Cache property mappings in ConfigurationPropertyName

Relocate `SystemEnvironmentPropertyMapper` methods into
`ConfigurationPropertyName` so that they can be cached to
improve performance

Closes gh-44858

Author: philwebb

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

@@ -20,8 +20,10 @@
 import java.util.Collection;
 import java.util.Collections;
 import java.util.List;
+import java.util.Locale;
 import java.util.Map;
 import java.util.function.Function;
+import java.util.function.IntFunction;
 
 import org.springframework.util.Assert;
 import org.springframework.util.StringUtils;
@@ -63,10 +65,14 @@ public final class ConfigurationPropertyName implements Comparable<Configuration
 
 	private final CharSequence[] uniformElements;
 
-	private String string;
-
 	private int hashCode;
 
+	private String[] string = new String[ToStringFormat.values().length];
+
+	private Boolean hasDashedElement;
+
+	private ConfigurationPropertyName systemEnvironmentLegacyName;
+
 	private ConfigurationPropertyName(Elements elements) {
 		this.elements = elements;
 		this.uniformElements = new CharSequence[elements.getSize()];
@@ -525,15 +531,41 @@ public int hashCode() {
 		return hashCode;
 	}
 
+	ConfigurationPropertyName asSystemEnvironmentLegacyName() {
+		ConfigurationPropertyName name = this.systemEnvironmentLegacyName;
+		if (name == null) {
+			name = ConfigurationPropertyName
+				.ofIfValid(buildSimpleToString('.', (i) -> getElement(i, Form.DASHED).replace('-', '.')));
+			this.systemEnvironmentLegacyName = (name != null) ? name : EMPTY;
+		}
+		return (name != EMPTY) ? name : null;
+	}
+
 	@Override
 	public String toString() {
-		if (this.string == null) {
-			this.string = buildToString();
+		return toString(ToStringFormat.DEFAULT);
+	}
+
+	String toString(ToStringFormat format) {
+		String string = this.string[format.ordinal()];
+		if (string == null) {
+			string = buildToString(format);
+			this.string[format.ordinal()] = string;
 		}
-		return this.string;
+		return string;
+	}
+
+	private String buildToString(ToStringFormat format) {
+		return switch (format) {
+			case DEFAULT -> buildDefaultToString();
+			case SYSTEM_ENVIRONMENT ->
+				buildSimpleToString('_', (i) -> getElement(i, Form.UNIFORM).toUpperCase(Locale.ENGLISH));
+			case LEGACY_SYSTEM_ENVIRONMENT -> buildSimpleToString('_',
+					(i) -> getElement(i, Form.ORIGINAL).replace('-', '_').toUpperCase(Locale.ENGLISH));
+		};
 	}
 
-	private String buildToString() {
+	private String buildDefaultToString() {
 		if (this.elements.canShortcutWithSource(ElementType.UNIFORM, ElementType.DASHED)) {
 			return this.elements.getSource().toString();
 		}
@@ -556,6 +588,32 @@ private String buildToString() {
 		return result.toString();
 	}
 
+	private String buildSimpleToString(char joinChar, IntFunction<String> elementConverter) {
+		StringBuilder result = new StringBuilder();
+		for (int i = 0; i < getNumberOfElements(); i++) {
+			if (!result.isEmpty()) {
+				result.append(joinChar);
+			}
+			result.append(elementConverter.apply(i));
+		}
+		return result.toString();
+	}
+
+	boolean hasDashedElement() {
+		Boolean hasDashedElement = this.hasDashedElement;
+		if (hasDashedElement != null) {
+			return hasDashedElement;
+		}
+		for (int i = 0; i < getNumberOfElements(); i++) {
+			if (getElement(i, Form.DASHED).indexOf('-') != -1) {
+				this.hasDashedElement = true;
+				return true;
+			}
+		}
+		this.hasDashedElement = false;
+		return false;
+	}
+
 	/**
 	 * Returns if the given name is valid. If this method returns {@code true} then the
 	 * name may be used with {@link #of(CharSequence)} without throwing an exception.
@@ -1132,4 +1190,13 @@ private interface ElementCharPredicate {
 
