I'm going to answer your question without discussing the relative merits of Certifications vs "real world experience."
Oracle has a number of Java certificates, starting with "Oracle Certified Associate, Java SE 7
Programmer". More info:http://docs.oracle.com/javase/tutorial/extra/certification/index.html
I found a site for practice tests, and am pleased with what I purchased there: http://enthuware.com
EDIT: Forgot to mention: are you familiar with JavaRanch, and it's "Cattle Drive" course? I don't know that the "Moose Badges" that are earned are that much help, but a couple of the recruiters I've talked to know of this site and course-of-study, and seem to have some respect for it. The main feature is that the emphasis is on code-review and stylistic nit-picking. If you have never coded on a team or never have had your code subject to review, or if you'd like some feedback on best practices, this course might be for you. It is $100 and self-paced, starts very easy and progresses to the use of databases via JSP/Servlets (most advanced "Moose Badge").
Funny, I just read a post yesterday from a fellow, young kid coming up who has earned three different Oracle Certifications and was asking for advice on how to land the "first job" when all the job descriptions are asking for 5 yrs experience.