Use String.toLowerCase()/toUpperCase() with Locale.ROOT consistently

This commit also adds Checkstyle rules for it.

benchmarks/benchmarks-core/src/jmh/java/io/micrometer/benchmark/core/DefaultLongTaskTimerBenchmark.java

@@ -25,6 +25,7 @@
 import org.openjdk.jmh.runner.options.Options;
 import org.openjdk.jmh.runner.options.OptionsBuilder;
 
+import java.util.Locale;
 import java.util.Random;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.IntStream;
@@ -58,7 +59,7 @@ public static void main(String[] args) throws RunnerException {
     public void setup() {
         clock = new MockClock();
         longTaskTimer = new DefaultLongTaskTimer(
-                new Meter.Id("ltt", Tags.empty(), TimeUnit.MILLISECONDS.toString().toLowerCase(), null,
+                new Meter.Id("ltt", Tags.empty(), TimeUnit.MILLISECONDS.toString().toLowerCase(Locale.ROOT), null,
                         Meter.Type.LONG_TASK_TIMER),
                 clock, TimeUnit.MILLISECONDS, DistributionStatisticConfig.DEFAULT, false);
         int randomIndex = random.nextInt(activeSampleCount);

config/checkstyle/checkstyle.xml

@@ -46,6 +46,22 @@
             <property name="message" value="Please use AssertJ imports." />
             <property name="ignoreComments" value="true" />
         </module>
+        <module name="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineJavaCheck">
+            <property name="id" value="toLowerCaseWithoutLocale"/>
+            <property name="format" value="\.toLowerCase\(\)"/>
+            <property name="maximum" value="0"/>
+            <property name="message"
+                      value="String.toLowerCase(Locale.ROOT) should be String.toLowerCase(Locale.ROOT)"/>
+            <property name="ignoreComments" value="true"/>
+        </module>
+        <module name="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineJavaCheck">
+            <property name="id" value="toUpperCaseWithoutLocale"/>
+            <property name="format" value="\.toUpperCase\(\)"/>
+            <property name="maximum" value="0"/>
+            <property name="message"
+                      value="String.toUpperCase(Locale.ROOT) should be String.toUpperCase(Locale.ROOT)"/>
+            <property name="ignoreComments" value="true"/>
+        </module>
 
         <!-- Whitespace -->
         <module name="SingleSpaceSeparator" />

implementations/micrometer-registry-azure-monitor/src/main/java/io/micrometer/azuremonitor/AzureMonitorMeterRegistry.java

@@ -28,6 +28,7 @@
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
+import java.util.Locale;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Stream;
@@ -114,7 +115,7 @@ protected void publish() {
 
     private Stream<MetricTelemetry> trackMeter(Meter meter) {
         return stream(meter.measure().spliterator(), false).map(ms -> {
-            MetricTelemetry mt = createMetricTelemetry(meter, ms.getStatistic().toString().toLowerCase());
+            MetricTelemetry mt = createMetricTelemetry(meter, ms.getStatistic().toString().toLowerCase(Locale.ROOT));
             mt.setValue(ms.getValue());
             return mt;
         });

implementations/micrometer-registry-cloudwatch2/src/main/java/io/micrometer/cloudwatch2/CloudWatchMeterRegistry.java

@@ -62,7 +62,7 @@ public class CloudWatchMeterRegistry extends StepMeterRegistry {
         Map<String, StandardUnit> standardUnitByLowercaseValue = new HashMap<>();
         for (StandardUnit standardUnit : StandardUnit.values()) {
             if (standardUnit != StandardUnit.UNKNOWN_TO_SDK_VERSION) {
-                standardUnitByLowercaseValue.put(standardUnit.toString().toLowerCase(), standardUnit);
+                standardUnitByLowercaseValue.put(standardUnit.toString().toLowerCase(Locale.ROOT), standardUnit);
             }
         }
         STANDARD_UNIT_BY_LOWERCASE_VALUE = Collections.unmodifiableMap(standardUnitByLowercaseValue);
@@ -308,7 +308,7 @@ StandardUnit toStandardUnit(@Nullable String unit) {
             if (unit == null) {
                 return StandardUnit.NONE;
             }
-            StandardUnit standardUnit = STANDARD_UNIT_BY_LOWERCASE_VALUE.get(unit.toLowerCase());
+            StandardUnit standardUnit = STANDARD_UNIT_BY_LOWERCASE_VALUE.get(unit.toLowerCase(Locale.ROOT));
             return standardUnit != null ? standardUnit : StandardUnit.NONE;
         }
 

implementations/micrometer-registry-datadog/src/test/java/io/micrometer/datadog/DatadogMeterRegistryTest.java

