1 多线程下载一个文件（普通的java工程：java实现）

来源：互联网发布：诺基亚n9deb的软件编辑：程序博客网时间：2024/05/21 09:34
原理图：
这里写图片描述
结果图：
代码如下：
import java.io.File;import java.io.InputStream;import java.io.RandomAccessFile;import java.net.HttpURLConnection;import java.net.URL;public class M1 {    //下载一个文件的线程数    private static int count = 3;    //下载地址，你替换path的网址就行了    public static String path = "http://img.blog.csdn.net/20160130160136042?watermark/2/text/aHR0cDovL2Jsb2cuY3Nkbi5uZXQv/font/5a6L5L2T/fontsize/400/fill/I0JBQkFCMA==/dissolve/70/gravity/Center";    public static void main(String[] args) {        URL url;        try {            url = new URL(path);            HttpURLConnection connection = (HttpURLConnection)url.openConnection();            connection.setRequestMethod("GET");            connection.setReadTimeout(5000);            connection.setConnectTimeout(5000);            if(connection.getResponseCode() == 200) {                //拿到要下载文件的大小                int length = connection.getContentLength();                //指定临时文件的路径和文件名                File file = new File(getFileName(path));                //创建随机文件存储对象                RandomAccessFile raf = new RandomAccessFile(file, "rwd");                //创建临时文件的大小，和服务器文件一模一样                raf.setLength(length);                //计算每个线程下载的字节数                int size = length / count;                for(int i = 0; i < count; ++i) {                    //计算3个线程下载数据的开始位置和结束位置                    int startIndex = i * size;                    int endIndex = (i + 1) * size - 1;                    //如果是最后一个线程，name结束位置做特殊处理                    if(i == count - 1) {                        endIndex = length - 1;                    }                    System.out.println("线程" + i  + "的开始位置：" + startIndex                            +"-------结束位置：" + endIndex);                    new MyDownloadThread(i, startIndex, endIndex).start();                }            }        } catch (Exception e) {            e.printStackTrace();        }    }    public static String getFileName(String path2) {        int index = path2.lastIndexOf("/");        return path2.substring(index + 1);    }}class MyDownloadThread extends Thread {    int threadId;    int startIndex;    int endIndex;    public MyDownloadThread(int i, int startIndex, int endIndex) {        this.threadId = i;        this.startIndex = startIndex;        this.endIndex = endIndex;    }    @Override    public void run() {        try {            URL url = new URL(M1.path);            HttpURLConnection connection = (HttpURLConnection)url.openConnection();            connection.setRequestMethod("GET");            connection.setReadTimeout(5000);            connection.setConnectTimeout(5000);            //设置请求数据的范围            connection.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);            //206说明请求的是部分数据，而200是请求的全部数据            if (connection.getResponseCode() == 206) {                InputStream inputStream = connection.getInputStream();                byte[] b = new byte[1024];                //当前下载的总子节数                int total = 0;                int len = 0;                //指定临时文件的路径和文件名                File file = new File(M1.getFileName(M1.path));                RandomAccessFile raf = new RandomAccessFile(file, "rwd");                //设置线程从哪个位置开始写入数据到临时文件                raf.seek(startIndex);                while((len = inputStream.read(b)) != -1) {                    raf.write(b,0,len);                    total += len;                    System.out.println("线程" + threadId + " 已经下载" + total);                }                raf.close();                System.out.println("线程" + threadId + "下载完毕----------");            }        } catch (Exception e) {            e.printStackTrace();        }    }}
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