Use Collections.isEmpty() instead of .size() == 0

Ensure that Collections.isEmpty() is used to check if there are no
elements in a collections. This is more explicit and can be faster than
calling .size().

Closes gh-4783

spring-boot-actuator/src/main/java/org/springframework/boot/actuate/autoconfigure/HealthIndicatorAutoConfigurationProperties.java

@@ -39,7 +39,7 @@ public class HealthIndicatorAutoConfigurationProperties {
 	}
 
 	public void setOrder(List<String> statusOrder) {
-		if (statusOrder != null && statusOrder.size() > 0) {
+		if (statusOrder != null && !statusOrder.isEmpty()) {
 			this.order = statusOrder;
 		}
 	}

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

@@ -76,7 +76,7 @@ public class OrderedHealthAggregator extends AbstractHealthAggregator {
 			}
 		}
 		// If no status is given return UNKNOWN
-		if (filteredCandidates.size() == 0) {
+		if (filteredCandidates.isEmpty()) {
 			return Status.UNKNOWN;
 		}
 		// Sort given Status instances by configured order

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

@@ -50,7 +50,7 @@ public abstract class AnyNestedCondition extends AbstractNestedCondition {
 
 	@Override
 	protected ConditionOutcome getFinalMatchOutcome(MemberMatchOutcomes memberOutcomes) {
-		return new ConditionOutcome(memberOutcomes.getMatches().size() > 0,
+		return new ConditionOutcome(!memberOutcomes.getMatches().isEmpty(),
 				"nested any match resulted in " + memberOutcomes.getMatches()
 						+ " matches and " + memberOutcomes.getNonMatches()
 						+ " non matches");

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

@@ -47,7 +47,7 @@ class OnResourceCondition extends SpringBootCondition {
 					? this.defaultResourceLoader : context.getResourceLoader();
 			List<String> locations = new ArrayList<String>();
 			collectValues(locations, attributes.get("resources"));
-			Assert.isTrue(locations.size() > 0,
+			Assert.isTrue(!locations.isEmpty(),
 					"@ConditionalOnResource annotations must specify at least one resource location");
 			for (String location : locations) {
 				if (!loader

spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/logging/AutoConfigurationReportLoggingInitializer.java

@@ -106,7 +106,7 @@ public class AutoConfigurationReportLoggingInitializer
 			this.report = ConditionEvaluationReport
 					.get(this.applicationContext.getBeanFactory());
 		}
-		if (this.report.getConditionAndOutcomesBySource().size() > 0) {
+		if (!this.report.getConditionAndOutcomesBySource().isEmpty()) {
 			if (isCrashReport && this.logger.isInfoEnabled()
 					&& !this.logger.isDebugEnabled()) {
 				this.logger.info("\n\nError starting ApplicationContext. "

spring-boot-cli/src/main/java/org/springframework/boot/cli/command/core/HintCommand.java

@@ -57,7 +57,7 @@ public class HintCommand extends AbstractCommand {
 			if (index == 0) {
 				showCommandHints(starting);
 			}
-			else if ((arguments.size() > 0) && (starting.length() > 0)) {
+			else if (!arguments.isEmpty() && (starting.length() > 0)) {
 				String command = arguments.remove(0);
 				showCommandOptionHints(command, Collections.unmodifiableList(arguments),
 						starting);

spring-boot-cli/src/main/java/org/springframework/boot/cli/command/init/ProjectGenerationRequest.java

@@ -385,7 +385,7 @@ class ProjectGenerationRequest {
 			if (types.size() == 1) {
 				return types.values().iterator().next();
 			}
-			else if (types.size() == 0) {
+			else if (types.isEmpty()) {
 				throw new ReportableException("No type found with build '" + this.build
 						+ "' and format '" + this.format
 						+ "' check the service capabilities (--list)");

spring-boot-cli/src/main/java/org/springframework/boot/cli/command/options/SourceOptions.java