@@ -23,6 +23,7 @@
 import org.junit.jupiter.api.extension.ExtendWith;
 import ru.lanwen.wiremock.ext.WiremockResolver;
 
+import java.util.Locale;
 import java.util.concurrent.TimeUnit;
 
 import static com.github.tomakehurst.wiremock.client.WireMock.*;
@@ -71,7 +72,7 @@ public boolean enabled() {
         server.stubFor(any(anyUrl()));
 
         Counter.builder("my.counter#abc")
-            .baseUnit(TimeUnit.MICROSECONDS.toString().toLowerCase())
+            .baseUnit(TimeUnit.MICROSECONDS.toString().toLowerCase(Locale.ROOT))
             .description("metric description")
             .register(registry)
             .increment(Math.PI);
@@ -121,7 +122,7 @@ public boolean enabled() {
         server.stubFor(any(anyUrl()));
 
         Counter.builder("my.counter#abc")
-            .baseUnit(TimeUnit.MICROSECONDS.toString().toLowerCase())
+            .baseUnit(TimeUnit.MICROSECONDS.toString().toLowerCase(Locale.ROOT))
             .description("metric description")
             .register(registry)
             .increment(Math.PI);

implementations/micrometer-registry-dynatrace/src/main/java/io/micrometer/dynatrace/v1/DynatraceMetricDefinition.java

@@ -20,6 +20,7 @@
 import io.micrometer.core.instrument.util.StringEscapeUtils;
 
 import java.util.Collections;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Set;
 import java.util.function.Function;
@@ -109,7 +110,7 @@ enum DynatraceUnit {
 
         private static Map<String, DynatraceUnit> UNITS_MAPPING = Collections
             .unmodifiableMap(Stream.of(DynatraceUnit.values())
-                .collect(Collectors.toMap(k -> k.toString().toLowerCase() + "s", Function.identity())));
+                .collect(Collectors.toMap(k -> k.toString().toLowerCase(Locale.ROOT) + "s", Function.identity())));
 
         @Nullable
         static DynatraceUnit fromPlural(@Nullable String plural) {

implementations/micrometer-registry-dynatrace/src/main/java/io/micrometer/dynatrace/v2/DynatraceExporterV2.java

@@ -559,7 +559,7 @@ private String extractMetricKey(String metadataLine) {
      * @return The UCUM-compliant string if known, otherwise returns the original unit
      */
     private static String mapUnitIfNeeded(String unit) {
-        return unit != null ? UCUM_TIME_UNIT_MAP.getOrDefault(unit.toLowerCase(), unit) : null;
+        return unit != null ? UCUM_TIME_UNIT_MAP.getOrDefault(unit.toLowerCase(Locale.ROOT), unit) : null;
     }
 
     /**
@@ -570,22 +570,22 @@ private static String mapUnitIfNeeded(String unit) {
     private static Map<String, String> ucumTimeUnitMap() {
         Map<String, String> mapping = new HashMap<>();
         // There are redundant elements in case the toString method of TimeUnit changes
-        mapping.put(TimeUnit.NANOSECONDS.toString().toLowerCase(), "ns");
+        mapping.put(TimeUnit.NANOSECONDS.toString().toLowerCase(Locale.ROOT), "ns");
         mapping.put("nanoseconds", "ns");
         mapping.put("nanosecond", "ns");
-        mapping.put(TimeUnit.MICROSECONDS.toString().toLowerCase(), "us");
+        mapping.put(TimeUnit.MICROSECONDS.toString().toLowerCase(Locale.ROOT), "us");
         mapping.put("microseconds", "us");
         mapping.put("microsecond", "us");
-        mapping.put(TimeUnit.MILLISECONDS.toString().toLowerCase(), "ms");
+        mapping.put(TimeUnit.MILLISECONDS.toString().toLowerCase(Locale.ROOT), "ms");
         mapping.put("milliseconds", "ms");
         mapping.put("millisecond", "ms");
-        mapping.put(TimeUnit.SECONDS.toString().toLowerCase(), "s");
+        mapping.put(TimeUnit.SECONDS.toString().toLowerCase(Locale.ROOT), "s");
         mapping.put("seconds", "s");
         mapping.put("second", "s");
-        mapping.put(TimeUnit.MINUTES.toString().toLowerCase(), "min");
+        mapping.put(TimeUnit.MINUTES.toString().toLowerCase(Locale.ROOT), "min");
         mapping.put("minutes", "min");
         mapping.put("minute", "min");
-        mapping.put(TimeUnit.HOURS.toString().toLowerCase(), "h");
+        mapping.put(TimeUnit.HOURS.toString().toLowerCase(Locale.ROOT), "h");
         mapping.put("hours", "h");
         mapping.put("hour", "h");
 

