diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-core/src/main/java/org/springframework/cloud/stream/binder/kafka/properties/JaasLoginModuleConfiguration.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-core/src/main/java/org/springframework/cloud/stream/binder/kafka/properties/JaasLoginModuleConfiguration.java
index 9934f30dd..871a880c8 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-core/src/main/java/org/springframework/cloud/stream/binder/kafka/properties/JaasLoginModuleConfiguration.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-core/src/main/java/org/springframework/cloud/stream/binder/kafka/properties/JaasLoginModuleConfiguration.java
@@ -17,6 +17,7 @@
 package org.springframework.cloud.stream.binder.kafka.properties;
 
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 
 import javax.security.auth.login.AppConfigurationEntry;
@@ -55,7 +56,7 @@ public class JaasLoginModuleConfiguration {
 	public void setControlFlag(String controlFlag) {
 		Assert.notNull(controlFlag, "cannot be null");
 		this.controlFlag = KafkaJaasLoginModuleInitializer.ControlFlag
-				.valueOf(controlFlag.toUpperCase());
+				.valueOf(controlFlag.toUpperCase(Locale.ROOT));
 	}
 
 	public Map<String, String> getOptions() {
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-reactive/src/test/java/org/springframework/cloud/stream/binder/reactorkafka/ReactorKafkaBinderIntegrationTests.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-reactive/src/test/java/org/springframework/cloud/stream/binder/reactorkafka/ReactorKafkaBinderIntegrationTests.java
index 7495dacdb..e1a04dfe6 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-reactive/src/test/java/org/springframework/cloud/stream/binder/reactorkafka/ReactorKafkaBinderIntegrationTests.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-reactive/src/test/java/org/springframework/cloud/stream/binder/reactorkafka/ReactorKafkaBinderIntegrationTests.java
@@ -20,6 +20,7 @@ import java.lang.reflect.Type;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.function.Function;
 
@@ -193,7 +194,7 @@ class ReactorKafkaBinderIntegrationTests {
 
 		@Bean
 		Function<Flux<ReceiverRecord<byte[], byte[]>>, Flux<String>> lowercase() {
-			return s -> s.map(rec -> new String(rec.value()).toLowerCase());
+			return s -> s.map(rec -> new String(rec.value()).toLowerCase(Locale.ROOT));
 		}
 
 		@Bean
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-reactive/src/test/java/org/springframework/cloud/stream/binder/reactorkafka/ReactorKafkaBinderObservationTests.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-reactive/src/test/java/org/springframework/cloud/stream/binder/reactorkafka/ReactorKafkaBinderObservationTests.java
index 474325af3..13a35377c 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-reactive/src/test/java/org/springframework/cloud/stream/binder/reactorkafka/ReactorKafkaBinderObservationTests.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-reactive/src/test/java/org/springframework/cloud/stream/binder/reactorkafka/ReactorKafkaBinderObservationTests.java
@@ -18,6 +18,7 @@ package org.springframework.cloud.stream.binder.reactorkafka;
 
 import java.lang.reflect.Type;
 import java.time.Duration;
+import java.util.Locale;
 import java.util.function.Function;
 import java.util.stream.Collectors;
 
@@ -147,7 +148,7 @@ public class ReactorKafkaBinderObservationTests {
 							observationRegistry);
 
 					return Mono.deferContextual(contextView -> Mono.just(record)
-							.map(rec -> new String(rec.value()).toLowerCase())
+							.map(rec -> new String(rec.value()).toLowerCase(Locale.ROOT))
 							.map(rec -> MessageBuilder.withPayload(rec).setHeader(IntegrationMessageHeaderAccessor.REACTOR_CONTEXT, contextView).build()))
 						.doOnTerminate(receiverObservation::stop)
 						.doOnError(receiverObservation::error)
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/main/java/org/springframework/cloud/stream/binder/kafka/streams/AbstractKafkaStreamsBinderProcessor.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/main/java/org/springframework/cloud/stream/binder/kafka/streams/AbstractKafkaStreamsBinderProcessor.java
index 2f289d316..30d11b0f2 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/main/java/org/springframework/cloud/stream/binder/kafka/streams/AbstractKafkaStreamsBinderProcessor.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/main/java/org/springframework/cloud/stream/binder/kafka/streams/AbstractKafkaStreamsBinderProcessor.java
@@ -18,6 +18,7 @@ package org.springframework.cloud.stream.binder.kafka.streams;
 
