Cleanup java sources

1. use `StandardCharsets.UTF_8` where feasible
2. use `.isEmpty()` where feasible
3. remove unnecessary `static` modifier of inner record or interface type
4. remove unnecessary `final` modifier of private or static method
5. remove unnecessary `toString()`

buildSrc/src/main/java/org/springframework/boot/build/architecture/ArchitectureCheck.java

@@ -89,7 +89,7 @@ void checkArchitecture() throws IOException {
 		if (!violations.isEmpty()) {
 			StringBuilder report = new StringBuilder();
 			for (EvaluationResult violation : violations) {
-				report.append(violation.getFailureReport().toString());
+				report.append(violation.getFailureReport());
 				report.append(String.format("%n"));
 			}
 			Files.writeString(outputFile.toPath(), report.toString(), StandardOpenOption.CREATE,

buildSrc/src/main/java/org/springframework/boot/build/autoconfigure/AutoConfigurationPlugin.java

@@ -154,7 +154,7 @@ private Provider<AutoConfigurationImports> autoConfigurationImports(Project proj
 		});
 	}
 
-	private static record AutoConfigurationImports(Path importsFile, List<String> imports) {
+	private record AutoConfigurationImports(Path importsFile, List<String> imports) {
 
 	}
 

buildSrc/src/main/java/org/springframework/boot/build/bom/BomPlugin.java

@@ -221,7 +221,7 @@ private void addClassifiedManagedDependencies(Node dependencyManagement) {
 						.collect(Collectors.toSet());
 					Node target = dependency;
 					for (String classifier : classifiers) {
-						if (classifier.length() > 0) {
+						if (!classifier.isEmpty()) {
 							if (target == null) {
 								target = new Node(null, "dependency");
 								target.appendNode("groupId", groupId);

buildSrc/src/main/java/org/springframework/boot/build/bom/bomr/MavenMetadataVersionResolver.java

@@ -69,7 +69,7 @@ private URI normalize(URI uri) {
 		if ("/".equals(uri.getPath())) {
 			return uri;
 		}
-		return URI.create(uri.toString() + "/");
+		return URI.create(uri + "/");
 	}
 
 	@Override

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/endpoint/web/WebEndpointAutoConfigurationTests.java

@@ -125,7 +125,7 @@ static class TestPathMatcher implements PathMapper {
 		@Override
 		public String getRootPath(EndpointId endpointId) {
 			if (endpointId.toString().endsWith("one")) {
-				return "1/" + endpointId.toString();
+				return "1/" + endpointId;
 			}
 			return null;
 		}

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/endpoint/annotation/EndpointDiscoverer.java

@@ -234,9 +234,8 @@ private void assertNoDuplicateOperations(EndpointBean endpointBean, MultiValueMa
 			String extensionBeanNames = extensions.stream()
 				.map(ExtensionBean::getBeanName)
 				.collect(Collectors.joining(", "));
-			throw new IllegalStateException("Unable to map duplicate endpoint operations: " + duplicates.toString()
-					+ " to " + endpointBean.getBeanName()
-					+ (extensions.isEmpty() ? "" : " (" + extensionBeanNames + ")"));
+			throw new IllegalStateException("Unable to map duplicate endpoint operations: " + duplicates + " to "
+					+ endpointBean.getBeanName() + (extensions.isEmpty() ? "" : " (" + extensionBeanNames + ")"));
 		}
 	}
 

spring-boot-project/spring-boot-actuator/src/main/java/org/springframework/boot/actuate/health/HealthEndpointSupport.java

@@ -127,7 +127,7 @@ private Object getContributor(String[] path, int pathOffset) {
 	private String getName(String[] path, int pathOffset) {
 		StringBuilder name = new StringBuilder();
 		while (pathOffset < path.length) {
-			name.append((name.length() != 0) ? "/" : "");
+			name.append((!name.isEmpty()) ? "/" : "");
 			name.append(path[pathOffset]);
 			pathOffset++;
 		}

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/condition/OnBeanCondition.java

