Use .toLowerCase and .toUpperCase(Locale.ROOT) (#10182)

* Use .toLowerCase and .toUpperCase(Locale.ROOT)

* Spaces

* add spaces after if(

29 files changed, 69 insertions, 50 deletions

diff --git a/server/src/main/java/com/vaadin/data/Binder.java b/server/src/main/java/com/vaadin/data/Binder.java
index 828130bd81..d417944f80 100644
--- a/server/src/main/java/com/vaadin/data/Binder.java
+++ b/server/src/main/java/com/vaadin/data/Binder.java
@@ -2585,7 +2585,7 @@ public class Binder<BEAN> implements Serializable {
     }
 
     private String minifyFieldName(String fieldName) {
-        return fieldName.toLowerCase(Locale.ENGLISH).replace("_", "");
+        return fieldName.toLowerCase(Locale.ROOT).replace("_", "");
     }
 
     private <V> void fireValueChangeEvent(ValueChangeEvent<V> event) {
diff --git a/server/src/main/java/com/vaadin/server/BootstrapHandler.java b/server/src/main/java/com/vaadin/server/BootstrapHandler.java
index ff9e816013..bd87f78d67 100644
--- a/server/src/main/java/com/vaadin/server/BootstrapHandler.java
+++ b/server/src/main/java/com/vaadin/server/BootstrapHandler.java
@@ -662,7 +662,7 @@ public abstract class BootstrapHandler extends SynchronizedRequestHandler {
         mainDiv.addClass("v-app");
         mainDiv.addClass(context.getThemeName());
         mainDiv.addClass(context.getUIClass().getSimpleName()
-                .toLowerCase(Locale.ENGLISH));
+                .toLowerCase(Locale.ROOT));
         if (style != null && !style.isEmpty()) {
             mainDiv.attr("style", style);
         }
diff --git a/server/src/main/java/com/vaadin/server/DefaultDeploymentConfiguration.java b/server/src/main/java/com/vaadin/server/DefaultDeploymentConfiguration.java
index 80db458c42..33f80015fb 100644
--- a/server/src/main/java/com/vaadin/server/DefaultDeploymentConfiguration.java
+++ b/server/src/main/java/com/vaadin/server/DefaultDeploymentConfiguration.java
@@ -16,6 +16,7 @@
 
 package com.vaadin.server;
 
+import java.util.Locale;
 import java.util.Properties;
 import java.util.logging.Logger;
 
@@ -144,7 +145,8 @@ public class DefaultDeploymentConfiguration
         }
 
         // Try lowercased system properties
-        val = System.getProperty(pkgName + parameterName.toLowerCase());
+        val = System
+                .getProperty(pkgName + parameterName.toLowerCase(Locale.ROOT));
         if (val != null) {
             return val;
         }
@@ -170,7 +172,8 @@ public class DefaultDeploymentConfiguration
 
         // Try lower case application properties for backward compatibility with
         // 3.0.2 and earlier
-        val = initParameters.getProperty(parameterName.toLowerCase());
+        val = initParameters
+                .getProperty(parameterName.toLowerCase(Locale.ROOT));
 
         return val;
     }
@@ -322,7 +325,8 @@ public class DefaultDeploymentConfiguration
                 Constants.SERVLET_PARAMETER_PUSH_MODE,
                 PushMode.DISABLED.toString());
         try {
-            pushMode = Enum.valueOf(PushMode.class, mode.toUpperCase());
+            pushMode = Enum.valueOf(PushMode.class,
+                    mode.toUpperCase(Locale.ROOT));
         } catch (IllegalArgumentException e) {
             getLogger().warning(Constants.WARNING_PUSH_MODE_NOT_RECOGNIZED);
             pushMode = PushMode.DISABLED;
diff --git a/server/src/main/java/com/vaadin/server/JsonCodec.java b/server/src/main/java/com/vaadin/server/JsonCodec.java
index a7f94de468..fc8e858b3b 100644
--- a/server/src/main/java/com/vaadin/server/JsonCodec.java
+++ b/server/src/main/java/com/vaadin/server/JsonCodec.java
@@ -33,6 +33,7 @@ import java.util.Date;
 import java.util.HashMap;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Set;
@@ -729,7 +730,7 @@ public class JsonCodec implements Serializable {
                     throw new RuntimeException("Can't encode "
                             + valueType.getName()
                             + " as it has multiple properties with the name "
-                            + fieldName.toLowerCase()
+                            + fieldName.toLowerCase(Locale.ROOT)
                             + ". This can happen if there are getters and setters for a public field (the framework can't know which to ignore) or if there are properties with only casing distinguishing between the names (e.g. getFoo() and getFOO())");
                 }
 