 import java.util.Arrays;
 import java.util.HashMap;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Optional;
@@ -370,7 +371,7 @@ public abstract class AbstractKafkaStreamsBinderProcessor implements Application
 				if (!concurrencyExplicitlyProvided[0]) {
 					concurrencyExplicitlyProvided[0] = name.getLastElement(ConfigurationPropertyName.Form.UNIFORM).equals("concurrency") &&
 						// name is normalized to contain only uniform elements and thus safe to call toLowerCase here.
-						ConfigurationPropertyName.of("spring.cloud.stream.bindings." + inboundName.toLowerCase() + ".consumer")
+						ConfigurationPropertyName.of("spring.cloud.stream.bindings." + inboundName.toLowerCase(Locale.ROOT) + ".consumer")
 							.isAncestorOf(name);
 				}
 				return result;
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/function/KafkaStreamsBinderWordCountBranchesFunctionTests.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/function/KafkaStreamsBinderWordCountBranchesFunctionTests.java
index e18186018..80f2e944b 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/function/KafkaStreamsBinderWordCountBranchesFunctionTests.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/function/KafkaStreamsBinderWordCountBranchesFunctionTests.java
@@ -19,6 +19,7 @@ package org.springframework.cloud.stream.binder.kafka.streams.function;
 import java.time.Duration;
 import java.util.Arrays;
 import java.util.Date;
+import java.util.Locale;
 import java.util.Map;
 import java.util.function.Function;
 
@@ -190,7 +191,7 @@ class KafkaStreamsBinderWordCountBranchesFunctionTests {
 
 			return input -> {
 				final Map<String, KStream<Object, WordCount>> stringKStreamMap = input
-						.flatMapValues(value -> Arrays.asList(value.toLowerCase().split("\\W+")))
+						.flatMapValues(value -> Arrays.asList(value.toLowerCase(Locale.ROOT).split("\\W+")))
 						.groupBy((key, value) -> value)
 						.windowedBy(TimeWindows.of(Duration.ofSeconds(5)))
 						.count(Materialized.as("WordCounts-branch"))
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/function/KafkaStreamsBinderWordCountFunctionTests.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/function/KafkaStreamsBinderWordCountFunctionTests.java
index 19dfe654a..57f0646b7 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/function/KafkaStreamsBinderWordCountFunctionTests.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/function/KafkaStreamsBinderWordCountFunctionTests.java
@@ -21,6 +21,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Date;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Optional;
 import java.util.concurrent.CountDownLatch;
@@ -397,7 +398,7 @@ class KafkaStreamsBinderWordCountFunctionTests {
 		Function<KStream<Object, String>, KStream<String, WordCount>> process() {
 
 			return input -> input
-					.flatMapValues(value -> Arrays.asList(value.toLowerCase().split("\\W+")))
+					.flatMapValues(value -> Arrays.asList(value.toLowerCase(Locale.ROOT).split("\\W+")))
 					.map((key, value) -> new KeyValue<>(value, value))
 					.groupByKey(Grouped.with(Serdes.String(), Serdes.String()))
 					.windowedBy(TimeWindows.of(Duration.ofMillis(5000)))
@@ -439,7 +440,7 @@ class KafkaStreamsBinderWordCountFunctionTests {
 		Function<KStream<Object, String>, KStream<?, WordCount>> process() {
 			return input -> input
 					.flatMapValues(
-							value -> Arrays.asList(value.toLowerCase().split("\\W+")))
+							value -> Arrays.asList(value.toLowerCase(Locale.ROOT).split("\\W+")))
 					.map((key, value) -> new KeyValue<>(value, value))
 					.groupByKey(Grouped.with(Serdes.String(), Serdes.String()))
 					.windowedBy(TimeWindows.ofSizeWithNoGrace(Duration.ofSeconds(5))).count(Materialized.as("foobar-WordCounts"))
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/DlqDestinationResolverTests.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/DlqDestinationResolverTests.java
index a83a71459..89d086c8b 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/DlqDestinationResolverTests.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/DlqDestinationResolverTests.java
@@ -18,6 +18,7 @@ package org.springframework.cloud.stream.binder.kafka.streams.integration;
 