@@ -332,7 +332,7 @@ private String createOnBeanNoMatchReason(MatchResult matchResult) {
 
 	private void appendMessageForNoMatches(StringBuilder reason, Collection<String> unmatched, String description) {
 		if (!unmatched.isEmpty()) {
-			if (reason.length() > 0) {
+			if (!reason.isEmpty()) {
 				reason.append(" and ");
 			}
 			reason.append("did not find any beans ");
@@ -347,7 +347,7 @@ private String createOnMissingBeanNoMatchReason(MatchResult matchResult) {
 		appendMessageForMatches(reason, matchResult.getMatchedAnnotations(), "annotated with");
 		appendMessageForMatches(reason, matchResult.getMatchedTypes(), "of type");
 		if (!matchResult.getMatchedNames().isEmpty()) {
-			if (reason.length() > 0) {
+			if (!reason.isEmpty()) {
 				reason.append(" and ");
 			}
 			reason.append("found beans named ");
@@ -360,7 +360,7 @@ private void appendMessageForMatches(StringBuilder reason, Map<String, Collectio
 			String description) {
 		if (!matches.isEmpty()) {
 			matches.forEach((key, value) -> {
-				if (reason.length() > 0) {
+				if (!reason.isEmpty()) {
 					reason.append(" and ");
 				}
 				reason.append("found beans ");

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/env/DevToolsHomePropertiesPostProcessor.java

@@ -144,7 +144,7 @@ protected File getHomeDirectory() {
 	}
 
 	@SafeVarargs
-	private final File getHomeDirectory(Supplier<String>... pathSuppliers) {
+	private File getHomeDirectory(Supplier<String>... pathSuppliers) {
 		for (Supplier<String> pathSupplier : pathSuppliers) {
 			String path = pathSupplier.get();
 			if (StringUtils.hasText(path)) {

spring-boot-project/spring-boot-devtools/src/main/java/org/springframework/boot/devtools/restart/ChangeableUrls.java

@@ -23,6 +23,7 @@
 import java.net.URL;
 import java.net.URLClassLoader;
 import java.net.URLDecoder;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collection;
 import java.util.Collections;
@@ -159,7 +160,7 @@ private static List<URL> getUrlsFromManifestClassPathAttribute(URL jarUrl, JarFi
 					urls.add(referenced);
 				}
 				else {
-					referenced = new URL(jarUrl, URLDecoder.decode(entry, "UTF-8"));
+					referenced = new URL(jarUrl, URLDecoder.decode(entry, StandardCharsets.UTF_8));
 					if (new File(referenced.getFile()).exists()) {
 						urls.add(referenced);
 					}

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/context/assertj/AssertProviderApplicationContextInvocationHandler.java

@@ -153,7 +153,7 @@ private Object invokeApplicationContextMethod(Method method, Object[] args) thro
 
 	private ApplicationContext getStartedApplicationContext() {
 		if (this.startupFailure != null) {
-			throw new IllegalStateException(toString() + " failed to start", this.startupFailure);
+			throw new IllegalStateException(this + " failed to start", this.startupFailure);
 		}
 		return this.applicationContext;
 	}

spring-boot-project/spring-boot-test/src/main/java/org/springframework/boot/test/web/client/TestRestTemplate.java

@@ -956,7 +956,7 @@ private RequestEntity<?> createRequestEntityWithRootAppliedUri(RequestEntity<?>
 	private URI applyRootUriIfNecessary(URI uri) {
 		UriTemplateHandler uriTemplateHandler = this.restTemplate.getUriTemplateHandler();
 		if ((uriTemplateHandler instanceof RootUriTemplateHandler rootHandler) && uri.toString().startsWith("/")) {
-			return URI.create(rootHandler.getRootUri() + uri.toString());
+			return URI.create(rootHandler.getRootUri() + uri);
 		}
 		return uri;
 	}

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/json/AbstractJsonMarshalTesterTests.java

@@ -169,7 +169,7 @@ void parseMapShouldReturnContent() throws Exception {
 		assertThat(tester.parse(MAP_JSON)).asMap().containsEntry("a", OBJECT);
 	}
 
-	protected static final ExampleObject createExampleObject(String name, int age) {
+	protected static ExampleObject createExampleObject(String name, int age) {
 		ExampleObject exampleObject = new ExampleObject();
 		exampleObject.setName(name);
 		exampleObject.setAge(age);

spring-boot-project/spring-boot-test/src/test/java/org/springframework/boot/test/mock/web/SpringBootMockServletContextTests.java

