Merge pull request #32655 from bertoltmeier

* gh-32655:
  Add checkstyle rule for List.of() / Set.of() / Map.of()

Closes gh-32655

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/BraveAutoConfiguration.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.actuate.autoconfigure.tracing;
 
+import java.util.Collections;
 import java.util.List;
 
 import brave.Tracer;
@@ -207,7 +208,7 @@ public class BraveAutoConfiguration {
 			Factory delegate = switch (this.tracingProperties.getPropagation().getType()) {
 				case B3 ->
 					B3Propagation.newFactoryBuilder().injectFormat(B3Propagation.Format.SINGLE_NO_PARENT).build();
-				case W3C -> new W3CPropagation(BRAVE_BAGGAGE_MANAGER, List.of());
+				case W3C -> new W3CPropagation(BRAVE_BAGGAGE_MANAGER, Collections.emptyList());
 			};
 			FactoryBuilder builder = BaggagePropagation.newFactoryBuilder(delegate);
 			baggagePropagationCustomizers.orderedStream().forEach((customizer) -> customizer.customize(builder));

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/OpenTelemetryAutoConfiguration.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.actuate.autoconfigure.tracing;
 
+import java.util.Collections;
 import java.util.List;
 import java.util.regex.Pattern;
 
@@ -137,8 +138,9 @@ public class OpenTelemetryAutoConfiguration {
 	@ConditionalOnMissingBean
 	OtelTracer micrometerOtelTracer(Tracer tracer, EventPublisher eventPublisher,
 			OtelCurrentTraceContext otelCurrentTraceContext) {
-		return new OtelTracer(tracer, otelCurrentTraceContext, eventPublisher, new OtelBaggageManager(
-				otelCurrentTraceContext, this.tracingProperties.getBaggage().getRemoteFields(), List.of()));
+		return new OtelTracer(tracer, otelCurrentTraceContext, eventPublisher,
+				new OtelBaggageManager(otelCurrentTraceContext, this.tracingProperties.getBaggage().getRemoteFields(),
+						Collections.emptyList()));
 	}
 
 	@Bean
@@ -202,8 +204,9 @@ public class OpenTelemetryAutoConfiguration {
 		@ConditionalOnProperty(prefix = "management.tracing.propagation", name = "type", havingValue = "B3")
 		TextMapPropagator b3BaggageTextMapPropagator(OtelCurrentTraceContext otelCurrentTraceContext) {
 			List<String> remoteFields = this.tracingProperties.getBaggage().getRemoteFields();
-			return TextMapPropagator.composite(B3Propagator.injectingSingleHeader(), new BaggageTextMapPropagator(
-					remoteFields, new OtelBaggageManager(otelCurrentTraceContext, remoteFields, List.of())));
+			return TextMapPropagator.composite(B3Propagator.injectingSingleHeader(),
+					new BaggageTextMapPropagator(remoteFields,
+							new OtelBaggageManager(otelCurrentTraceContext, remoteFields, Collections.emptyList())));
 		}
 
 		@Bean

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/wavefront/WavefrontTracingAutoConfiguration.java

@@ -16,7 +16,7 @@
 
 package org.springframework.boot.actuate.autoconfigure.tracing.wavefront;
 
-import java.util.Set;
+import java.util.Collections;
 
 import brave.handler.SpanHandler;
 import com.wavefront.sdk.common.WavefrontSender;
@@ -84,7 +84,7 @@ public class WavefrontTracingAutoConfiguration {
 		WavefrontSpanHandler wavefrontSpanHandler(WavefrontProperties properties, WavefrontSender wavefrontSender,
 				SpanMetrics spanMetrics, ApplicationTags applicationTags) {
 			return new WavefrontSpanHandler(properties.getSender().getMaxQueueSize(), wavefrontSender, spanMetrics,
-					properties.getSourceOrDefault(), applicationTags, Set.of());
+					properties.getSourceOrDefault(), applicationTags, Collections.emptySet());
 		}
 
 		@Configuration(proxyBeanMethods = false)

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/zipkin/HttpSender.java

@@ -19,6 +19,7 @@ package org.springframework.boot.actuate.autoconfigure.tracing.zipkin;
 import java.io.ByteArrayOutputStream;
 import java.io.IOException;
 import java.io.UncheckedIOException;
+import java.util.Collections;
 import java.util.List;
 import java.util.zip.GZIPOutputStream;
 
@@ -68,7 +69,7 @@ abstract class HttpSender extends Sender {
 	@Override
 	public CheckResult check() {
 		try {
-			sendSpans(List.of()).execute();
+			sendSpans(Collections.emptyList()).execute();
 			return CheckResult.OK;
 		}
 		catch (IOException | RuntimeException ex) {

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/zipkin/ZipkinHttpSenderTests.java

@@ -19,6 +19,7 @@ package org.springframework.boot.actuate.autoconfigure.tracing.zipkin;
 import java.io.IOException;
 import java.nio.charset.StandardCharsets;
 import java.time.Duration;
+import java.util.Collections;
 import java.util.List;
 import java.util.Objects;
 import java.util.concurrent.atomic.AtomicReference;
@@ -53,7 +54,7 @@ abstract class ZipkinHttpSenderTests {
 	@Test
 	void sendSpansShouldThrowIfCloseWasCalled() throws IOException {
 		this.sut.close();
-		assertThatThrownBy(() -> this.sut.sendSpans(List.of())).isInstanceOf(ClosedSenderException.class);
+		assertThatThrownBy(() -> this.sut.sendSpans(Collections.emptyList())).isInstanceOf(ClosedSenderException.class);
 	}
 
 	protected void makeRequest(List<byte[]> encodedSpans, boolean async) throws IOException {