diff --git a/server/src/main/java/com/vaadin/server/JsonPaintTarget.java b/server/src/main/java/com/vaadin/server/JsonPaintTarget.java
index b643fbb7a9..4cfb389851 100644
--- a/server/src/main/java/com/vaadin/server/JsonPaintTarget.java
+++ b/server/src/main/java/com/vaadin/server/JsonPaintTarget.java
@@ -26,6 +26,7 @@ import java.util.Deque;
 import java.util.HashSet;
 import java.util.Iterator;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.logging.Level;
@@ -289,7 +290,7 @@ public class JsonPaintTarget implements PaintTarget {
                     for (int k = 0; k < 4 - ss.length(); k++) {
                         sb.append('0');
                     }
-                    sb.append(ss.toUpperCase());
+                    sb.append(ss.toUpperCase(Locale.ROOT));
                 } else {
                     sb.append(ch);
                 }
diff --git a/server/src/main/java/com/vaadin/server/VaadinPortlet.java b/server/src/main/java/com/vaadin/server/VaadinPortlet.java
index d4a7d0e62d..c00b6461d9 100644
--- a/server/src/main/java/com/vaadin/server/VaadinPortlet.java
+++ b/server/src/main/java/com/vaadin/server/VaadinPortlet.java
@@ -20,6 +20,7 @@ import java.io.Serializable;
 import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.Enumeration;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
 import java.util.logging.Level;
@@ -561,7 +562,8 @@ public class VaadinPortlet extends GenericPortlet
      */
     protected VaadinPortletRequest createVaadinRequest(PortletRequest request) {
         PortalContext portalContext = request.getPortalContext();
-        String portalInfo = portalContext.getPortalInfo().toLowerCase().trim();
+        String portalInfo = portalContext.getPortalInfo()
+                .toLowerCase(Locale.ROOT).trim();
         VaadinPortletService service = getService();
 
         if (portalInfo.contains("gatein")) {
diff --git a/server/src/main/java/com/vaadin/server/themeutils/SASSAddonImportFileCreator.java b/server/src/main/java/com/vaadin/server/themeutils/SASSAddonImportFileCreator.java
index a313e8c0fe..d1cdf0dd63 100644
--- a/server/src/main/java/com/vaadin/server/themeutils/SASSAddonImportFileCreator.java
+++ b/server/src/main/java/com/vaadin/server/themeutils/SASSAddonImportFileCreator.java
@@ -24,6 +24,7 @@ import java.net.URL;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.logging.Level;
 import java.util.logging.Logger;
@@ -101,12 +102,12 @@ public class SASSAddonImportFileCreator {
             // last
             List<String> paths = new ArrayList<>(addonThemes.keySet());
             Collections.sort(paths, (String path1, String path2) -> {
-                if (path1.toLowerCase().endsWith(".css")
-                        && path2.toLowerCase().endsWith(".scss")) {
+                if (path1.toLowerCase(Locale.ROOT).endsWith(".css")
+                        && path2.toLowerCase(Locale.ROOT).endsWith(".scss")) {
                     return -1;
                 }
-                if (path1.toLowerCase().endsWith(".scss")
-                        && path2.toLowerCase().endsWith(".css")) {
+                if (path1.toLowerCase(Locale.ROOT).endsWith(".scss")
+                        && path2.toLowerCase(Locale.ROOT).endsWith(".css")) {
                     return 1;
                 }
                 return 0;
diff --git a/server/src/main/java/com/vaadin/server/widgetsetutils/WidgetSetBuilder.java b/server/src/main/java/com/vaadin/server/widgetsetutils/WidgetSetBuilder.java
index 608f84782c..80c8fc7874 100644
--- a/server/src/main/java/com/vaadin/server/widgetsetutils/WidgetSetBuilder.java
+++ b/server/src/main/java/com/vaadin/server/widgetsetutils/WidgetSetBuilder.java
@@ -29,6 +29,7 @@ import java.net.URISyntaxException;
 import java.net.URL;
 import java.util.Collection;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.Map;
 import java.util.regex.Matcher;
 import java.util.regex.Pattern;
@@ -180,7 +181,7 @@ public class WidgetSetBuilder {
     }
 