implementations/micrometer-registry-elastic/src/main/java/io/micrometer/elastic/ElasticMeterRegistry.java

@@ -18,6 +18,7 @@
 import io.micrometer.common.lang.NonNull;
 import io.micrometer.common.util.StringUtils;
 import io.micrometer.core.instrument.*;
+import io.micrometer.core.instrument.Timer;
 import io.micrometer.core.instrument.distribution.HistogramSnapshot;
 import io.micrometer.core.instrument.step.StepMeterRegistry;
 import io.micrometer.core.instrument.util.MeterPartition;
@@ -31,10 +32,7 @@
 import java.time.ZoneOffset;
 import java.time.ZonedDateTime;
 import java.time.format.DateTimeFormatter;
-import java.util.ArrayList;
-import java.util.Date;
-import java.util.List;
-import java.util.Optional;
+import java.util.*;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 import java.util.function.Consumer;
@@ -349,7 +347,7 @@ String writeDocument(Meter meter, Consumer<StringBuilder> consumer) {
         StringBuilder sb = new StringBuilder(actionLine);
         String timestamp = generateTimestamp();
         String name = getConventionName(meter.getId());
-        String type = meter.getId().getType().toString().toLowerCase();
+        String type = meter.getId().getType().toString().toLowerCase(Locale.ROOT);
         sb.append("{\"")
             .append(config.timestampFieldName())
             .append("\":\"")

implementations/micrometer-registry-ganglia/src/main/java/io/micrometer/ganglia/GangliaMeterRegistry.java

@@ -32,6 +32,7 @@
 import org.slf4j.LoggerFactory;
 
 import java.io.IOException;
+import java.util.Locale;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 
@@ -134,7 +135,7 @@ protected void publish() {
 
     private void announceMeter(Meter meter) {
         for (Measurement measurement : meter.measure()) {
-            announce(meter, measurement.getValue(), measurement.getStatistic().toString().toLowerCase());
+            announce(meter, measurement.getValue(), measurement.getStatistic().toString().toLowerCase(Locale.ROOT));
         }
     }
 

implementations/micrometer-registry-health/src/main/java/io/micrometer/health/ServiceLevelObjective.java

@@ -161,7 +161,7 @@ public double getValue(MeterRegistry registry) {
         public String getValueAsString(MeterRegistry registry) {
             double value = getValue(registry);
             return Double.isNaN(value) ? "no value available"
-                    : getBaseUnit() != null && getBaseUnit().toLowerCase().contains("percent")
+                    : getBaseUnit() != null && getBaseUnit().toLowerCase(Locale.ROOT).contains("percent")
                             ? WHOLE_OR_SHORT_DECIMAL.get().format(value * 100) + "%"
                             : WHOLE_OR_SHORT_DECIMAL.get().format(value);
         }
@@ -366,7 +366,7 @@ public abstract static class NumericQuery {
             abstract Double getValue(MeterRegistry registry);
 
             private String thresholdString(double threshold) {
-                return baseUnit != null && baseUnit.toLowerCase().contains("percent")
+                return baseUnit != null && baseUnit.toLowerCase(Locale.ROOT).contains("percent")
                         ? WHOLE_OR_SHORT_DECIMAL.get().format(threshold * 100) + "%"
                         : WHOLE_OR_SHORT_DECIMAL.get().format(threshold);
             }

implementations/micrometer-registry-influx/src/main/java/io/micrometer/influx/InfluxApiVersion.java

@@ -20,6 +20,7 @@
 
 import java.io.UnsupportedEncodingException;
 import java.net.URLEncoder;
+import java.util.Locale;
 
