NIO之ByteBuffer

0 <= mark <= position  <= limit <= capacity

clear（扩）：(position,limit),It sets the limit to the capacity and the position to zero
flip(部分回退，级联)： (position,limit) ,It sets the limit to the current position and then sets the position to zero.
reset（部分回退）：(position),Resets this buffer's position to the previously-marked position.
rewind（倒带，彻底回退）：(position),It leaves the limit unchanged and sets the position to zero
mark:(mark),Sets this buffer's mark at its position.