     static boolean isWidgetset(String gwtModuleName) {
-        return gwtModuleName.toLowerCase().contains("widgetset");
+        return gwtModuleName.toLowerCase(Locale.ROOT).contains("widgetset");
     }
 
     private static String readFile(File widgetsetFile) throws IOException {
diff --git a/server/src/main/java/com/vaadin/ui/AbstractColorPicker.java b/server/src/main/java/com/vaadin/ui/AbstractColorPicker.java
index 608cdd9cfa..74b7e1f2b1 100644
--- a/server/src/main/java/com/vaadin/ui/AbstractColorPicker.java
+++ b/server/src/main/java/com/vaadin/ui/AbstractColorPicker.java
@@ -17,6 +17,7 @@ package com.vaadin.ui;
 
 import java.io.Serializable;
 import java.util.Collection;
+import java.util.Locale;
 import java.util.Objects;
 
 import org.jsoup.nodes.Attributes;
@@ -492,8 +493,8 @@ public abstract class AbstractColorPicker extends AbstractField<Color> {
             doSetValue(new Color(Integer.parseInt(hexColor, 16)));
         }
         if (design.hasAttr("popup-style")) {
-            setPopupStyle(PopupStyle.valueOf(
-                    "POPUP_" + attributes.get("popup-style").toUpperCase()));
+            setPopupStyle(PopupStyle.valueOf("POPUP_"
+                    + attributes.get("popup-style").toUpperCase(Locale.ROOT)));
         }
         if (design.hasAttr("position")) {
             String[] position = attributes.get("position").split(",");
diff --git a/server/src/main/java/com/vaadin/ui/components/grid/GridDropTarget.java b/server/src/main/java/com/vaadin/ui/components/grid/GridDropTarget.java
index 342946d5c9..edb1534a05 100644
--- a/server/src/main/java/com/vaadin/ui/components/grid/GridDropTarget.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/GridDropTarget.java
@@ -16,6 +16,7 @@
 package com.vaadin.ui.components.grid;
 
 import java.util.LinkedHashMap;
+import java.util.Locale;
 import java.util.Map;
 
 import com.vaadin.shared.Registration;
@@ -156,7 +157,7 @@ public class GridDropTarget<T> extends DropTargetExtension<Grid<T>> {
 
             GridDropEvent<T> event = new GridDropEvent<>(getParent(),
                     dataPreserveOrder,
-                    DropEffect.valueOf(dropEffect.toUpperCase()),
+                    DropEffect.valueOf(dropEffect.toUpperCase(Locale.ROOT)),
                     getUI().getActiveDragSource(), dropTargetRow, dropLocation,
                     mouseEventDetails);
 
