попробуйте этот
public void writeFile(String arg1,String arg2) {
try {
if (!dir.exists()) {
if (dir.mkdirs()) {
Toast.makeText(getBaseContext(), "Directory created",
Toast.LENGTH_SHORT).show();
} else {
Toast.makeText(getBaseContext(),
"Error writng file " + filename, Toast.LENGTH_LONG)
.show();
}
}
else {
File file = new File(dir, filename);
if (!file.exists()) {
file.createNewFile();
}
FileWriter fileWritter = new FileWriter(file, true);
BufferedWriter bufferWritter = new BufferedWriter(fileWritter);
bufferWritter.write(arg1 + "\n");
bufferWritter.close();
} catch (Exception e) {
e.printStackTrace();
Toast.makeText(getBaseContext(),
"Error writng file " + e.toString(), Toast.LENGTH_LONG)
.show();
}
}