jackson - Return literal JSON strings in spring mvc @ResponseBody

Question

I am storing objects in my database as JSON strings. I want to make a REST service that exposes these strings. When I write my methods however, the strings I get back have their quotes escaped. For example, I have included a method that returns a String,

@RequestMapping(value = "test", method = RequestMethod.GET)
public @ResponseBody
String getTest() {
    return "{"a":1, "b":"foo"}";
}

but when I call this method in the browser I get a back "{"a":1, "b":"foo"}" when what I really want to happen is {"a": 1, "b": "foo"}. I think "String" as the return type is likely the problem, but what else can I do? A wrapper class does the same thing:

{
  "value" : "{"a":1, "b":"foo"}"
}

I could serialize it and then return the object, but that seems a bit ridiculous. Here is a possibly the relevant portion of my configuration file:

@Override
public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    super.configureMessageConverters(converters);
    converters.add(mappingJacksonHttpMessageConverter());
}

@Bean
MappingJacksonHttpMessageConverter mappingJacksonHttpMessageConverter() {
    MappingJacksonHttpMessageConverter mappingJacksonHttpMessageConverter = new MappingJacksonHttpMessageConverter();
    ObjectMapper objectMapper = new ObjectMapper();
    objectMapper.setSerializationInclusion(JsonSerialize.Inclusion.NON_NULL);
    mappingJacksonHttpMessageConverter.setObjectMapper(objectMapper);
    mappingJacksonHttpMessageConverter.setPrettyPrint(true);
    return mappingJacksonHttpMessageConverter;
}

Thanks

EDIT: as was suggested below, it seems the string is being double encoded. Commenting out the 2 classes in my configuration fixes this issue. However, I still have other places where I want to return Objects and would like to keep those running through that common serializing bean that I know where to configure. So I see my options as: a) Do all the serializing myself. All methods return Strings, and those that are already JSON return themselves, and those that are objects all return JSONUtil.toJson(object). I don't love this approach, but I know it will work. b) Use a wrapper class that looks kind of like:

public static class Wrapper {

    @JsonRawValue
    private final String value;
}

This leads to an awkward "value" at the front though that has no real meaning.

Basically what I want is @JsonRawValue, but to have it work on RequestMapping methods instead of properties. Thoughts? Opinions? Other suggestions?

Answer 1

This works with Jackson 2 (at least):

@Controller
public class YourController {

    @RequestMapping(..)
    public @ResponseBody Json get() {
        return new Json("{ "attr" : "value" }");
    }
}

class Json {

    private final String value;

    public Json(String value) {
        this.value = value;
    }

    @JsonValue
    @JsonRawValue
    public String value() {
        return value;
    }
}

Not particularly pretty but works. I only wish Spring supported this:

@RequestMapping(..)
public @JsonRawValue @ResponseBody String get() {
    // ...
}