder;
 import java.nio.charset.UnsupportedCharsetException;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
 
@@ -629,7 +630,7 @@ public class UrlPathHelper {
 
 	private String removeJsessionid(String requestUri) {
 		String key = ";jsessionid=";
-		int index = requestUri.toLowerCase().indexOf(key);
+		int index = requestUri.toLowerCase(Locale.ROOT).indexOf(key);
 		if (index == -1) {
 			return requestUri;
 		}

spring-web/src/test/java/org/springframework/http/client/AbstractHttpRequestFactoryTests.java

@@ -169,7 +169,7 @@ abstract class AbstractHttpRequestFactoryTests extends AbstractMockWebServerTest
 
 		try (ClientHttpResponse response = request.execute()) {
 			assertThat(response.getStatusCode()).as("Invalid response status").isEqualTo(HttpStatus.OK);
-			assertThat(request.getMethod().name()).as("Invalid method").isEqualTo(path.toUpperCase(Locale.ENGLISH));
+			assertThat(request.getMethod().name()).as("Invalid method").isEqualTo(path.toUpperCase(Locale.ROOT));
 		}
 	}
 

spring-webflux/src/main/java/org/springframework/web/reactive/accept/ParameterContentTypeResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2017 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.
@@ -51,7 +51,7 @@ public class ParameterContentTypeResolver implements RequestedContentTypeResolve
 	}
 
 	private static String formatKey(String key) {
-		return key.toLowerCase(Locale.ENGLISH);
+		return key.toLowerCase(Locale.ROOT);
 	}
 
 

spring-webflux/src/main/java/org/springframework/web/reactive/function/client/DefaultClientRequestObservationConvention.java

@@ -17,6 +17,7 @@
 package org.springframework.web.reactive.function.client;
 
 import java.io.IOException;
+import java.util.Locale;
 import java.util.regex.Pattern;
 
 import io.micrometer.common.KeyValue;
@@ -92,7 +93,7 @@ public class DefaultClientRequestObservationConvention implements ClientRequestO
 	@Nullable
 	public String getContextualName(ClientRequestObservationContext context) {
 		ClientRequest request = context.getRequest();
-		return (request != null ? "http " + request.method().name().toLowerCase() : null);
+		return (request != null ? "http " + request.method().name().toLowerCase(Locale.ROOT) : null);
 	}
 
 	@Override

spring-webflux/src/main/java/org/springframework/web/reactive/resource/CachingResourceResolver.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 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.
@@ -20,6 +20,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.stream.Collectors;
 
 import reactor.core.publisher.Mono;
@@ -140,7 +141,7 @@ public class CachingResourceResolver extends AbstractResourceResolver {
 		return Arrays.stream(StringUtils.tokenizeToStringArray(header, ","))
 				.map(token -> {
 					int index = token.indexOf(';');
-					return (index >= 0 ? token.substring(0, index) : token).trim().toLowerCase();
+					return (index >= 0 ? token.substring(0, index) : token).trim().toLowerCase(Locale.ROOT);
 				})
 				.filter(this.contentCodings::contains)
 				.sorted()

spring-webflux/src/main/java/org/springframework/web/reactive/resource/EncodedResourceResolver.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.
@@ -28,6 +28,7 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 
 import reactor.core.publisher.Mono;
@@ -169,7 +170,7 @@ public class EncodedResourceResolver extends AbstractResourceResolver {
 	private String getAcceptEncoding(ServerWebExchange exchange) {
 		ServerHttpRequest request = exchange.getRequest();
 		String header = request.getHeaders().getFirst(HttpHeaders.ACCEPT_ENCODING);
-		return (header != null ? header.toLowerCase() : null);
+		return (header != null ? header.toLowerCase(Locale.ROOT) : null);
 	}
 
 	private String getExtension(String coding) {

spring-webflux/src/main/java/org/springframework/web/reactive/resource/ResourceWebHandler.java

@@ -339,7 +339,7 @@ public class ResourceWebHandler implements WebHandler, InitializingBean {
 			this.mediaTypes = new HashMap<>(mediaTypes.size());
 		}
 		mediaTypes.forEach((ext, type) ->
-				this.mediaTypes.put(ext.toLowerCase(Locale.ENGLISH), type));
+				this.mediaTypes.put(ext.toLowerCase(Locale.ROOT), type));
 	}
 