 /**
  * Enum for the version of the InfluxDB API.
@@ -32,8 +33,8 @@ public enum InfluxApiVersion {
     V1 {
         @Override
         String writeEndpoint(final InfluxConfig config) {
-            String influxEndpoint = config.uri() + "/write?consistency=" + config.consistency().name().toLowerCase()
-                    + "&precision=ms&db=" + config.db();
+            String influxEndpoint = config.uri() + "/write?consistency="
+                    + config.consistency().name().toLowerCase(Locale.ROOT) + "&precision=ms&db=" + config.db();
             if (StringUtils.isNotBlank(config.retentionPolicy())) {
                 influxEndpoint += "&rp=" + config.retentionPolicy();
             }

implementations/micrometer-registry-influx/src/main/java/io/micrometer/influx/InfluxMeterRegistry.java

@@ -30,6 +30,7 @@
 import java.net.URLEncoder;
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.concurrent.ThreadFactory;
 import java.util.concurrent.TimeUnit;
 import java.util.stream.Stream;
@@ -175,14 +176,14 @@ Stream<String> writeMeter(Meter m) {
             String fieldKey = measurement.getStatistic()
                 .getTagValueRepresentation()
                 .replaceAll("(.)(\\p{Upper})", "$1_$2")
-                .toLowerCase();
+                .toLowerCase(Locale.ROOT);
             fields.add(new Field(fieldKey, value));
         }
         if (fields.isEmpty()) {
             return Stream.empty();
         }
         Meter.Id id = m.getId();
-        return Stream.of(influxLineProtocol(id, id.getType().name().toLowerCase(), fields.stream()));
+        return Stream.of(influxLineProtocol(id, id.getType().name().toLowerCase(Locale.ROOT), fields.stream()));
     }
 
     private Stream<String> writeLongTaskTimer(LongTaskTimer timer) {

implementations/micrometer-registry-influx/src/test/java/io/micrometer/influx/InfluxMeterRegistryVersionsTest.java

@@ -29,6 +29,7 @@
 
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 
@@ -386,7 +387,7 @@ private void publishSimpleStat(InfluxConfig config) {
         InfluxMeterRegistry registry = new InfluxMeterRegistry(config, new MockClock());
 
         Counter.builder("my.counter")
-            .baseUnit(TimeUnit.MICROSECONDS.name().toLowerCase())
+            .baseUnit(TimeUnit.MICROSECONDS.name().toLowerCase(Locale.ROOT))
             .description("metric description")
             .register(registry)
             .increment(Math.PI);

implementations/micrometer-registry-new-relic/src/main/java/io/micrometer/newrelic/NewRelicInsightsAgentClientProvider.java

@@ -24,6 +24,7 @@
 
 import java.util.Collections;
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.TimeUnit;
 
@@ -93,7 +94,7 @@ public Map<String, Object> writeLongTaskTimer(LongTaskTimer timer) {
         Map<String, Object> attributes = new HashMap<>();
         addAttribute(ACTIVE_TASKS, timer.activeTasks(), attributes);
         addAttribute(DURATION, timer.duration(timer.baseTimeUnit()), attributes);
-        addAttribute(TIME_UNIT, timer.baseTimeUnit().name().toLowerCase(), attributes);
+        addAttribute(TIME_UNIT, timer.baseTimeUnit().name().toLowerCase(Locale.ROOT), attributes);
         // process meter's name, type and tags
         addMeterAsAttributes(timer.getId(), attributes);
         return attributes;
@@ -141,7 +142,7 @@ public Map<String, Object> writeTimeGauge(TimeGauge gauge) {
         }
         Map<String, Object> attributes = new HashMap<>();
         addAttribute(VALUE, value, attributes);
-        addAttribute(TIME_UNIT, gauge.baseTimeUnit().name().toLowerCase(), attributes);
+        addAttribute(TIME_UNIT, gauge.baseTimeUnit().name().toLowerCase(Locale.ROOT), attributes);
         // process meter's name, type and tags
         addMeterAsAttributes(gauge.getId(), attributes);
         return attributes;
@@ -167,7 +168,7 @@ public Map<String, Object> writeTimer(Timer timer) {
         addAttribute(AVG, timer.mean(timeUnit), attributes);
         addAttribute(TOTAL_TIME, timer.totalTime(timeUnit), attributes);
         addAttribute(MAX, timer.max(timeUnit), attributes);
-        addAttribute(TIME_UNIT, timeUnit.name().toLowerCase(), attributes);
+        addAttribute(TIME_UNIT, timeUnit.name().toLowerCase(Locale.ROOT), attributes);
         // process meter's name, type and tags
         addMeterAsAttributes(timer.getId(), attributes);
         return attributes;
@@ -180,7 +181,7 @@ public Map<String, Object> writeFunctionTimer(FunctionTimer timer) {
         addAttribute(COUNT, timer.count(), attributes);
         addAttribute(AVG, timer.mean(timeUnit), attributes);
         addAttribute(TOTAL_TIME, timer.totalTime(timeUnit), attributes);
-        addAttribute(TIME_UNIT, timeUnit.name().toLowerCase(), attributes);
+        addAttribute(TIME_UNIT, timeUnit.name().toLowerCase(Locale.ROOT), attributes);
         // process meter's name, type and tags
         addMeterAsAttributes(timer.getId(), attributes);
         return attributes;

