Use Locale.ROOT consistently for toLower/toUpperCase

See gh-33708

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 String getName() {
 	@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.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;
@@ -568,7 +569,8 @@ public void setDisallowedFields(@Nullable String... disallowedFields) {
 		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;
 		}
@@ -1157,7 +1159,7 @@ protected boolean isAllowed(String field) {
 		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 MimeType(String type, String subtype, @Nullable Map<String, String> param
 		Assert.hasLength(subtype, "'subtype' must not be empty");
 		checkToken(type);
 		checkToken(subtype);
-		this.type = type.toLowerCase(Locale.ENGLISH);
-		this.subtype = subtype.toLowerCase(Locale.ENGLISH);
+		this.type = type.toLowerCase(Locale.ROOT);
+		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

@@ -409,7 +409,8 @@ public void setCharacterEncoding(@Nullable String characterEncoding) {
 	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);
@@ -487,7 +488,7 @@ public void setContentType(@Nullable String contentType) {
 			}
 			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

@@ -223,7 +223,7 @@ private void setExplicitCharacterEncoding(@Nullable String characterEncoding) {
 				}
 				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(";")) {
@@ -243,7 +243,7 @@ private void setExplicitCharacterEncoding(@Nullable String characterEncoding) {
 	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;
 			}
@@ -351,7 +351,7 @@ public void setContentType(@Nullable String contentType) {
 			}
 			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

@@ -392,7 +392,7 @@ 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");
 
@@ -422,7 +422,7 @@ 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)));
 	}
 
 	/**
@@ -697,7 +697,7 @@ public HttpMethod getAccessControlRequestMethod() {
 	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 @@ private static MultiValueMap<String, MediaType> parseMimeTypes() {
 				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 static List<MediaType> getMediaTypes(@Nullable String filename) {
 		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

@@ -26,6 +26,7 @@
 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.ExecutionException;
@@ -139,7 +140,7 @@ private HttpRequest buildRequest(HttpHeaders headers, @Nullable Body body) {
 		}
 
 		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 @@ public JdkClientHttpResponse(HttpResponse<InputStream> response) {
 
 	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 String getName() {
 	@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 @@ public JdkClientHttpResponse(HttpResponse<Flow.Publisher<List<ByteBuffer>>> resp
 
 	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 String getName() {
 
 	@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

@@ -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.
@@ -111,7 +111,7 @@ public ServletServerHttpRequest(MultiValueMap<String, String> headers, HttpServl
 
 	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 String getName() {
 
 	@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 void setMediaTypes(Properties mediaTypes) {
 	 * 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 MappingMediaTypeFileExtensionResolver(@Nullable Map<String, MediaType> me
 		if (mediaTypes != null) {
 			Set<String> allFileExtensions = new HashSet<>(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 List<String> getAllFileExtensions() {
 	 */
 	@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 @@ protected String getMediaTypeKey(NativeWebRequest webRequest) {
 		// 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 RestClientResponseException(
 	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 ForwardedHeaderRemovingRequest(HttpServletRequest request) {
 		}
 
 		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 @@ protected void doFilterInternal(HttpServletRequest request, HttpServletResponse
 		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 Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
 	}
 
 	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();
 		}