grpc

Invoking a Grpc endpoint using the Java-SDK

In this example, you will run a Grpc service and client using Dapr's invoke feature.

Pre-requisites

• Dapr CLI.
• Java JDK 17 (or greater):
  • Microsoft JDK 17
  • Oracle JDK 17
  • OpenJDK 17
• Apache Maven version 3.x.

Checking out the code

Clone this repository:

git clone https://github.com/dapr/java-sdk.git
cd java-sdk

Then build the Maven project:

# make sure you are in the `java-sdk` directory.
mvn install

Get into the examples' directory:

cd examples

Running the example's service

The first component is the service. It has a simple API with the SayHello method. This method will print out each message received from the client. The proto file below contains the description of the HelloWorld service found in the ./proto/examples/helloworld.proto file:

  service HelloWorld {
    // Sends a greeting
    rpc SayHello (HelloRequest) returns (HelloReply) {}
  }

  // The request message containing the user's name.
  message HelloRequest {
    string name = 1;
  }

  // The response message containing the greetings
  message HelloReply {
    string message = 1;
  }

In the HelloWorldService.java file, you will find the HelloWorldService class, containing the main method and handling logic. You can see that it extends HelloWorldImplBase automatically generated by proto to implement sayhello method.

  static class HelloWorldImpl extends HelloWorldGrpc.HelloWorldImplBase {

    /**
     * Handling of the 'sayHello' method.
     *
     * @param req Request to say something.
     * @return Response with when it was said.
     */
    @Override
    public void sayHello(HelloRequest req, StreamObserver<HelloReply> responseObserver) {
      HelloReply reply = HelloReply.newBuilder().setMessage("Hello " + req.getName()).build();
      responseObserver.onNext(reply);
      responseObserver.onCompleted();
    }
  }

Now run the service code:

dapr run --app-id hellogrpc --app-port 5000 --app-protocol grpc -- java -jar target/dapr-java-sdk-examples-exec.jar io.dapr.examples.invoke.grpc.HelloWorldService -p 5000

The app-id argument is used to identify this service in Dapr's runtime. The app-port determines which port Dapr's runtime should call into this service. The protocol argument informs Dapr which protocol it should use to invoke the application: grpc or http(default).

Running the example's client

The other component is the client. It will add user name to the grpc request and send it to the server. Open the HelloWorldClient.java file, it uses the DaprClient's grpc channel and sends request directly to the dapr side car through it, including necessary headers.

private static class HelloWorldClient {
///...
  public static void main(String[] args) throws Exception {
    String user = "World";
    try (DaprClient client = new DaprClientBuilder().build()) {
      HelloWorldGrpc.HelloWorldBlockingStub blockingStub = HelloWorldGrpc.newBlockingStub(client.getGrpcChannel());
      // Adds Dapr interceptors to populate gRPC metadata automatically.
      blockingStub = DaprClientGrpcInterceptors.intercept("hellogrpc", blockingStub);

      logger.info("Will try to greet " + user + " ...");
      try {
        HelloRequest request = HelloRequest.newBuilder().setName(user).build();
        HelloReply response = blockingStub.sayHello(request);
        logger.info("Greeting: " + response.getMessage());
      } catch (StatusRuntimeException e) {
        logger.log(Level.WARNING, "RPC failed: {0}", e.getStatus());
      }
    }
  }
///...
}

Finally, open a new command line terminal and run the client code to send some messages.

dapr run --app-id invokegrpc --app-protocol grpc -- java -jar target/dapr-java-sdk-examples-exec.jar io.dapr.examples.invoke.grpc.HelloWorldClient

Cleanup

To stop the apps run (or press CTRL+C):

dapr stop --app-id hellogrpc
dapr stop --app-id invokegrpc

Thanks for playing.