Basically you could take the
String representing your root directory. Use that to create a java.io.File.
Using the listFiles method of that File, create an array of Files in that directory.
(This array will contain both files and directories represented by java.io.File objects so you may want to create another method to actually get only files or only the directories)
You can then iterate through this array, using isFile you can determine if the indexed File is indeed a file and if the name equals the name of the file you are looking for. If you find it you are all set.
If you do not find it iterate through the array and recursively send each directory back to this method.
Sorry I did not include code. I thought I had something to recursively list files/directories but could not ifnd it.
If you still have questions I can try again to find it.