[Xperia Tablet Z Q&A, Help & Troubleshooting] davidzou2131:
No problem.

Requirements

Program to open ZIP files

Flashtool (flashtool.net/downloads.php)

Flash mode and Fastboot drivers installed (Comes with Flashtool. Find the installer at C:\Flashtool\drivers\)

A few things you should know about recovery

If you plan on using an official Sony ROM with an unlocked bootloader, the recovery needs to be part of the kernel image.

Sony's official kernel images do not contain a recovery.

The kernel gets overwritten when you flash new ROMs (Official and Custom), so you will lose recovery every time you flash a ROM.

Thus you must reflash the kernel with recovery every time you change ROMS.

Kernel's for different versions of ROMs should not be used interchangeably.

It always best to use the kernel made for the ROM.

Flash official ROM before flashing recovery

If you are planning on using an official ROM, flash the official ROM in Download Mode before flashing the recovery (for the reason mentioned above - kernel gets overwritten).

You should wipe USERDATA to minimise compatibility issues.

Do this first before proceeding.

Downloading a kernel with recovery

Fellow xda member [NUT] has an awesome kernel builder tool which allows you to create kernel images with built in recoveries.

Head over to nut.xperia-files.com and navigate to XZDualRecovery > Kernel Builder

Check the checkbox "Yes, I have unlocked my bootloader!".

Select the Make and model of your device (Xperia Tablet Z SGP321 in your case).

Then select the firmware version you will be using (10.7.A.0.228 in your case).

Cross your fingers. If someone has already uploaded the kernel for that version, you can simply download the link provided. Otherwise you will need to upload the kernel. If you have an FTF, simply open it as a zip file and upload the kernel.sin inside.

Flashing Kernel with Recovery

Open the zip file downloaded from the Kernel Builder and open the tmp folder. Extract the boot.img file inside the tmp folder to somewhere on your computer.

Open Flashtool.

Click on the Flash Icon.

Select Fastboot mode.

Click "Select Kernel to Flash".

Put device into Fastboot mode. (2012+ devices: Press and hold VOL+ button while plugging in USB cable)

Once connected, a file selection dialogue will show. Select the boot.img file extracted earlier. You may need to select the type of file (sin, elf, img) before you can see the file in the explorer.

Flashing will start immediately after selection. Check the log and ensure there are no errors.

Unplug the USB cable.

You now have recovery (Two recoveries to be specific - as XZDualRecovery has PhilZ and TWRP).

I would recommend TWRP as it is easier to use and has more features than PhilZ (Based on CWM).

The VOL+ key is associated with PhilZ and the VOL- key for TWRP.

To enter recovery, simply turn the device on and when the notification LED turns Magenta (Pink) start pressing the button associated with the recovery you want to use.

e.g. Press VOL- a few times for TWRP.

Flashing zips

Copy your ZIPs to your SD card.

In TWRP, tap the Install button.

Select the zip file you want to flash

Swipe to the right to start flashing.

Rooting

Download the latest SuperSU zip (download.chainfire.eu/supersu)

Copy to SD card.

Flash zip in recovery.

Enjoy root.