OPC UA标准，用于编写简单的Java客户端/服务器

Question

I am new to OPC and is required to develop a simple OPC server using Java to test a connection with a OPC client, retrieve data through the server from a database and returning the data to the OPC client. I am having difficulties understanding the standards of OPC UA and would appreciate if anyone could highlight the standards/things to note regarding the standard in the Java OPC UA server application. For example, for a web server, HTTP header is the standard. So while receiving a HTTP request, I can decipher the HTTP header for the content and create a response header in the right format for the client browser to understand.

Answer 1

To be exactly, Read request has an option maxAge:

The maxAge parameter is used to direct the Server to access the value from the underlying data source, such as a device, if its copy of the data is older than that which the maxAge specifies. If the Server cannot meet the requested maximum age, it returns its “best effort” value rather than rejecting the request. (OPC UA Spec Part 4)