Merge pull request #21523 from dreis2211

* pr/21523:
  Polish 'Optimize SystemEnvironmentPropertyMapper'
  Optimize SystemEnvironmentPropertyMapper
  Call append only when necessary
  Use chars rather than strings

Closes gh-21523

Author: philwebb

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/ConfigurationPropertyName.java

@@ -510,6 +510,18 @@ public static ConfigurationPropertyName of(CharSequence name) {
 		return of(name, false);
 	}
 
+	/**
+	 * Return a {@link ConfigurationPropertyName} for the specified string or {@code null}
+	 * if the name is not valid.
+	 * @param name the source name
+	 * @return a {@link ConfigurationPropertyName} instance
+	 * @throws InvalidConfigurationPropertyNameException if the name is not valid
+	 * @since 2.3.1
+	 */
+	public static ConfigurationPropertyName ofIfValid(CharSequence name) {
+		return of(name, true);
+	}
+
 	/**
 	 * Return a {@link ConfigurationPropertyName} for the specified string.
 	 * @param name the source name

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/context/properties/source/SystemEnvironmentPropertyMapper.java

@@ -58,7 +58,7 @@ private String convertName(ConfigurationPropertyName name, int numberOfElements)
 		StringBuilder result = new StringBuilder();
 		for (int i = 0; i < numberOfElements; i++) {
 			if (result.length() > 0) {
-				result.append("_");
+				result.append('_');
 			}
 			result.append(name.getElement(i, Form.UNIFORM).toUpperCase(Locale.ENGLISH));
 		}
@@ -69,7 +69,7 @@ private String convertLegacyName(ConfigurationPropertyName name) {
 		StringBuilder result = new StringBuilder();
 		for (int i = 0; i < name.getNumberOfElements(); i++) {
 			if (result.length() > 0) {
-				result.append("_");
+				result.append('_');
 			}
 			result.append(convertLegacyNameElement(name.getElement(i, Form.ORIGINAL)));
 		}
@@ -116,13 +116,19 @@ private boolean isLegacyAncestorOf(ConfigurationPropertyName name, Configuration
 		if (!hasDashedEntries(name)) {
 			return false;
 		}
+		ConfigurationPropertyName legacyCompatibleName = buildLegacyCompatibleName(name);
+		return legacyCompatibleName != null && legacyCompatibleName.isAncestorOf(candidate);
+	}
+
+	private ConfigurationPropertyName buildLegacyCompatibleName(ConfigurationPropertyName name) {
 		StringBuilder legacyCompatibleName = new StringBuilder();
 		for (int i = 0; i < name.getNumberOfElements(); i++) {
-			legacyCompatibleName.append((i != 0) ? "." : "");
+			if (i != 0) {
+				legacyCompatibleName.append('.');
+			}
 			legacyCompatibleName.append(name.getElement(i, Form.DASHED).replace('-', '.'));
 		}
-		return ConfigurationPropertyName.isValid(legacyCompatibleName)
-				&& ConfigurationPropertyName.of(legacyCompatibleName).isAncestorOf(candidate);
+		return ConfigurationPropertyName.ofIfValid(legacyCompatibleName);
 	}
 
 	boolean hasDashedEntries(ConfigurationPropertyName name) {

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/context/properties/source/ConfigurationPropertyNameTests.java

@@ -210,6 +210,18 @@ void ofWhenNameIsEmptyShouldReturnEmptyName() {
 		assertThat(name.append("foo").toString()).isEqualTo("foo");
 	}
 
+	@Test
+	void ofIfValidWhenNameIsValidReturnsName() {
+		ConfigurationPropertyName name = ConfigurationPropertyName.ofIfValid("spring.bo-ot");
+		assertThat(name).hasToString("spring.bo-ot");
+	}
+
+	@Test
+	void ofIfValidWhenNameIsNotValidReturnsNull() {
+		ConfigurationPropertyName name = ConfigurationPropertyName.ofIfValid("spring.bo!oot");
+		assertThat(name).isNull();
+	}
+
 	@Test
 	void adaptWhenNameIsNullShouldThrowException() {
 		assertThatIllegalArgumentException().isThrownBy(() -> ConfigurationPropertyName.adapt(null, '.'))