Improve Jackson configuration for the actuator endpoints to include package private constructors.

module/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/endpoint/jackson/JacksonEndpointAutoConfiguration.java

@@ -16,6 +16,7 @@
 
 package org.springframework.boot.actuate.autoconfigure.endpoint.jackson;
 
+import com.fasterxml.jackson.annotation.JsonAutoDetect.Visibility;
 import com.fasterxml.jackson.annotation.JsonInclude.Include;
 import tools.jackson.databind.json.JsonMapper;
 
@@ -42,6 +43,7 @@ EndpointJsonMapper endpointJsonMapper() {
 		JsonMapper jsonMapper = JsonMapper.builder()
 			.changeDefaultPropertyInclusion(
 					(value) -> value.withValueInclusion(Include.NON_NULL).withContentInclusion(Include.NON_NULL))
+			.changeDefaultVisibility((vc) -> vc.withCreatorVisibility(Visibility.NON_PRIVATE))
 			.build();
 		return () -> jsonMapper;
 	}

module/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/endpoint/jackson/JacksonEndpointAutoConfigurationTests.java

@@ -25,7 +25,10 @@
 import org.junit.jupiter.api.Test;
 import tools.jackson.databind.json.JsonMapper;
 
+import org.springframework.boot.actuate.autoconfigure.endpoint.jackson.example.SomeResponseBody;
+import org.springframework.boot.actuate.endpoint.OperationResponseBody;
 import org.springframework.boot.actuate.endpoint.jackson.EndpointJsonMapper;
+import org.springframework.boot.actuate.web.mappings.MappingsEndpoint.ApplicationMappingsDescriptor;
 import org.springframework.boot.autoconfigure.AutoConfigurations;
 import org.springframework.boot.test.context.runner.ApplicationContextRunner;
 import org.springframework.context.annotation.Bean;
@@ -91,6 +94,23 @@ void endpointJsonMapperDoesNotSerializeNullValues() {
 		});
 	}
 
+	@Test
+	void endpointShouldDeserializeOperationResponseBodies() {
+		this.runner.run((context) -> {
+			JsonMapper jsonMapper = context.getBean(EndpointJsonMapper.class).get();
+			String json = """
+					{
+					"value1": "a",
+					"value2": "b",
+					}
+					""";
+			SomeResponseBody responseBody = jsonMapper.readValue(json, SomeResponseBody.class);
+			assertThat(responseBody.getValue1()).isEqualTo("a");
+			assertThat(responseBody.getValue2()).isEqualTo("b");
+		});
+
+	}
+
 	@Configuration(proxyBeanMethods = false)
 	static class TestEndpointMapperConfiguration {
 

module/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/endpoint/jackson/example/SomeResponseBody.java

@@ -0,0 +1,49 @@
+/*
+ * Copyright 2012-present 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.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.springframework.boot.actuate.autoconfigure.endpoint.jackson.example;
+
+import org.springframework.boot.actuate.endpoint.OperationResponseBody;
+
+/**
+ * A class that reassembles something like
+ * {@code org.springframework.boot.micrometer.metrics.actuate.endpoint.MetricsEndpoint.MetricDescriptor},
+ * not exposing a public constructor, only package level. They could be deserialized with
+ * Jackson 2 out of the box, but not with Jackson 3 anymore. Constructors with one
+ * argument still deserialize as is, so this need to have two or more.
+ *
+ * @author Michael J. Simons
+ */
+public final class SomeResponseBody implements OperationResponseBody {
+
+	private final String value1;
+
+	private final String value2;
+
+	SomeResponseBody(String value1, String value2) {
+		this.value1 = value1;
+		this.value2 = value2;
+	}
+
+	public String getValue1() {
+		return this.value1;
+	}
+
+	public String getValue2() {
+		return this.value2;
+	}
+
+}