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一、实现单线程下载器

1.1环境准备

开发工具：IDEA
JDK版本：8
编码：utf-8
下载的资源：https://profile-avatar.csdnimg.cn/2fe9f00ded33433385db6b55fc7a4195_weixin_52062043.jpg
我们以我的头像为例

项目目录

Constant：存放常量的类
HttpUtils：http工具包
Downloader：下载器
Main:主类

1.2文件的下载

类似于我们本地文件 从一个磁盘复制到另外一个磁盘。
对于互联网的下载，我们需要将本地和下载服务器建立链接

1.3 主类Main 的实现

public class Main {public static void main(String[] args) {String url = null;Scanner scanner = new Scanner(System.in);if (args == null || args.length<1){while (url==null || " ".equals(url)){url = scanner.nextLine();}}else{url = args[0];}System.out.println("你输入的网址是： "+url);System.out.println("开始下载");Downloader downloader = new Downloader();downloader.download(url);System.out.println("下载完毕");}
}

这里的代码应该就没有多说的了 都很简单，接下来我们就应该去写Downloader的代码了

1.4 Downloader和一些工具类的实现

1、我们来看看Downloader 类的定义。
接下来我们就在download(String url)里写逻辑了

public class Downloader {public void download(String url) {}
}

---

2、首先我们要获取文件名和 文件的保存路径，然后和服务器建立链接
得到链接对象 httpUrlConnection

public void download(String url) {//获取文件名String httpFileName = HttpUtils.getHttpFileName(url);//文件的下载路径httpFileName = Constant.PATH+"\\"+httpFileName;//获取链接对象HttpURLConnection httpUrlConnection = null;try {httpUrlConnection = HttpUtils.getHttpUrlConnection(url);} catch (IOException e) {throw new RuntimeException(e);}}

这里我们用到了 HttpUtils工具类和Constant常量我们去看看怎么实现的吧
HttpUtils

public class HttpUtils {/*** 获取 HttpURLConnection 链接对象* @param url* @return* @throws IOException*/public static HttpURLConnection getHttpUrlConnection(String url) throws IOException {URL httpUrl = new URL(url);//获取链接URLConnection urlConnection = httpUrl.openConnection();//向网站所在的服务器发送标识信息urlConnection.setRequestProperty("User-Agent","Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36 Edg/118.0.2088.46");return (HttpURLConnection)urlConnection;}/*** 获取文件名* @param url* @return*/public static String getHttpFileName(String url){int index = url.lastIndexOf("/");return url.substring(index+1);}
}

这里指的注意了：urlConnection.setRequestProperty("User-Agent","Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36 Edg/118.0.2088.46");这行代码是模仿浏览器对服务器发的请求。怎么知道这个的呢？
1、先打开浏览器 按f12 打开开发者工具，找到网络的选项
然后打开一个网络请求就能看到很多内容了

Constant

public class Constant {public static final  String PATH = "E:\\XBDownloader";
}

---

3、我们有了要保存的位置，就因该看看有没有该文件夹，没有就应该创建

		//判断文件甲是否存在// 创建File对象File path = new File(Constant.PATH);if(!path.exists()){//不存在就创建文件夹boolean mkdirs = path.mkdirs();if(!mkdirs){System.out.println("创建失败");}}

---

4、根据链接对象httpUrlConnection 来下载文件到本地

try(//获得输入流InputStream inputStream = httpUrlConnection.getInputStream();//缓冲流BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);//输出流 把文件缓存到磁盘FileOutputStream fileOutputStream = new FileOutputStream(httpFileName);BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);){int len = -1;while ( (len =bufferedInputStream.read()) != -1){bufferedOutputStream.write(len);}} catch (IOException e) {System.out.println("文件下载失败");throw new RuntimeException(e);} finally {//关闭链接对象httpUrlConnection.disconnect();}

解释
1、InputStream inputStream = httpUrlConnection.getInputStream();：这行代码通过调用httpUrlConnection对象的getInputStream()方法来获取输入流，该输入流包含了从网络URL下载的文件数据。
2、BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);：这行代码创建了一个缓冲输入流对象bufferedInputStream，它包装了之前获取的输入流。缓冲输入流可以提高读取文件的性能，因为它可以减少实际的磁盘I/O操作次数。
3、FileOutputStream fileOutputStream = new FileOutputStream(httpFileName);：这行代码创建了一个文件输出流对象fileOutputStream，它将用于将文件数据写入到本地磁盘上的指定文件名（httpFileName）中。
4、BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);：这行代码创建了一个缓冲输出流对象bufferedOutputStream，它包装了之前创建的文件输出流。缓冲输出流可以提高写入文件的性能，因为它可以减少实际的磁盘I/O操作次数。

