Write date in data file

i want to write date in excle when run the case

i have two question
1.what can i do ,if i want to user the Relative paths about the excle .
i tried with
FileOutputStream outFile = new FileOutputStream(new File(“'//AM/FormData.xlsx”))
but there has error

java.io.FileNotFoundException: '\AM\FormData.xlsx (The system cannot find the path specified)
2.can i write the date in file under data file ,if can ,how do i?