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The C based gRPC (C++, Python, Ruby, Objective-C, PHP, C#)
https://grpc.io/
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82 lines
2.9 KiB
82 lines
2.9 KiB
# Step-3: Implement a server. |
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This step extends the generated server skeleton code to write a simple server |
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that provides the hello service. This in introduces two new classes |
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- a service implementation [GreetingsImpl.java](src/main/java/ex/grpc/GreetingsImpl.java). |
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- a server that hosts the service implementation and allows to accessed over the network: [GreetingsServer.java](src/main/java/ex/grpc/GreetingsServer.java). |
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## Service implementation |
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[GreetingsSImpl.java](src/main/java/ex/grpc/GreetingsImpl.java) |
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implements the behaviour we require of our GreetingService. There are a |
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number of important features of gRPC being used here: |
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``` |
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public void hello(Helloworld.HelloRequest req, |
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StreamObserver<Helloworld.HelloReply> responseObserver) { |
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Helloworld.HelloReply reply = Helloworld.HelloReply.newBuilder().setMessage( |
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"Hello " + req.getName()).build(); |
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responseObserver.onValue(reply); |
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responseObserver.onCompleted(); |
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} |
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``` |
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- it provides a class `GreetingsImpl` that implements a generated interface `GreetingsGrpc.Greetings` |
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- `GreetingsGrpc.Greetings` declares the method `hello` that was declared in the proto [IDL](src/main/proto/helloworld.proto) |
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- `hello's` signature is typesafe: |
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hello(Helloworld.HelloRequest req, StreamObserver<Helloworld.HelloReply> responseObserver) |
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- `hello` takes two parameters: |
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`Helloworld.HelloRequest`: the request |
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`StreamObserver<Helloworld.HelloReply>`: a response observer, an interface to be called with the response value |
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- to complete the call |
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- the return value is constructed |
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- the responseObserver.onValue() is called with the response |
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- responseObserver.onCompleted() is called to indicate that no more work will done on the RPC. |
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## Server implementation |
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[GreetingsServer.java](src/main/java/ex/grpc/GreetingsServer.java) shows the |
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other main feature to required to provde gRPC service; how to allow a service |
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implementation to be accessed from the network. |
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``` |
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private void start() throws Exception { |
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server = NettyServerBuilder.forPort(port) |
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.addService(GreetingsGrpc.bindService(new GreetingsImpl())) |
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.build(); |
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server.startAsync(); |
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server.awaitRunning(5, TimeUnit.SECONDS); |
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} |
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``` |
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- it provides a class `GreetingsServer` that holds a `ServerImpl` that will run the server |
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- in the `start` method, `GreetingServer` binds the `GreetingsService` implementation to a port and begins running it |
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- there is also a `stop` method that takes care of shutting down the service and cleaning up when the program exits |
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## Build it |
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This is the same as before: our client and server are part of the same maven |
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package so the same command builds both. |
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``` |
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$ mvn package |
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``` |
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## Try them out |
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We've added simple shell scripts to simplifying running the examples. Now |
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that they are built, you can run the server with. |
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``` |
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$ ./run_greetings_server.sh |
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``` |
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In another termainal window and confirm that it receives a message. |
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``` |
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$ ./run_greetings_client.sh |
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```
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