使用HttpUrlConnection多线程下载文件

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package com.example.administrator.myapplication;import java.io.IOException;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.MalformedURLException;import java.net.URL;/** * Created by Mr.MJ on 2017/1/22. */public class DownUtil {    //定义下载的资源路径    private String path;    //下载文件保存路径    private String targetFile;    //定义下线线程条数    private int threadNum;    //定义下载线程的对象    private DownThread[] downThreads;    //下载文件大小    private int fileSize;    public DownUtil(String path, String targetFile, int threadNum) {        this.path = path;        this.targetFile = targetFile;        this.threadNum = threadNum;        //初始化downThreads数组        downThreads=new DownThread[threadNum];    }    public  void download(){        try {            URL url=new URL(path);            HttpURLConnection conn= (HttpURLConnection) url.openConnection();            conn.setConnectTimeout(5*1000);            conn.setRequestMethod("GET");            conn.setRequestProperty("Accept","image/gif,image/jpeg,image/pjpeg,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("Acceppt-Language","zh-CN");            conn.setRequestProperty("Charset","UTF-8");            conn.setRequestProperty("Connection","Keep_Alive");            //得到文件的大小            fileSize= conn.getContentLength();            int currentPartSize=fileSize/threadNum+1;            RandomAccessFile file=new RandomAccessFile(targetFile,"rw");            file.setLength(fileSize);            file.close();            for(int i=0;i<threadNum;i++){                //定义每个线程下载的起始位置                int startPos=i*currentPartSize;                RandomAccessFile currentPart=new RandomAccessFile(targetFile,"rw");                //定义该线程的下载位置                currentPart.seek(startPos);                downThreads[i]=new DownThread(startPos,currentPartSize,currentPart);                downThreads[i].start();            }        } catch (MalformedURLException e) {            e.printStackTrace();        } catch (IOException e) {            e.printStackTrace();        }    }    //计算进度条进度     public double getComplete(){        int sizeSum=0;        for(int i=0;i<threadNum;i++){            sizeSum+=downThreads[i].length;        }        return  sizeSum*1.0/fileSize;    }    private class DownThread extends Thread{        //当前线程的下载位置        private int startPos;        //当前线程负责下载的文件大小        private int currentPartSize;        public DownThread(int startPos,int currentPartSize,RandomAccessFile currentPart) {            this.startPos = startPos;            this.currentPartSize=currentPartSize;            this.currentPart=currentPart;        }        //当前线程需要下载的文件块        private RandomAccessFile currentPart;        //定义线程已下载的字节数        private int length;        @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/jpeg,image/pjpeg,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("Acceppt-Language","zh-CN");                conn.setRequestProperty("Charset","UTF-8");                conn.setRequestProperty("Connection","Keep_Alive");                InputStream inputStream = conn.getInputStream();                skipFully(inputStream,startPos);                byte[] buffer=new byte[1024];                int hasRead=0;                while(length<currentPartSize&&(hasRead=inputStream.read(buffer))>0){                    currentPart.write(buffer,0,hasRead);                    length+=hasRead;                }                currentPart.close();                inputStream.close();            } catch (MalformedURLException e) {                e.printStackTrace();            } catch (IOException e) {                e.printStackTrace();            }        }    }        public static void skipFully(InputStream inStream,long bytes) throws IOException {            long remainning=bytes;            long len=0;            while(remainning>0){                inStream.skip(remainning);                remainning-=len;            }        }}
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