I got a couple of SAML implementation questions to clear up my confusion ...
I need to implement SSO in a java web app.
In order to do so, do I need Shi
You should post such questions to the relevant mailing lists run by the Shibboleth Project.
OpenSAML is a very low level toolkit for implementing SAML solutions, Shibboleth is a SSO package for web applications supporting SAML that happens to be built with OpenSAML. Building security solutions is complex and requires expertise. If you don't have that expertise, you'll do a bad job of it, and OpenSAML is not documented such that a typical developer could build a solution from scratch.
Consider using a complete implementation, whether it's Shibboleth or something else. If you can't live with Apache and native code and need Java, then you should try one of the extant Java SP options that exist. Even if they were inadequate, you should build on them and not duplicate them.