@@ -20,6 +20,7 @@
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLDecoder;
+import java.nio.charset.StandardCharsets;
 
 import jakarta.servlet.ServletContext;
 import org.junit.jupiter.api.Test;
@@ -80,7 +81,7 @@ protected String getResourceLocation(String path) {
 		};
 		URL resource = context.getResource("/");
 		assertThat(resource).isNotNull();
-		File file = new File(URLDecoder.decode(resource.getPath(), "UTF-8"));
+		File file = new File(URLDecoder.decode(resource.getPath(), StandardCharsets.UTF_8));
 		assertThat(file).exists().isDirectory();
 		String[] contents = file.list((dir, name) -> !(".".equals(name) || "..".equals(name)));
 		assertThat(contents).isNotNull();

spring-boot-project/spring-boot-testcontainers/src/main/java/org/springframework/boot/testcontainers/service/connection/ServiceConnectionContextCustomizer.java

@@ -91,8 +91,7 @@ List<ContainerConnectionSource<?>> getSources() {
 	 * Relevant details from {@link ContainerConnectionSource} used as a
 	 * MergedContextConfiguration cache key.
 	 */
-	private static record CacheKey(String connectionName, Set<Class<?>> connectionDetailsTypes,
-			Container<?> container) {
+	private record CacheKey(String connectionName, Set<Class<?>> connectionDetailsTypes, Container<?> container) {
 
 		CacheKey(ContainerConnectionSource<?> source) {
 			this(source.getConnectionName(), source.getConnectionDetailsTypes(), source.getContainerSupplier().get());

spring-boot-project/spring-boot-testcontainers/src/test/java/org/springframework/boot/testcontainers/ImportTestcontainersTests.java

@@ -162,7 +162,7 @@ interface ContainerDefinitions {
 	}
 
 	@Retention(RetentionPolicy.RUNTIME)
-	static @interface ContainerAnnotation {
+	@interface ContainerAnnotation {
 
 	}
 

spring-boot-project/spring-boot-testcontainers/src/test/java/org/springframework/boot/testcontainers/properties/TestcontainersPropertySourceAutoConfigurationTests.java

@@ -68,7 +68,7 @@ RedisContainer redisContainer(DynamicPropertyRegistry properties) {
 	}
 
 	@ConfigurationProperties("container")
-	static record ContainerProperties(int port) {
+	record ContainerProperties(int port) {
 	}
 
 	static class TestBean {

spring-boot-project/spring-boot-tools/spring-boot-autoconfigure-processor/src/main/java/org/springframework/boot/autoconfigureprocessor/AutoConfigureAnnotationProcessor.java

@@ -345,7 +345,7 @@ private String toCommaDelimitedString(List<Object> list) {
 			}
 			StringBuilder result = new StringBuilder();
 			for (Object item : list) {
-				result.append((result.length() != 0) ? "," : "");
+				result.append((!result.isEmpty()) ? "," : "");
 				result.append(item);
 			}
 			return result.toString();

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/json-shade/java/org/springframework/boot/configurationprocessor/json/JSONStringer.java

@@ -173,7 +173,7 @@ public JSONStringer endObject() throws JSONException {
 	 * @throws JSONException if processing of json failed
 	 */
 	JSONStringer open(Scope empty, String openBracket) throws JSONException {
-		if (this.stack.isEmpty() && this.out.length() > 0) {
+		if (this.stack.isEmpty() && !this.out.isEmpty()) {
 			throw new JSONException("Nesting problem: multiple top-level roots");
 		}
 		beforeValue();
@@ -423,7 +423,7 @@ else if (context != Scope.NULL) {
 	 */
 	@Override
 	public String toString() {
-		return this.out.length() == 0 ? null : this.out.toString();
+		return this.out.isEmpty() ? null : this.out.toString();
 	}
 
 }

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/main/java/org/springframework/boot/configurationprocessor/metadata/ItemMetadata.java

@@ -65,7 +65,7 @@ private String buildName(String prefix, String name) {
 			fullName.append(prefix);
 		}
 		if (name != null) {
-			if (fullName.length() > 0) {
+			if (!fullName.isEmpty()) {
 				fullName.append('.');
 			}
 			fullName.append(ConfigurationMetadata.toDashedCase(name));

spring-boot-project/spring-boot-tools/spring-boot-jarmode-layertools/src/test/java/org/springframework/boot/jarmode/layertools/TestPrintStream.java

