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");
 		});
 	}