The user can decompile the code with the jad command:
jad
jad com.example.demo.arthas.user.UserController{{execute T2}}
jad com.example.demo.arthas.user.UserController
The --source-only option can only print out the source code:
--source-only
jad --source-only com.example.demo.arthas.user.UserController{{execute T2}}
jad --source-only com.example.demo.arthas.user.UserController