@@ -37,7 +37,7 @@
  */
 class TestPrintStream extends PrintStream implements AssertProvider<PrintStreamAssert> {
 
-	private final Class<? extends Object> testClass;
+	private final Class<?> testClass;
 
 	TestPrintStream(Object testInstance) {
 		super(new ByteArrayOutputStream());

spring-boot-project/spring-boot-tools/spring-boot-loader-classic/src/main/java/org/springframework/boot/loader/PropertiesLauncher.java

@@ -26,6 +26,7 @@
 import java.net.URL;
 import java.net.URLConnection;
 import java.net.URLDecoder;
+import java.nio.charset.StandardCharsets;
 import java.util.ArrayList;
 import java.util.Collections;
 import java.util.Iterator;
@@ -227,7 +228,7 @@ private InputStream getResource(String config) throws Exception {
 
 	private String handleUrl(String path) throws UnsupportedEncodingException {
 		if (path.startsWith("jar:file:") || path.startsWith("file:")) {
-			path = URLDecoder.decode(path, "UTF-8");
+			path = URLDecoder.decode(path, StandardCharsets.UTF_8);
 			if (path.startsWith("file:")) {
 				path = path.substring("file:".length());
 				if (path.startsWith("//")) {

spring-boot-project/spring-boot-tools/spring-boot-loader-classic/src/main/java/org/springframework/boot/loader/jar/JarURLConnection.java

@@ -20,12 +20,12 @@
 import java.io.FileNotFoundException;
 import java.io.IOException;
 import java.io.InputStream;
-import java.io.UnsupportedEncodingException;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLConnection;
 import java.net.URLEncoder;
 import java.net.URLStreamHandler;
+import java.nio.charset.StandardCharsets;
 import java.security.Permission;
 
 /**
@@ -318,13 +318,8 @@ private void write(String source, ByteArrayOutputStream outputStream) {
 			for (int i = 0; i < length; i++) {
 				int c = source.charAt(i);
 				if (c > 127) {
-					try {
-						String encoded = URLEncoder.encode(String.valueOf((char) c), "UTF-8");
-						write(encoded, outputStream);
-					}
-					catch (UnsupportedEncodingException ex) {
-						throw new IllegalStateException(ex);
-					}
+					String encoded = URLEncoder.encode(String.valueOf((char) c), StandardCharsets.UTF_8);
+					write(encoded, outputStream);
 				}
 				else {
 					if (c == '%') {

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/AbstractAotMojo.java

@@ -227,7 +227,7 @@ public void report(Diagnostic<? extends JavaFileObject> diagnostic) {
 		}
 
 		boolean hasReportedErrors() {
-			return this.message.length() > 0;
+			return !this.message.isEmpty();
 		}
 
 		@Override

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/AbstractRunMojo.java

@@ -342,7 +342,7 @@ private void addClasspath(List<String> args) throws MojoExecutionException {
 		try {
 			StringBuilder classpath = new StringBuilder();
 			for (URL ele : getClassPathUrls()) {
-				if (classpath.length() > 0) {
+				if (!classpath.isEmpty()) {
 					classpath.append(File.pathSeparator);
 				}
 				classpath.append(new File(ele.toURI()));

spring-boot-project/spring-boot-tools/spring-boot-maven-plugin/src/main/java/org/springframework/boot/maven/CommandLineBuilder.java

@@ -98,7 +98,7 @@ static class ClasspathBuilder {
 		static String build(List<URL> classpathElements) {
 			StringBuilder classpath = new StringBuilder();
 			for (URL element : classpathElements) {
-				if (classpath.length() > 0) {
+				if (!classpath.isEmpty()) {
 					classpath.append(File.pathSeparator);
 				}
 				classpath.append(toFile(element));

