Add ifPresent utility methods on RuntimeHints

This commit adds a utility method to register a type for reflection if
it is available on the classpath. It also adds a method to register a
resource pattern if a given location is available.

Closes gh-28617

Author: snicoll

spring-core/src/main/java/org/springframework/aot/hint/ReflectionHints.java

@@ -30,6 +30,7 @@
 
 import org.springframework.aot.hint.TypeHint.Builder;
 import org.springframework.lang.Nullable;
+import org.springframework.util.ClassUtils;
 
 /**
  * Gather the need for reflection at runtime.
@@ -95,6 +96,22 @@ public ReflectionHints registerType(Class<?> type, Consumer<TypeHint.Builder> ty
 		return registerType(TypeReference.of(type), typeHint);
 	}
 
+	/**
+	 * Register or customize reflection hints for the specified type if it
+	 * is available using the specified {@link ClassLoader}.
+	 * @param classLoader the classloader to use to check if the type is present
+	 * @param typeName the type to customize
+	 * @param typeHint a builder to further customize hints for that type
+	 * @return {@code this}, to facilitate method chaining
+	 */
+	public ReflectionHints registerTypeIfPresent(@Nullable ClassLoader classLoader,
+			String typeName, Consumer<TypeHint.Builder> typeHint) {
+		if (ClassUtils.isPresent(typeName, classLoader)) {
+			registerType(TypeReference.of(typeName), typeHint);
+		}
+		return this;
+	}
+
 	/**
 	 * Register or customize reflection hints for the types defined by the
 	 * specified list of {@link TypeReference type references}. The specified

spring-core/src/main/java/org/springframework/aot/hint/ResourceHints.java

@@ -65,6 +65,24 @@ public Stream<ResourceBundleHint> resourceBundles() {
 		return this.resourceBundleHints.stream();
 	}
 
+	/**
+	 * Register a pattern if the given {@code location} is available on the
+	 * classpath. This delegates to {@link ClassLoader#getResource(String)}
+	 * which validates directories as well. The location is not included in
+	 * the hint.
+	 * @param classLoader the classloader to use
+	 * @param location a '/'-separated path name that should exist
+	 * @param resourceHint a builder to customize the resource pattern
+	 * @return {@code this}, to facilitate method chaining
+	 */
+	public ResourceHints registerPatternIfPresent(@Nullable ClassLoader classLoader, String location, Consumer<ResourcePatternHints.Builder> resourceHint) {
+		ClassLoader classLoaderToUse = (classLoader != null) ? classLoader : getClass().getClassLoader();
+		if (classLoaderToUse.getResource(location) != null) {
+			registerPattern(resourceHint);
+		}
+		return this;
+	}
+
 	/**
 	 * Register that the resources matching the specified pattern should be
 	 * made available at runtime.

spring-core/src/test/java/org/springframework/aot/hint/ReflectionHintsTests.java

@@ -27,6 +27,8 @@
 import org.springframework.util.ReflectionUtils;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verifyNoInteractions;
 
 /**
  * Tests for {@link ReflectionHints}.
@@ -45,6 +47,23 @@ void registerType() {
 				typeWithMemberCategories(String.class, MemberCategory.DECLARED_FIELDS));
 	}
 
+	@Test
+	void registerTypeIfPresentRegisterExistingClass() {
+		this.reflectionHints.registerTypeIfPresent(null, String.class.getName(),
+				hint -> hint.withMembers(MemberCategory.DECLARED_FIELDS));
+		assertThat(this.reflectionHints.typeHints()).singleElement().satisfies(
+				typeWithMemberCategories(String.class, MemberCategory.DECLARED_FIELDS));
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	void registerTypeIfPresentIgnoreMissingClass() {
+		Consumer<TypeHint.Builder> hintBuilder = mock(Consumer.class);
+		this.reflectionHints.registerTypeIfPresent(null, "com.example.DoesNotExist", hintBuilder);
+		assertThat(this.reflectionHints.typeHints()).isEmpty();
+		verifyNoInteractions(hintBuilder);
+	}
+
 	@Test
 	void getTypeUsingType() {
 		this.reflectionHints.registerType(TypeReference.of(String.class),

spring-core/src/test/java/org/springframework/aot/hint/ResourceHintsTests.java

@@ -26,6 +26,8 @@
 import org.springframework.aot.hint.ResourceHintsTests.Nested.Inner;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.mockito.Mockito.mock;
+import static org.mockito.Mockito.verifyNoInteractions;
 
 /**
  * Tests for {@link ResourceHints}.
@@ -91,6 +93,23 @@ void registerPatternWithIncludesAndExcludes() {
 				List.of("com/example/to-ignore.properties")));
 	}
 
+	@Test
+	void registerIfPresentRegisterExistingLocation() {
+		this.resourceHints.registerPatternIfPresent(null, "META-INF/",
+				resourceHint -> resourceHint.includes("com/example/*.properties"));
+		assertThat(this.resourceHints.resourcePatterns()).singleElement().satisfies(
+				patternOf("com/example/*.properties"));
+	}
+
+	@Test
+	@SuppressWarnings("unchecked")
+	void registerIfPresentIgnoreMissingLocation() {
+		Consumer<ResourcePatternHints.Builder> hintBuilder = mock(Consumer.class);
+		this.resourceHints.registerPatternIfPresent(null, "location/does-not-exist/", hintBuilder);
+		assertThat(this.resourceHints.resourcePatterns()).isEmpty();
+		verifyNoInteractions(hintBuilder);
+	}
+
 	@Test
 	void registerResourceBundle() {
 		this.resourceHints.registerResourceBundle("com.example.message");