【Java学习】模拟断点下载(文件断点复制)(21)

学了随机访问流 RandomAccessFile 可以操作文件指针,就想模拟一下断点下载.
将g:\模拟软件.rar
复制到g:\模拟软件copy.rar
利用一次复制任意一部分,下次继续从上次下载到的指针位置开始下载,不覆盖已经复制了一部分的源文件,继续拼接成完整的文件.

package com.westos.morning;

import java.io.*;
import java.util.Scanner;

public class Demo5 {
    public static void main(String[] args) throws IOException {
        String srcRount="g:\\模拟软件.rar";//源文件路径
        String detRount="g:\\模拟软件copy.rar";//目的文件路径
        File srcfile = new File(srcRount);//封装源文件
        RandomAccessFile in = new RandomAccessFile(srcfile, "rw");
        FileOutputStream out = new FileOutputStream(detRount, true);//复制后的文件路径
        RandomAccessFile pointerFile = new RandomAccessFile("pointer.pro", "rw");//用于保存文件指针位置

        Scanner scanner = new Scanner(System.in);
        System.out.println("********************************************************************");
        System.out.println("*描述:\n" +
                "*一.按1后,如果输入的兆b大于源文件兆b数,将全部下载.\n" +
                "*二.按1后,如果输入的兆b数小于源文件兆b,则断点下载.再运行按2即可接连断点全部下载\n" +
                "*三.不按1直接按2,将全部下载." );
        System.out.println("********************************************************************\n");
        System.out.println("按1下载指定字节数,按2下载其余部分");
        if (scanner.hasNextLine()) {
            int num = Integer.parseInt(scanner.nextLine());
            switch (num) {
                case 1:
                    pointerFile.writeInt(num);//写入标记1
                    System.out.println("输入你先下载多少mb(整数):");
                    int mb = Integer.parseInt(scanner.nextLine());
                    long l = pauseDownload(in, out, mb);//拿到下载多少mb时候的指针位置
                    pointerFile.writeLong(l);//写入保存复制文件当前复制到的指针
                    pointerFile.seek(0);//置用于保存指针的pointer.txt文件指针到开头
                    break;
                case 2:
                    if (pointerFile.length() == 0) {
                        //这是不按1下载前一部分,而是直接按2,下载后一半部分
                        //这时候就下载全部
                        continueDownload(in, out, 0);
                        pointerFile.writeInt(num);//写入标记2
                        pointerFile.writeLong(0);
                        pointerFile.seek(0);//置用于保存指针的pointer.txt文件指针到开头
                        break;
                    } else if (pointerFile.readInt() == 1) {
                        long p = pointerFile.readLong();//读出文件上次的指针
                        //System.out.println(p);
                        continueDownload(in, out, p);//从上次下载指针的下一位置继续下载
                        pointerFile.seek(0);//置用于保存指针的pointer.txt文件指针到开头
                        pointerFile.writeInt(num);//写入标记2
                        pointerFile.writeLong(0);
                        pointerFile.seek(0);//置用于保存指针的pointer.txt文件指针到开头
                        break;
                    } else {
                        System.out.println("你已经下载了");
                        break;
                    }
                default:
                    System.out.println("输入错误");
                    break;
            }
        }

    }


    private static long pauseDownload(RandomAccessFile in, FileOutputStream out, int mb) throws IOException {
        int len = 0;
        byte[] bytes = new byte[1024];
        while (in.getFilePointer() < mb * 1024 * 1024 && (len = in.read(bytes)) != -1) {
            out.write(bytes, 0, len);
            out.flush();
        }
        return in.getFilePointer();
    }

    private static void continueDownload(RandomAccessFile in, FileOutputStream out, long p) throws IOException {
        int len = 0;
        byte[] bytes = new byte[1024];
        while ((len = in.read(bytes)) != -1) {
            if (in.getFilePointer() > p)
                out.write(bytes, 0, len);
            out.flush();
        }

    }
}

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结果:

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谢谢!