1.5 结果

输入我上面提供的资源地址就能下载了

二、加上进度条

文件目录

新增加了DownloaderInfo类

2.1 DownloaderInfo实现

根据进度条可知 这我们应该开的另外一个线程，让它不断的去读取文件大小来统计下载速度
所以我们实现一个 Runnable 接口并重写 run() 方法

public class DownloaderInfo implements Runnable{@Overridepublic void run() {}
}

---

定义成员变量

public class DownloaderInfo implements Runnable{//下载文件总大小private long httpFileContentLength;//本地已经下载的大小public Double finishedSize;//前一次下载大小public  double proDownSize;//本次下载大小public volatile double downSize;public DownloaderInfo() {}public DownloaderInfo(long httpFileContentLength) {this.httpFileContentLength = httpFileContentLength;}
}

这里需要注意 public volatile double downSize;这里加 volatile 关键字。让内存时刻保持最新值，因为这里有两个线程来操作的。
第一个线程 是下载线程 每次都会更新当前值
第二线程就是监控线程，每次读取它来监控下载进度

---

重写 @Override run()方法

@Overridepublic void run() {//计算文件总大小 单位是MString downFileSize = String.format("%.2f",httpFileContentLength/ Constant.MB);//计算每秒下载速度KBint speed = (int)((downSize-proDownSize) / 1024d);proDownSize= downSize;//剩余文件大小double remainSize = httpFileContentLength - finishedSize - downSize;//计算剩余时间double rTime = remainSize / 1024 / speed;String remainTime = String.format("%.1f", rTime);if("Infinity".equals(remainTime)){remainTime = "————";}//已经下载大小String currentFileSize = String.format("%.2f", ((downSize - finishedSize) / Constant.MB));String downInfo = String.format("下载进度：%s mb / %s mb ==== 速度：%s kb/s ====剩余时间 %s 秒",currentFileSize, downFileSize, speed, remainTime);System.out.print("\r");System.out.print(downInfo);}

---

2.2修改Downloader类

既然我们需要时刻监控这个类的下载情况那么我们就需要创建线程
这里我用的是ScheduledThreadPool 线程池 用于创建一个定时任务执行器

添加成员变量 定时任务执行器

private ScheduledExecutorService scheduled = Executors.newScheduledThreadPool(1);

然后在download()方法里添加监控线程

//创建获取下载信息的对象
downloaderInfo = new DownloaderInfo(contentLength);
downloaderInfo.finishedSize=Double.longBitsToDouble(localFileLength) ;
//监控线程
scheduled.scheduleAtFixedRate(downloaderInfo,0,1, TimeUnit.SECONDS);

最后不要忘记释放资源

 } finally {//关闭链接对象httpUrlConnection.disconnect();scheduled.shutdownNow();}

---

2.3更新后的完整Downloader类

package com.xbfinal.core;import com.xbfinal.utils.Constant;
import com.xbfinal.utils.FileUtils;
import com.xbfinal.utils.HttpUtils;import java.io.*;
import java.net.HttpURLConnection;
import java.util.concurrent.Executors;
import java.util.concurrent.ScheduledExecutorService;
import java.util.concurrent.ScheduledThreadPoolExecutor;
import java.util.concurrent.TimeUnit;/*** @version 1.0* @Author 笑霸final* @Date 2023/10/18 18:46* @注释 下载器类*/
public class Downloader {//    private ScheduledExecutorService  scheduled = new ScheduledThreadPoolExecutor(1);
//    private ScheduledExecutorService scheduled = Executors.newScheduledThreadPool(1);private ScheduledExecutorService scheduled = Executors.newScheduledThreadPool(1);public void download(String url) {//获取文件名String httpFileName = HttpUtils.getHttpFileName(url);//文件的下载路径httpFileName = Constant.PATH+"\\"+httpFileName;//获取本地文件大小long localFileLength = FileUtils.getFileSize(httpFileName);//获取链接对象HttpURLConnection httpUrlConnection = null;DownloaderInfo downloaderInfo = null;try {httpUrlConnection = HttpUtils.getHttpUrlConnection(url);//获取下载文件的总大小int contentLength = httpUrlConnection.getContentLength();//判断文件是否已经下载过？if(localFileLength >= contentLength){try{System.out.println("已经下载过无须在下载~~~");return;}finally {//关闭链接对象httpUrlConnection.disconnect();}}//创建获取下载信息的对象downloaderInfo = new DownloaderInfo(contentLength);downloaderInfo.finishedSize=Double.longBitsToDouble(localFileLength) ;//监控线程scheduled.scheduleAtFixedRate(downloaderInfo,0,1, TimeUnit.SECONDS);} catch (IOException e) {throw new RuntimeException(e);}//判断文件甲是否存在// 创建File对象File path = new File(Constant.PATH);if(!path.exists()){//不存在就创建文件夹boolean mkdirs = path.mkdirs();if(!mkdirs){System.out.println("创建失败");}}try(//获得输入流InputStream inputStream = httpUrlConnection.getInputStream();//缓冲流BufferedInputStream bufferedInputStream = new BufferedInputStream(inputStream);//输出流 把文件缓存到磁盘FileOutputStream fileOutputStream = new FileOutputStream(httpFileName);BufferedOutputStream bufferedOutputStream = new BufferedOutputStream(fileOutputStream);){int len = -1;byte[] bytes = new byte[Constant.BYTE_SIZE];while ( (len =bufferedInputStream.read(bytes)) != -1){downloaderInfo.downSize+=len;bufferedOutputStream.write(bytes,0,len);}} catch (IOException e) {System.out.println("文件下载失败");throw new RuntimeException(e);} finally {//关闭链接对象httpUrlConnection.disconnect();scheduled.shutdownNow();}}
}

