Spring MVC 3.2 and JSON ObjectMapper issue

Question

I have recently upgraded my Spring version to 3.2.0 from 3.1.2. I find that that JSON properties like wrap root element, prevent null values that are defined in ObjectMapper

Answer 1

Disclaimer: I could not determine why the code in question is not working, but I could reproduce the problem. This answer does provide an alternate approach that works for me.

It could be a bug, as I can reproduce the problem with both with explicit config:

and via the mvc:message-converter:

where both give me {"foo":null,"bar":"bar"} when using the example class

Demo.java

import org.springframework.stereotype.Controller;
import org.springframework.web.bind.annotation.*;
import org.codehaus.jackson.annotate.JsonProperty;

@Controller
@RequestMapping("/data")
public class Data {
    @RequestMapping
    @ResponseBody
    public Dummy dataIndex() {
        return new Dummy();
    }

    public class Dummy {
        String foo = null;
        @JsonProperty
        public String foo() {
            return foo;
        }
        String bar = "bar";
        @JsonProperty
        public String bar() {
            return bar;
        }
    }
}

However, I would have thought the mvc:message-converter method would work, only because I have seen issues overriding the default bean registration that performs (see Web MVC Framework) and using the nested configuration is preferred(?).

Maybe the Jackson 2 support has caused some backwards compatibility issues with Jackson 1?

However, switching to the MappingJackson2HttpMessageConverter (supported in Spring 3.1.2 and Spring 3.2), I am able to alter the ObjectMapper configuration to not write null values and wrap the JSON output... but only when using the config inside the !

I get {"Dummy":{"bar":"bar"}} with the following changes:

pom.xml

   com.fasterxml.jackson.core
   jackson-core
   2.1.0


    com.fasterxml.jackson.core
    jackson-databind
    2.1.0


    com.fasterxml.jackson.core
    jackson-annotations
    2.1.0

CustomJacksonObjectMapper.java

import com.fasterxml.jackson.databind.ObjectMapper;
import com.fasterxml.jackson.databind.DeserializationFeature;
import com.fasterxml.jackson.databind.SerializationFeature;
import static com.fasterxml.jackson.annotation.JsonInclude.*;

public class CustomJacksonObjectMapper extends ObjectMapper {

public CustomJacksonObjectMapper() {
    super();
    this.configure(DeserializationFeature.UNWRAP_ROOT_VALUE, true);
    this.configure(SerializationFeature.WRAP_ROOT_VALUE, true);
    this.setSerializationInclusion(Include.NON_NULL);
   }
}

Demo.java switch to new package structure for Jackson 2

import com.fasterxml.jackson.annotation.JsonProperty;

demo-servlet.xml

Lastly, according to the SerializationConfig.Feature documentation, WRITE_NULL_PROPERTIES feature is deprecated < v2.0 and you should be using SerializationConfig.setSerializationInclusion() anyway. I assume this is why the @SuppressWarnings("deprecation") exists in your code. In Jackson >= v2.0, it has been removed, hence the code change in the CustomJacksonObjectMapper.java example.

Configuring ObjectMapper in Spring proposes an alternate solution.

Hope it helps!