Generating Class Class File Files for Java, C #, and Objective-C

We have a project with a server (Java + Spring) and clients on Android, iPhone and Windows Phone. All interactions will be implemented through the JSON format. We want to describe our protocol only once and generate the Java, C # and Obj-C classes for all clients according to this description. We are looking for a tool similar to the Google ProtoBuf compiler (protoc). But ProtoBuf generates too complex code, which is useless for us in this case, because we want to use JSON instead of binary serialization. Are there ready-to-use solutions?