 import java.time.Duration;
 import java.util.Arrays;
+import java.util.Locale;
 import java.util.Map;
 import java.util.function.Function;
 
@@ -124,7 +125,7 @@ class DlqDestinationResolverTests {
 
 			return input -> input
 					.flatMapValues(
-							value -> Arrays.asList(value.toLowerCase().split("\\W+")))
+							value -> Arrays.asList(value.toLowerCase(Locale.ROOT).split("\\W+")))
 					.map((key, value) -> new KeyValue<>(value, value))
 					.groupByKey(Grouped.with(Serdes.String(), Serdes.String()))
 					.windowedBy(TimeWindows.of(Duration.ofSeconds(5))).count(Materialized.as("foo-WordCounts-x"))
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsBinderMultipleInputTopicsTest.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsBinderMultipleInputTopicsTest.java
index 8e14655ee..41b131de2 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsBinderMultipleInputTopicsTest.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsBinderMultipleInputTopicsTest.java
@@ -19,6 +19,7 @@ package org.springframework.cloud.stream.binder.kafka.streams.integration;
 import java.util.ArrayList;
 import java.util.Arrays;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.function.Function;
 
@@ -149,7 +150,7 @@ class KafkaStreamsBinderMultipleInputTopicsTest {
 
 			return input -> input
 					.flatMapValues(
-							value -> Arrays.asList(value.toLowerCase().split("\\W+")))
+							value -> Arrays.asList(value.toLowerCase(Locale.ROOT).split("\\W+")))
 					.map((key, value) -> new KeyValue<>(value, value))
 					.groupByKey(Grouped.with(Serdes.String(), Serdes.String()))
 					.count(Materialized.as("WordCounts-tKWCWSIAP0")).toStream()
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsBinderTombstoneTests.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsBinderTombstoneTests.java
index e4f436ccb..38db7eeb4 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsBinderTombstoneTests.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsBinderTombstoneTests.java
@@ -19,6 +19,7 @@ package org.springframework.cloud.stream.binder.kafka.streams.integration;
 import java.time.Duration;
 import java.util.Arrays;
 import java.util.Date;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Properties;
 import java.util.function.Function;
@@ -173,7 +174,7 @@ class KafkaStreamsBinderTombstoneTests {
 		public Function<KStream<Object, String>, KStream<String, WordCount>> process() {
 
 			return input -> input
-					.flatMapValues(value -> Arrays.asList(value.toLowerCase().split("\\W+")))
+					.flatMapValues(value -> Arrays.asList(value.toLowerCase(Locale.ROOT).split("\\W+")))
 					.map((key, value) -> new KeyValue<>(value, value))
 					.groupByKey(Grouped.with(Serdes.String(), Serdes.String()))
 					.windowedBy(TimeWindows.of(Duration.ofMillis(5000)))
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsNativeEncodingDecodingDisabledTests.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsNativeEncodingDecodingDisabledTests.java
index 4e4ab9b9c..b67dab139 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsNativeEncodingDecodingDisabledTests.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsNativeEncodingDecodingDisabledTests.java
@@ -19,6 +19,7 @@ package org.springframework.cloud.stream.binder.kafka.streams.integration;
 import java.nio.charset.StandardCharsets;
 import java.time.Duration;
 import java.util.Arrays;
+import java.util.Locale;
 import java.util.Map;
 import java.util.function.Function;
 
