Allow customer resolver and property sources

Add factory methods to `AbstractEnvironment` that allow a custom
`ConfigurablePropertyResolver` and `MutablePropertySources` instance
to be used.

See gh-26462

spring-core/src/main/java/org/springframework/core/env/AbstractEnvironment.java

@@ -107,10 +107,9 @@ public abstract class AbstractEnvironment implements ConfigurableEnvironment {
 
 	private final Set<String> defaultProfiles = new LinkedHashSet<>(getReservedDefaultProfiles());
 
-	private final MutablePropertySources propertySources = new MutablePropertySources();
+	private final MutablePropertySources propertySources;
 
-	private final ConfigurablePropertyResolver propertyResolver =
-			new PropertySourcesPropertyResolver(this.propertySources);
+	private final ConfigurablePropertyResolver propertyResolver;
 
 
 	/**
@@ -121,9 +120,44 @@ public abstract class AbstractEnvironment implements ConfigurableEnvironment {
 	 * @see #customizePropertySources(MutablePropertySources)
 	 */
 	public AbstractEnvironment() {
-		customizePropertySources(this.propertySources);
+		this(new MutablePropertySources());
 	}
 
+	/**
+	 * Create a new {@code Environment} instance with a specific
+	 * {@link MutablePropertySources} instance, calling back to
+	 * {@link #customizePropertySources(MutablePropertySources)} during
+	 * construction to allow subclasses to contribute or manipulate
+	 * {@link PropertySource} instances as appropriate.
+	 * @see #customizePropertySources(MutablePropertySources)
+	 * @since 5.3.4
+	 */
+	protected AbstractEnvironment(MutablePropertySources propertySources) {
+		this.propertySources = propertySources;
+		this.propertyResolver = createPropertyResolver(propertySources);
+		customizePropertySources(propertySources);
+	}
+
+
+	/**
+	 * Factory method used to create the {@link ConfigurablePropertyResolver}
+	 * instance used by the Environment.
+	 * @see #getPropertyResolver()
+	 * @since 5.3.4
+	 */
+	protected ConfigurablePropertyResolver createPropertyResolver(
+			MutablePropertySources propertySources) {
+		return new PropertySourcesPropertyResolver(propertySources);
+	}
+
+	/**
+	 * Return the {@link ConfigurablePropertyResolver} being used by the
+	 * {@link Environment}.
+	 * @see #createPropertyResolver(MutablePropertySources)
+	 */
+	protected final ConfigurablePropertyResolver getPropertyResolver() {
+		return this.propertyResolver;
+	}
 
 	/**
 	 * Customize the set of {@link PropertySource} objects to be searched by this

spring-core/src/main/java/org/springframework/core/env/StandardEnvironment.java

@@ -60,6 +60,14 @@ public class StandardEnvironment extends AbstractEnvironment {
 	public static final String SYSTEM_PROPERTIES_PROPERTY_SOURCE_NAME = "systemProperties";
 
 
+	public StandardEnvironment() {
+	}
+
+	protected StandardEnvironment(MutablePropertySources propertySources) {
+		super(propertySources);
+	}
+
+
 	/**
 	 * Customize the set of property sources with those appropriate for any standard
 	 * Java environment:

spring-core/src/test/java/org/springframework/core/env/CustomEnvironmentTests.java

@@ -129,6 +129,47 @@ class CustomEnvironmentTests {
 		assertThat(env.getDefaultProfiles()).containsExactly(AbstractEnvironment.RESERVED_DEFAULT_PROFILE_NAME);
 	}
 
+	@Test
+	public void withCustomMutablePropertySources() {
+		class CustomMutablePropertySources extends MutablePropertySources {
+		}
+		MutablePropertySources propertySources = new CustomMutablePropertySources();
+		ConfigurableEnvironment env = new AbstractEnvironment(propertySources) {
+		};
+		assertThat(env.getPropertySources()).isInstanceOf(CustomMutablePropertySources.class);
+	}
+
+	@Test
+	void withCustomPropertyResolver() {
+		class CustomPropertySourcesPropertyResolver extends PropertySourcesPropertyResolver {
+
+			public CustomPropertySourcesPropertyResolver(
+					PropertySources propertySources) {
+				super(propertySources);
+			}
+
+			@Override
+			public String getProperty(String key) {
+				return super.getProperty(key)+"-test";
+			}
+
+		}
+		ConfigurableEnvironment env = new AbstractEnvironment() {
+
+			@Override
+			protected ConfigurablePropertyResolver createPropertyResolver(
+					MutablePropertySources propertySources) {
+				return new CustomPropertySourcesPropertyResolver(propertySources);
+			}
+
+		};
+		Map<String, Object> values = new LinkedHashMap<>();
+		values.put("spring", "framework");
+		PropertySource<?> propertySource = new MapPropertySource("test", values);
+		env.getPropertySources().addFirst(propertySource);
+		assertThat(env.getProperty("spring")).isEqualTo("framework-test");
+	}
+
 	private Profiles defaultProfile() {
 		return Profiles.of(AbstractEnvironment.RESERVED_DEFAULT_PROFILE_NAME);
 	}

spring-web/src/main/java/org/springframework/web/context/support/StandardServletEnvironment.java

@@ -54,6 +54,14 @@ public class StandardServletEnvironment extends StandardEnvironment implements C
 	public static final String JNDI_PROPERTY_SOURCE_NAME = "jndiProperties";
 
 
+	public StandardServletEnvironment() {
+	}
+
+	protected StandardServletEnvironment(MutablePropertySources propertySources) {
+		super(propertySources);
+	}
+
+
 	/**
 	 * Customize the set of property sources with those contributed by superclasses as
 	 * well as those appropriate for standard servlet-based environments: