Using Gson instead of Jackson in Jersey

Question

I have a RESTful service that consumes and produces JSON objects, and I would like Jersey to use Gson instead of Jackson.

How can this be done...?

Answer 1

You need to write custom implementations of MessageBodyReader and MessageBodyWriter (possibly in the same class) and register with Jersey (if you use package scanning, the @Provider annotation is enough) -- pretty much like JacksonJsonProvider does it:

@Provider
@Consumes({MediaType.APPLICATION_JSON, "text/json"})
@Produces({MediaType.APPLICATION_JSON, "text/json"})
class GsonJsonProvider implements
    MessageBodyReader<Object>,
    MessageBodyWriter<Object> { ...

Answer 2

You can find a fully working example here: https://github.com/DominikAngerer/java-GsonJerseyProvider

There will be an working implementation of http://eclipsesource.com/blogs/2012/11/02/integrating-gson-into-a-jax-rs-based-application/ but with some new achievements - like an GsonUtil for Expose only things.

import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;
import java.io.OutputStream;
import java.io.OutputStreamWriter;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;

import javax.ws.rs.Consumes;
import javax.ws.rs.Produces;
import javax.ws.rs.WebApplicationException;
import javax.ws.rs.core.MediaType;
import javax.ws.rs.core.MultivaluedMap;
import javax.ws.rs.ext.MessageBodyReader;
import javax.ws.rs.ext.MessageBodyWriter;
import javax.ws.rs.ext.Provider;

@Provider
@Produces(MediaType.APPLICATION_JSON)
@Consumes(MediaType.APPLICATION_JSON)
public class GsonJerseyProvider implements MessageBodyWriter<Object>,
        MessageBodyReader<Object> {

    private static final String UTF_8 = "UTF-8";

    @Override
    public boolean isReadable(Class<?> type, Type genericType,
            java.lang.annotation.Annotation[] annotations, MediaType mediaType) {
        return true;
    }

    @Override
    public Object readFrom(Class<Object> type, Type genericType,
            Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, String> httpHeaders, InputStream entityStream)
            throws IOException {
        InputStreamReader streamReader = new InputStreamReader(entityStream,
                UTF_8);
        try {
            return GsonUtil.getInstance().fromJson(streamReader, genericType);
        } catch (com.google.gson.JsonSyntaxException e) {
            // Log exception
        } finally {
            streamReader.close();
        }
        return null;
    }

    @Override
    public boolean isWriteable(Class<?> type, Type genericType,
            Annotation[] annotations, MediaType mediaType) {
        return true;
    }

    @Override
    public long getSize(Object object, Class<?> type, Type genericType,
            Annotation[] annotations, MediaType mediaType) {
        return -1;
    }

    @Override
    public void writeTo(Object object, Class<?> type, Type genericType,
            Annotation[] annotations, MediaType mediaType,
            MultivaluedMap<String, Object> httpHeaders,
            OutputStream entityStream) throws IOException,
            WebApplicationException {
        OutputStreamWriter writer = new OutputStreamWriter(entityStream, UTF_8);
        try {
            GsonUtil.getInstance().toJson(object, genericType, writer);
        } finally {
            writer.close();
        }
    }
}

Answer 3

Payara 4

I had a hard time to get my custom Gson @Provider working with Jersey embedded in GlassFish / Payara. In that case you must set the property jersey.config.server.disableMoxyJson to true.

For example:

@ApplicationPath("/api")
public class MyApplication extends Application {
    @Override
    public Map<String, Object> getProperties() {
        Map<String, Object> props = new HashMap<>();
        props.put("jersey.config.server.disableMoxyJson", true);
        return props;
    }
}

See also:

• https://jersey.github.io/documentation/latest/appendix-properties.html
• Customizing JSON marhsalling with GlassFish v4

Same thing goes for a Jersey client:

new ClientConfig()
        .register(MyGsonProvider.class)
        .property("jersey.config.client.disableMoxyJson", true);

Payara 5

Payara 5 supports the JSON Binding API, so it does not make sense to keep using Gson. I would advice to migrate to JSON-B.