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/zipkin/ZipkinRestTemplateSenderTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.actuate.autoconfigure.tracing.zipkin;
 
 import java.io.IOException;
 import java.util.Base64;
+import java.util.Collections;
 import java.util.List;
 
 import org.junit.jupiter.api.AfterEach;
@@ -95,12 +96,13 @@ class ZipkinRestTemplateSenderTests extends ZipkinHttpSenderTests {
 		this.mockServer.expect(requestTo(ZIPKIN_URL)).andExpect(method(HttpMethod.POST))
 				.andRespond(withStatus(HttpStatus.INTERNAL_SERVER_ERROR));
 		if (async) {
-			CallbackResult callbackResult = makeAsyncRequest(List.of());
+			CallbackResult callbackResult = makeAsyncRequest(Collections.emptyList());
 			assertThat(callbackResult.success()).isFalse();
 			assertThat(callbackResult.error()).isNotNull().hasMessageContaining("500 Internal Server Error");
 		}
 		else {
-			assertThatThrownBy(() -> makeSyncRequest(List.of())).hasMessageContaining("500 Internal Server Error");
+			assertThatThrownBy(() -> makeSyncRequest(Collections.emptyList()))
+					.hasMessageContaining("500 Internal Server Error");
 		}
 	}
 

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/zipkin/ZipkinWebClientSenderTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.actuate.autoconfigure.tracing.zipkin;
 
 import java.io.IOException;
 import java.util.Base64;
+import java.util.Collections;
 import java.util.List;
 import java.util.function.Consumer;
 
@@ -106,12 +107,13 @@ class ZipkinWebClientSenderTests extends ZipkinHttpSenderTests {
 	void sendSpansShouldHandleHttpFailures(boolean async) throws InterruptedException {
 		mockBackEnd.enqueue(new MockResponse().setResponseCode(500));
 		if (async) {
-			CallbackResult callbackResult = makeAsyncRequest(List.of());
+			CallbackResult callbackResult = makeAsyncRequest(Collections.emptyList());
 			assertThat(callbackResult.success()).isFalse();
 			assertThat(callbackResult.error()).isNotNull().hasMessageContaining("500 Internal Server Error");
 		}
 		else {
-			assertThatThrownBy(() -> makeSyncRequest(List.of())).hasMessageContaining("500 Internal Server Error");
+			assertThatThrownBy(() -> makeSyncRequest(Collections.emptyList()))
+					.hasMessageContaining("500 Internal Server Error");
 		}
 
 		requestAssertions((request) -> assertThat(request.getMethod()).isEqualTo("POST"));

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/kafka/KafkaPropertiesTests.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.autoconfigure.kafka;
 
+import java.util.Collections;
 import java.util.Map;
 
 import org.apache.kafka.common.config.SslConfigs;
@@ -55,7 +56,7 @@ class KafkaPropertiesTests {
 
 	@Test
 	void adminDefaultValuesAreConsistent() {
-		KafkaAdmin admin = new KafkaAdmin(Map.of());
+		KafkaAdmin admin = new KafkaAdmin(Collections.emptyMap());
 		Admin adminProperties = new KafkaProperties().getAdmin();
 		assertThat(admin).hasFieldOrPropertyWithValue("fatalIfBrokerNotAvailable", adminProperties.isFailFast());
 		assertThat(admin).hasFieldOrPropertyWithValue("modifyTopicConfigs", adminProperties.isModifyTopicConfigs());

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/web/WebResourcesRuntimeHintsTests.java

@@ -18,6 +18,7 @@ package org.springframework.boot.autoconfigure.web;
 
 import java.net.URL;
 import java.net.URLClassLoader;
+import java.util.Collections;
 import java.util.List;
 import java.util.function.Consumer;
 
@@ -52,7 +53,7 @@ class WebResourcesRuntimeHintsTests {
 
 	@Test
 	void registerHintsWithNoLocation() {
-		RuntimeHints hints = register(new TestClassLoader(List.of()));
+		RuntimeHints hints = register(new TestClassLoader(Collections.emptyList()));
 		assertThat(hints.resources().resourcePatternHints()).isEmpty();
 	}
 

src/checkstyle/checkstyle.xml

@@ -54,6 +54,13 @@
 				value="Please use BDD-style (given, when, then) using BDDMockito imports." />
 			<property name="ignoreComments" value="true" />
 		</module>
+		<module name="com.puppycrawl.tools.checkstyle.checks.regexp.RegexpSinglelineJavaCheck">
+			<property name="maximum" value="0"/>
+			<property name="format" value="(List|Map|Set)\.of\(\)" />
+			<property name="message"
+					  value="Please use Collections.emptyList()/emptyMap()/emptySet() for creating empty lists/maps/sets." />
+			<property name="ignoreComments" value="true" />
+		</module>
 		<module name="io.spring.javaformat.checkstyle.check.SpringJavadocCheck">
 			<property name="publicOnlySinceTags" value="true" />
 			<property name="requireSinceTag" value="true" />