FileChannel 数据传输（文件拷贝）

import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.IOException;
import java.nio.channels.FileChannel;

public class FileChannelTest {

    public static void main(String[] args) {
        try (
            FileChannel fromChannel = new FileInputStream("files/text.txt").getChannel();
            FileChannel toChannel = new FileOutputStream("files/textTo.txt").getChannel();
        ) {
            // 效率高，底层会利用操作系统的零拷贝进行优化，上限是 2g 数据
            //fromChannel.transferTo(0, fromChannel.size(), toChannel);
            long size = fromChannel.size();
            // left 表示剩余多少字节
            // transferTo() 方法会返回实际传输的字节数，可能为0
            for (long left = size; left > 0; ) {
                left -= fromChannel.transferTo((size - left), left, toChannel);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

}