package NetworkProgramming;

import java.io.InputStream;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.URL;

public class DownUtil {

//顶一下载资源的路径

private String path;

//指定下载资源的文件保存位置

private String targetFile;

//定义下载资源的线程数量

private int threadNum;

//定义下载文件的总大小

private int fileSize;

//定义下载的Thread对象

private DownThread[] threads;

public DownUtil(String path, String targetFile, int threadNum) {

this.path = path;

this.targetFile = targetFile;

this.threadNum = threadNum;

//初始化Threads数组

threads = new DownThread[threadNum];

}

public void download() throws Exception {

URL url = new URL(path);

HttpURLConnection conn = (HttpURLConnection) url.openConnection();

conn.setConnectTimeout(5 * 1000);

conn.setRequestMethod("GET");

conn.setRequestProperty(

"Accept",

"image/gif,image/jepg,image/pjpeg,application/x-shockwave-flash," +

"application/xaml+xml,application/vnd.ms-xpsdocument,application/x-ms-xbap," +

"application/x-ms-application,application/vnd.ms-excel," +

"application/vnd.ms-powerpoint,application/msword,*/*"

);

conn.setRequestProperty("Accept-Language", "zh-CN");

conn.setRequestProperty("Charset", "UTF-8");

conn.setRequestProperty("Connection", "Keep-Alive");

//得到文件大小

fileSize = conn.getContentLength();

conn.disconnect();

int currentPartSize = fileSize / threadNum + 1;

RandomAccessFile file = new RandomAccessFile(targetFile, "rw");

//设置本地文件大小

file.setLength(fileSize);

file.close();

for (int i = 0; i < threadNum; i++) {

//计算每个线程的下载开始位置

int startPos = i * currentPartSize;

//每个线程使用一个RandomAccessFile进行下载

RandomAccessFile currentPart = new RandomAccessFile(targetFile, "rw");

//定位下载位置

currentPart.seek(startPos);

//创建线程

threads[i] = new DownThread(startPos, currentPartSize, currentPart);

threads[i].start();

}

}

public double getCompleteRate() {

//统计多个线程已经下载的总大小

int sumSize = 0;

for (int i = 0; i < threadNum; i++) {

sumSize += threads[i].length;

}

//返回百分比

return sumSize * 1.0 / fileSize;

}

private class DownThread extends Thread {

//当前线程的下载位置

private int startPos;

//当前线程需要下载的文件大小

private int currentPartSize;

//当前线程需要下载的文件快

private RandomAccessFile currentPart;

//定义该线程已下载的字节数

public int length;

public DownThread(int startPos, int currentPartSize, RandomAccessFile currentPart) {

this.startPos = startPos;

this.currentPart = currentPart;

this.currentPartSize = currentPartSize;

}

@Override

public void run() {

try {

URL url = new URL(path);

HttpURLConnection conn = (HttpURLConnection) url.openConnection();

conn.setConnectTimeout(5 * 1000);

conn.setRequestMethod("GET");

conn.setRequestProperty(

"Accept",

"image/gif,image/jepg,image/pjpeg,application/x-shockwave-flash," +

"application/xaml+xml,application/vnd.ms-xpsdocument,application/x-ms-xbap," +

"application/x-ms-application,application/vnd.ms-excel," +

"application/vnd.ms-powerpoint,application/msword,*/*"

);

conn.setRequestProperty("Accept-Language", "zh-CN");

conn.setRequestProperty("Charset", "UTF-8");

InputStream inputStream = conn.getInputStream();

//跳过startPos个字节,表明该线程只下载自己负责的部分文件

inputStream.skip(startPos);

byte[] buffer = new byte[1024];

int hasRead = 0;

//读取网络文件

while (length < currentPartSize && (hasRead = inputStream.read(buffer)) >0) {

currentPart.write(buffer, 0, hasRead);

length += hasRead;

}

currentPart.close();

inputStream.close();

} catch (Exception e) {

e.printStackTrace();

}

}

}

public static void main(String[] args) throws Exception {

//初始化对象

final DownUtil downUtil = new DownUtil("https://i2.hdslb.com/bfs/archive/7aaabf9a278e7147c928bfad79c64b8d5628447c.jpg@160w_100h.jpg",

"test.png", 4);

downUtil.download();

new Thread(

() -> {

while (downUtil.getCompleteRate() < 1) {

//每隔0.1s查询一次任务完成进度

//GUI程序中可根据改进度绘制进度条

System.out.println("已完成:" + downUtil.getCompleteRate());

try {

Thread.sleep(5);

} catch (Exception e) {

e.printStackTrace();

}

}

}

).start();

}

}