OneAgent SDK documentation (https://github.com/Dynatrace/OneAgent-SDK) describes how to implement tracing for Custom Service methods.
The docs for het java implementation however (https://github.com/Dynatrace/OneAgent-SDK-for-Java) have no section on this. Does this mean that it is not possible for java?
This is likely because we already support definition of custom services for Java through Dynatrace with no requirement to modify the code. You just tell Dynatrace which methods should become custom services: https://www.dynatrace.com/support/help/how-to-use-dynatrace/transactions-and-services/configuration/...