jackson-dataformat-xml turns #ResponseBody to XML - json

Question

So I had a perfectly working Spring app. Most of my controller methods are for ajax calls that return JSON via #ResponseBody with the jackson api and returns my Java POJO to JSON.
I have a need to turn XML to JSON, so I find that Jackson has a tool for that, and I add this to my POM to use the library:
<dependency>
<groupId>com.fasterxml.jackson.dataformat</groupId>
<artifactId>jackson-dataformat-xml</artifactId>
<version>2.9.0</version>
</dependency>
So that I may use this:
XmlMapper xmlMapper = new XmlMapper();
JsonNode node = xmlMapper.readTree(sb.toString().getBytes());
But now the #ResponseBody is returning XML and not JSON. I Remove the dependency and the controllers return JSON again.
Any way to get both? I want the xmlMapper, and JSON from the response body.

Answer 1

jackson-dataformat-xml appears to be registering a MappingJackson2HttpMessageConverter with a XmlMapper, along with other HttpMessageConverters that work with XML. If you always intended to return JSON from your controllers, you can change what HttpMessageConverter your app uses by overriding configureMessageConverters
For Spring 5.0 and above,
#Configuration
public class HttpResponseConfig implements WebMvcConfigurer {
#Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
converters.removeIf(converter -> supportsXml(converter) || hasXmlMapper(converter));
}
private boolean supportsXml(HttpMessageConverter<?> converter) {
return converter.getSupportedMediaTypes().stream()
.map(MimeType::getSubtype)
.anyMatch(subType -> subType.equalsIgnoreCase("xml"));
}
private boolean hasXmlMapper(HttpMessageConverter<?> converter) {
return converter instanceof MappingJackson2HttpMessageConverter
&& ((MappingJackson2HttpMessageConverter)converter).getObjectMapper().getClass().equals(XmlMapper.class);
}
}
For older versions of Spring, replace implements WebMvcConfigurer with extends WebMvcConfigurerAdapter

Answer 2

Add Accept: application/json to HTTP request header.

Answer 3

Read this for an analysis of how Spring does content negotiation and allows producing either XML or JSON.
The simplest way is to add an extension at the URL: Instead of /path/resource use /path/resource.json
You may also add a format parameter e.g. /path/resource?format=json or pass an appropriate Accept header

Answer 4

In my case, the XmlMapper was actually inserted into the application context as an #Bean. The other solutions here did not work for me. It seems like one of those issues where context matters, so for people coming here from a different context than the other answerers, here's another angle: I had to insert my own ObjectMapper.
#Configuration
public class XmlMapperConfiguration {
#Bean // me, culprit
public XmlMapper xmlMapper() {
return new XmlMapper();
}
#Bean // to make sure the rest of the application still works with JSON
public ObjectMapper objectMapper() {
return new ObjectMapper();
}
}
I'm going to throw in an #Primary on the ObjectMapper one. It seems suspicious that Spring would even choose that one consistently. Since XmlMapper extends ObjectMapper, why would it not take that one, so #Primary won't hurt.