Serialize a map of key-value pairs as JSON attributes with values in response using JAX-RS

In the response from a REST API call I got a JSON payload.

Source JSON

It contains a parameters map containing key-value pairs like this:

{
   "account":    {
  
      "sample_id": 1424876658095,
      "parameters":       [
                  {
            "name": "email",
            "value": "hello@xyz.com"
         },
                  {
            "name": "first_name",
            "value": "FIRSTNAME"
         },
                  {
            "name": "last_name",
            "value": "LASTNAME"
         }
      ]
   },
   "assests": [   {
      
      "tran_id": "1234567",
      
   }]
}

Target JSON

I would like to process this response in Java and transform or serialize it to a JSON response like this:


{
   "account":    {
    
      "sample_id": 1424876658095,
      "email_id": "hello@xyz.com",
      "first_name": "FIRSTNAME",
      "last_name": "LASTNAME",
   },
   "assets": [   {
     
      "tran_id": "1234567",
     
   }]
}

Question

I am using the JAX-RS specification for the REST API, but I am not able to find any library to process the response.

Any ideas?

Solution

If you want to leverage the Jackson serialization within JAX-Rs, you need to implement as custom serializer.

There are two steps to do that:

Create the custom serializer

Here is a sample of a custom Jackson serializer for your needs based on beans AccountBean and ParameterBean:

public class AccountBeanSerializer extends JsonSerializer<AccountBean> {
    @Override
    public void serialize(AccountBean accountBean, JsonGenerator jgen,
            SerializerProvider provider) throws IOException,
            JsonProcessingException {
        jgen.writeStartObject();
        jgen.writeNumberField("sample_id", accountBean.getSampleId());
        List<ParameterBean> parameters = accountBean.getParameters();
        for (ParameterBean parameterBean : parameters) {
            jgen.writeStringField(parameterBean.getName(),
                    parameterBean.getValue());
        }
        jgen.writeEndObject();
    }
}

I assume the class for your response if something like that:

class ResponseBean
    field account = class AccountBean
       field sampleId (long)
       field parameters = class ParameterBean
    (...)

Register the custom serializer

You need then to provide a custom Jackson configuration within a context resolver. For this, you can create an implementation of the interface ContextResolver annotated with Provider.

@Provider
public class CustomJacksonConfig implements ContextResolver<ObjectMapper> {
    private ObjectMapper objectMapper;

    public JacksonConfig() {
        this.objectMapper = new ObjectMapper();
        SimpleModule module = new SimpleModule("MyModule", new Version(1, 0, 0, null));
        module.addSerializer(AccountBean.class, new AccountSerializer());
        this.objectMapper.registerModule(module);
    }

    public ObjectMapper getContext(Class<?> objectType) {
        return objectMapper;
    }
}

Following links could help you:

Hope this helps, Thierry