diff --git a/server/src/main/java/com/vaadin/ui/components/grid/TreeGridDropTarget.java b/server/src/main/java/com/vaadin/ui/components/grid/TreeGridDropTarget.java
index 1d440b5fec..e471f350bc 100644
--- a/server/src/main/java/com/vaadin/ui/components/grid/TreeGridDropTarget.java
+++ b/server/src/main/java/com/vaadin/ui/components/grid/TreeGridDropTarget.java
@@ -16,6 +16,7 @@
 package com.vaadin.ui.components.grid;
 
 import java.util.LinkedHashMap;
+import java.util.Locale;
 import java.util.Map;
 
 import com.vaadin.shared.Registration;
@@ -30,7 +31,7 @@ import com.vaadin.ui.TreeGrid;
  * counterpart of GridDropTargetExtensionConnector.
  *
  * @param <T>
- *         Type of the TreeGrid bean.
+ *            Type of the TreeGrid bean.
  * @author Vaadin Ltd
  * @since 8.1
  */
@@ -41,22 +42,22 @@ public class TreeGridDropTarget<T> extends GridDropTarget<T> {
      * drop.
      *
      * @param target
-     *         TreeGrid to be extended.
+     *            TreeGrid to be extended.
      * @param dropMode
-     *         Drop mode that describes the allowed drop locations within the
-     *         TreeGrid's row.
+     *            Drop mode that describes the allowed drop locations within the
+     *            TreeGrid's row.
      */
     public TreeGridDropTarget(TreeGrid<T> target, DropMode dropMode) {
         super(target, dropMode);
     }
 
     /**
-     * Attaches drop listener for the current drop target. {@link
-     * TreeGridDropListener#drop(TreeGridDropEvent)} is called when drop event
-     * happens on the client side.
+     * Attaches drop listener for the current drop target.
+     * {@link TreeGridDropListener#drop(TreeGridDropEvent)} is called when drop
+     * event happens on the client side.
      *
      * @param listener
-     *         Listener to handle drop event.
+     *            Listener to handle drop event.
      * @return Handle to be used to remove this listener.
      */
     public Registration addTreeGridDropListener(
@@ -79,7 +80,7 @@ public class TreeGridDropTarget<T> extends GridDropTarget<T> {
 
             TreeGridDropEvent<T> event = new TreeGridDropEvent<>(getParent(),
                     dataPreserveOrder,
-                    DropEffect.valueOf(dropEffect.toUpperCase()),
+                    DropEffect.valueOf(dropEffect.toUpperCase(Locale.ROOT)),
                     getUI().getActiveDragSource(), dropTargetRow, dropLocation,
                     mouseEventDetails, depth, collapsed);
 
