How to safely save a file to disk in android?

The typical way to safely create a file on most reasonable platforms (Linux/Android is one of them) is to create a temporary file and then rename the file, as mentioned in the question & answers that you linked to. Note the emphasis on rename; renaming a file is usually an atomic operation within the same filesystem, copying one is not. In addition, this method only requires enough space for a single copy of the data.

Therefore you create a file in the target directory using a temporary name and then use File.renameTo() to give it a proper name. By using a standard naming convention for the temporary files you can always find and delete them, even if your application terminates unexpectedly due to e.g. a device power-off.

If you are really paranoid, you may want to insert a few calls to FileDescriptor.sync() or equivalent...

EDIT:

BTW, you do not mention what kind of IOException your are getting and whether you have tracked down its cause. If it's due to insufficient space, fine, but if we are talking about a faulty SD card, then there is no such thing as "safe" in this case.

EDIT 2:

In order to check the available free space, you can create a File object for the destination directory (i.e. the directory where your file will end up) and call File.getFreeSpace(). Keep in mind that this check does not provide any guarantees - you may still end up without enough space if e.g. another process writes data to the medium.

I know this is too late to answer, but will help anyone who come across this will find it helpful.

You need to use AtomicFile.

Following code snippet may help.

public void writeFile(File file, byte[] data) {
    AtomicFile aFile = new AtomicFile(file);
    FileOutputStream fos = null;

    try {
        fos = aFile.startWrite();
        fos.write(data);
        // Close stream and commit new data.
        aFile.finishWrite(fos);
        fos = null;
    } catch (IOException e) {
        Log.e(TAG, "Cannot write file " + file.getPath(), e);
    } finally {
        if (fos != null) {
            // Something went wrong.
            // Close stream and roll back data.
            aFile.failWrite(fos);
        }
    }
}