java - How to inject dependency into Jackson Custom deserializer

Question

I want to enable a custom jackson deserializer of some fields of type String. The deserializer also needs to be injected with a guice based dependency bean. SampleCode below:

public class CustomDeserializer extends StdDeserializer<String> {

    private SomeDependecy dependency;

    public StringDeserializer() {
        this(null);
    }

    public StringDeserializer(Class<?> vc) {
        super(vc);
    }

    @Override
    public String deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        return dependency.perform(p.getValueAsString());
    }
}

I cannot register a module based on Class type as it is generic (String.class, Complex Datatype( but not every one require a custome deserializer)). Is there a way to achieve the above without using static methods?

PS: I did search net but could not find a cleaner solution without using statics . All the suggestions where around using Some static method to get context and bean.

Answer 1

Looks like there is another approach (Thanks to one of my colleague) using injectableValues on the objectMapper instance and then fetch the dependency through DeserializationContext ctxt. Following is the code.

ObjectMapper guice module.

public class MerchantConverterModule extends AbstractModule {

    @Override
    protected void configure() {

    }

    @Provides
    @Singleton
    public ObjectMapper objectMapper() {

        ObjectMapper objectMapper = new ObjectMapper();

        /**
         * Add dependency object to object mapper.
         */
        objectMapper.setInjectableValues(new InjectableValues
            .Std()
            .addValue("DependencyName", dependency));

        return objectMapper;
    }


}

Code of your custom deserializer

public class CustomDeserializer extends StdDeserializer<String> {

    private SomeDependecy dependency;

    public StringDeserializer() {
        this(null);
    }

    @Override
    public String deserialize(JsonParser p, DeserializationContext ctxt) throws IOException, JsonProcessingException {
        return getDependency(ctxt).perform(p.getValueAsString());
    }

    private SomeDependency getDependency(DeserializationContext ctxt) {
        SomeDependency dependency = (SomeDependency) ctxt
                .findInjectableValue("DependencyName", null, null);

        return dependency;
    }
}

findInjectableValue method is a final method, so you might need to tweak your unit test code to mock finals.

NOTE: The drawback is that there is a tight coupling between the objectmapper and deserializer.