diff --git a/server/src/main/java/com/vaadin/ui/declarative/Design.java b/server/src/main/java/com/vaadin/ui/declarative/Design.java
index 61d35297d0..7c65992967 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/Design.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/Design.java
@@ -265,7 +265,7 @@ public class Design implements Serializable {
             String prefix = context.getPackagePrefix(packageName);
             if (prefix == null) {
                 prefix = packageName.replace('.', '_')
-                        .toLowerCase(Locale.ENGLISH);
+                        .toLowerCase(Locale.ROOT);
                 context.addPackagePrefix(prefix, packageName);
             }
             prefix += "-";
diff --git a/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java b/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java
index e8fa278aba..c508b693f8 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/DesignAttributeHandler.java
@@ -25,6 +25,7 @@ import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.ConcurrentHashMap;
 import java.util.logging.Level;
@@ -330,7 +331,7 @@ public class DesignAttributeHandler implements Serializable {
             if (builder.length() != 0) {
                 builder.append('-');
             }
-            builder.append(word.toLowerCase());
+            builder.append(word.toLowerCase(Locale.ROOT));
         }
         return builder.toString();
     }
@@ -356,13 +357,13 @@ public class DesignAttributeHandler implements Serializable {
             // written in lower case
             if (matcher.group(1).isEmpty()) {
                 matcher.appendReplacement(result,
-                        matched.toLowerCase() + matcher.group(3));
+                        matched.toLowerCase(Locale.ROOT) + matcher.group(3));
                 // otherwise the first character of the group stays uppercase,
                 // while the others are lower case
             } else {
                 matcher.appendReplacement(result,
                         matcher.group(1) + matched.substring(0, 1)
-                                + matched.substring(1).toLowerCase()
+                                + matched.substring(1).toLowerCase(Locale.ROOT)
                                 + matcher.group(3));
             }
             // in both cases the uppercase letter of the next word (or string's
diff --git a/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java b/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java
index 2caecda8f4..f1e7e25329 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/FieldBinder.java
@@ -104,7 +104,7 @@ public class FieldBinder implements Serializable {
     private void resolveFields(Class<?> classWithFields) {
         for (Field memberField : getFields(classWithFields)) {
             if (Component.class.isAssignableFrom(memberField.getType())) {
-                fieldMap.put(memberField.getName().toLowerCase(Locale.ENGLISH),
+                fieldMap.put(memberField.getName().toLowerCase(Locale.ROOT),
                         memberField);
             }
         }
@@ -180,7 +180,7 @@ public class FieldBinder implements Serializable {
                 return false;
             }
             // validate that the field can be found
-            Field field = fieldMap.get(fieldName.toLowerCase(Locale.ENGLISH));
+            Field field = fieldMap.get(fieldName.toLowerCase(Locale.ROOT));
             if (field == null) {
                 getLogger()
                         .fine("No field was found by identifier " + identifier);
diff --git a/server/src/main/java/com/vaadin/ui/declarative/converters/DesignEnumConverter.java b/server/src/main/java/com/vaadin/ui/declarative/converters/DesignEnumConverter.java
index de7f5ad5b7..1360671d00 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/converters/DesignEnumConverter.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/converters/DesignEnumConverter.java
@@ -53,7 +53,7 @@ public class DesignEnumConverter<T extends Enum>
         }
         try {
             T result = (T) Enum.valueOf(type,
-                    value.toUpperCase(Locale.ENGLISH));
+                    value.toUpperCase(Locale.ROOT));
             return Result.ok(result);
         } catch (Exception e) {
             return Result.error(e.getMessage());
@@ -66,7 +66,7 @@ public class DesignEnumConverter<T extends Enum>
             return null;
         }
 
-        return value.name().toLowerCase(Locale.ENGLISH);
+        return value.name().toLowerCase(Locale.ROOT);
     }
 
 }
diff --git a/server/src/main/java/com/vaadin/ui/declarative/converters/DesignResourceConverter.java b/server/src/main/java/com/vaadin/ui/declarative/converters/DesignResourceConverter.java
index d3d2b13170..c0fa46469c 100644
--- a/server/src/main/java/com/vaadin/ui/declarative/converters/DesignResourceConverter.java
+++ b/server/src/main/java/com/vaadin/ui/declarative/converters/DesignResourceConverter.java
@@ -63,7 +63,7 @@ public class DesignResourceConverter implements Converter<String, Resource> {
         String protocol = value.split("://")[0];
         try {
             ResourceConverterByProtocol converter = ResourceConverterByProtocol
-                    .valueOf(protocol.toUpperCase(Locale.ENGLISH));
+                    .valueOf(protocol.toUpperCase(Locale.ROOT));
             return Result.ok(converter.parse(value));
         } catch (IllegalArgumentException iae) {
             return Result.error("Unrecognized protocol: " + protocol);
diff --git a/server/src/main/java/com/vaadin/ui/dnd/DropTargetExtension.java b/server/src/main/java/com/vaadin/ui/dnd/DropTargetExtension.java
index 76c7195f60..5ee7b0e861 100644
--- a/server/src/main/java/com/vaadin/ui/dnd/DropTargetExtension.java
+++ b/server/src/main/java/com/vaadin/ui/dnd/DropTargetExtension.java
@@ -18,6 +18,7 @@ package com.vaadin.ui.dnd;
 import java.util.Arrays;
 import java.util.LinkedHashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
 
