How to autowire default XmlMapper in Spring Boot application

Question

I'm having some issues autowiring the default Jackson XmlMapper in one of my Spring Boot projects. I've created a simple example project that illustrates this.

What I'm doing here is roughly based on this:

http://docs.spring.io/spring-boot/docs/1.2.2.RELEASE/reference/htmlsingle/#howto-write-an-xml-rest-service

http://docs.spring.io/spring-boot/docs/1.2.2.RELEASE/reference/htmlsingle/#howto-customize-the-jackson-objectmapper

From pom.xml

<!-- ... -->

<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>1.2.2.RELEASE</version>
</parent>

<!-- ... -->

<dependencies>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter</artifactId>
    </dependency>
    <dependency>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-web</artifactId>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.dataformat</groupId>
        <artifactId>jackson-dataformat-xml</artifactId>
    </dependency>
</dependencies>

<!-- ... -->

The main class:

@SpringBootApplication
public class DemoApplication {

    public static void main(String[] args) {
        SpringApplication.run(DemoApplication.class, args);
    }
}

The Demo POJO, not specifying @XmlRootElement, so it won't use JAXB:

@JsonInclude(Include.NON_NULL)
public class Demo {
    private String stringProperty;
    private int intProperty;
    public String getStringProperty() {
        return stringProperty;
    }
    public void setStringProperty(String stringProperty) {
        this.stringProperty = stringProperty;
    }
    public int getIntProperty() {
        return intProperty;
    }
    public void setIntProperty(int intProperty) {
        this.intProperty = intProperty;
    }
}

The Demo Controller:

@RestController
public class DemoController {
    @Autowired 
    private ObjectMapper objectMapper;
    // @Autowired 
    // private XmlMapper xmlMapper;

    @RequestMapping(value = "/demo", method = RequestMethod.GET)
    public Demo getDemo() {
        Demo demo = new Demo();
        demo.setStringProperty("Hello world!");
        demo.setIntProperty(42);
        return demo;
    }
}

Everything works fine the way it is, depending on Accept headers, either JSON or XML will be returned.

I can easily autowire the default ObjectMapper configured by Spring Boot. So far so good.

If I comment in the autowiring of the XmlMapper I get:

Caused by: org.springframework.beans.factory.NoSuchBeanDefinitionException: No qualifying bean of type [com.fasterxml.jackson.dataformat.xml.XmlMapper] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.support.DefaultListableBeanFactory.raiseNoSuchBeanDefinitionException(DefaultListableBeanFactory.java:1301)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1047)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:942)
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:533)
... 18 more

Any idea why this is? I would have assumed it to work the same way as the ObjectMapper. Just to clarify, I don't want to customise the mappers, I simply want a reference to the default ones created by Spring Boot.

Answer 1

Based on the answer by @Andy Wilkinson I did some more digging and found a way to get at what I wanted. Spring Boot does not expose the XmlMapper as a Bean but it does expose the message converter it is used in, which is MappingJackson2XmlHttpMessageConverter. So I could auto-wire that bean and get the ObjectMapper (which is now an XmlMapper) from it.

The Demo Controller from my question now looks like this:

    @RestController
    public class DemoController {
        @Autowired 
        private ObjectMapper objectMapper;
        @Autowired
        private MappingJackson2XmlHttpMessageConverter xmlConverter;

        @RequestMapping(value = "/demo", method = RequestMethod.GET)
        public Demo getDemo() {
            Demo demo = new Demo();
            demo.setStringProperty("Hello world!");
            demo.setIntProperty(42);
            ObjectMapper xmlMapper = xmlConverter.getObjectMapper();
            return demo;
        }
    }

Answer 2

Spring Boot does not expose the XmlMapper as a bean as it would conflict with the ObjectMapper bean that's used for JSON mapping (Jackson's XmlMapper is a subclass of Jackson's ObjectMapper).

Answer 3

There are two ways of doing so:

@Bean
public XmlMapper xmlMapper(MappingJackson2XmlHttpMessageConverter converter) {
    return (XmlMapper) converter.getObjectMapper();
}

And

@Bean
@Primary
public ObjectMapper objectMapper(MappingJackson2XmlHttpMessageConverter converter) {
    return converter.getObjectMapper();
}

If you want support for JSON and XML then you should register those beans by yourself with BeanFactoryPostProcessor method described in How to create multiple beans of same type according to configuration in Spring?