JSON single element arrays

[Jason Rowland]

When I annotate a list and it only has one element, with JSON, it renders as a map and not an array.

{

    "@size": "1",

    "list": {

        "name": "Jason"

    }

}

I expect it to be this:

{

    "@size": "1",

    "list": [

        {

            "name": "Jason"

        }

    ]

}

How do I accomplish this?

[Noam Tenne]

Can you provide a gist of some sort that reproduces this? 

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[Jason Rowland]

Here is a gist with simple strings as the element in the array.

https://gist.github.com/jsonxr/6065040

[Noam Tenne]

Thanks. 

The Grails plugin doesn't have any special effect in this case so the question should probably be posted to the Jersey user list.

--

[Jason Rowland]

It is really a result of using an old jersey implementation.  The jersey in the plugin is 1.14, but the latest is now >2.0 which fixes this issue. I attempted to convert the plugin locally to use 2.0 but was blocked because SpringServlet isn't in 2.1 yet.

[Noam Tenne]

Has this by any chance fixed on the latest revision of Jersey 1.x?

We plan to move the plugin to JAX-RS 2.0, but it'll probably be on a different branch because it breaks backwards compatibility 

[Christian Junk]

Hi!

The following workaround is working for me for all non-domain objects. I am using Jackson for serializing the objects to JSON. This fixes the 'single-element-array' problem:

1. Add Jackson as dependency to your BuilddConfig.groovy

runtime 'com.fasterxml.jackson.jaxrs:jackson-jaxrs-json-provider:2.0.5'

2. Create a class JsonMessageBodyWriter.groovy in grails-app/providers

import com.fasterxml.jackson.databind.ObjectMapper

import javax.ws.rs.Produces

import javax.ws.rs.ext.Provider

import static org.grails.jaxrs.support.ConverterUtils.*

import static org.grails.jaxrs.support.ProviderUtils.*

import grails.converters.JSON

import grails.converters.XML

import java.lang.annotation.Annotation

import java.lang.reflect.ParameterizedType

import java.lang.reflect.Type

import javax.ws.rs.WebApplicationException

import javax.ws.rs.core.MediaType

import javax.ws.rs.core.MultivaluedMap

import javax.ws.rs.ext.MessageBodyWriter

@Provider

@Produces("application/json")

class JsonMessageBodyWriter implements MessageBodyWriter {

    @Override

    boolean isWriteable(Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {

        return true

    }

    @Override

    long getSize(Object t, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType) {

        return -1

    }

    @Override

    void writeTo(Object t, Class<?> type, Type genericType, Annotation[] annotations, MediaType mediaType, MultivaluedMap<String, Object> httpHeaders, OutputStream entityStream) throws IOException, WebApplicationException {

        new ObjectMapper().writeValue(entityStream, t);

    }

}

Regards,

Christian

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