Support consistent ordering of string adapting properties

This commit introduces support for consistent ordering of Properties
created by CollectionFactory.createStringAdaptingProperties().

Specifically, the created Properties instance sorts properties
alphanumerically based on their keys.

Closes gh-23081

spring-beans/src/test/java/org/springframework/beans/factory/config/YamlProcessorTests.java

@@ -17,6 +17,7 @@
 package org.springframework.beans.factory.config;
 
 import java.util.LinkedHashMap;
+import java.util.List;
 import java.util.Map;
 
 import org.junit.Test;
@@ -25,6 +26,7 @@ import org.yaml.snakeyaml.scanner.ScannerException;
 
 import org.springframework.core.io.ByteArrayResource;
 
+import static java.util.stream.Collectors.toList;
 import static org.assertj.core.api.Assertions.assertThat;
 import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
 
@@ -33,6 +35,7 @@ import static org.assertj.core.api.Assertions.assertThatExceptionOfType;
  *
  * @author Dave Syer
  * @author Juergen Hoeller
+ * @author Sam Brannen
  */
 public class YamlProcessorTests {
 
@@ -107,17 +110,27 @@ public class YamlProcessorTests {
 	@Test
 	@SuppressWarnings("unchecked")
 	public void flattenedMapIsSameAsPropertiesButOrdered() {
-		this.processor.setResources(new ByteArrayResource("foo: bar\nbar:\n spam: bucket".getBytes()));
+		this.processor.setResources(new ByteArrayResource("cat: dog\nfoo: bar\nbar:\n spam: bucket".getBytes()));
 		this.processor.process((properties, map) -> {
-			assertThat(properties.get("bar.spam")).isEqualTo("bucket");
-			assertThat(properties).hasSize(2);
 			Map<String, Object> flattenedMap = processor.getFlattenedMap(map);
+			assertThat(flattenedMap).isInstanceOf(LinkedHashMap.class);
+
+			assertThat(properties).hasSize(3);
+			assertThat(flattenedMap).hasSize(3);
+
+			assertThat(properties.get("bar.spam")).isEqualTo("bucket");
 			assertThat(flattenedMap.get("bar.spam")).isEqualTo("bucket");
-			assertThat(flattenedMap.size()).isEqualTo(2);
-			boolean condition = flattenedMap instanceof LinkedHashMap;
-			assertThat(condition).isTrue();
+
 			Map<String, Object> bar = (Map<String, Object>) map.get("bar");
 			assertThat(bar.get("spam")).isEqualTo("bucket");
+
+			List<Object> keysFromProperties = properties.keySet().stream().collect(toList());
+			List<Object> keysFromFlattenedMap = flattenedMap.keySet().stream().collect(toList());
+			assertThat(keysFromProperties).containsExactlyInAnyOrderElementsOf(keysFromFlattenedMap);
+			// Keys in the Properties object are sorted.
+			assertThat(keysFromProperties).containsExactly("bar.spam", "cat", "foo");
+			// But the flattened map retains the order from the input.
+			assertThat(keysFromFlattenedMap).containsExactly("cat", "foo", "bar.spam");
 		});
 	}
 

spring-core/src/main/java/org/springframework/core/CollectionFactory.java

@@ -329,14 +329,18 @@ public final class CollectionFactory {
 	}
 
 	/**
-	 * Create a variant of {@code java.util.Properties} that automatically adapts
-	 * non-String values to String representations on {@link Properties#getProperty}.
+	 * Create a variant of {@link java.util.Properties} that automatically adapts
+	 * non-String values to String representations in {@link Properties#getProperty}.
+	 * <p>In addition, the returned {@code Properties} instance sorts properties
+	 * alphanumerically based on their keys.
 	 * @return a new {@code Properties} instance
 	 * @since 4.3.4
+	 * @see #createSortedProperties(boolean)
+	 * @see #createSortedProperties(Properties, boolean)
 	 */
 	@SuppressWarnings("serial")
 	public static Properties createStringAdaptingProperties() {
-		return new Properties() {
+		return new SortedProperties(false) {
 			@Override
 			@Nullable
 			public String getProperty(String key) {
@@ -359,6 +363,7 @@ public final class CollectionFactory {
 	 * storing properties in a file
 	 * @return a new {@code Properties} instance
 	 * @since 5.2
+	 * @see #createStringAdaptingProperties()
 	 * @see #createSortedProperties(Properties, boolean)
 	 */
 	public static Properties createSortedProperties(boolean omitComments) {
@@ -384,6 +389,7 @@ public final class CollectionFactory {
 	 * storing properties in a file
 	 * @return a new {@code Properties} instance
 	 * @since 5.2
+	 * @see #createStringAdaptingProperties()
 	 * @see #createSortedProperties(boolean)
 	 */
 	public static Properties createSortedProperties(Properties properties, boolean omitComments) {