How to connect a Camel route to a REST Service to receive an event-stream

Question

Within a Camel route I need to connect to a service with a HTTP GET request and leave the connection open to receive events. The Camel connection never receives events from the service.

I can use Postman to perform this operation successfully:successful Postman connection, so I know the service is running as expected.

My Camel Route calls the service endpoint as a GET with the same parameters used in Postman in the header of this call:

.setHeader(Exchange.HTTP_METHOD, constant(org.apache.camel.component.http.HttpMethods.GET))
.setHeader("Connection", simple("keep-alive"))
.setHeader("Accept", simple("text/event-stream"))
.setHeader("Accept-Encoding", simple("gzip, deflate, br"))
.setHeader("Postman-Token", simple("6ec7dfb3-6a4e-46ad-9f29-329a854f2649"))
.to("http://localhost:5000/events")

I know the service receives this call and creates event messages to send back, but they're never received by the Camel route. Also, a Postman connection that's made at the same time as the Camel connection does receive the event messages.

Q) What is the correct way to configure a Camel route to receive service events?

Answer 1

OkHttpClient can be used with a RealEventSource and a custom EventSourceListener to receive server side events.

Steps:

1. create a custom Listener class that extends EventSourceListener and has methods for handling events from the RealEventSource.

• onEvent() processes the server-side-event data received from the Service
• onOpen(), onClose(), onFailure() may also be useful

2. create a Client class that instantiates your Listener

• creates the OkHttpClient
• creates the Request to send to the Service
• creates a RealEventSource(Request, Listener)
• calls realEventSource.connect(okHttpClient);

3. create a AccessToken class for the values needed to access your Service
4. in the camel Route class instantiate the Client

• Client myClient = new Client();

5. in Route.configure() call

   .process(new Processor() { public void process(Exchange exchange) throws Exception { myClient.Connect(); } })

References: OkHttpClient realeventsource