Use .isEmpty() where feasible

See gh-38739

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

@@ -221,7 +221,7 @@ public class BomPlugin implements Plugin<Project> {
 						.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);

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

@@ -127,7 +127,7 @@ abstract class HealthEndpointSupport<C, T> {
 	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 @@ class OnBeanCondition extends FilteringSpringBootCondition implements Configurat
 
 	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 @@ class OnBeanCondition extends FilteringSpringBootCondition implements Configurat
 		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 @@ class OnBeanCondition extends FilteringSpringBootCondition implements Configurat
 			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-tools/spring-boot-autoconfigure-processor/src/main/java/org/springframework/boot/autoconfigureprocessor/AutoConfigureAnnotationProcessor.java

@@ -345,7 +345,7 @@ public class AutoConfigureAnnotationProcessor extends AbstractProcessor {
 			}
 			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 class JSONStringer {
 	 * @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 @@ public class JSONStringer {
 	 */
 	@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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -65,7 +65,7 @@ public final class ItemMetadata implements Comparable<ItemMetadata> {
 			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-maven-plugin/src/main/java/org/springframework/boot/maven/AbstractAotMojo.java

@@ -227,7 +227,7 @@ public abstract class AbstractAotMojo extends AbstractDependencyFilterMojo {
 		}
 
 		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

@@ -329,7 +329,7 @@ public abstract class AbstractRunMojo extends AbstractDependencyFilterMojo {
 		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 @@ final class CommandLineBuilder {
 		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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -121,7 +121,7 @@ class StartupInfoLogger {
 		}
 		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(")");
@@ -143,7 +143,7 @@ class StartupInfoLogger {
 			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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -52,7 +52,7 @@ public abstract class DataObjectPropertyName {
 				}
 				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 @@ class MapBinder extends AggregateBinder<Map<Object, Object>> {
 		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 @@ public final class ConfigurationPropertyName implements Comparable<Configuration
 		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 @@ public final class ConfigurationPropertyName implements Comparable<Configuration
 			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 final class ConfigurationPropertyName implements Comparable<Configuration
 	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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2020 the original author or authors.
+ * Copyright 2012-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -57,7 +57,7 @@ final class SystemEnvironmentPropertyMapper implements PropertyMapper {
 	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 @@ final class SystemEnvironmentPropertyMapper implements PropertyMapper {
 	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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -158,7 +158,7 @@ public class BasicJsonParser extends AbstractJsonParser {
 			}
 			index++;
 		}
-		if (build.length() > 0) {
+		if (!build.isEmpty()) {
 			list.add(build.toString().trim());
 		}
 		return list;

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/log4j2/ColorConverter.java

@@ -130,7 +130,7 @@ public final class ColorConverter extends LogEventPatternConverter {
 		for (PatternFormatter formatter : this.formatters) {
 			formatter.format(event, buf);
 		}
-		if (buf.length() > 0) {
+		if (!buf.isEmpty()) {
 			AnsiElement element = this.styling;
 			if (element == null) {
 				// Assume highlighting

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/logging/logback/LogbackLoggingSystem.java

@@ -258,14 +258,14 @@ public class LogbackLoggingSystem extends AbstractLoggingSystem implements BeanF
 		List<Throwable> suppressedExceptions = new ArrayList<>();
 		for (Status status : loggerContext.getStatusManager().getCopyOfStatusList()) {
 			if (status.getLevel() == Status.ERROR) {
-				errors.append((errors.length() > 0) ? String.format("%n") : "");
+				errors.append((!errors.isEmpty()) ? String.format("%n") : "");
 				errors.append(status.toString());
 				if (status.getThrowable() != null) {
 					suppressedExceptions.add(status.getThrowable());
 				}
 			}
 		}
-		if (errors.length() == 0) {
+		if (errors.isEmpty()) {
 			if (!StatusUtil.contextHasStatusListener(loggerContext)) {
 				StatusPrinter.printInCaseOfErrorsOrWarnings(loggerContext);
 			}

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/r2dbc/ConnectionFactoryBuilder.java

@@ -212,7 +212,7 @@ public final class ConnectionFactoryBuilder {
 
 		private ConnectionFactoryOptions delegateFactoryOptions(ConnectionFactoryOptions options) {
 			String protocol = toString(options.getRequiredValue(ConnectionFactoryOptions.PROTOCOL));
-			if (protocol.trim().length() == 0) {
+			if (protocol.trim().isEmpty()) {
 				throw new IllegalArgumentException(String.format("Protocol %s is not valid.", protocol));
 			}
 			String[] protocols = protocol.split(COLON, 2);