MarshallingHttpMessageConverter

Introduction

In Spring, marshalling and unmarshalling refer to the process of converting Java objects to a format that can be easily transmitted over the network (e.g., XML or JSON) and vice versa. Spring provides a mechanism for achieving this through the use of `HttpMessageConverter` implementations. These converters allow you to serialize and deserialize Java objects when handling HTTP requests and responses.

Here, I'll provide examples of how to use Spring's `MarshallingHttpMessageConverter` with both XML and JSON formats.

1. Configure Spring MVC for MarshallingHttpMessageConverter

First, you need to configure Spring MVC to use the `MarshallingHttpMessageConverter`. This typically involves adding it to the list of message converters in your Spring configuration.

For XML (using JAXB):

<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
<property name="messageConverters">
<list>
<bean class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter">
<property name="marshaller" ref="jaxb2Marshaller" />
<property name="unmarshaller" ref="jaxb2Marshaller" />
</bean>
</list>
</property>
</bean>

<bean id="jaxb2Marshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
<property name="packagesToScan">
<list>
<value>com.example.model</value> 
</list>
</property>
</bean>

For JSON (using Jackson):

<bean class="org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter">
<property name="messageConverters">
<list>
<bean class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter" />
</list>
</property>
</bean>

2. Create JAXB-annotated Model Class

For XML marshalling, you need to create a model class and annotate it with JAXB annotations:

@XmlRootElement
public class Person {
private String name;
private int age;

// Getters and setters
}

3. Controller for XML Marshalling

import org.springframework.web.bind.annotation.*;
import org.springframework.http.MediaType;

@RestController
@RequestMapping("/api")
public class PersonController {

@GetMapping(value = "/person", produces = MediaType.APPLICATION_XML_VALUE)
public Person getPerson() {
Person person = new Person();
person.setName("John");
person.setAge(30);
return person;
}
}

4. Controller for JSON Marshalling

import org.springframework.web.bind.annotation.*;
import org.springframework.http.MediaType;

@RestController
@RequestMapping("/api")
public class PersonController {

@GetMapping(value = "/person", produces = MediaType.APPLICATION_JSON_VALUE)
public Person getPerson() {
Person person = new Person();
person.setName("John");
person.setAge(30);
return person;
}
}

With these configurations and controllers in place, Spring will automatically use the `MarshallingHttpMessageConverter` (either for XML or JSON) to marshal the `Person` object when it returns from the controller method.

When you access the `/api/person` endpoint, you'll get the serialized XML or JSON response based on the content type specified in the `produces` attribute of the `@GetMapping` annotation.

Remember to include the necessary dependencies for JAXB or Jackson in your project's build configuration.

MarshallingHttpMessageConverter - Spring