三、多线程下载器

3.1下载思路

最开始 我们是一个线程负责下，如果我们多个线程下载是不是就需要把资源文件分块？然后不同的线程负责下不同的块！最后拼接起来对吧


每次发送请求给服务器说 下载具体的那一块就行了http协议也支持

目录

3.2 更新HttpUtils类

我们添加新的方法

/*** 分块下载的获取链接* @param url       下载地址* @param startPost 块的起始位置* @param startEnd  块的结束位置* @return*/public static HttpURLConnection getHttpUrlConnection(String url,long startPost,long startEnd) throws IOException {HttpURLConnection httpUrlConnection = getHttpUrlConnection(url);System.out.println("下载的区间是"+startPost+"-"+startEnd );if(startEnd != 0){//第一块+中间数据块httpUrlConnection.setRequestProperty("RANGE","bytes="+startPost+"-"+startEnd);}else{//最后一块的数据httpUrlConnection.setRequestProperty("RANGE","bytes="+startPost+"-");}return httpUrlConnection;}

("RANGE","bytes="+startPost+"-"+startEnd) 这里也是固定的

/*** 获取文件名* @param url* @return*/public static String getHttpFileName(String url){int index = url.lastIndexOf("/");return url.substring(index+1);}

/***获取下载文件的大小* @param url* @return* @throws IOException*/public static long getHttpFileLength(String url) throws IOException {HttpURLConnection httpUrlConnection= null;try{httpUrlConnection = getHttpUrlConnection(url);return httpUrlConnection.getContentLengthLong();}finally {assert httpUrlConnection != null;httpUrlConnection.disconnect();}}

3.3更新后的常量类Constant

public class Constant {public static final  String PATH = "E:\\XBDownloader\\";public static final Double MB = 1024d * 1024d;public static final int BYTE_SIZE = 1024 * 100;public static final int THREAD_NOW = 5;
}

3.4下载任务DownloaderTask的实现

这个类就是我们以后多线的一个线程内,将来开很多线程都是实例化这个类,因为要合并分块,要等所有的分块下载完成后,才能合并,所以需要返回值.
所以我们要实现Callable接口

@Data
@AllArgsConstructor
@NoArgsConstructor
public class DownloaderTask implements Callable<Boolean> {
@Overridepublic Boolean call() throws Exception {}
}

给它添加成员变量

@Data
@AllArgsConstructor
@NoArgsConstructor
public class DownloaderTask implements Callable<Boolean> {//urlprivate String url;//块的起始地址private long startPost;//块的结束地址private long startEnd;//块的编号private int part;
@Overridepublic Boolean call() throws Exception {}
} 

---

接下来我吗就重写call方法

 @Overridepublic Boolean call() throws Exception {//获取文件名String httpFileName = HttpUtils.getHttpFileName(url);//分块的文件名httpFileName +=".temp"+part;//下载路径httpFileName = Constant.PATH+httpFileName;//分块下载的链接HttpURLConnection httpUrlConnection = HttpUtils.getHttpUrlConnection(url, startPost, startEnd);try(InputStream inputStream = httpUrlConnection.getInputStream();BufferedInputStream bis = new BufferedInputStream(inputStream);RandomAccessFile randomAccess = new RandomAccessFile(httpFileName,"rw")){byte[] buffer = new byte[Constant.BYTE_SIZE];int len=-1;//循环读取数据while ((len =bis.read(buffer)) !=-1){//1秒内下载数据之和  (原子类)DownloaderInfo.downSize.add(len);randomAccess.write(buffer,0,len);}}catch (FileNotFoundException e){System.out.println("文件未找到");return false;}catch (Exception e){System.out.println("未知问题");return false;}finally {//释放链接httpUrlConnection.disconnect();}return true;}

