Polish "Fix ordering of metadata entries"

See gh-26230

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

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -160,21 +160,22 @@ class JsonConverter {
 
 	private static class ItemMetadataComparator implements Comparator<ItemMetadata> {
 
-		private final Comparator<ItemMetadata> itemComparator = Comparator.comparing(this::isDeprecated)
-				.thenComparing(ItemMetadata::getName).thenComparing(ItemMetadata::getSourceType);
+		private static final Comparator<ItemMetadata> GROUP = Comparator.comparing(ItemMetadata::getName)
+				.thenComparing(ItemMetadata::getSourceType, Comparator.nullsFirst(Comparator.naturalOrder()));
 
-		private final Comparator<ItemMetadata> groupComparator = Comparator.comparing(ItemMetadata::getName)
-				.thenComparing(ItemMetadata::getSourceType);
+		private static final Comparator<ItemMetadata> ITEM = Comparator.comparing(ItemMetadataComparator::isDeprecated)
+				.thenComparing(ItemMetadata::getName)
+				.thenComparing(ItemMetadata::getSourceType, Comparator.nullsFirst(Comparator.naturalOrder()));
 
 		@Override
 		public int compare(ItemMetadata o1, ItemMetadata o2) {
 			if (o1.isOfItemType(ItemType.GROUP)) {
-				return this.groupComparator.compare(o1, o2);
+				return GROUP.compare(o1, o2);
 			}
-			return this.itemComparator.compare(o1, o2);
+			return ITEM.compare(o1, o2);
 		}
 
-		private boolean isDeprecated(ItemMetadata item) {
+		private static boolean isDeprecated(ItemMetadata item) {
 			return item.getDeprecation() != null;
 		}
 

spring-boot-project/spring-boot-tools/spring-boot-configuration-processor/src/test/java/org/springframework/boot/configurationprocessor/metadata/JsonMarshallerTests.java

 /*
- * Copyright 2012-2019 the original author or authors.
+ * Copyright 2012-2021 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.
@@ -139,4 +139,32 @@ class JsonMarshallerTests {
 				"com.example.Bar", "\"com.example.bravo.aaa\"", "com.example.Foo");
 	}
 
+	@Test
+	void orderingForSameGroupWithNullSourceType() throws IOException {
+		ConfigurationMetadata metadata = new ConfigurationMetadata();
+		metadata.add(ItemMetadata.newGroup("com.acme.alpha", null, "com.example.Foo", null));
+		metadata.add(ItemMetadata.newGroup("com.acme.alpha", null, null, null));
+		ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+		JsonMarshaller marshaller = new JsonMarshaller();
+		marshaller.write(metadata, outputStream);
+		String json = outputStream.toString();
+		assertThat(json).containsSubsequence("\"groups\"", "\"name\": \"com.acme.alpha\"",
+				"\"name\": \"com.acme.alpha\"", "\"sourceType\": \"com.example.Foo\"");
+	}
+
+	@Test
+	void orderingForSamePropertyNamesWithNullSourceType() throws IOException {
+		ConfigurationMetadata metadata = new ConfigurationMetadata();
+		metadata.add(ItemMetadata.newProperty("com.example.bravo", "aaa", "java.lang.Boolean", null, null, null, null,
+				null));
+		metadata.add(ItemMetadata.newProperty("com.example.bravo", "aaa", "java.lang.Integer", "com.example.Bar", null,
+				null, null, null));
+		ByteArrayOutputStream outputStream = new ByteArrayOutputStream();
+		JsonMarshaller marshaller = new JsonMarshaller();
+		marshaller.write(metadata, outputStream);
+		String json = outputStream.toString();
+		assertThat(json).containsSubsequence("\"groups\"", "\"properties\"", "\"com.example.bravo.aaa\"",
+				"\"java.lang.Boolean\"", "\"com.example.bravo.aaa\"", "\"java.lang.Integer\"", "\"com.example.Bar");
+	}
+
 }