@@ -75,7 +76,7 @@ public class DropTargetExtension<T extends AbstractComponent>
         registerRpc(
                 (DropTargetRpc) (types, data, dropEffect, mouseEventDetails) ->
                 onDrop(types, data,
-                        DropEffect.valueOf(dropEffect.toUpperCase()),
+                        DropEffect.valueOf(dropEffect.toUpperCase(Locale.ROOT)),
                         mouseEventDetails));
     }
 
diff --git a/server/src/main/java/com/vaadin/util/FileTypeResolver.java b/server/src/main/java/com/vaadin/util/FileTypeResolver.java
index 500e8736e7..48d7916967 100644
--- a/server/src/main/java/com/vaadin/util/FileTypeResolver.java
+++ b/server/src/main/java/com/vaadin/util/FileTypeResolver.java
@@ -19,6 +19,7 @@ package com.vaadin.util;
 import java.io.File;
 import java.io.Serializable;
 import java.util.Collections;
+import java.util.Locale;
 import java.util.Map;
 import java.util.StringTokenizer;
 import java.util.concurrent.ConcurrentHashMap;
@@ -270,7 +271,8 @@ public class FileTypeResolver implements Serializable {
             }
 
             // Return type from extension map, if found
-            final String type = EXT_TO_MIME_MAP.get(ext.toLowerCase());
+            final String type = EXT_TO_MIME_MAP
+                    .get(ext.toLowerCase(Locale.ROOT));
             if (type != null) {
                 return type;
             }
@@ -358,7 +360,7 @@ public class FileTypeResolver implements Serializable {
      *            the new mime-type for <code>extension</code>.
      */
     public static void addExtension(String extension, String MIMEType) {
-        EXT_TO_MIME_MAP.put(extension.toLowerCase(), MIMEType);
+        EXT_TO_MIME_MAP.put(extension.toLowerCase(Locale.ROOT), MIMEType);
     }
 
     /**
diff --git a/server/src/test/java/com/vaadin/data/BinderCustomPropertySetTest.java b/server/src/test/java/com/vaadin/data/BinderCustomPropertySetTest.java
index 31c48447a6..cde97441aa 100644
--- a/server/src/test/java/com/vaadin/data/BinderCustomPropertySetTest.java
+++ b/server/src/test/java/com/vaadin/data/BinderCustomPropertySetTest.java
@@ -79,7 +79,7 @@ public class BinderCustomPropertySetTest {
 
         @Override
         public String getCaption() {
-            return name.toUpperCase(Locale.ENGLISH);
+            return name.toUpperCase(Locale.ROOT);
         }
 
     }
diff --git a/server/src/test/java/com/vaadin/tests/components/grid/GridValueProvider.java b/server/src/test/java/com/vaadin/tests/components/grid/GridValueProvider.java
index 6b3d85900d..00961487d3 100644
--- a/server/src/test/java/com/vaadin/tests/components/grid/GridValueProvider.java
+++ b/server/src/test/java/com/vaadin/tests/components/grid/GridValueProvider.java
@@ -69,7 +69,7 @@ public class GridValueProvider {
                 upperCasePerson);
 
         persons.addFilter(col.getValueProvider(),
-                value -> value.toUpperCase(Locale.ENGLISH).equals(value));
+                value -> value.toUpperCase(Locale.ROOT).equals(value));
 
         List<Person> queryPersons = persons.fetch(new Query<>())
                 .collect(Collectors.toList());
diff --git a/server/src/test/java/com/vaadin/tests/design/DesignFormatterTest.java b/server/src/test/java/com/vaadin/tests/design/DesignFormatterTest.java
index 9f6253067a..de346dd0aa 100644
--- a/server/src/test/java/com/vaadin/tests/design/DesignFormatterTest.java
+++ b/server/src/test/java/com/vaadin/tests/design/DesignFormatterTest.java
@@ -25,6 +25,7 @@ import java.math.BigDecimal;
 import java.text.SimpleDateFormat;
 import java.util.Date;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.TimeZone;
 
