How to change the file encoding

[大熊]

For work reason, I always process some kinds of file encodings: gbk,
shift-jis, utf8, utf16, ...
By vim, after open or new a file,  I can use ": e ++enc=encoding" or
": w ++enc=encoding" to chang the file encoding which is different
from the default setting.
How do it under emacs, a single command or a package?

Thanks!

-- 
不是所有的特仑苏都是牛奶