@@ -153,7 +154,7 @@ public abstract class KafkaStreamsNativeEncodingDecodingDisabledTests {
 
 			return input -> input
 				.flatMapValues(
-					value -> Arrays.asList(value.toLowerCase().split("\\W+")))
+					value -> Arrays.asList(value.toLowerCase(Locale.ROOT).split("\\W+")))
 				.map((key, value) -> new KeyValue<>(value, value))
 				.groupByKey(Grouped.with(Serdes.String(), Serdes.String()))
 				.windowedBy(TimeWindows.of(Duration.ofSeconds(5))).count(Materialized.as("foo-WordCounts-x"))
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsNativeEncodingDecodingEnabledTests.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsNativeEncodingDecodingEnabledTests.java
index 3211d1106..5954bf270 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsNativeEncodingDecodingEnabledTests.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka-streams/src/test/java/org/springframework/cloud/stream/binder/kafka/streams/integration/KafkaStreamsNativeEncodingDecodingEnabledTests.java
@@ -18,6 +18,7 @@ package org.springframework.cloud.stream.binder.kafka.streams.integration;
 
 import java.time.Duration;
 import java.util.Arrays;
+import java.util.Locale;
 import java.util.Map;
 import java.util.function.Function;
 
@@ -137,7 +138,7 @@ public abstract class KafkaStreamsNativeEncodingDecodingEnabledTests {
 
 			return input -> input
 					.flatMapValues(
-							value -> Arrays.asList(value.toLowerCase().split("\\W+")))
+							value -> Arrays.asList(value.toLowerCase(Locale.ROOT).split("\\W+")))
 					.map((key, value) -> new KeyValue<>(value, value))
 					.groupByKey(Grouped.with(Serdes.String(), Serdes.String()))
 					.windowedBy(TimeWindows.of(Duration.ofSeconds(5))).count(Materialized.as("foo-WordCounts-x"))
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/main/java/org/springframework/cloud/stream/binder/kafka/KafkaMessageChannelBinder.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/main/java/org/springframework/cloud/stream/binder/kafka/KafkaMessageChannelBinder.java
index f68576438..cad961104 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/main/java/org/springframework/cloud/stream/binder/kafka/KafkaMessageChannelBinder.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/main/java/org/springframework/cloud/stream/binder/kafka/KafkaMessageChannelBinder.java
@@ -26,6 +26,7 @@ import java.util.Collection;
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
@@ -1478,7 +1479,7 @@ public class KafkaMessageChannelBinder extends
 			if (producerProperties.isDynamicPartitionUpdatesEnabled() &&
 				producerProperties.getPartitionKeyExpression() != null &&
 				!(producerProperties.getPartitionKeyExpression().getExpressionString()
-					.toLowerCase().contains("payload"))) {
+					.toLowerCase(Locale.ROOT).contains("payload"))) {
 				kafkaPartitionHandler =
 					new PartitionHandler(ExpressionUtils.createStandardEvaluationContext(beanFactory),
 						producerProperties, beanFactory);
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/test/java/org/springframework/cloud/stream/binder/kafka/integration/ProducerOnlyTransactionTests.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/test/java/org/springframework/cloud/stream/binder/kafka/integration/ProducerOnlyTransactionTests.java
index 2fbb2766d..c958948e9 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/test/java/org/springframework/cloud/stream/binder/kafka/integration/ProducerOnlyTransactionTests.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/test/java/org/springframework/cloud/stream/binder/kafka/integration/ProducerOnlyTransactionTests.java
@@ -16,6 +16,7 @@
 
 package org.springframework.cloud.stream.binder.kafka.integration;
 
