Process request message fields in gRPC Server Interceptor [Java]

[Bill Li]

Hi,

I have a question regarding how I can access each field of the input request object in ServerInterceptor. The following is my code:

public <ReqT, RespT> ServerCall.Listener<ReqT> interceptCall(ServerCall<ReqT, RespT> serverCall,
Metadata metadata,
ServerCallHandler<ReqT, RespT> serverCallHandler) {
    ServerCall.Listener<ReqT> listener = serverCallHandler.startCall(serverCall, metadata);
    return new ForwardingServerCallListener.SimpleForwardingServerCallListener<>(listener) {
        @Override
        public void onMessage(ReqT message) {
            System.out.println(message.toString());
            super.onMessage(message);
        }
    };
}

After printing it out, the following output appears:

request_config {

  field_1: "field_1"

  field_2: "field_2"

  field_3: "field_3"

}

I didn't find any obvious methods in the source code or examples online on processing each fields in the message. Does anyone have examples on how to access each field?

Thanks,

Bill

[Eric Anderson]

Generally the message will be a protobuf message, so you can cast to com.google.protobuf.Message (after doing an instanceof check). You can then use a method like message.getAllFields to introspect. If a field contains a message, you can process the tree recursively.

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