Hi guys here is the method for rooting your Galaxy S2 GT I9100 on XXLSJ Jellybean 4.1.2
There's are the Tools needed for gaining Root access
You will need Odin
XXLSJ Firmware Package
Once downloaded, extract the firmware package and open the Odin in your computer.
Turn Off your Galaxy S2 so you can enter recovery mode by pressing the Volume Up key + power button at the same time while the device is turned Off. If the device starts in the normal mode, you need to re try the process of the entering the device into the download mode.
Now Open Odin, One of the ID:COM boces will be yellow this verifies that your phone is successfully connected to your computer.
Now click on PDA and select the .TAR file in the package you downloaded.
Like the picture Check Auto reboot and F.Reset Time.
Hit start button and installation will start.
This might take some time, after installation has finished your phone will reboot, First reboot may take some time.
Congrats, you have successfully rooted Samsung Galaxy S2 on Android 4.1.2 Jelly Bean XXLSJ firmware