高性能文件拷贝

package cn.itcast.nio.c3;

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

public class TestFileChannelTransferTo {
    public static void main(String[] args) {
        try (
                FileChannel from = new FileInputStream("data.txt").getChannel();
                FileChannel to = new FileOutputStream("to.txt").getChannel();
        ) {
            from.transferTo(0, from.size(), to);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}

NIO文件流拷贝文件

使用零拷贝

这样写法有问题 transferTo 方法最多只能传输2G的文件

进行优化代码

package cn.itcast.nio.c3;

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

public class TestFileChannelTransferTo {
    public static void main(String[] args) {
        try (
                FileChannel from = new FileInputStream("data.txt").getChannel();
                FileChannel to = new FileOutputStream("to.txt").getChannel();
        ) {
            // 效率高，底层会利用操作系统的零拷贝进行优化, 2g 数据
            long size = from.size();
            // left 变量代表还剩余多少字节
            for (long left = size; left > 0; ) {
                System.out.println("position:" + (size - left) + " left:" + left);
                left -= from.transferTo((size - left), left, to);
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
}