java 文件拷贝

public static void forTransfer(String f1, String f2) throws Exception {
long length = 2097152000;
FileInputStream in = new FileInputStream(f1);
FileOutputStream out = new FileOutputStream(f2);
FileChannel inc = in.getChannel();
FileChannel outc = out.getChannel();
while (inc.position() != inc.size()) {
long duration = inc.size() - inc.position();
if (duration < 2097152000)
length = duration;
else
length = 2097152000;
inc.transferTo(inc.position(), length, outc);
inc.position(inc.position() + length);
}
inc.close();
outc.close();
}