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/StartupInfoLogger.java

@@ -118,7 +118,7 @@ private void appendContext(StringBuilder message) {
 		}
 		append(context, "started by ", () -> System.getProperty("user.name"));
 		append(context, "in ", () -> System.getProperty("user.dir"));
-		if (context.length() > 0) {
+		if (!context.isEmpty()) {
 			message.append(" (");
 			message.append(context);
 			message.append(")");
@@ -140,7 +140,7 @@ private void append(StringBuilder message, String prefix, Callable<Object> call,
 			value = defaultValue;
 		}
 		if (StringUtils.hasLength(value)) {
-			message.append((message.length() > 0) ? " " : "");
+			message.append((!message.isEmpty()) ? " " : "");
 			message.append(prefix);
 			message.append(value);
 		}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/DataObjectPropertyName.java

@@ -52,7 +52,7 @@ public static String toDashedForm(String name) {
 				}
 				else {
 					ch = (ch != '_') ? ch : '-';
-					if (Character.isUpperCase(ch) && result.length() > 0 && result.charAt(result.length() - 1) != '-') {
+					if (Character.isUpperCase(ch) && !result.isEmpty() && result.charAt(result.length() - 1) != '-') {
 						result.append('-');
 					}
 					result.append(Character.toLowerCase(ch));

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/bind/MapBinder.java

@@ -211,7 +211,7 @@ private boolean isScalarValue(ConfigurationPropertySource source, ConfigurationP
 		private String getKeyName(ConfigurationPropertyName name) {
 			StringBuilder result = new StringBuilder();
 			for (int i = this.root.getNumberOfElements(); i < name.getNumberOfElements(); i++) {
-				if (result.length() != 0) {
+				if (!result.isEmpty()) {
 					result.append('.');
 				}
 				result.append(name.getElement(i, Form.ORIGINAL));

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/ConfigurationPropertyName.java

@@ -543,7 +543,7 @@ private String buildToString() {
 		StringBuilder result = new StringBuilder(elements * 8);
 		for (int i = 0; i < elements; i++) {
 			boolean indexed = isIndexed(i);
-			if (result.length() > 0 && !indexed) {
+			if (!result.isEmpty() && !indexed) {
 				result.append('.');
 			}
 			if (indexed) {
@@ -615,7 +615,7 @@ private static Elements elementsOf(CharSequence name, boolean returnNullIfInvali
 			Assert.isTrue(returnNullIfInvalid, "Name must not be null");
 			return null;
 		}
-		if (name.length() == 0) {
+		if (name.isEmpty()) {
 			return Elements.EMPTY;
 		}
 		if (name.charAt(0) == '.' || name.charAt(name.length() - 1) == '.') {
@@ -674,7 +674,7 @@ public static ConfigurationPropertyName adapt(CharSequence name, char separator)
 	static ConfigurationPropertyName adapt(CharSequence name, char separator,
 			Function<CharSequence, CharSequence> elementValueProcessor) {
 		Assert.notNull(name, "Name must not be null");
-		if (name.length() == 0) {
+		if (name.isEmpty()) {
 			return EMPTY;
 		}
 		Elements elements = new ElementsParser(name, separator).parse(elementValueProcessor);

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/SystemEnvironmentPropertyMapper.java

@@ -57,7 +57,7 @@ private String convertName(ConfigurationPropertyName name) {
 	private String convertName(ConfigurationPropertyName name, int numberOfElements) {
 		StringBuilder result = new StringBuilder();
 		for (int i = 0; i < numberOfElements; i++) {
-			if (result.length() > 0) {
+			if (!result.isEmpty()) {
 				result.append('_');
 			}
 			result.append(name.getElement(i, Form.UNIFORM).toUpperCase(Locale.ENGLISH));
@@ -68,7 +68,7 @@ private String convertName(ConfigurationPropertyName name, int numberOfElements)
 	private String convertLegacyName(ConfigurationPropertyName name) {
 		StringBuilder result = new StringBuilder();
 		for (int i = 0; i < name.getNumberOfElements(); i++) {
-			if (result.length() > 0) {
+			if (!result.isEmpty()) {
 				result.append('_');
 			}
 			result.append(convertLegacyNameElement(name.getElement(i, Form.ORIGINAL)));

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/json/BasicJsonParser.java

@@ -158,7 +158,7 @@ else if (current == '\\') {
 			}
 			index++;
 		}
-		if (build.length() > 0) {
+		if (!build.isEmpty()) {
 			list.add(build.toString().trim());
 		}
 		return list;