One option is to use a proxy server like KepServerEx www.kepware.com to access OPC DA data via OPC UA and use https://github.com/wadesalazar/NIFI-OPCUA
If you need more direct access to OPC DA you have 2 choices. 1) build native Java client and wrap it with the service and/or processor Nifi APIs. or 2) build / obtain a Windows executable program that can be called or interfaced with Java and Nifi
The reason why 1) is so difficult and 2) is necessary is COM. COM was, is, a
binary-interface standard for introduced by Microsoft in
1993. It is used to enable inter-process communication and dynamic object
creation Ironically I believe it was an attempt at an "open" standard for RPC.
There
is no public Java implementation for COM and developing for OPC DA /
HDA / A&E in Java is a real pain. The only tried and true path
forward for a native Java OPC DA client is is JInterop
http://www.j-interop.org/ . See http://openscada.org/projects/utgard/
for a reference implementation. J-Interop is old and sparsely
supported There may be a compiler that can create the necessary Java
class files ( similar to what JInterop has provided )
https://msdn.microsoft.com/en-us/library/ms691398(v=vs.85).aspx but it
is in Visual J++ 6.0. ( if you happen to have this please email me
Going with option 2 is better supported but still not easy. You may use a commercial OPC DA stack/client/library, such
as https://www.prosysopc.com/products/ to build an executable that you
can call with nifi execute process or Integrate into a processor using
JNI. This does require your Nifi hosts to be Windows machines.
If
you are looking to stay on Linux but use this approach. A relatively
recent development is Rad Hat's .Net frame work for RHEL, it isnt clear
to me if it supports COM but I believe it may. This might allow one to
use a commercial OPC stack to build an executable that could be used.
I love to help you or anyone else build an OPC DA connector for Apache Nifi. Let me know how I can help.