implementations/micrometer-registry-new-relic/src/main/java/io/micrometer/newrelic/NewRelicInsightsApiClientProvider.java

@@ -16,6 +16,7 @@
 package io.micrometer.newrelic;
 
 import io.micrometer.core.instrument.*;
+import io.micrometer.core.instrument.Timer;
 import io.micrometer.core.instrument.config.NamingConvention;
 import io.micrometer.core.instrument.util.DoubleFormat;
 import io.micrometer.core.instrument.util.MeterPartition;
@@ -26,10 +27,7 @@
 
 import java.net.InetSocketAddress;
 import java.net.Proxy;
-import java.util.Arrays;
-import java.util.HashMap;
-import java.util.List;
-import java.util.Map;
+import java.util.*;
 import java.util.concurrent.TimeUnit;
 import java.util.concurrent.atomic.AtomicInteger;
 import java.util.stream.Collectors;
@@ -125,7 +123,7 @@ public Stream<String> writeLongTaskTimer(LongTaskTimer timer) {
         TimeUnit timeUnit = timer.baseTimeUnit();
         return Stream.of(event(timer.getId(), new Attribute(ACTIVE_TASKS, timer.activeTasks()),
                 new Attribute(DURATION, timer.duration(timeUnit)),
-                new Attribute(TIME_UNIT, timeUnit.name().toLowerCase())));
+                new Attribute(TIME_UNIT, timeUnit.name().toLowerCase(Locale.ROOT))));
     }
 
     @Override
@@ -156,7 +154,7 @@ public Stream<String> writeTimeGauge(TimeGauge gauge) {
         double value = gauge.value();
         if (Double.isFinite(value)) {
             return Stream.of(event(gauge.getId(), new Attribute(VALUE, value),
-                    new Attribute(TIME_UNIT, gauge.baseTimeUnit().name().toLowerCase())));
+                    new Attribute(TIME_UNIT, gauge.baseTimeUnit().name().toLowerCase(Locale.ROOT))));
         }
         return Stream.empty();
     }
@@ -171,17 +169,18 @@ public Stream<String> writeSummary(DistributionSummary summary) {
     @Override
     public Stream<String> writeTimer(Timer timer) {
         TimeUnit timeUnit = timer.baseTimeUnit();
-        return Stream.of(event(timer.getId(), new Attribute(COUNT, timer.count()),
-                new Attribute(AVG, timer.mean(timeUnit)), new Attribute(TOTAL_TIME, timer.totalTime(timeUnit)),
-                new Attribute(MAX, timer.max(timeUnit)), new Attribute(TIME_UNIT, timeUnit.name().toLowerCase())));
+        return Stream
+            .of(event(timer.getId(), new Attribute(COUNT, timer.count()), new Attribute(AVG, timer.mean(timeUnit)),
+                    new Attribute(TOTAL_TIME, timer.totalTime(timeUnit)), new Attribute(MAX, timer.max(timeUnit)),
+                    new Attribute(TIME_UNIT, timeUnit.name().toLowerCase(Locale.ROOT))));
     }
 
     @Override
     public Stream<String> writeFunctionTimer(FunctionTimer timer) {
         TimeUnit timeUnit = timer.baseTimeUnit();
         return Stream.of(event(timer.getId(), new Attribute(COUNT, timer.count()),
                 new Attribute(AVG, timer.mean(timeUnit)), new Attribute(TOTAL_TIME, timer.totalTime(timeUnit)),
-                new Attribute(TIME_UNIT, timeUnit.name().toLowerCase())));
+                new Attribute(TIME_UNIT, timeUnit.name().toLowerCase(Locale.ROOT))));
     }
 
     @Override