 	/**
@@ -532,7 +532,7 @@ public class ResourceWebHandler implements WebHandler, InitializingBean {
 		if (!CollectionUtils.isEmpty(this.mediaTypes)) {
 			String ext = StringUtils.getFilenameExtension(filename);
 			if (ext != null) {
-				mediaType = this.mediaTypes.get(ext.toLowerCase(Locale.ENGLISH));
+				mediaType = this.mediaTypes.get(ext.toLowerCase(Locale.ROOT));
 			}
 		}
 		if (mediaType == null) {

spring-webflux/src/main/java/org/springframework/web/reactive/result/condition/AbstractNameValueExpression.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.
@@ -16,6 +16,8 @@
 
 package org.springframework.web.reactive.result.condition;
 
+import java.util.Locale;
+
 import org.springframework.lang.Nullable;
 import org.springframework.util.ObjectUtils;
 import org.springframework.web.server.ServerWebExchange;
@@ -106,7 +108,7 @@ abstract class AbstractNameValueExpression<T> implements NameValueExpression<T>
 
 	@Override
 	public int hashCode() {
-		int result = (isCaseSensitiveName() ? this.name : this.name.toLowerCase()).hashCode();
+		int result = (isCaseSensitiveName() ? this.name : this.name.toLowerCase(Locale.ROOT)).hashCode();
 		result = 31 * result + ObjectUtils.nullSafeHashCode(this.value);
 		result = 31 * result + (this.isNegated ? 1 : 0);
 		return result;

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/condition/AbstractNameValueExpression.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.
@@ -16,6 +16,8 @@
 
 package org.springframework.web.servlet.mvc.condition;
 
+import java.util.Locale;
+
 import jakarta.servlet.http.HttpServletRequest;
 
 import org.springframework.lang.Nullable;
@@ -108,7 +110,7 @@ abstract class AbstractNameValueExpression<T> implements NameValueExpression<T>
 
 	@Override
 	public int hashCode() {
-		int result = (isCaseSensitiveName() ? this.name.hashCode() : this.name.toLowerCase().hashCode());
+		int result = (isCaseSensitiveName() ? this.name.hashCode() : this.name.toLowerCase(Locale.ROOT).hashCode());
 		result = 31 * result + (this.value != null ? this.value.hashCode() : 0);
 		result = 31 * result + (this.isNegated ? 1 : 0);
 		return result;

spring-webmvc/src/main/java/org/springframework/web/servlet/mvc/method/annotation/AbstractMessageConverterMethodProcessor.java

@@ -532,7 +532,7 @@ public abstract class AbstractMessageConverterMethodProcessor extends AbstractMe
 		if (!StringUtils.hasText(extension)) {
 			return true;
 		}
-		extension = extension.toLowerCase(Locale.ENGLISH);
+		extension = extension.toLowerCase(Locale.ROOT);
 		if (this.safeExtensions.contains(extension)) {
 			return true;
 		}

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/CachingResourceResolver.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.
@@ -20,6 +20,7 @@ import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.stream.Collectors;
 
 import jakarta.servlet.http.HttpServletRequest;
@@ -147,7 +148,7 @@ public class CachingResourceResolver extends AbstractResourceResolver {
 		return Arrays.stream(StringUtils.tokenizeToStringArray(header, ","))
 				.map(token -> {
 					int index = token.indexOf(';');
-					return (index >= 0 ? token.substring(0, index) : token).trim().toLowerCase();
+					return (index >= 0 ? token.substring(0, index) : token).trim().toLowerCase(Locale.ROOT);
 				})
 				.filter(this.contentCodings::contains)
 				.sorted()

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/EncodedResourceResolver.java

@@ -28,6 +28,7 @@ import java.util.Arrays;
 import java.util.Collections;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 
 import jakarta.servlet.http.HttpServletRequest;
@@ -166,7 +167,7 @@ public class EncodedResourceResolver extends AbstractResourceResolver {
 	@Nullable
 	private String getAcceptEncoding(HttpServletRequest request) {
 		String header = request.getHeader(HttpHeaders.ACCEPT_ENCODING);
-		return (header != null ? header.toLowerCase() : null);
+		return (header != null ? header.toLowerCase(Locale.ROOT) : null);
 	}
 
 	private String getExtension(String coding) {

spring-webmvc/src/main/java/org/springframework/web/servlet/resource/ResourceHttpRequestHandler.java

