Hi,

(Long post, sorry, and I think there is a lot more that should be said, but maybe this will do for now, but yes, should be documented a lot better…)

This has been improving with each release. You’ll want version 4.2.0, that would be the best (https://downloads.prosysopc.com/opcua/Prosys_OPC_UA_SDK_for_Java_4_Release_Notes.html#version-4-2-0), unless you connect to an S7 device (see other latest threas of this forum since we have problems with that currently, in case try 4.1.4). Additionally it should be mentioned that with 4.2.0 connecting might take longer (this is currently directly related to the number of custom Structures since we need to read them all), working on improvements on that for the next release.. (which should be soon).

Basically as it is, any Structure can be handled like this, i.e. “dynamically”, since we enhanced the Structure interface to contain all relevant APIs from SDK’s DynamicStructure in 4.x. Note that this example is missing all error handling etc. This is something I can give right now, making a proper full example will take some time. Let me know if you encounter any issues.

i.e. meaning that the SDK is already doing it dynamically in the latest versions.

Additionally it should be mentioned that Structure has toBuilder which will return a Structure.Builder that will build instances of the same type (initializes with current values of fields). The same builder can obtained from the StructureSpecification.toStructureBuilder(). StructureSpecifications can be obtained from UaClient.getEncoderContext().getStructureSpecification(UaNodeId id) after connecting. And UaNodeId is an “upgraded” NodeId (has UaNamespace object instead of the index, and that in turn contains the namespaceuri; I’ll skip details for now, can be discussed later in some other post if needed), can be made with the static factory methods of that class (via NodeId/ExpandedNodeId + NamespaceTable from the client).

I might need clarifications on what exactly you mean by “caching” here.

StructureSpecification instances are immutable, SDK will keep track of them with the TypeDictionary and/or EncoderContext (basically EncoderContext will delegate to TypeDictionary if needed). If your value is always the same type, i.e. your MonitoredDataItemListener handler is not shared between items, then the Structure.specification() is the same java object each time.

If you see an ExtensionObject, it means that the SDK was not able to decode the Structure (binary-wise they are transmitted as an ExtensionObject within the Variant) for some reason. An ExtensionObject itself is not a Structure, it instead contains the raw binary (or XML or JSON) data plus an encoding id (this is NOT the DataType NodeId). And in some cases within the our SDK it could also hold an already decoded Structure, but if you see an ExtensionObject like that (from the DataValue) then it is not decoded.

You can try passing that ExtensionObject to (UaClient) client.getTypeDictionary().decode(extensionObject). However you’ll most likely get an exception thrown if you received the ExtensionObject in the first place, since SDK should do that part automatically. Basically this API is from the era where this part was not automatic.

Most likely something prevented the TypeDictionary from being properly initialized. If that happened you should see an ERROR or WARN log when you did connect the UaClient. Some servers might define the metadata incorrectly (or it might be missing completely). In those case we cannot do much.

If at all possible, I would recommend to try with the latest version, 4.3.0. One of the main points was improving the initialization process of the TypeDictionary, thus the logging is a lot better there as well. If not all Structure types of the server could not be resolved to StructureSpecifications, it will log on WARN level which could not be resolved. IF the ExtensionObject.getTypeId() you received corresponds to the binary-encoding-id of one of the Structure types that could not be resolved then that is why. And note that the DataType NodeId is different from the binary-encoding-id NodeId (that is the NodeId of HasEncoding non-hierarchical reference target from the DataType that has the BrowseName “Default Binary”).

Hi Hans-Uwe,

Thanks for confirming. This is great to hear.

BR, Jouni