Suggestion

[insad]

A kind suggestion to change the line

String methodName = handleName + "." + method.getName();

in method "JsonRpcInvoker.invoke()" by

    String methodName = (handleName != null ? handleName + "." : "") + method.getName();

This way a method without a handleName prefix can be called by setting null for the handleName parameter in "JsonRpcInvoker.get()" method, like is necessary e.g. for this server code: http://jsonrpcphp.org/ - it's not possible to have a method with a name like "handle.method()" in a PHP class.

[insad]

A second suggestion to automatically set the content-type header of the rpc request to "application/json"