Take some popular ones, like Spring/hibernate, and learn others when you have to in work. Besides, different versions are not that big a hop. You can't remember it well if you don't use it, anyway.
IOC as the core, everything else is extension, know it when you need it. After all, that's still the way most projects use it as of today.
many
【在 m******t 的大作中提到】 : : Don't worry, still useful to finish the Spring 1.1 book. 2.0 introduced many : convenient features, but the philosophy and concepts remain the same.
c*m
16 楼
我觉的也最常用的也就7,8种而已
【在 B*********h 的大作中提到】 : those 23 are the most used, but not all that existed.