Java-->多线程断点续传

--> 在多线程复制的基础上加入断点续传的功能

-->Test 测试类

 package com.dragon.java.multithreaddownload;

 import java.io.File;

 /*
  * 多线程断点续传（下载）
  */
 public class Test {
     public static void main(String[] args) {
         // @SuppressWarnings("resource")
         // Scanner scanner = new Scanner(System.in);
         // System.out.println("请输入文件路径：");
                 // 直接写死文件和线程数..
         File srcFile = new File("F:/mp4/01_Java.mp4");
         // System.out.println("请输入线程数：");
         // int n = scanner.nextInt();
         int n = 4;
         if (!srcFile.exists()) {
             System.out.println("该文件不存在！");
         }

         File desFile = new File(srcFile.getParent(), "new" + srcFile.getName());

                 // 单线程复制长度
         long partLenghth = srcFile.length() / n + 1;
         for (int i = 1; i < n + 1; i++) {
                         // 启动线程
             new MyThread(srcFile, desFile, partLenghth * (i - 1), partLenghth
                     * i).start();

         }
     }
 }

--> MyThread 线程实现类

 package com.dragon.java.multithreaddownload;

 import java.io.File;
 import java.io.IOException;
 import java.io.RandomAccessFile;

 public class MyThread extends Thread {
     private File srcFile;
     private File desFile;
     private long start;
     private long end;

     MyThread() {
         super();
     }

     MyThread(File srcFile, File desFile, long start, long end) {
         super();
         this.srcFile = srcFile;
         this.desFile = desFile;
         this.start = start;
         this.end = end;
     }

     @Override
     public void run() {
                 // 创建配置文件存储中断时的文件指针
         File configFile = new File(desFile.getParent(), Thread.currentThread()
                 .getId() + ".config");
         if (!configFile.exists() && desFile.exists()) {

 System.out.println(Thread.currentThread().getName() + "已经完成了下载");
             return;
         }
                 // 将流写在try() 中可以不需手动关闭流
         try (RandomAccessFile rafSrc = new RandomAccessFile(srcFile, "r");
                 RandomAccessFile rafDes = new RandomAccessFile(desFile, "rw");
                 RandomAccessFile rafConfig = new RandomAccessFile(configFile,
                         "rw");) {

             rafConfig.setLength(8);

                         // 当不是第一次下载时，将配置文件中的指针传递给开始指针
             long pointer = rafConfig.readLong();
             if (pointer != 0) {
                 start = pointer;
             }
             rafSrc.seek(start);
             rafDes.seek(start);

 // 显示完成度 System.out.println(Thread.currentThread().getName() + "已下载："
                     + ((float) pointer / srcFile.length()) * 100 + "%");

             int len = -1;
             byte[] buffer = new byte[32];
             while ((len = rafSrc.read(buffer)) != -1) {
                 rafDes.write(buffer, 0, len);
                 pointer = rafSrc.getFilePointer();
                 rafConfig.seek(0);
                 rafConfig.writeLong(pointer);
                                 // 当每个线程完成任务时结束线程
                 if (rafSrc.getFilePointer() >= end) {
                     break;
                 }
             }
         } catch (IOException e) {
             System.out.println(e);
         }
                 // 删除配置文件
         configFile.delete();
     }
 }