Hi,

I recently got assigned to a project that uses the Prosys OPC UA Java SDK. We’ve got the problem that network connection stability issues can result in our client never receiving alarm events from the server. Going a step further, I’d also like to be able to make our application receive missed alarm events after a JVM restart (e.g. due to application restarts or deployments).

I spent the last 2 days reading Prosys Java SDK tutorials, JavaDocs, blog articles, and tried to get my OPC UA client to somehow get alarm events from the server that were missed. Here’s where I currently stand:

What works: my client connects to the server, creates a MonitoredEventItem with a listener, and receives notifications when I trigger alarms on the server side. I also created a MonitoredDataItem with a listener to see how that compares to the MonitoredEventItem – this also works.
What doesn’t work as I expect: when I shut down the client, trigger an alarm on the server, and restart the client, then this alarm event is not received by the client. The current MonitoredDataItem’s value is queried immediately.

Some things I tried:

– client.setAutoReconnect(true) / client.setKeepSubscriptions(true). The server keeps the sessions and subscriptions for a while after the client shuts down (JVM termination), but after connecting again, a new session/subscription is assigned and the previous ones just lie around on the server and never get used again.

– client.setSessionName(“SomeConstant”). The server still created new sessions (same name, but different ids), rather than reusing an existing session.

– client.setAutoReconnect(false) / client.reconnect(). This doesn’t work after a JVM restart; it seems this is only possible if you’ve called connect() once. But connect() creates a new session/subscription, which I don’t want.

– subscription.readAll(0d, TimestampsToReturn.Both). This only returned data items, but no missed alarm events.

Note: I’m using version 1.5.0 of the Prosys SDK. Also, I tried these tests with the non-secure security mode and an anonymous user token policy.

What else can I try? Does the OPC UA standard or Prosys Java SDK support sessions/subscriptions reconnects after JVM restarts? If not, what’s the most robust possible solution to avoid missing alarm events?

Thanks for any help,

Ben