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/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() + ").");