如何使Vertx MongoClient操作同步但不阻止Java中的事件循环？

Question

I am trying to save a new document to MongoDB using the Vertx MongoClient as follows:

MongoDBConnection.mongoClient.save("booking", query, res -> {
    if(res.succeeded()) {
        documentID = res.result();
        System.out.println("MongoDB inserted successfully. + document ID is : " + documentID);
    }
    else {
        System.out.println("MongoDB insertion failed.");
    }
});

if(documentID != null) {

    // MongoDB document insertion successful. Reply with a booking ID
    String resMsg = "A confirmed booking has been successfully created with booking id as " + documentID + 
        ". An email has also been triggered to the shared email id " + emailID;

    documentID = null;

    return new JsonObject().put("fulfillmentText", resMsg);
}
else {
    // return intent response
    documentID = null;
    return new JsonObject().put("fulfillmentText", 
        "There is some issues while booking the shipment. Please start afreash.");
}

The above code successfully writes the query jsonObject to MongoDB collection booking . However, the function which contains this code always returns with There is some issues while booking the shipment. Please start afreash There is some issues while booking the shipment. Please start afreash .

This is happening probably because the MongoClient save() handler "res" is asynchronous. But, I want to return conditional responses based on successful save() operation and on failed save operation.

How to achieve it in Vertx Java?

Answer 1

Your assumption is correct, you dont wait for the async response from the database. What you can do, is to wrap it in a Future like this:

  public Future<JsonObject> save() {
    Future<JsonObject> future = Future.future();
    MongoDBConnection.mongoClient.save("booking", query, res -> {
      if(res.succeeded()) {
        documentID = res.result();
        if(documentID != null) {
          System.out.println("MongoDB inserted successfully. + document ID is : " + documentID);
          String resMsg = "A confirmed booking has been successfully created with booking id as " + documentID +
            ". An email has also been triggered to the shared email id " + emailID;
          future.complete(new JsonObject().put("fulfillmentText", resMsg));
        }else{
          future.complete(new JsonObject().put("fulfillmentText",
            "There is some issues while booking the shipment. Please start afreash."))
        }
      } else {
        System.out.println("MongoDB insertion failed.");
        future.fail(res.cause());
      }
    });
    return future;
  }

Then i assume you have and endpoint that eventually calls this, eg:

router.route("/book").handler(this::addBooking);

... then you can call the save method and serve a different response based on the result

public void addBooking(RoutingContext ctx){
    save().setHandler(h -> {
        if(h.succeeded()){
            ctx.response().end(h.result());
        }else{
            ctx.response().setStatusCode(500).end(h.cause());
        }
    })
}

Answer 2

You can use RxJava 2 and a reactive Mongo Client ( io.vertx.reactivex.ext.mongo.MongoClient )

Here is a code snippet:

Deployer

public class Deployer extends AbstractVerticle {

   private static final Logger logger = getLogger(Deployer.class);

   @Override
   public void start(Future<Void> startFuture) {
      DeploymentOptions options = new DeploymentOptions().setConfig(config());

      JsonObject mongoConfig = new JsonObject()
            .put("connection_string",
                  String.format("mongodb://%s:%s@%s:%d/%s",
                        config().getString("mongodb.username"),
                        config().getString("mongodb.password"),
                        config().getString("mongodb.host"),
                        config().getInteger("mongodb.port"),
                        config().getString("mongodb.database.name")));

      MongoClient client = MongoClient.createShared(vertx, mongoConfig);

      RxHelper.deployVerticle(vertx, new BookingsStorage(client), options)
            .subscribe(e -> {
               logger.info("Successfully Deployed");
               startFuture.complete();
            }, error -> {
               logger.error("Failed to Deployed", error);
               startFuture.fail(error);
            });
   }
}

BookingsStorage

public class BookingsStorage extends AbstractVerticle {

   private MongoClient mongoClient;

   public BookingsStorage(MongoClient mongoClient) {
      this.mongoClient = mongoClient;
   }

   @Override
   public void start() {
      var eventBus = vertx.eventBus();
      eventBus.consumer("GET_ALL_BOOKINGS_ADDRESS", this::getAllBookings);
   }

   private void getAllBookings(Message msg) {
      mongoClient.rxFindWithOptions("GET_ALL_BOOKINGS_COLLECTION", new JsonObject(), sortByDate())
            .subscribe(bookings -> {
                     // do something with bookings
                     msg.reply(bookings);
                  },
                  error -> {
                     fail(msg, error);
                  }
            );
   }

   private void fail(Message msg, Throwable error) {
      msg.fail(500, "An unexpected error occurred: " + error.getMessage());
   }

   private FindOptions sortByDate() {
      return new FindOptions().setSort(new JsonObject().put("date", 1));
   }
}

HttpRouterVerticle

// inside a router handler: 

 vertx.eventBus().rxSend("GET_ALL_BOOKINGS_ADDRESS", new JsonObject())
                 .subscribe(bookings -> {
                     // do something with bookings
                  },
                    e -> {
                      // handle error
                 });