Alternative to RandomAccessFile.setLength()

Question

In case the underlining file system does not support RandomAccessFile.setLength(..) operation, is there any equivalent file operation in Java , eg writing empty content until certain size?

Thanks in advance.

Answer 1

Increasing the size can be done quite simply:

File file = new File(filename);
long destSize = 1000000;
long orgSize = file.length();
if (destiSize > orgSize) {
    long diff = destSize - orgSize;
    try (FileOutputStream fos = new FileOutputStream(file, true)) {
        byte[] buf = new byte[4096];
        while (diff > 0) {
            int len = (int) Math.min(buf.length, diff);
            fos.write(buf, 0, len);
            diff -= len;
        }
    }
}

Truncating is harder, because there is no method in RandomAccessFile or other classes, I'm aware of. The "simplest" approach is to create a new file, copy the original data to it, until destSize is reached, delete the old file and rename the new file to the name of the old one.