@@ -96,7 +96,7 @@ public class SourceOptions {
 		}
 		this.args = Collections.unmodifiableList(
 				nonOptionArguments.subList(sourceArgCount, nonOptionArguments.size()));
-		Assert.isTrue(sources.size() > 0, "Please specify at least one file");
+		Assert.isTrue(!sources.isEmpty(), "Please specify at least one file");
 		this.sources = Collections.unmodifiableList(sources);
 	}
 

spring-boot-cli/src/main/java/org/springframework/boot/cli/compiler/ExtendedGroovyClassLoader.java

@@ -187,7 +187,7 @@ public class ExtendedGroovyClassLoader extends GroovyClassLoader {
 			if (urls.isEmpty()) {
 				findGroovyJarsFromClassPath(parent, urls);
 			}
-			Assert.state(urls.size() > 0, "Unable to find groovy JAR");
+			Assert.state(!urls.isEmpty(), "Unable to find groovy JAR");
 			return new ArrayList<URL>(urls).toArray(new URL[urls.size()]);
 		}
 

spring-boot-samples/spring-boot-sample-websocket-jetty/src/main/java/samples/websocket/jetty/snake/SnakeTimer.java

@@ -42,7 +42,7 @@ public class SnakeTimer {
 	private static final ConcurrentHashMap<Integer, Snake> snakes = new ConcurrentHashMap<Integer, Snake>();
 
 	public static synchronized void addSnake(Snake snake) {
-		if (snakes.size() == 0) {
+		if (snakes.isEmpty()) {
 			startTimer();
 		}
 		snakes.put(Integer.valueOf(snake.getId()), snake);
@@ -54,7 +54,7 @@ public class SnakeTimer {
 
 	public static synchronized void removeSnake(Snake snake) {
 		snakes.remove(Integer.valueOf(snake.getId()));
-		if (snakes.size() == 0) {
+		if (snakes.isEmpty()) {
 			stopTimer();
 		}
 	}

spring-boot-samples/spring-boot-sample-websocket-tomcat/src/main/java/samples/websocket/tomcat/snake/SnakeTimer.java

@@ -42,7 +42,7 @@ public class SnakeTimer {
 	private static final ConcurrentHashMap<Integer, Snake> snakes = new ConcurrentHashMap<Integer, Snake>();
 
 	public static synchronized void addSnake(Snake snake) {
-		if (snakes.size() == 0) {
+		if (snakes.isEmpty()) {
 			startTimer();
 		}
 		snakes.put(Integer.valueOf(snake.getId()), snake);
@@ -54,7 +54,7 @@ public class SnakeTimer {
 
 	public static synchronized void removeSnake(Snake snake) {
 		snakes.remove(Integer.valueOf(snake.getId()));
-		if (snakes.size() == 0) {
+		if (snakes.isEmpty()) {
 			stopTimer();
 		}
 	}

spring-boot-samples/spring-boot-sample-websocket-undertow/src/main/java/samples/websocket/undertow/snake/SnakeTimer.java

@@ -42,7 +42,7 @@ public class SnakeTimer {
 	private static final ConcurrentHashMap<Integer, Snake> snakes = new ConcurrentHashMap<Integer, Snake>();
 
 	public static synchronized void addSnake(Snake snake) {
-		if (snakes.size() == 0) {
+		if (snakes.isEmpty()) {
 			startTimer();
 		}
 		snakes.put(Integer.valueOf(snake.getId()), snake);
@@ -54,7 +54,7 @@ public class SnakeTimer {
 
 	public static synchronized void removeSnake(Snake snake) {
 		snakes.remove(Integer.valueOf(snake.getId()));
-		if (snakes.size() == 0) {
+		if (snakes.isEmpty()) {
 			stopTimer();
 		}
 	}

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

@@ -73,7 +73,7 @@ public class PropertiesMergingResourceTransformer implements ResourceTransformer
 
 	@Override
 	public boolean hasTransformedResource() {
-		return this.data.size() > 0;
+		return !this.data.isEmpty();
 	}
 