 import org.junit.Before;
@@ -290,9 +291,9 @@ public class DesignFormatterTest {
                 formatter.format(new ThemeResource(themePath)));
 
         assertEquals(fontAwesomeUrl, formatter.format(FontAwesome.AMBULANCE));
-        assertEquals(someOtherFontUrl.toLowerCase(),
+        assertEquals(someOtherFontUrl.toLowerCase(Locale.ROOT),
                 formatter.format(new GenericFontIcon("SomeOther", 0xf0f9))
-                        .toLowerCase());
+                        .toLowerCase(Locale.ROOT));
 
         assertEquals(fileSystemPath,
                 formatter.format(new FileResource(new File(fileSystemPath))));
diff --git a/server/src/test/java/com/vaadin/tests/server/ClasspathHelper.java b/server/src/test/java/com/vaadin/tests/server/ClasspathHelper.java
index 738f0be806..bd0dbbc6e0 100644
--- a/server/src/test/java/com/vaadin/tests/server/ClasspathHelper.java
+++ b/server/src/test/java/com/vaadin/tests/server/ClasspathHelper.java
@@ -69,7 +69,7 @@ public class ClasspathHelper {
                         .map(path -> getClassFromFile(path,
                                 classesRoot.toPath()))
                         .filter(Objects::nonNull).collect(Collectors.toList());
-            } else if (classesRoot.getName().toLowerCase(Locale.ENGLISH)
+            } else if (classesRoot.getName().toLowerCase(Locale.ROOT)
                     .endsWith(".jar")) {
                 URI uri = URI.create("jar:" + classesRoot.toURI());
                 FileSystem fileSystem;
diff --git a/server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java b/server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java
index 8a31b8cf98..ba2c424a09 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/AbstractListenerMethodsTestBase.java
@@ -7,6 +7,7 @@ import java.lang.reflect.InvocationTargetException;
 import java.lang.reflect.Method;
 import java.util.Collection;
 import java.util.HashSet;
+import java.util.Locale;
 import java.util.Set;
 
 import org.easymock.EasyMock;
@@ -43,7 +44,7 @@ public abstract class AbstractListenerMethodsTestBase {
                     String packageName = "com.vaadin.tests.server";
                     if (Component.class.isAssignableFrom(c)) {
                         packageName += ".component."
-                                + c.getSimpleName().toLowerCase();
+                                + c.getSimpleName().toLowerCase(Locale.ROOT);
                         continue;
                     }
 
diff --git a/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateFieldDeclarativeTest.java b/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateFieldDeclarativeTest.java
index 80040804cd..6f18a424b8 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateFieldDeclarativeTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateFieldDeclarativeTest.java
@@ -69,7 +69,7 @@ public abstract class AbstractLocalDateFieldDeclarativeTest<T extends AbstractLo
                         + "date-out-of-range-message='%s' resolution='%s' "
                         + "date-format='%s' lenient parse-error-message='%s'/>",
                 getComponentTag(), end, start, dateOutOfRange,
-                resolution.name().toLowerCase(Locale.ENGLISH), dateFormat,
+                resolution.name().toLowerCase(Locale.ROOT), dateFormat,
                 parseErrorMsg);
 
         T component = getComponentClass().newInstance();
diff --git a/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateTimeFieldDeclarativeTest.java b/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateTimeFieldDeclarativeTest.java
index a4768c6f24..61fff27072 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateTimeFieldDeclarativeTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/abstractdatefield/AbstractLocalDateTimeFieldDeclarativeTest.java
@@ -74,7 +74,7 @@ public abstract class AbstractLocalDateTimeFieldDeclarativeTest<T extends Abstra
                         + "date-format='%s' lenient parse-error-message='%s'/>",
                 getComponentTag(), DATE_FORMATTER.format(end),
                 DATE_FORMATTER.format(start), dateOutOfRange,
-                resolution.name().toLowerCase(Locale.ENGLISH), dateFormat,
+                resolution.name().toLowerCase(Locale.ROOT), dateFormat,
                 parseErrorMsg);
 
