In your sentences: "for one year" - for about 12 months "all year" - since the start of the year (e.g. 2013), usually said near the end of the year.

- I have been working all year : I have been working for at least 12 months. ( This can very from you working at least 12 months, but you could be doing more than one job. - depending on how you state it and the context of the rest.) - I have been working for one year : I have been working for 12 months. ( so for a full year ) :if you said, "I have been working here for one year." - Then you worked there for 12 full months. hope that helps!