+import java.util.Locale;
 import java.util.Map;
 
 import org.apache.kafka.clients.consumer.Consumer;
@@ -86,7 +87,7 @@ class ProducerOnlyTransactionTests {
 		props.put(ConsumerConfig.KEY_DESERIALIZER_CLASS_CONFIG, ByteArrayDeserializer.class);
 		props.put(ConsumerConfig.VALUE_DESERIALIZER_CLASS_CONFIG, ByteArrayDeserializer.class);
 		props.put(ConsumerConfig.AUTO_OFFSET_RESET_CONFIG, "earliest");
-		props.put(ConsumerConfig.ISOLATION_LEVEL_CONFIG, IsolationLevel.READ_COMMITTED.name().toLowerCase());
+		props.put(ConsumerConfig.ISOLATION_LEVEL_CONFIG, IsolationLevel.READ_COMMITTED.name().toLowerCase(Locale.ROOT));
 		Consumer<?, ?> consumer = new KafkaConsumer<>(props);
 		embeddedKafkaBrokera.consumeFromAllEmbeddedTopics(consumer);
 		ConsumerRecord<?, ?> record = KafkaTestUtils.getSingleRecord(consumer, "output");
diff --git a/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/test/java/org/springframework/cloud/stream/binder/kafka/integration2/ConsumerProducerTransactionTests.java b/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/test/java/org/springframework/cloud/stream/binder/kafka/integration2/ConsumerProducerTransactionTests.java
index a0919cff1..3af3dccc2 100644
--- a/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/test/java/org/springframework/cloud/stream/binder/kafka/integration2/ConsumerProducerTransactionTests.java
+++ b/binders/kafka-binder/spring-cloud-stream-binder-kafka/src/test/java/org/springframework/cloud/stream/binder/kafka/integration2/ConsumerProducerTransactionTests.java
@@ -18,6 +18,7 @@ package org.springframework.cloud.stream.binder.kafka.integration2;
 
 import java.util.ArrayList;
 import java.util.List;
+import java.util.Locale;
 import java.util.Set;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.TimeUnit;
@@ -130,7 +131,7 @@ class ConsumerProducerTransactionTests {
 				if (in.equals("two")) {
 					throw new RuntimeException("fail");
 				}
-				return in.toUpperCase();
+				return in.toUpperCase(Locale.ROOT);
 			};
 		}
 
diff --git a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/binder/PollableConsumerTests.java b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/binder/PollableConsumerTests.java
index 46655c833..0391ae731 100644
--- a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/binder/PollableConsumerTests.java
+++ b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/binder/PollableConsumerTests.java
@@ -18,6 +18,7 @@ package org.springframework.cloud.stream.binder;
 
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.concurrent.CountDownLatch;
 import java.util.concurrent.atomic.AtomicInteger;
@@ -116,7 +117,7 @@ class PollableConsumerTests {
 			@Override
 			public Message<?> preSend(Message<?> message, MessageChannel channel) {
 				return MessageBuilder
-					.withPayload(((String) message.getPayload()).toUpperCase())
+					.withPayload(((String) message.getPayload()).toUpperCase(Locale.ROOT))
 					.copyHeaders(message.getHeaders()).build();
 			}
 
@@ -301,7 +302,7 @@ class PollableConsumerTests {
 			public Message<?> preSend(Message<?> message, MessageChannel channel) {
 				return MessageBuilder
 					.withPayload(
-						new String((byte[]) message.getPayload()).toUpperCase())
+						new String((byte[]) message.getPayload()).toUpperCase(Locale.ROOT))
 					.copyHeaders(message.getHeaders()).build();
 			}
 
@@ -328,7 +329,7 @@ class PollableConsumerTests {
 			@Override
 			public Message<?> preSend(Message<?> message, MessageChannel channel) {
 				return MessageBuilder
-					.withPayload(((String) message.getPayload()).toUpperCase())
+					.withPayload(((String) message.getPayload()).toUpperCase(Locale.ROOT))
 					.copyHeaders(message.getHeaders()).build();
 			}
 
@@ -379,7 +380,7 @@ class PollableConsumerTests {
 			@Override
 			public Message<?> preSend(Message<?> message, MessageChannel channel) {
 				return MessageBuilder
-					.withPayload(((String) message.getPayload()).toUpperCase())
+					.withPayload(((String) message.getPayload()).toUpperCase(Locale.ROOT))
 					.copyHeaders(message.getHeaders()).build();
 			}
 
diff --git a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/FunctionPostProcessingTests.java b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/FunctionPostProcessingTests.java
index 621251304..e92aa919b 100644
--- a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/FunctionPostProcessingTests.java
+++ b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/FunctionPostProcessingTests.java
@@ -16,6 +16,7 @@
 
 package org.springframework.cloud.stream.function;
 
