If you know php, how much time does it take to learn jsp??

Jsp?

At least 3, but better count with 4

JSP like Java Server Pages?

If you know Java, 1d..

JSP is basically Java. As a Java dev, it took me like half a day. Some ground principles are similar to PHP, others are not. In the end, it's another tool you can learn quickly, but mastery will take a long time. Not that you necessarily should master JSPs in 2k18 by the way...

Jsp is now legacy stuff. It was a nice approach back in a day. Now it's pushed off the scene bcz all the things that make it similar to php are in fact flaws of one or another sort.

You can learn it for knowledge base but I urge you to use smth else [unless you're bound to jsp in some legacy codebase].
The best scenario would to only use java for bkend. Leave f-end for tools which are designed for it: js, angular, vue, wtv.

Jsf, gwt, other attempts to bring java to f-end seemed promissing. But they weren't. While these technologies do in fact deliver, they waste wayyy more time, energy and server resources than, say, using angular would.

@netikras Agreed. but you'd be surprised how many banks still use JSPs. Also, Liferay...

@piehole please don't mention that pile of garbage making everyone's life miserable. Fuck I hate liferay.... I even have a separate pack of Ibuprofen dedicated to the times I have to deal with LR. The pack is almost empty now. Bought it 2 weeks ago.

I do have a clue how widely used all these legacy farts are. I'm the one who has to work with them 😁
but there's not a single reason in the world to start new projects with legacy tech. These projects will be doomed from the first day.

@netikras I got an 8-month gig for Liferay, because I could see a lot of companies in my area were searching for people with JEE/LR/JSP knowledge. So I thought, why not, must be a sexy technology. Heh...

Well, I didn't hate it, but man, the docs are utter shit, the community is utterly clueless, and what should take 5 minutes takes hours to google, and further hours to debug/test. Like, try sorting your articles based on the number of comments within a certain time limit, I dare ya. A function that you get by default in many CMS', we spent days implementing. Honestly, it was an experience, but I'm glad that gig has passed... :))