Enable json serialization of Multimap in Spring Boot Project

Question

I want to serialize some google guava Multimap in a spring boot application.

public class SomeDTO {
    @JsonProperty
    Multimap<A, B> prop = HashMultimap.create();
}

Without using a customized jackson serializer, I get some result like

{
   "prop ":
   {
       "empty": false
   }
}

Which is definitley not what I seek to get. I thought of something like:

{
  "nodes": {
    "key0": [
      {
        "prop0": 2,
        "prop1": 4
      },
      {
        "prop0": 5,
        "prop1": 6
      }
    ],
    "key1": [
      {
        "prop0": 23,
        "prop1": 0
      }
    ]
  }
}

Adding

        <dependency>
            <groupId>com.fasterxml.jackson.datatype</groupId>
            <artifactId>jackson-datatype-guava</artifactId>
            <version>${jackson.version}</version>
        </dependency>

to the pom.xml seems not sufficient... However, I'm just starting with this whole spring // pivotal universe, so I guess I miss something obvious.

Answer 1

The solution i came up with is simply adding a @Bean to my main @Configuration:

import com.fasterxml.jackson.databind.Module;
import com.fasterxml.jackson.datatype.guava.GuavaModule;
// More-obvious imports missing

@Configuration
@EnableAutoConfiguration
@ComponentScan
public class Application extends SpringBootServletInitializer {

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

    @Override
    protected final SpringApplicationBuilder configure(final SpringApplicationBuilder application) {
        return application.sources(Application.class);
    }

    @Bean
    ObjectMapper customizeJacksonConfiguration() {
        ObjectMapper om = new ObjectMapper();
        om.registerModule(new GuavaModule());
        return om;
    }
}

Afaik, the ObjectMapper Bean approach has one drawback: Everytime an ObjectMapper is created this way, all previous configuration gets thrown away.

If you want to add a module to jackson - instead of overriding previous configuration, this approach is better:

import com.fasterxml.jackson.databind.Module;
import com.fasterxml.jackson.datatype.guava.GuavaModule;
// More-obvious imports missing

@Configuration
@EnableAutoConfiguration
@ComponentScan
public class Application extends SpringBootServletInitializer {

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

    @Override
    protected final SpringApplicationBuilder configure(final SpringApplicationBuilder application) {
        return application.sources(Application.class);
    }

    @Bean
    public Module guavaModule() {
        return new GuavaModule();
    }
}