Hi Joseph,
It would be great if you could tell us from what SAP system you would like to read the data.
At the moment SAP provides two java platforms for On-Premise: SAP NetWeaver AS Java and SAP HANA XS Advanced.
SAP NetWeaver AS Java is a Java EE 5 certified server. A good starting point for developing applications for it is Developing Java EE 5 Applications - SAP Library
In the end of last year, with SPS 11 of SAP HANA, the XS Advanced architecture was introduced. It is based on Cloud Foundry and the microservice architecture. It provides several runtimes, including Apache Tomcat 8 and Aapche TomEE 1.7 which is a Java EE 6 Web Profile certified server. For more information see SAP HANA SPS 11: New Developer Features; XS Advanced. Also a good starting point is the developer guide for XS Advanced that you could find at http://help.sap.com/hana/SAP_HANA_Developer_Guide_for_SAP_HANA_XS_Advanced_Model_en.pdf
Best regards,
Nikolay