A N M Bazlur Rahman: A few things-
- The basics syntax-e.g. you can write loops, switch, if-else etc
- Object-oriented concept
- Collection framework
- Date time
- A bit servlet API
- A basic concept of concurrency ( threading)
- A build tool ( e.g. maven/Gradle)
A majority of applications are written using Spring Framework, so once you have done learning the above, you can start learning this framework. But I would assume you would learn this once you are in the industry.
You can target this list; it is pretty achievable. The most important thing is that you’ll have to practice enough that these are on your muscle memory; for example, when you have to write a loop, you don’t have to think; instead, it will automatically come to your finger. That’s the kind of skill you’d need.
However, this list isn’t complete, but by the time you finish this list, you will know what to do next by yourself. Of course, if you still have questions, you can always come here and ask questions.
All the best.