 	@Override

spring-boot/src/main/java/org/springframework/boot/context/config/ConfigFileApplicationListener.java

@@ -504,7 +504,7 @@ public class ConfigFileApplicationListener implements EnvironmentPostProcessor,
 				}
 				return;
 			}
-			if (profiles.size() > 0) {
+			if (!profiles.isEmpty()) {
 				addProfiles(profiles);
 				this.logger.debug("Activated profiles "
 						+ StringUtils.collectionToCommaDelimitedString(profiles));

spring-boot/src/main/java/org/springframework/boot/context/config/DelegatingApplicationContextInitializer.java

@@ -52,7 +52,7 @@ public class DelegatingApplicationContextInitializer implements
 	public void initialize(ConfigurableApplicationContext context) {
 		ConfigurableEnvironment environment = context.getEnvironment();
 		List<Class<?>> initializerClasses = getInitializerClasses(environment);
-		if (initializerClasses.size() > 0) {
+		if (!initializerClasses.isEmpty()) {
 			applyInitializerClasses(context, initializerClasses);
 		}
 	}

spring-boot/src/main/java/org/springframework/boot/context/embedded/AbstractFilterRegistrationBean.java

@@ -261,13 +261,13 @@ abstract class AbstractFilterRegistrationBean extends RegistrationBean {
 					DEFAULT_URL_MAPPINGS);
 		}
 		else {
-			if (servletNames.size() > 0) {
+			if (!servletNames.isEmpty()) {
 				this.logger.info("Mapping filter: '" + registration.getName()
 						+ "' to servlets: " + servletNames);
 				registration.addMappingForServletNames(dispatcherTypes, this.matchAfter,
 						servletNames.toArray(new String[servletNames.size()]));
 			}
-			if (this.urlPatterns.size() > 0) {
+			if (!this.urlPatterns.isEmpty()) {
 				this.logger.info("Mapping filter: '" + registration.getName()
 						+ "' to urls: " + this.urlPatterns);
 				registration.addMappingForUrlPatterns(dispatcherTypes, this.matchAfter,

spring-boot/src/main/java/org/springframework/boot/context/embedded/RegistrationBean.java

@@ -137,7 +137,7 @@ public abstract class RegistrationBean implements ServletContextInitializer, Ord
 				"Registration is null. Was something already registered for name=["
 						+ this.name + "]?");
 		registration.setAsyncSupported(this.asyncSupported);
-		if (this.initParameters.size() > 0) {
+		if (!this.initParameters.isEmpty()) {
 			registration.setInitParameters(this.initParameters);
 		}
 	}

spring-boot/src/main/java/org/springframework/boot/context/web/SpringBootServletInitializer.java

@@ -119,7 +119,7 @@ public abstract class SpringBootServletInitializer implements WebApplicationInit
 				.findAnnotation(getClass(), Configuration.class) != null) {
 			application.getSources().add(getClass());
 		}
-		Assert.state(application.getSources().size() > 0,
+		Assert.state(!application.getSources().isEmpty(),
 				"No SpringApplication sources have been defined. Either override the "
 						+ "configure method or add an @Configuration annotation");
 		// Ensure error pages are registered

spring-boot/src/main/java/org/springframework/boot/test/SpringApplicationContextLoader.java

@@ -123,7 +123,7 @@ public class SpringApplicationContextLoader extends AbstractContextLoader {
 		Set<Object> sources = new LinkedHashSet<Object>();
 		sources.addAll(Arrays.asList(mergedConfig.getClasses()));
 		sources.addAll(Arrays.asList(mergedConfig.getLocations()));
-		Assert.state(sources.size() > 0, "No configuration classes "
+		Assert.state(!sources.isEmpty(), "No configuration classes "
 				+ "or locations found in @SpringApplicationConfiguration. "
 				+ "For default configuration detection to work you need "
 				+ "Spring 4.0.3 or better (found " + SpringVersion.getVersion() + ").");