How to write data with FileOutputStream without losing old data?
Use the constructor that takes a File and a boolean
FileOutputStream(File file, boolean append)
and set the boolean to true. That way, the data you write will be appended to the end of the file, rather than overwriting what was already there.
Use the constructor for appending material to the file:
FileOutputStream(File file, boolean append)
Creates a file output stream to write to the file represented by the specified File object.
So to append to a file say "abc.txt" use
FileOutputStream fos=new FileOutputStream(new File("abc.txt"),true);