Use sorted properties to ensure output is repeatable

Closes gh-21593

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

@@ -30,6 +30,8 @@ import org.gradle.api.tasks.OutputFile;
 import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.TaskAction;
 
+import org.springframework.core.CollectionFactory;
+
 /**
  * A {@link Task} for generating metadata describing a project's auto-configuration
  * classes.
@@ -73,7 +75,7 @@ public class AutoConfigurationMetadata extends AbstractTask {
 	}
 
 	private Properties readAutoConfiguration() throws IOException {
-		Properties autoConfiguration = new Properties();
+		Properties autoConfiguration = CollectionFactory.createSortedProperties(true);
 		Properties springFactories = readSpringFactories(
 				new File(this.sourceSet.getOutput().getResourcesDir(), "META-INF/spring.factories"));
 		autoConfiguration.setProperty("autoConfigurationClassNames",

buildSrc/src/main/java/org/springframework/boot/build/starters/StarterMetadata.java

@@ -32,6 +32,8 @@ import org.gradle.api.tasks.InputFiles;
 import org.gradle.api.tasks.OutputFile;
 import org.gradle.api.tasks.TaskAction;
 
+import org.springframework.core.CollectionFactory;
+
 /**
  * A {@link Task} for generating metadata that describes a starter.
  *
@@ -68,7 +70,7 @@ public class StarterMetadata extends AbstractTask {
 
 	@TaskAction
 	void generateMetadata() throws IOException {
-		Properties properties = new Properties();
+		Properties properties = CollectionFactory.createSortedProperties(true);
 		properties.setProperty("name", getProject().getName());
 		properties.setProperty("description", getProject().getDescription());
 		properties.setProperty("dependencies", String.join(",", this.dependencies.getResolvedConfiguration()

buildSrc/src/main/java/org/springframework/boot/build/test/autoconfigure/TestSliceMetadata.java

@@ -42,6 +42,7 @@ import org.gradle.api.tasks.OutputFile;
 import org.gradle.api.tasks.SourceSet;
 import org.gradle.api.tasks.TaskAction;
 
+import org.springframework.core.CollectionFactory;
 import org.springframework.core.io.FileSystemResource;
 import org.springframework.core.type.AnnotationMetadata;
 import org.springframework.core.type.classreading.MetadataReader;
@@ -91,7 +92,7 @@ public class TestSliceMetadata extends AbstractTask {
 	}
 
 	private Properties readTestSlices() throws IOException {
-		Properties testSlices = new Properties();
+		Properties testSlices = CollectionFactory.createSortedProperties(true);
 		try (URLClassLoader classLoader = new URLClassLoader(
 				StreamSupport.stream(this.sourceSet.getRuntimeClasspath().spliterator(), false).map(this::toURL)
 						.toArray(URL[]::new))) {