+import java.util.Locale;
 import java.util.function.Function;
 import java.util.function.Supplier;
 
@@ -241,7 +242,7 @@ class FunctionPostProcessingTests {
 		public Function<String, String> uppercase() {
 			return new PostProcessingFunction<String, String>() {
 				public String apply(String input) {
-					return input.toUpperCase();
+					return input.toUpperCase(Locale.ROOT);
 				}
 
 				public void postProcess(Message<String> result) {
@@ -260,7 +261,7 @@ class FunctionPostProcessingTests {
 			if (input.equals("error")) {
 				throw new RuntimeException("intentional");
 			}
-			return input.toUpperCase();
+			return input.toUpperCase(Locale.ROOT);
 		}
 
 		@Override
diff --git a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/GreenfieldFunctionEnableBindingTests.java b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/GreenfieldFunctionEnableBindingTests.java
index 470291011..bca3d8502 100644
--- a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/GreenfieldFunctionEnableBindingTests.java
+++ b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/GreenfieldFunctionEnableBindingTests.java
@@ -18,6 +18,7 @@ package org.springframework.cloud.stream.function;
 
 import java.nio.charset.StandardCharsets;
 import java.util.Date;
+import java.util.Locale;
 import java.util.function.Consumer;
 import java.util.function.Function;
 import java.util.function.Supplier;
@@ -94,7 +95,7 @@ class GreenfieldFunctionEnableBindingTests {
 
 		@Bean
 		public Function<String, String> toUpperCase() {
-			return String::toUpperCase;
+			return v -> v.toUpperCase(Locale.ROOT);
 		}
 
 	}
diff --git a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/HeaderTests.java b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/HeaderTests.java
index f3b71374a..15bf8ac39 100644
--- a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/HeaderTests.java
+++ b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/HeaderTests.java
@@ -16,6 +16,7 @@
 
 package org.springframework.cloud.stream.function;
 
+import java.util.Locale;
 import java.util.function.Function;
 
 import org.junit.jupiter.api.BeforeAll;
@@ -142,7 +143,7 @@ public class HeaderTests {
 	public static class FunctionMessageConfiguration {
 		@Bean
 		public Function<Message<String>, Message<String>> uppercase() {
-			return msg -> MessageBuilder.withPayload(msg.getPayload().toUpperCase()).build();
+			return msg -> MessageBuilder.withPayload(msg.getPayload().toUpperCase(Locale.ROOT)).build();
 		}
 	}
 
diff --git a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/ImplicitFunctionBindingTests.java b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/ImplicitFunctionBindingTests.java
index ad9a4c08f..a15485cda 100644
--- a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/ImplicitFunctionBindingTests.java
+++ b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/ImplicitFunctionBindingTests.java
@@ -23,6 +23,7 @@ import java.util.Arrays;
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.function.BiConsumer;
 import java.util.function.Consumer;
@@ -244,7 +245,7 @@ class ImplicitFunctionBindingTests {
 				// good, we expected it
 			}
 
-			Function<byte[], String> function = v -> new String(v).toUpperCase();
+			Function<byte[], String> function = v -> new String(v).toUpperCase(Locale.ROOT);
 			FunctionBindingTestUtils.bind(context, function);
 
 			input.send(new GenericMessage<byte[]>("hello".getBytes()));
@@ -1434,7 +1435,7 @@ class ImplicitFunctionBindingTests {
 		public Function<Flux<Message<Person>>, Flux<Message<Person>>> reactivePojoMessage() {
 			return flux -> flux.map(message -> {
 				Person p = message.getPayload();
-				p.setName(p.getName().toUpperCase());
+				p.setName(p.getName().toUpperCase(Locale.ROOT));
 				return MessageBuilder.withPayload(p).copyHeaders(message.getHeaders()).build();
 			});
 		}
@@ -1636,7 +1637,7 @@ class ImplicitFunctionBindingTests {
 
