"(Whenever the future perfect clause will happen)我在中国工作一年了" seems the simplest way to express future perfect。For example, 到下个月，我在中国工作一年了。I don't see that there is a need for translating "will have", because it is already in the future, and the condition is met. I think the example of "I will have worked in China for one year" is incomplete, because future perfect needs a time marker to be used.

But...I am also a beginner, so if I am wrong please let me know.