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

Generics Solution

Here's a generic version of Json converter

package com.github.platform.util;

import java.io.IOException;
import java.lang.reflect.InvocationTargetException;
import com.google.protobuf.AbstractMessage.Builder;
import com.google.protobuf.Message;
import com.google.protobuf.MessageOrBuilder;
import com.google.protobuf.util.JsonFormat;

/**
 * Generic ProtoJsonUtil to be used to serialize and deserialize Proto to json
 * 
 * @author Marcello.deeSales@gmail.com
 *
 */
public final class ProtoJsonUtil {

  /**
   * Makes a Json from a given message or builder
   * 
   * @param messageOrBuilder is the instance
   * @return The string representation
   * @throws IOException if any error occurs
   */
  public static String toJson(MessageOrBuilder messageOrBuilder) throws IOException {
    return JsonFormat.printer().print(messageOrBuilder);
  }

  /**
   * Makes a new instance of message based on the json and the class
   * @param  is the class type
   * @param json is the json instance
   * @param clazz is the class instance
   * @return An instance of T based on the json values
   * @throws IOException if any error occurs
   */
  @SuppressWarnings({"unchecked", "rawtypes"})
  public static  T fromJson(String json, Class clazz) throws IOException {
    // https://stackoverflow.com/questions/27642021/calling-parsefrom-method-for-generic-protobuffer-class-in-java/33701202#33701202
    Builder builder = null;
    try {
      // Since we are dealing with a Message type, we can call newBuilder()
      builder = (Builder) clazz.getMethod("newBuilder").invoke(null);

    } catch (IllegalAccessException | IllegalArgumentException | InvocationTargetException
        | NoSuchMethodException | SecurityException e) {
      return null;
    }

    // The instance is placed into the builder values
    JsonFormat.parser().ignoringUnknownFields().merge(json, builder);

    // the instance will be from the build
    return (T) builder.build();
  }
}

Using it is as simple as follows:

Message instance

GetAllGreetings.Builder allGreetingsBuilder = GetAllGreetings.newBuilder();

allGreetingsBuilder.addGreeting(makeNewGreeting("Marcello", "Hi %s, how are you", Language.EN))
        .addGreeting(makeNewGreeting("John", "Today is hot, %s, get some ice", Language.ES))
        .addGreeting(makeNewGreeting("Mary", "%s, summer is here! Let's go surfing!", Language.PT));

GetAllGreetings allGreetings = allGreetingsBuilder.build();

To Json Generic

String json = ProtoJsonUtil.toJson(allGreetingsLoaded);
log.info("Json format: " + json);

From Json Generic

GetAllGreetings parsed = ProtoJsonUtil.fromJson(json, GetAllGreetings.class);
log.info("The Proto deserialized from Json " + parsed);