 		@Bean
 		public Function<String, String> uppercase() {
-			return v -> v.toUpperCase();
+			return v -> v.toUpperCase(Locale.ROOT);
 		}
 
 		@Bean
diff --git a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/MultipleInputOutputFunctionTests.java b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/MultipleInputOutputFunctionTests.java
index c71772ed0..6a99e39d5 100644
--- a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/MultipleInputOutputFunctionTests.java
+++ b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/MultipleInputOutputFunctionTests.java
@@ -18,6 +18,7 @@ package org.springframework.cloud.stream.function;
 
 import java.nio.charset.StandardCharsets;
 import java.time.Duration;
+import java.util.Locale;
 import java.util.function.Consumer;
 import java.util.function.Function;
 
@@ -296,7 +297,7 @@ class MultipleInputOutputFunctionTests {
 
 		@Bean
 		public Function<String, String> uppercase() {
-			return value -> value.toUpperCase();
+			return value -> value.toUpperCase(Locale.ROOT);
 		}
 
 		@Bean
@@ -378,8 +379,8 @@ class MultipleInputOutputFunctionTests {
 		@Bean
 		public Function<Tuple2<Flux<Person>, Flux<Employee>>, Flux<String>> multiInputSingleOutput() {
 			return tuple -> {
-				Flux<String> stringStream = tuple.getT1().map(p -> p.getName().toUpperCase());
-				Flux<String> intStream = tuple.getT2().map(p -> p.getName().toUpperCase());
+				Flux<String> stringStream = tuple.getT1().map(p -> p.getName().toUpperCase(Locale.ROOT));
+				Flux<String> intStream = tuple.getT2().map(p -> p.getName().toUpperCase(Locale.ROOT));
 				return Flux.merge(stringStream, intStream);
 			};
 		}
diff --git a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/RoutingFunctionTests.java b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/RoutingFunctionTests.java
index 7407a248e..a2d16cfca 100644
--- a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/RoutingFunctionTests.java
+++ b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/RoutingFunctionTests.java
@@ -18,6 +18,7 @@ package org.springframework.cloud.stream.function;
 
 import java.lang.reflect.Field;
 import java.util.List;
+import java.util.Locale;
 import java.util.function.Consumer;
 import java.util.function.Function;
 
@@ -376,7 +377,6 @@ class RoutingFunctionTests {
 		@Bean
 		public Function<Message<String>, Message<String>> enrich() {
 			return x -> {
-				System.out.println("===> enrich");
 				return MessageBuilder.withPayload(x.getPayload()).setHeader("spring.cloud.function.definition", "uppercase").build();
 			};
 		}
@@ -384,8 +384,7 @@ class RoutingFunctionTests {
 		@Bean
 		public Function<String, String> uppercase() {
 			return x -> {
-				System.out.println("===> uppercase");
-				return x.toUpperCase();
+				return x.toUpperCase(Locale.ROOT);
 			};
 		}
 
diff --git a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/StreamBridgeTests.java b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/StreamBridgeTests.java
index 5d7ec5982..e55c8b055 100644
--- a/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/StreamBridgeTests.java
+++ b/core/spring-cloud-stream-integration-tests/src/test/java/org/springframework/cloud/stream/function/StreamBridgeTests.java
@@ -18,6 +18,7 @@ package org.springframework.cloud.stream.function;
 
