Seriously want to know how to change logstash @timestamp to specified timezone

the input @timestamp = "2016-09-01T10:05:16.490Z"
and I want to change it to "+08:00" timezone.
so ,the output @timestamp should be "2016-09-01T18:05:16.490Z"

And the answer or discuss are not allowed to talk about "do not do this ..." or "it's not recommend to change .."
I really serious want to know "how" not "don't " cuz I won't put the logs into ES. It's just a collection of logs and I should know when the log arrived.