Is there a LaTex java .jar?

I have been there and here I share with you some ideas which may not be the answer to your question but might be helpful for the work you want to do.

Sometimes ago I developed a java application and for the report generator, I wanted to use LaTeX to achieve some very beautiful reports. While trying to achieve my goal I found some tools (some are java archives and some aren't):

1. New Typesetting System (NTS) is a reimplementation of the typesetting system TeX in Java.
2. JLR by NIXO SOFT as you have also mentioned in your question.
3. For math only there is jLaTeXMath which is a fork of jMathTex.
4. In this StackOverflow question, you can find some suggestions.
5. Here they explain how to run tex on JVM. Have a look at it.

The problem is, none of the solutions above worked me (However at that time I was not aware of the NTS). What I did at the end, was to create my own mini-latex-distribution consisting binaries and packages that I needed for my reports and deployed it with my java application. Sadly, depending on the type of report you want to generate, this mini-distribution might ended up being several hundred megabytes. I'm afraid I don't know (and I'm not sure if exists) any solution which solely rely on java archives (jar).

I'm one of the authors of LaTeX Render Server, which might be used as a starting point. It's just some small REST service, which is accepting raw latex code and will return a url representing a pdf file of the processed output (generated with pdflatex). The output is stored on the file system. The urls are bascically immutable and could be embedded into some webpage/application. It's necessary to use some reverse proxy (nginx/httpd) in front of it for authentication/authorization and failover/scaling purposes.

The library could also be used to embed the renderer with an application, but you'll still need a native installation of LaTeX on the system.