@@ -318,7 +318,7 @@ public class ResourceHttpRequestHandler extends WebContentGenerator
 	 */
 	public void setMediaTypes(Map<String, MediaType> mediaTypes) {
 		mediaTypes.forEach((ext, mediaType) ->
-				this.mediaTypes.put(ext.toLowerCase(Locale.ENGLISH), mediaType));
+				this.mediaTypes.put(ext.toLowerCase(Locale.ROOT), mediaType));
 	}
 
 	/**
@@ -708,7 +708,7 @@ public class ResourceHttpRequestHandler extends WebContentGenerator
 			String filename = resource.getFilename();
 			String ext = StringUtils.getFilenameExtension(filename);
 			if (ext != null) {
-				mediaType = this.mediaTypes.get(ext.toLowerCase(Locale.ENGLISH));
+				mediaType = this.mediaTypes.get(ext.toLowerCase(Locale.ROOT));
 			}
 			if (mediaType == null) {
 				List<MediaType> mediaTypes = MediaTypeFactory.getMediaTypes(filename);

spring-webmvc/src/main/java/org/springframework/web/servlet/view/xslt/XsltView.java

@@ -20,6 +20,7 @@ import java.io.IOException;
 import java.io.InputStream;
 import java.io.Reader;
 import java.util.Enumeration;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
 
@@ -417,7 +418,7 @@ public class XsltView extends AbstractUrlBasedView {
 		}
 		if (StringUtils.hasText(encoding)) {
 			// Only apply encoding if content type is specified but does not contain charset clause already.
-			if (contentType != null && !contentType.toLowerCase().contains(WebUtils.CONTENT_TYPE_CHARSET_PREFIX)) {
+			if (contentType != null && !contentType.toLowerCase(Locale.ROOT).contains(WebUtils.CONTENT_TYPE_CHARSET_PREFIX)) {
 				contentType = contentType + WebUtils.CONTENT_TYPE_CHARSET_PREFIX + encoding;
 			}
 		}

spring-websocket/src/main/java/org/springframework/web/socket/WebSocketExtension.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.
@@ -72,7 +72,7 @@ public class WebSocketExtension {
 		Assert.hasLength(name, "Extension name must not be empty");
 		this.name = name;
 		if (!CollectionUtils.isEmpty(parameters)) {
-			Map<String, String> map = new LinkedCaseInsensitiveMap<>(parameters.size(), Locale.ENGLISH);
+			Map<String, String> map = new LinkedCaseInsensitiveMap<>(parameters.size(), Locale.ROOT);
 			map.putAll(parameters);
 			this.parameters = Collections.unmodifiableMap(map);
 		}

spring-websocket/src/main/java/org/springframework/web/socket/adapter/standard/StandardToWebSocketExtensionAdapter.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.
@@ -42,7 +42,7 @@ public class StandardToWebSocketExtensionAdapter extends WebSocketExtension {
 
 	private static Map<String, String> initParameters(Extension extension) {
 		List<Extension.Parameter> parameters = extension.getParameters();
-		Map<String, String> result = new LinkedCaseInsensitiveMap<>(parameters.size(), Locale.ENGLISH);
+		Map<String, String> result = new LinkedCaseInsensitiveMap<>(parameters.size(), Locale.ROOT);
 		for (Extension.Parameter parameter : parameters) {
 			result.put(parameter.getName(), parameter.getValue());
 		}

spring-websocket/src/main/java/org/springframework/web/socket/client/standard/StandardWebSocketClient.java

@@ -203,7 +203,7 @@ public class StandardWebSocketClient extends AbstractWebSocketClient {
 
 	private static int getPort(URI uri) {
 		if (uri.getPort() == -1) {
-			String scheme = uri.getScheme().toLowerCase(Locale.ENGLISH);
+			String scheme = uri.getScheme().toLowerCase(Locale.ROOT);
 			return ("wss".equals(scheme) ? 443 : 80);
 		}
 		return uri.getPort();