You might get a better response if you ask this question here: Java SDK Application Development
However, I don't think the version of the SDK that you're using will work with Java 1.8 - it was published for probably Java 1.5 or 1.6, but has worked for you with 1.7 with no issues. However, my understanding is that there have been some internal changes in 1.8 that might cause it to not work. You might try upgrading to SP7, which I believe is the latest version, but I'm not absolutely certain that will work. Also, CRS 2008 went out of support at the beginning of this year, so you won't be able to get any help from SAP Support with it.
-Dell