Mainframe ... I suggest looking at the IBM Toolbox for Java / JTOpen is a library of Java classes supporting the client/server and internet programming models to a system running OS/400, i5/OS, or IBM i.
If you wanna go deep and do it yourself:
all depends from real business case (what real needs, tasks and goals).
always possible organize process for delegate parts for most relevant tools.
- Mainfraims have database (which is could be DB2 in most cases), Talend support it
- Mainframes supports IBM MQ, Talend as well support it
So it possible todo in Talend what Talend can, and use DB2 or MQ as interface
Of course - possible todo all with different libraries ... but this is would be also not a Talend