         T component = getComponentClass().newInstance();
diff --git a/server/src/test/java/com/vaadin/tests/server/component/abstracttextfield/AbstractTextFieldDeclarativeTest.java b/server/src/test/java/com/vaadin/tests/server/component/abstracttextfield/AbstractTextFieldDeclarativeTest.java
index 7ba3e6aaca..2416620afe 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/abstracttextfield/AbstractTextFieldDeclarativeTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/abstracttextfield/AbstractTextFieldDeclarativeTest.java
@@ -43,7 +43,7 @@ public abstract class AbstractTextFieldDeclarativeTest<T extends AbstractTextFie
                 "<%s maxlength='%d' placeholder='%s' "
                         + "value-change-mode='%s' value-change-timeout='%d'/>",
                 getComponentTag(), maxLength, placeholder,
-                mode.name().toLowerCase(Locale.ENGLISH), timeout);
+                mode.name().toLowerCase(Locale.ROOT), timeout);
 
         T component = getComponentClass().newInstance();
 
diff --git a/server/src/test/java/com/vaadin/tests/server/component/customlayout/CustomLayoutTest.java b/server/src/test/java/com/vaadin/tests/server/component/customlayout/CustomLayoutTest.java
index 8ebc620328..a9b23d7af0 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/customlayout/CustomLayoutTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/customlayout/CustomLayoutTest.java
@@ -74,7 +74,7 @@ public class CustomLayoutTest {
             field = list.get(0);
         } else {
             for (Field fld : list) {
-                if (fld.getName().toLowerCase(Locale.ENGLISH)
+                if (fld.getName().toLowerCase(Locale.ROOT)
                         .startsWith("buffer")) {
                     field = fld;
                     break;
diff --git a/server/src/test/java/com/vaadin/tests/server/component/grid/GridDeclarativeTest.java b/server/src/test/java/com/vaadin/tests/server/component/grid/GridDeclarativeTest.java
index 8d1d6c6955..a4f824d6fa 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/grid/GridDeclarativeTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/grid/GridDeclarativeTest.java
@@ -82,9 +82,9 @@ public class GridDeclarativeTest extends AbstractListingDeclarativeTest<Grid> {
                         + "<th plain-text column-ids='id'>Id</th></tr>"
                         + "</thead></table></%s>",
                 getComponentTag(),
-                heightMode.toString().toLowerCase(Locale.ENGLISH),
+                heightMode.toString().toLowerCase(Locale.ROOT),
                 frozenColumns, heightByRows,
-                SelectionMode.MULTI.toString().toLowerCase(Locale.ENGLISH),
+                SelectionMode.MULTI.toString().toLowerCase(Locale.ROOT),
                 getComponentTag());
 
         testRead(design, grid);
diff --git a/server/src/test/java/com/vaadin/tests/server/component/reachtextarea/RichTextAreaDeclarativeTest.java b/server/src/test/java/com/vaadin/tests/server/component/reachtextarea/RichTextAreaDeclarativeTest.java
index e7cab55f94..6cac635c6a 100644
--- a/server/src/test/java/com/vaadin/tests/server/component/reachtextarea/RichTextAreaDeclarativeTest.java
+++ b/server/src/test/java/com/vaadin/tests/server/component/reachtextarea/RichTextAreaDeclarativeTest.java
@@ -61,7 +61,7 @@ public class RichTextAreaDeclarativeTest
         int timeout = 67;
         String design = String.format(
                 "<%s value-change-mode='%s' value-change-timeout='%d'/>",
-                getComponentTag(), mode.name().toLowerCase(Locale.ENGLISH),
+                getComponentTag(), mode.name().toLowerCase(Locale.ROOT),
                 timeout);
 
         RichTextArea component = new RichTextArea();