Question regarding the location in a map reduce function

[Markus Pilman]

Hi all,

I am very new to Hadoop and I have a (it seems to me it should be quite simple) 
question regarding MapReduce:

I wanted to implement a simple Map Reduce to create an inverted index over a 
list of files on my DFS. The code is quite easy, but I cannot figure out, how I 
get to the exact location of the string I get the location of the text I am 
analyzing in a map run. So my map function has the following signature:

                public void map(Object key, Text value, Context context)
                                throws IOException, InterruptedException {
                                // my code would go here 
                }

I figured out, that the key is a long - but I could not figure out, what this 
long is. In particular I need to know: 
- on which file am I working
- which line and column

How would I need to do that?

Any help/hint would be very appreciated!

Thanks Markus