Slim down java project to ReadExample

[daddebackstrom]

Hello Milo, and thank you so much for letting us use your project to connect to OPC servers :)

I want to use your project to connect to and read ONE value from a Kepware OPC Server Ex V6 instance. I suppose it's the ReadExample class that could be used as a template here?

If I want to extract that example to my own slim project, which jar-files would I need? I obviously don't need the server part...

Regards,
David

[kevinherron]

Hopefully you're using some kind of build tool like Maven or Gradle that resolves dependencies for you.

The main artifact you'll need is sdk-client.jar (and all of its dependencies). The Maven dependency would look something like this:

<dependency>
    <groupId>org.eclipse.milo</groupId>
    <artifactId>sdk-client</artifactId>
    <version>0.5.4</version>
</dependency>

Use the examples as a guide, not a template. I see people trying to copy the structure of ClientExampleRunner into their application and that's not really the point; it just exists to run examples, not as something you should be copying. The stuff to pay attention to is in the example itself.

[daddebackstrom]

Hello again Kevin!

I've come quite far and managed to create a little spring boot application with a REST endpoint where another client is able to call my client and ask for a value (see the code below). My question now is: is this best practice? Doing read after read? Should I have a subscription running instead? I don't want to overload the KepWare server....

Again, thank you so much for taking the time so answer a newbie :)

@RequestMapping("/readnodevalue")
public NodeValue readNodeValue(@RequestParam(value = "nodeId", defaultValue = "") String nodeId) {

    try {
        DataValue dataValue = opcUaClient.readValue(0.0, TimestampsToReturn.Both, new NodeId(2, nodeId)).get();

        String value = dataValue.getValue().getValue().toString();

        logger.info("Identifier={}, Value={}", nodeId, value);

        return new NodeValue(nodeId, value);

    } catch (Exception e) {
        logger.info("Error! - {}", e.getMessage());
        return new NodeValue(nodeId, "0.0");
    }
}

[kevinherron]

I think it probably depends how often the endpoint will be called and if it's always going to be for the same NodeId.

A subscription is generally more efficient but with that you will have more bookkeeping and setup/teardown to do.

[daddebackstrom]

The value will be read at maximum once an hour and right now it will always be the same node.

[kevinherron]

Using a read instead of subscribing is completely fine then.

[daddebackstrom]

Ok, thank you very much Kevin! Your stack works really well, nice job :) Take care