Java gRPC Server Not Starting

Question

I am trying to implement gRPC service in my code with condition to use one instance of the server class the code building successfully but i got a runtime error.

How can I fix this error?

Exception in thread "main" java.lang.NullPointerException: bindableService
   at com.google.common.base.Preconditions.checkNotNull(Preconditions.java:897)
   at io.grpc.internal.AbstractServerImplBuilder.addService(AbstractServerImplBuilder.java:120)
   at io.grpc.internal.AbstractServerImplBuilder.addService(AbstractServerImplBuilder.java:56)
   at com.mypackage.cu.comms.CURequestHandlerService.<init>(Unknown Source)
   at com.mypackage.cu.comms.CURequestHandlerService.start(Unknown Source)
   at com.mypackage.cu.entities.ControlUnit.initSystem(Unknown Source)
   at com.mypackage.cu.entities.ControlUnit.run(Unknown Source)
   at com.mypackage.cu.entities.ControlUnit.main(Unknown Source)

• the genrated grpc java class is CURequestHandlerGrpc.
• the server class CURequestHandlerService:

import io.grpc.Server;
import io.grpc.ServerBuilder;
import io.grpc.stub.StreamObserver;
\\ ..

public class CURequestHandlerService extends CURequestHandlerGrpc.CURequestHandlerImplBase {
  private final Server server;
  private static CURequestHandlerService INSTANCE = null;
  private CURequestHandlerService(int port) {
    this.server = ServerBuilder.forPort(port)
            .addService(INSTANCE)
            .build();
  }

  public static void start(int port) {
    if (INSTANCE == null)
      INSTANCE = new CURequestHandlerService(port);

    try {
      INSTANCE.server.start();
    } catch (IOException e) {
      System.out.println("Can't start GRPC server!");
    }
  }

• in main class

CURequestHandlerService.start(16440);

I am using Ant since it is an old project and i maintaining it. I add all grpc dependencies jars to dependencies directory.

• my dependencies jars:

amqp-client-5.7.3.jar
failureaccess-1.0.1.jar
grpc-all-1.27.0.jar
grpc-api-1.27.0.jar
grpc-auth-1.27.0.jar
grpc-context-1.27.0.jar
grpc-core-1.27.0.jar
grpc-netty-1.27.0.jar
grpc-netty-shaded-1.27.0.jar
grpc-protobuf-1.27.0.jar
grpc-protobuf-lite-1.27.0.jar
grpc-stub-1.27.0.jar
grpc-testing-1.27.0.jar
guava-28.2-jre.jar
json-smart-1.2.jar
lettuce-4.3.0.Final-shaded.jar
libthrift-0.9.3.jar
opencensus-api-0.20.0.jar
opencensus-contrib-grpc-metrics-0.20.0.jar
perfmark-api-0.21.0.jar
protobuf-java-3.11.3.jar
protobuf-java-util-3.11.3.jar
protoc-gen-grpc-java-1.27.0-linux-x86_64.exe
slf4j-api-1.7.22.jar
slf4j-simple-1.7.22.jar

Answer 1

I found out the problem it is not a dependency issue after reading the server example in grpc-java repository. I underhanded that you must split the server class from the implementation class which extends form the Grpc generated class.

• server class

/**
 * Grpc instance class that used to initiate the server and call implementation class
 */
public class GrpcServer {
    private final Server server;
    private static GrpcServer INSTANCE = null;
    private GrpcServer(int port) {
        this.server = ServerBuilder.forPort(port)
                .addService(new CURequestHandlerService())
                .build();
    }

    public static void start(int port) {
        if (INSTANCE == null)
            INSTANCE = new GrpcServer(port);

        try {
            INSTANCE.server.start();
            System.out.println("GRPC server started");
        } catch (IOException e) {
            System.out.println("Can't start GRPC server!");
        }
    }
}

• implementation class

**
 * Request Handler class contains the implementation for all functions initiated in proto files
 * The implemented function 
 * */
public class CURequestHandlerService extends CURequestHandlerGrpc.CURequestHandlerImplBase{


  public synchronized void Method1(Messages.Method1Input input,
                                         StreamObserver<Messages.Method1Output> output) {
    //...
    output.onNext(outputResponse);
    output.onCompleted();
  }