Polish empty string checks

See gh-23550

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/amqp/RabbitProperties.java

@@ -290,7 +290,7 @@ public class RabbitProperties {
 	}
 
 	public void setVirtualHost(String virtualHost) {
-		this.virtualHost = "".equals(virtualHost) ? "/" : virtualHost;
+		this.virtualHost = StringUtils.hasLength(virtualHost) ? virtualHost : "/";
 	}
 
 	public AddressShuffleMode getAddressShuffleMode() {

spring-boot-project/spring-boot-cli/src/main/java/org/springframework/boot/cli/command/shell/CommandCompleter.java

@@ -33,6 +33,7 @@ import jline.console.completer.StringsCompleter;
 import org.springframework.boot.cli.command.Command;
 import org.springframework.boot.cli.command.options.OptionHelp;
 import org.springframework.boot.cli.util.Log;
+import org.springframework.util.StringUtils;
 
 /**
  * JLine {@link Completer} for Spring Boot {@link Command}s.
@@ -74,7 +75,7 @@ public class CommandCompleter extends StringsCompleter {
 		int completionIndex = super.complete(buffer, cursor, candidates);
 		int spaceIndex = buffer.indexOf(' ');
 		String commandName = ((spaceIndex != -1) ? buffer.substring(0, spaceIndex) : "");
-		if (!"".equals(commandName.trim())) {
+		if (StringUtils.hasText(commandName)) {
 			for (Command command : this.commands) {
 				if (command.getName().equals(commandName)) {
 					if (cursor == buffer.length() && buffer.endsWith(" ")) {

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

@@ -298,7 +298,7 @@ public class ConfigurationMetadataAnnotationProcessor extends AbstractProcessor
 	private void processEndpoint(AnnotationMirror annotation, TypeElement element) {
 		Map<String, Object> elementValues = this.metadataEnv.getAnnotationElementValues(annotation);
 		String endpointId = (String) elementValues.get("id");
-		if (endpointId == null || "".equals(endpointId)) {
+		if (endpointId == null || endpointId.isEmpty()) {
 			return; // Can't process that endpoint
 		}
 		String endpointKey = ItemMetadata.newItemMetadataPrefix("management.endpoint.", endpointId);

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

@@ -180,8 +180,8 @@ class MetadataGenerationEnvironment {
 			reason = (String) elementValues.get("reason");
 			replacement = (String) elementValues.get("replacement");
 		}
-		reason = "".equals(reason) ? null : reason;
-		replacement = "".equals(replacement) ? null : replacement;
+		reason = (reason == null || reason.isEmpty()) ? null : reason;
+		replacement = (replacement == null || replacement.isEmpty()) ? null : replacement;
 		return new ItemDeprecation(reason, replacement);
 	}
 

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

@@ -180,7 +180,7 @@ class TypeUtils {
 		if (javadoc != null) {
 			javadoc = NEW_LINE_PATTERN.matcher(javadoc).replaceAll("").trim();
 		}
-		return "".equals(javadoc) ? null : javadoc;
+		return (javadoc == null || javadoc.isEmpty()) ? null : javadoc;
 	}
 
 	/**

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

@@ -171,7 +171,7 @@ public class ConfigurationMetadata {
 	public static String nestedPrefix(String prefix, String name) {
 		String nestedPrefix = (prefix != null) ? prefix : "";
 		String dashedName = toDashedCase(name);
-		nestedPrefix += "".equals(nestedPrefix) ? dashedName : "." + dashedName;
+		nestedPrefix += (nestedPrefix == null || nestedPrefix.isEmpty()) ? dashedName : "." + dashedName;
 		return nestedPrefix;
 	}
 

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

@@ -316,7 +316,7 @@ public class PropertiesLauncher extends Launcher {
 		for (String path : commaSeparatedPaths.split(",")) {
 			path = cleanupPath(path);
 			// "" means the user wants root of archive but not current directory
-			path = "".equals(path) ? "/" : path;
+			path = (path == null || path.isEmpty()) ? "/" : path;
 			paths.add(path);
 		}
 		if (paths.isEmpty()) {
@@ -631,7 +631,7 @@ public class PropertiesLauncher extends Launcher {
 			}
 			EntryFilter filter = new PrefixMatchingArchiveFilter(root);
 			List<Archive> archives = asList(parent.getNestedArchives(null, filter));
-			if (("".equals(root) || ".".equals(root)) && !path.endsWith(".jar")
+			if ((root == null || root.isEmpty() || ".".equals(root)) && !path.endsWith(".jar")
 					&& parent != PropertiesLauncher.this.parent) {
 				// You can't find the root with an entry filter so it has to be added
 				// explicitly. But don't add the root of the parent archive.

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

@@ -413,7 +413,7 @@ public class JarFile extends AbstractJarFile implements Iterable<java.util.jar.J
 	public static void registerUrlProtocolHandler() {
 		String handlers = System.getProperty(PROTOCOL_HANDLER, "");
 		System.setProperty(PROTOCOL_HANDLER,
-				("".equals(handlers) ? HANDLERS_PACKAGE : handlers + "|" + HANDLERS_PACKAGE));
+				((handlers == null || handlers.isEmpty()) ? HANDLERS_PACKAGE : handlers + "|" + HANDLERS_PACKAGE));
 		resetCachedUrlHandlers();
 	}