Model class files code generation for Java, C# and Objective-C

Question

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