 import java.lang.reflect.Field;
 import java.net.URI;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Objects;
 import java.util.Set;
@@ -819,7 +820,7 @@ class StreamBridgeTests {
 	public static class DynamicProducerDestinationConfig {
 		@Bean
 		public Function<Message<String>, Message<String>> uppercase() {
-			return msg -> MessageBuilder.withPayload(msg.getPayload().toUpperCase())
+			return msg -> MessageBuilder.withPayload(msg.getPayload().toUpperCase(Locale.ROOT))
 				.setHeader("spring.cloud.stream.sendto.destination", "dynamicTopic").build();
 		}
 	}
@@ -1003,7 +1004,7 @@ class StreamBridgeTests {
 		public IntegrationFlow transform(StreamBridge bridge) {
 			return IntegrationFlow.from("foo").transform(v -> {
 					String s = new String((byte[]) v);
-					return s.toUpperCase();
+					return s.toUpperCase(Locale.ROOT);
 				})
 				.handle(v -> bridge.send("output", v))
 				.get();
diff --git a/core/spring-cloud-stream/src/main/java/org/springframework/cloud/stream/binder/DefaultBinderFactory.java b/core/spring-cloud-stream/src/main/java/org/springframework/cloud/stream/binder/DefaultBinderFactory.java
index 0eae62ed9..a570741e7 100644
--- a/core/spring-cloud-stream/src/main/java/org/springframework/cloud/stream/binder/DefaultBinderFactory.java
+++ b/core/spring-cloud-stream/src/main/java/org/springframework/cloud/stream/binder/DefaultBinderFactory.java
@@ -26,6 +26,7 @@ import java.util.Enumeration;
 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.Properties;
@@ -220,7 +221,7 @@ public class DefaultBinderFactory implements BinderFactory, DisposableBean, Appl
 	}
 
 	private <T> String getKafkaStreamsBinderSimpleName(Class<? extends T> bindingTargetType) {
-		return bindingTargetType.getSimpleName().toLowerCase();
+		return bindingTargetType.getSimpleName().toLowerCase(Locale.ROOT);
 	}
 
 	private <T> boolean isKafkaStreamsType(Class<? extends T> bindingTargetType) {
@@ -233,7 +234,7 @@ public class DefaultBinderFactory implements BinderFactory, DisposableBean, Appl
 
 		if (!MessageChannel.class.isAssignableFrom(bindingTargetType)
 				&& !PollableMessageSource.class.isAssignableFrom(bindingTargetType)) {
-			String bindingTargetTypeName = StringUtils.hasText(name) ? name : bindingTargetType.getSimpleName().toLowerCase();
+			String bindingTargetTypeName = StringUtils.hasText(name) ? name : bindingTargetType.getSimpleName().toLowerCase(Locale.ROOT);
 			Binder<T, ConsumerProperties, ProducerProperties> binderInstance = getBinderInstance(bindingTargetTypeName);
 			return binderInstance;
 		}
diff --git a/schema-registry/spring-cloud-stream-schema-registry-server/src/test/java/org/springframework/cloud/stream/schema/registry/server/SchemaRegistryServerAvroTests.java b/schema-registry/spring-cloud-stream-schema-registry-server/src/test/java/org/springframework/cloud/stream/schema/registry/server/SchemaRegistryServerAvroTests.java
index 7bbd30c95..064d18d13 100644
--- a/schema-registry/spring-cloud-stream-schema-registry-server/src/test/java/org/springframework/cloud/stream/schema/registry/server/SchemaRegistryServerAvroTests.java
+++ b/schema-registry/spring-cloud-stream-schema-registry-server/src/test/java/org/springframework/cloud/stream/schema/registry/server/SchemaRegistryServerAvroTests.java
@@ -23,6 +23,7 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashMap;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.Map.Entry;
 import java.util.Optional;
@@ -81,12 +82,12 @@ class SchemaRegistryServerAvroTests {
 			.parse(resourceToString("classpath:/avro_user_definition_schema_v2.json"));
 
 	private static final String AVRO_USER_SCHEMA_DEFAULT_NAME_STRATEGY_SUBJECT = AVRO_USER_AVRO_SCHEMA_V1.getName()
-			.toLowerCase();
+			.toLowerCase(Locale.ROOT);
 
 
 	private static final String AVRO_USER_SCHEMA_QUALIFED_NAME_STRATEGY_SUBJECT = AVRO_USER_AVRO_SCHEMA_V1
 			.getFullName()
-			.toLowerCase();
+			.toLowerCase(Locale.ROOT);
 
 	private static final Schema AVRO_USER_REGISTRY_SCHEMA_V1 = toSchema(
 			AVRO_USER_SCHEMA_DEFAULT_NAME_STRATEGY_SUBJECT,