I got a Java certification at a large enterprise years and years ago. The only benefit I gained from it was that it forced me to systematically learn the language in greater detail than I would have otherwise. I personally found the experience valuable, and I think I have a higher level of skill with Java than many of my coworkers as a result, but no one is going to accept the certificate as proof of that.
tl;dr: Certification tests provide decent motivation to keep you trudging through hundreds of pages of technical documentation.
If you work for a proper tech company or startup as software engineer, no one will care about Java certifications.
If your goal is to work at some large enterprise(where tech is not the focus) or banks, then it might be useful.