Question

I have program in which I have to load a PNG as a String and then save it again, but after I save it it becomes unreadable. If I open both the loaded PNG and the saved String in the editor, I can see that java created linebreaks all over the file. If this is is the problem, how can I avoid this?

    public static void main(String[] args)
    {
        try
        {
            File file1 = new File("C://andim//testFile.png");
            StringBuffer content = new StringBuffer();
            BufferedReader reader = null;
            reader = new BufferedReader(new FileReader(file1));
            String s = null;         
            while ((s = reader.readLine()) != null) 
            {
                content.append(s).append(System.getProperty("line.separator"));                      
            }
            reader.close();
            String loaded=content.toString();
            File file2=new File("C://andim//testString.png");
            FileWriter filewriter = new FileWriter(file2);
            filewriter.write(loaded);           
            filewriter.flush();
            filewriter.close();
        }
        catch(Exception exception)
        {
            exception.printStackTrace();
        }

    }

Answer 1

I have program in which I have to load a PNG as a String and then save it again, but after I save it it becomes unreadable.

Yes, I’m not surprised. You’re treating arbitrary binary data as if it’s text data (in whatever your platform default encoding is, to boot). It’s not. Don’t do that. It’s possible that in some encodings you’ll get away with it – until you start trying to pass the string elsewhere in a way that strips unprintable characters etc.

If you must convert arbitrary binary data to text, use base64 or hex. If possible, avoid the conversion to text in the first place though. If you just want to copy a file, use InputStream and OutputStream – not Reader and Writer.

This is a big general point: keep data in its “native” representation as long as you possibly can. Only convert data to a different representation when you absolutely have to, and be very careful about it.