Add reflection hints for PropertyNamingStrategies

See gh-33080

spring-boot-project/spring-boot-autoconfigure/src/main/java/org/springframework/boot/autoconfigure/jackson/JacksonRuntimeHints.java

@@ -0,0 +1,54 @@
+package org.springframework.boot.autoconfigure.jackson;
+
+import com.fasterxml.jackson.databind.PropertyNamingStrategies;
+import com.fasterxml.jackson.databind.PropertyNamingStrategy;
+import org.springframework.aot.hint.ReflectionHints;
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.RuntimeHintsRegistrar;
+import org.springframework.util.ClassUtils;
+
+import java.lang.reflect.Field;
+import java.lang.reflect.Modifier;
+import java.util.stream.Stream;
+
+/**
+ * {@link RuntimeHintsRegistrar} for Jackson.
+ * This is necessary for the configuration of Jackson's propertyNamingStrategy
+ * to work in native build and execution.
+ *
+ * @author Ralf Ueberfuhr
+ */
+class JacksonRuntimeHints implements RuntimeHintsRegistrar {
+
+	/*
+	 * We need this for
+	 *
+	 *     JacksonAutoConfiguration
+	 *       .Jackson2ObjectMapperBuilderCustomizerConfiguration
+	 *       .StandardJackson2ObjectMapperBuilderCustomizer
+	 *       .configurePropertyNamingStrategyField(...)
+	 *
+	 * to get the field using reflection!
+	 */
+
+	@Override
+	public void registerHints(RuntimeHints hints, ClassLoader classLoader) {
+		if(ClassUtils.isPresent("com.fasterxml.jackson.databind.PropertyNamingStrategy", classLoader)) {
+			registerHints(hints.reflection());
+		}
+	}
+
+	private void registerHints(ReflectionHints reflection) {
+		Field[] fieldsOfStrategies = PropertyNamingStrategies.class.getDeclaredFields();
+		// Jackson 2.12 pre
+		Field[] fieldsOfStrategy = PropertyNamingStrategy.class.getDeclaredFields();
+		// Find all static fields that provide a PropertyNamingStrategy
+		// (this way we automatically support new constants
+		// that may be added by Jackson in the future)
+		Stream.concat(Stream.of(fieldsOfStrategies), Stream.of(fieldsOfStrategy))
+				.filter(f -> Modifier.isStatic(f.getModifiers()))
+				.filter(f -> f.getType().isAssignableFrom(PropertyNamingStrategy.class))
+				.forEach(reflection::registerField);
+	}
+
+}

spring-boot-project/spring-boot-autoconfigure/src/main/resources/META-INF/spring/aot.factories

@@ -1,5 +1,6 @@
 org.springframework.aot.hint.RuntimeHintsRegistrar=\
-org.springframework.boot.autoconfigure.template.TemplateRuntimeHints
+org.springframework.boot.autoconfigure.template.TemplateRuntimeHints,\
+org.springframework.boot.autoconfigure.jackson.JacksonRuntimeHints
 
 org.springframework.beans.factory.aot.BeanFactoryInitializationAotProcessor=\
 org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingProcessor

spring-boot-project/spring-boot-autoconfigure/src/test/java/org/springframework/boot/autoconfigure/jackson/JacksonRuntimeHintsTests.java

@@ -0,0 +1,41 @@
+package org.springframework.boot.autoconfigure.jackson;
+
+import com.fasterxml.jackson.databind.PropertyNamingStrategies;
+import com.fasterxml.jackson.databind.PropertyNamingStrategy;
+import org.junit.jupiter.api.Test;
+import org.springframework.aot.hint.RuntimeHints;
+import org.springframework.aot.hint.predicate.ReflectionHintsPredicates;
+import org.springframework.aot.hint.predicate.RuntimeHintsPredicates;
+
+import java.util.stream.Stream;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+class JacksonRuntimeHintsTests {
+
+	@Test
+	void shouldRegisterHints() {
+		shouldRegisterFieldHintsFor(PropertyNamingStrategies.class,
+				"LOWER_CAMEL_CASE", "UPPER_CAMEL_CASE",
+				"SNAKE_CASE", "UPPER_SNAKE_CASE",
+				"LOWER_CASE", "KEBAB_CASE", "LOWER_DOT_CASE");
+	}
+
+	@Test
+	void shouldRegisterJackson_2_12_pre_Hints() {
+		shouldRegisterFieldHintsFor(PropertyNamingStrategy.class,
+				"LOWER_CAMEL_CASE", "UPPER_CAMEL_CASE",
+				"SNAKE_CASE",
+				"LOWER_CASE", "KEBAB_CASE", "LOWER_DOT_CASE");
+	}
+
+	private void shouldRegisterFieldHintsFor(Class<?> clazz, String... fieldNames) {
+		RuntimeHints hints = new RuntimeHints();
+		new JacksonRuntimeHints().registerHints(hints, getClass().getClassLoader());
+		ReflectionHintsPredicates reflection = RuntimeHintsPredicates.reflection();
+		Stream.of(fieldNames)
+				.map(name -> reflection.onField(clazz, name))
+				.forEach(predicate -> assertThat(predicate).accepts(hints));
+	}
+
+}