3.5更新Downloader

添线程池成员变量(负责多线程下载)

 //任务线程池对象private ThreadPoolExecutor poolExecutor = new ThreadPoolExecutor(Constant.THREAD_NOW, // 核心线程数Constant.THREAD_NOW, // 最大线程数0, TimeUnit.SECONDS, // 空闲线程存活时间，这里设置为0，表示线程不会自动终止new ArrayBlockingQueue<>(Constant.THREAD_NOW) // 任务队列，用于存储待执行的任务
);

添加文件切分的方法

 /*** 文件切分* @param url* @param futureList*/public void split(String url , ArrayList<Future> futureList){try {//获取下载文件大小long httpFileLength = HttpUtils.getHttpFileLength(url);//计算切分后文件的大小long size= httpFileLength/Constant.THREAD_NOW;//计算分块个数for (int i = 0; i < Constant.THREAD_NOW; i++) {//下载起始位置long startPost = i*size;//计算结束位置long startEnd;if(i==Constant.THREAD_NOW-1){startEnd=0;}else{startEnd=startPost+size;}if(startPost!=0){startPost++;}//创建任务DownloaderTask downloaderTask = new DownloaderTask(url, startPost, startEnd,i);//将任务提交到线程池中Future<Boolean> submit = poolExecutor.submit(downloaderTask);futureList.add(submit);}} catch (IOException e) {throw new RuntimeException(e);}}

---

合并文件的方法

/*** 合并文件的方法* @param fileName* @return*/public boolean merge(String fileName){System.out.print("\r");System.out.println("开始合并文件");byte[] buffer = new byte[Constant.BYTE_SIZE];int len = -1;try( RandomAccessFile accessFile = new RandomAccessFile(fileName,"rw")){for (int i = 0; i < Constant.THREAD_NOW; i++) {try( FileInputStream fileInputStream = new FileInputStream(fileName+".temp"+i);BufferedInputStream bis = new BufferedInputStream(fileInputStream)){while ((len = bis.read(buffer)) != -1){accessFile.write(buffer,0,len);}}}System.out.print("\r");System.out.println("文件合并完毕");} catch (FileNotFoundException e) {System.out.println("文件未找到");return false;} catch (IOException e) {System.out.println("未知错误");return false;}return true;}

---

最后清空临时文件

  /*** 清空临时文件* @param fileName* @return*/public boolean clearTemp(String fileName){for (int i = 0; i < Constant.THREAD_NOW; i++) {File file = new File(fileName + ".temp" + i);file.delete();}return true;}

3.6Downloader中的download()方法

public void download(String url) {//获取文件名String httpFileName = HttpUtils.getHttpFileName(url);//文件的下载路径httpFileName = Constant.PATH+httpFileName;//获取本地文件大小long localFileLength = FileUtils.getFileSize(httpFileName);//获取链接对象HttpURLConnection httpUrlConnection = null;DownloaderInfo downloaderInfo = null;try {httpUrlConnection = HttpUtils.getHttpUrlConnection(url);//获取下载文件的总大小int contentLength = httpUrlConnection.getContentLength();//判断文件是否已经下载过？if(localFileLength >= contentLength){try{System.out.println("已经下载过无须在下载~~~");return;}finally {//关闭链接对象httpUrlConnection.disconnect();}}//创建获取下载信息的对象downloaderInfo = new DownloaderInfo(contentLength);
//            downloaderInfo.finishedSize=Double.longBitsToDouble(localFileLength) ;//监控线程 每1秒执行一次scheduled.scheduleAtFixedRate(downloaderInfo,1,1, TimeUnit.SECONDS);//切分任务ArrayList<Future> list = new ArrayList<>();split(url,list);//获取集合中的数据list.forEach(future -> {try {future.get();//方便后续合并文件 所有文件下载未完成会阻塞} catch (InterruptedException e) {throw new RuntimeException(e);} catch (ExecutionException e) {throw new RuntimeException(e);}} );//合并文件merge(httpFileName);//删除临时文件clearTemp(httpFileName);} catch (IOException e) {throw new RuntimeException(e);} finally {//关闭链接对象httpUrlConnection.disconnect();scheduled.shutdownNow();poolExecutor.shutdownNow();}}

最后运行的结果