Java: JSON -> Protobuf & back conversion

Question

I have an existing system, which is using protobuf-based communication protocol between GUI and server. Now I would like to add some persistence, but at the moment

Answer 1

Here is my utility class, you may use:

package <removed>;
import com.google.protobuf.Message;
import com.google.protobuf.MessageOrBuilder;
import com.google.protobuf.util.JsonFormat;
/**
 * Author @espresso stackoverflow.
 * Sample use:
 *      Model.Person reqObj = ProtoUtil.toProto(reqJson, Model.Person.getDefaultInstance());
        Model.Person res = personSvc.update(reqObj);
        final String resJson = ProtoUtil.toJson(res);
 **/
public class ProtoUtil {
    public static <T extends Message> String toJson(T obj){
        try{
            return JsonFormat.printer().print(obj);
        }catch(Exception e){
            throw new RuntimeException("Error converting Proto to json", e);
        }
    }
   public static <T extends MessageOrBuilder> T toProto(String protoJsonStr, T message){
        try{
            Message.Builder builder = message.getDefaultInstanceForType().toBuilder();
            JsonFormat.parser().ignoringUnknownFields().merge(protoJsonStr,builder);
            T out = (T) builder.build();
            return out;
        }catch(Exception e){
            throw new RuntimeException(("Error converting Json to proto", e);
        }
    }
}

Answer 2

For protobuf 2.5, use the dependency:

"com.googlecode.protobuf-java-format" % "protobuf-java-format" % "1.2"

Then use the code:

com.googlecode.protobuf.format.JsonFormat.merge(json, builder)
com.googlecode.protobuf.format.JsonFormat.printToString(proto)

Answer 3

We are currently using protobuf-java-format to convert our Protobuf messages (anything subclass of Message) into a JSON format to send over our web API.

Simply do:

  JsonFormat.printToString(protoMessage)