Hi Oliver,
Hmm... where to start... 
OK, first, this is the SCN space for SAP HANA Cloud Platform - it's neither for NetWeaver Portal nor NetWeaver AS Java (which provides the foundation support for Java EE technology).
Second, there is no J2EE7. The last J2EE version was 1.4 back in 2003. Assuming you mean Java EE 7.
Also there is no "NetWeaver Portal 7.4 on cloud". If you mean SAP HANA Cloud Portal, that's a different product which is *not* based on NetWeaver Portal. You can find more info in the SAP HANA Cloud Portal space.
Finally, when you say "We want to integrate J2EE7 under NetWeaver" this assumes you have a server implementing the Java EE 7 standard which you want to somehow integrate with SAP NetWeaver. I don't think you can do that natively. Perhaps you mean instead NetWeaver AS Java to implement Java EE 7? In any case, if you have more specific questions about any of the mentioned products, please feel free to post them in the respective SCN spaces.
HTH!
--Vlado