jsondecoder.java

public class JsonDecoder<T> extends MessageToMessageDecoder<String, T> {

    private static final Gson GSON = new GsonBuilder().create();

    private final Class<T> clazz;

    public JsonDecoder(Class<T> clazz, Class<?>... acceptedMsgTypes) {
        super(acceptedMsgTypes);
        this.clazz = checkNotNull(clazz);
    }

    @Override
    public T decode(ChannelHandlerContext ctx, String msg) throws Exception {
        return GSON.fromJson(msg, clazz);
    }
}