If you have been looking for a simple and straight forward method for rooting your Sony Xperia Z2 "Rafaelbelo" has posted an in depth guide to get you there. This method does not require that you have a locked bootloader. It doesn't even require that you have a custom recovery installed. Basically this method requires you to downgrade the your device and then run towelroot! That is pretty simple if you ask me. Some other devices, especially the Galaxy S5 also achieve root in this way. Head to the link below for the proper downloads and the full instructions.
Via XDA