How to set the number of connections?

### Question：reference.setConnections(10);//设置未生效

There is only one connection. How do you make multiple connections？

server

public class EchoServer {
    public static void main(String[] args) throws IOException {
        ServiceConfig<EchoService> service = new ServiceConfig<>();
        service.setInterface(EchoService.class);
        service.setRef(new EchoImpl());

        DubboBootstrap bootstrap = DubboBootstrap.getInstance();
        bootstrap.application(new ApplicationConfig("tri-stub-server"))
//               .registry(new RegistryConfig("multicast://127.0.0.1:2181"))
                .protocol(new ProtocolConfig(CommonConstants.TRIPLE, 3002))
                .service(service)
                .start();
        System.out.println("Dubbo triple stub server started");
        System.in.read();
    }
}

client

public class EchoClient {
    public static void main(String[] args) throws IOException {
        for (int i = 0; i < 3; i++) {
            new Thread(()->{
                DubboBootstrap bootstrap = DubboBootstrap.newInstance();
                System.out.println(bootstrap);
                ReferenceConfig<EchoService> ref = new ReferenceConfig<>();
                ref.setInterface(EchoService.class);
                ref.setProtocol(CommonConstants.TRIPLE);
                ref.setProxy(CommonConstants.NATIVE_STUB);
                ref.setTimeout(3000);
                ref.setUrl("tri://127.0.0.1:3002");
                ref.setConnections(10);//设置未生效
                bootstrap.application(new ApplicationConfig("tri-stub-client"))
                        .reference(ref)
                        .start();

                EchoService echoService = ref.get();
//                Scanner sc = new Scanner(System.in);
                while (true){
//                    String input = sc.next();
                    EchoRequest request = EchoRequest.newBuilder().setMessage("input").build();
                    EchoResponse echoResponse = echoService.echo(request);
                    System.out.println("Received reply:" + echoResponse.getMessage());
                }
            }).start();
        }
        System.in.read();

    }
}