1. maven dependencies

The maven dependencies are same with server project.

Just copy those dependencies from server project to client project.

2. proto file

The proto file is the contract between client and server.

Just copy the proto file from server project to client project. So that, the client can communicate with the server apis with codes generated from the proto file.

3. client

3.1 channel (make connection)

The grpc library provides channel, that the client can connect the service and access the apis using channel.

ManagedChannelBuilder.forAddress("localhost", 9091)

with no security method usePlaintext()

3.2 stub (access apis)

3.2.1 The stub is generated from proto file.

Using newBlockingStub():

Whenever the client sends the request, the client will wait for the server response. It means that the client cannot do further process.

Using newFutureStub():

Creates a new ListenableFuture-style stub that supports unary calls on the service.

It is completable feature concept.

Using newStub():

It is a synchronous call. Once the client makes a request to the api, it will not wait for the response from the server. It will do the further process. Once the server sends the response it will capture the response from the server.

3.2.2 construct the login request using builder class

User.LoginRequest loginRequest = User.LoginRequest.newBuilder().setUsername("nick").setPassword("npass").build();

3.2.3 send request and get response

ser.APIResponse apiResponse = userBlockingStub.login(loginRequest);

Exception

If the server does not register the service in addService(), it will get exception io.grpc.StatusRuntimeException: UNIMPLEMENTED: Method not found

Exception in thread "main" io.grpc.StatusRuntimeException: UNIMPLEMENTED: Method not found: user/login
	at io.grpc.stub.ClientCalls.toStatusRuntimeException(ClientCalls.java:240)
	at io.grpc.stub.ClientCalls.getUnchecked(ClientCalls.java:221)
	at io.grpc.stub.ClientCalls.blockingUnaryCall(ClientCalls.java:140)
	at nd.pemo.grpcclientsample.userGrpc$userBlockingStub.login(userGrpc.java:211)
	at nd.pemo.client.GRPCClient.main(GRPCClient.java:31)

or from BloomRPC:

{
  "error": "12 UNIMPLEMENTED: Method not found: user/login"
}

See Status status = Status.UNIMPLEMENTED.withDescription("Method not found: " + methodName); in grpc-core-1.27.0.jar!/io/grpc/internal/ServerImpl.class

Ref

grpc server cpp demo

grpc client cpp demo

grpc client with springboot demo

grpc server with springboot demo

grpc client java demo

grpc server java demo

sprintboot with grpc server. Fork from nils

gRPC Java Client App Implementation

grpc sample on github