Honestly, for the effort you would need to go to in rooting the device, installing required services/software and then maintaining it, surely it would be much better to rewrite it as an android app or maybe use something like cordova. This has the added advantage of being easier to roll out to multiple devices should the need arise.

Ehm...

I have two web applications, one use java/tomcat/postgresql, another php/mysql. I need to run them in offline mode on tablet. Thus I have to make decision rewrite them into ordinal android applications, or use as is.

If you want to run something locally in an Android device then you have to make them run as an Android app. Or as part of one.

So, do you see any big disadvantages in compare with ordinal Android app, in installation oracle jvm, php, mysql, postgresql prebuilded for arm cpu into rooted android? Note, that web application will have only one user/client in such case.

If whoever is going to use this doesn't mind about the huge overhead (relative to usual portable devices capabilities), then it's fine. I don't see this happening, though.

Look, I don't want to sound rude, but who gave you such a silly idea? (trying too hard to not say something else over here). The programs you mention were clearly not intended for execution inside such a device. Some of them might even need a full rewrite in order to even launch.

Going into details, some of the disadvantages are these:

• Higher CPU and RAM consumption, specially RAM. And you need power to keep data in RAM so...
• Higher battery consumption, due to the first. And the fact you would be actually running several applications instead of one.
• One of the required technologies might (will) not work. Android does not bring your usual Oracle Java SE VM with JIT Compillation and like 3 garbage collectors to choose from, it uses either Dalvik VM or that new one whose name I don't remember. The default public libraries and APIs are different. Even the internal OS doesn't bring all the binaries a standard Linux distro does, and you would need an app like BusyBox in order to install them.
• Will surely require root. Users are often discouraged of rooting their devices because they usually end up bricking them, one way or another, and because it voids any active guarantee. Good luck convincing them to do it without saying the phrase "free gems for Clash Royale" at least once.
• Those technologies are intended for use by several users. What's the point of going full client/server if only one user will use the server?

Besides, you have Java, C and SQLite at your disposal, all out of the box and properly optimized for use in mobile devices. Why not use that in a mobile device application?

Finally, I'm not saying that what you have in mind is impossible, because technically it should be possible, but is that effort worth it?