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Version: 0.24.0

Query Network State Service

An implementation of the QueryNetworkStateService will provide an object-oriented wrapper for the gRPC library, with the ability to retrieve information about the state of the network. This is done with the following 3 steps:

  1. Create callbacks which will be called when gRPC messages are received from a client.
  2. Register the callbacks with an instance of the QueryNetworkStateService.
  3. Add your QueryNetworkStateService instance as a gRPC service.
info

The below examples make use of a helper library provided by Zepben, which is included as a transitive dependency of the SDK, or can be added directly from Maven Central.

You do NOT have to do this, you can register the services directly with a Netty gRPC (or other) server instead.

The classes you need for performing these actions can be imported from the SDK:

import com.zepben.evolve.conn.grpc.GrpcServer;
import com.zepben.evolve.streaming.data.CurrentStateEvent;
import com.zepben.evolve.streaming.get.QueryNetworkStateService;

Creating callbacks​

Each supported message in QueryNetworkStateService requires a callback, which will be triggered when any client messages are received. Implementation of these callbacks can be done as either lambdas, or full method/function implementations that can be passed as method references.

onGetCurrentStates​

The onGetCurrentStates callback is triggered for each request for the current states between two date/times, and should return a list of the current state events that occurred between those date/times (inclusive)

// Using a lambda expression
QueryNetworkStateService.GetCurrentStates getCurrentStatesLambda = (from, to) ->
    Stream.of(
        // Put the batches you wish to return here, e.g. List.of(item1, item2), List.of(item3).
    );

// Using a method
class QueryNetworkStateServiceImpl {

    Stream<List<CurrentStateEvent>> getCurrentStates(LocalDateTime from, LocalDateTime to){
        var batches = ... // Some logic to build the batches of events.
        return batches.stream();
    }

}

Registering callbacks​

Registering the callbacks with the service is as simple as passing them into the QueryNetworkStateService constructor.

// Using lambda expressions
QueryNetworkStateService service = new QueryNetworkStateService(getCurrentStatesLambda);

// Using method references
class QueryNetworkStateServiceImpl {

    QueryNetworkStateService service = new QueryNetworkStateService(this::getCurrentStates);

}

Registering the service​

For the above code to have any effect, you need to register the service with a gRPC server. Once this has been done, you should start to receive callbacks for each request sent from a gRPC client.

class Main {

    public static void main(String[] args) {
        var grpcServer = new GrpcServerImpl(9001, service);
        grpcServer.start();
    }

    class GrpcServerImpl extends GrpcServer {

        GrpcServerImpl(int port, QueryNetworkStateService service) {
            super(port, 0, null, List.of());
            getServerBuilder().addService(service);
        }

    }

}

Putting it all together​

Putting each of the steps above together, you can build the scaffold of a working application

Main.java:

import com.zepben.evolve.streaming.get.QueryNetworkStateService;
import com.zepben.evolve.streaming.data.CurrentStateEvent;

import java.util.stream.Stream;

class Main {

    public static void main(String[] args) {
        QueryNetworkStateService service = new QueryNetworkStateService(
            (QueryNetworkStateService.GetCurrentStates) (from, to) -> Stream.of(
                // Put the batches you wish to return here, e.g. List.of(item1, item2), List.of(item3).
            )
        );

        var grpcServer = new GrpcServerImpl(9001, service);
        grpcServer.start();
    }

}

GrpcServerImpl.java:

import com.zepben.evolve.conn.grpc.GrpcServer;
import com.zepben.evolve.streaming.get.QueryNetworkStateService;

import java.util.List;

class GrpcServerImpl extends GrpcServer {

    GrpcServerImpl(int port, QueryNetworkStateService service) {
        super(port, 0, null, List.of());
        getServerBuilder().addService(service);
    }

}