JCA on Web server

To anyone who may advice:
    I am currently evaluating the feasibility of integration between a web- based application (written in JSP and running on Jakarta Tomcat) and SAP system, in which, I will only want to 'download' data from SAP.
    I have searched in the Internet and found that there are few architectures that could help me in achieving the objective. However, I am confused and would like anyone who may advice to clear my following doubts:
1) What is the differences between J2EE Connector Architecture (JCA) and SAP Java Connector (JCO)?
2) Does J2EE Connector Architecture really need to be implemented on an application server? In order words, can I achieve the above objective by using JCA but still running the system on web- server (particularly Jakarta- Tomcat)
3) What is the best practice to develop such a system (to achieve the above objective)?
4) Any good examples/ references (including source code/ demo page) that I could refer to?
     Thanks.

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