How do I use JAXB annotations with Spring RestTemplate?

Question

I'm trying to automatically deserialize XML formatted response using Spring's RestTemplate. I'm using Jackson's jackson-dataformat-xml module, for which Spring Boot is set to auto-configure. I want to use JAXB annotations in the class I want to deserialize to, but it won't seem to work. Here's a sample of what I want the class to look like:

@XmlRootElement(name="Book")
public class Book {

    @XmlElement(name="Title")
    private String title;
    @XmlElement(name="Author")
    private String author;

}

This is based on the following XML sample:

<Book>
    <Title>My Book</Title>
    <Author>Me</Author>
</Book>

However, with class annotated like that above, the fields are always set null. I did some experiments and found out that the deserialization works if I use Jackson's @JsonProperty to annotate the child elements:

@XmlRootElement(name="Book")
public class Book {

    @JsonProperty("Title")
    private String title;
    @JsonProperty("Author")
    private String author;

}

It works, but somehow I feel like it's kind of awkward. Is there a way to get the JAXB annotations work like in my first example?

Jackson provides jackson-module-jaxb-annotations module for the XML databinding to work with JAXB annotations. However, I'm not sure how to setup the ObjectMapper being used by RestTemplate to use this module.

Answer 1

To address this issue, I needed to register an instance of JaxbAnnotationModule to every ObjectMapper used by converters added to Spring's RestTemplate. The class is included in Jackson's jackson-module-jaxb-annotations module, which I added to my build through Gradle.

With the dependency added to my project, what I did next was to configure the RestTemplate used by my application. The ObjectMapper instances are being used by MappingJackson2XmlHttpMessageConverters configured automatically by Spring. I had to register JaxbAnnotationModule instance to each ObjectMapper used in every converter, so the first task was to find all MappingJackson2XmlHttpMessageConverters using:

//create module
JaxbAnnotationModule jaxbAnnotationModule = new JaxbAnnotationModule();

restTemplate.getMessageConverters().stream().filter(converter -> {
    return converter instanceof MappingJackson2XmlHttpMessageConverter;
})

Once I had all the relevant converters, I then registered the module to each of their ObjectMappers:

forEach(converter -> {
    ((MappingJackson2XmlHttpMessageConverter) converter)
            .getObjectMapper()
            .register(jaxbAnnotationModule);
});