code: package io.ray.serve.router;
  
  import com.google.common.collect.ImmutableMap;
  import io.ray.api.BaseActorHandle;
  import io.ray.api.ObjectRef;
  import io.ray.runtime.metric.Count;
  import io.ray.runtime.metric.Metrics;
  import io.ray.serve.generated.RequestMetadata;
  import io.ray.serve.metrics.RayServeMetrics;
  import io.ray.serve.poll.KeyListener;
  import io.ray.serve.poll.KeyType;
  import io.ray.serve.poll.LongPollClient;
  import io.ray.serve.poll.LongPollNamespace;
  import java.util.HashMap;
  import java.util.Map;
  
  /** Router process incoming queries: assign a replica. */
  public class Router {
  
    private ReplicaSet replicaSet;
  
    private Count numRouterRequests;
  
    private LongPollClient longPollClient;
  
    public Router(BaseActorHandle controllerHandle, String deploymentName) {
      this.replicaSet = new ReplicaSet(deploymentName);
  
      RayServeMetrics.execute(
          () ->
              this.numRouterRequests =
                  Metrics.count()
                      .name(RayServeMetrics.SERVE_NUM_ROUTER_REQUESTS.getName())
                      .description(RayServeMetrics.SERVE_NUM_ROUTER_REQUESTS.getDescription())
                      .unit("")
                      .tags(ImmutableMap.of(RayServeMetrics.TAG_DEPLOYMENT, deploymentName))
                      .register());
  
      Map<KeyType, KeyListener> keyListeners = new HashMap<>();
      keyListeners.put(
          new KeyType(LongPollNamespace.RUNNING_REPLICAS, deploymentName),
          workerReplicas -> replicaSet.updateWorkerReplicas(workerReplicas)); // cross language
      this.longPollClient = new LongPollClient(controllerHandle, keyListeners);
    }
  
    /**
     * Assign a query and returns an object ref represent the result.
     *
     * @param requestMetadata the metadata of incoming queries.
     * @param requestArgs the request body of incoming queries.
     * @return ray.ObjectRef
     */
    public ObjectRef<Object> assignRequest(RequestMetadata requestMetadata, Object[] requestArgs) {
      RayServeMetrics.execute(() -> numRouterRequests.inc(1.0));
      return replicaSet.assignReplica(new Query(requestMetadata, requestArgs));
    }
  
    public ReplicaSet getReplicaSet() {
      return replicaSet;
    }
  
    public LongPollClient getLongPollClient() {
      return longPollClient;
    }
  }
  