Gateway Basics

Gateway is a level of abstraction above Connector. It is the bridge between Connector and Handler, making it easier to create event-driven application. Several connectors can be attached to one gateway, after which any requests routed to the gateway will be multicasted to the attached connectors’ producers.

The complete architecture of gateways is:

Gateway comprises of Incoming Sink and Outgoing Sink:

Incoming sink

This sink accepts events from various types of dispatcher, including consumers, timers, producer and programmatically from handlers.

Consumers:

Consumers read messages from a datasources (file, message queues, etc.) or accept messages from external system (e.g using a web server), then convert it to a Message and put into the Gateway’s incoming sink. Consumer can sometimes be a timer which schedules messages to be generated and be put into the incoming sink. Each timer will accept a Supplier<Message>.

Producers:

Response from the producers can be put it into the incoming sink, making them available to be consumed by other handlers.

Handlers:

Handlers can manually create the message and programmatically put it into the incoming sink.

After a message is put into the incoming sink, it will be routed to different handlers based on the configured policies and rules. The corresponding handlers will then be executed with the following parameters:

executionContext:

contains the Message to be consumed, the DeferredObject to be fulfilled and the caller (the gateway that this message comes from). Only the first call to resolve() or reject() will be considered, after that all subsequent calls are ignored.

applicationContext

contains all application-related information, including access to gateways, configurations, etc.

Outgoing sink

Execution strategies

Using gateways

To create a gateway, attach connectors and bind handlers

var appContext = new GridgoContext();
var connector = appContext.openGateway("Orders")
                          .attachConnector("kafka:orders?brokers=127.0.0.1")
                          .attachConnector(someConnector)
                          .subscribe(handler1).withPolicy(somePolicy).finishSubscribing()
                          .subscribe(handler2).when(someCondition).with(someStrategy).finishSubscribing();

Attempting to open gateway with the same name will cause a DuplicateGatewayException

To access an opened gateway:

var gateway = appContext.findGateway("Orders"); // return a Optional<Gateway>
if (gateway.isPresent()) {
    // do some works with the gateway
}

or access the list of opened gateway

var gateways = appContext.getGateways(); // return a List<Gateway>