 	}
 
+	/**
+	 * Formats for {@code toString}.
+	 */
+	enum ToStringFormat {
+
+		DEFAULT, SYSTEM_ENVIRONMENT, LEGACY_SYSTEM_ENVIRONMENT
+
+	}
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2023 the original author or authors.
+ * Copyright 2012-2025 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.
@@ -22,7 +22,7 @@
 import java.util.Locale;
 import java.util.function.BiPredicate;
 
-import org.springframework.boot.context.properties.source.ConfigurationPropertyName.Form;
+import org.springframework.boot.context.properties.source.ConfigurationPropertyName.ToStringFormat;
 
 /**
  * {@link PropertyMapper} for system environment variables. Names are mapped by removing
@@ -42,44 +42,14 @@ final class SystemEnvironmentPropertyMapper implements PropertyMapper {
 
 	@Override
 	public List<String> map(ConfigurationPropertyName configurationPropertyName) {
-		String name = convertName(configurationPropertyName);
-		String legacyName = convertLegacyName(configurationPropertyName);
+		String name = configurationPropertyName.toString(ToStringFormat.SYSTEM_ENVIRONMENT);
+		String legacyName = configurationPropertyName.toString(ToStringFormat.LEGACY_SYSTEM_ENVIRONMENT);
 		if (name.equals(legacyName)) {
 			return Collections.singletonList(name);
 		}
 		return Arrays.asList(name, legacyName);
 	}
 
-	private String convertName(ConfigurationPropertyName name) {
-		return convertName(name, name.getNumberOfElements());
-	}
-
-	private String convertName(ConfigurationPropertyName name, int numberOfElements) {
-		StringBuilder result = new StringBuilder();
-		for (int i = 0; i < numberOfElements; i++) {
-			if (!result.isEmpty()) {
-				result.append('_');
-			}
-			result.append(name.getElement(i, Form.UNIFORM).toUpperCase(Locale.ENGLISH));
-		}
-		return result.toString();
-	}
-
-	private String convertLegacyName(ConfigurationPropertyName name) {
-		StringBuilder result = new StringBuilder();
-		for (int i = 0; i < name.getNumberOfElements(); i++) {
-			if (!result.isEmpty()) {
-				result.append('_');
-			}
-			result.append(convertLegacyNameElement(name.getElement(i, Form.ORIGINAL)));
-		}
-		return result.toString();
-	}
-
-	private Object convertLegacyNameElement(String element) {
-		return element.replace('-', '_').toUpperCase(Locale.ENGLISH);
-	}
-
 	@Override
 	public ConfigurationPropertyName map(String propertySourceName) {
 		return convertName(propertySourceName);
@@ -113,31 +83,11 @@ private boolean isAncestorOf(ConfigurationPropertyName name, ConfigurationProper
 	}
 
 	private boolean isLegacyAncestorOf(ConfigurationPropertyName name, ConfigurationPropertyName candidate) {
-		if (!hasDashedEntries(name)) {
+		if (!name.hasDashedElement()) {
 			return false;
 		}
-		ConfigurationPropertyName legacyCompatibleName = buildLegacyCompatibleName(name);
+		ConfigurationPropertyName legacyCompatibleName = name.asSystemEnvironmentLegacyName();
 		return legacyCompatibleName != null && legacyCompatibleName.isAncestorOf(candidate);
 	}
 
-	private ConfigurationPropertyName buildLegacyCompatibleName(ConfigurationPropertyName name) {
-		StringBuilder legacyCompatibleName = new StringBuilder();
-		for (int i = 0; i < name.getNumberOfElements(); i++) {
-			if (i != 0) {
-				legacyCompatibleName.append('.');
-			}
-			legacyCompatibleName.append(name.getElement(i, Form.DASHED).replace('-', '.'));
-		}
-		return ConfigurationPropertyName.ofIfValid(legacyCompatibleName);
-	}
-
-	boolean hasDashedEntries(ConfigurationPropertyName name) {
-		for (int i = 0; i < name.getNumberOfElements(); i++) {
-			if (name.getElement(i, Form.DASHED).indexOf('-') != -1) {
-				return true;
-			}
-		}
-		return false;
-	}
-
 }