Java多线程下载辅助类达成

发布时间：2021-11-23 13:11:52 所属栏目：教程来源：互联网

导读：使用声明：类名：MultiThreadDownloadUtil API： (1)download(String path,int count); path：文件URL； count：线程数量； package org.xiazdong.multidownload.util; import Java.io.File; import java.io.InputStream; import java.io.RandomAccessFile;

使用声明：

类名：MultiThreadDownloadUtil

API：

(1)download(String path,int count);

path：文件URL；

count：线程数量；

package org.xiazdong.multidownload.util;

import Java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;


public class MultiThreadDownloadUtil{
    private static int filesize;
    private static int block;
    private static String filename;
    private static int downloadsize;
    private class MyThread extends Thread{
        private int i;          //线程ID
        private String path;    //下载文件的URL

        public MyThread(int i, String path) {
            this.i = i;
            this.path = path;
            downloadsize = 0;
        }
        @Override
        public void run() {
            try{
                System.out.println("线程"+(i+1)+"开始下载");
                //1.打开文件，并定位位置
                RandomAccessFile raf = new RandomAccessFile(new File(filename), "rwd");
                raf.seek(i*block);          //定位到此线程要负责下载的位置
                int start = i*block;
                int end = (i+1)*block-1;
                //2.连接服务器
                URL url = new URL(path);
                HttpURLConnection conn = (HttpURLConnection)url.openConnection();
                conn.setRequestMethod("GET");
                conn.setRequestProperty("range", "bytes="+start+"-"+end);   //发出请求头

                if(conn.getResponseCode()==206){        //注意：分段下载的返回码为206，而不是200
                    InputStream in = conn.getInputStream();
                    int length = 0;
                    byte[]data = new byte[1024];
                    while((length=in.read(data))!=-1){
                        raf.write(data,0,length);       //写入本地文件
                    }
                }
                //显示下载进度
                downloadsize += (end-start);
                System.out.println("已下载"+downloadsize/1024.0+"k,共"+filesize/1024.0+"k");
                //3.关闭文件
                raf.close();
                System.out.println("线程"+(i+1)+"结束下载...");
            }
            catch(Exception e){
                e.printStackTrace();
            }
        }
    }
    /**
     * 下载文件
     * @param path          URL
     * @param threadcount   线程数
     * @throws Exception
     */
    public static void download(String path,int threadcount) throws Exception{
        filename = path.substring(path.lastIndexOf('/')+1);
        filesize = getFileSize(path);
        block = getBlockSize(filesize,threadcount);
        createLocalRandomFile(filesize);
        MultiThreadDownloadUtil mdu = new MultiThreadDownloadUtil();
        for(int i=0;i<threadcount;i++){
            mdu.new MyThread(i,path).start();
        }
    }
    /**
     * 创建一个本地文件，并设置文件的大小
     * @param filesize
     * @throws Exception
     */
    private static void createLocalRandomFile(int filesize) throws Exception {
        RandomAccessFile raf = new RandomAccessFile(new File(filename), "rwd");
        raf.setLength(filesize);
        raf.close();
    }
    /**
     * 根据文件总大小和线程数求出每个线程要下载的数据量
     * @param filesize
     * @param threadcount
     * @return
     */
    private static int getBlockSize(int filesize, int threadcount) {
        return filesize%threadcount==0?filesize/threadcount:(filesize/threadcount+1);
    }
    /**
     * 求出文件总大小
     * @param path
     * @return
     * @throws Exception
     */
    private static int getFileSize(String path) throws Exception{
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection)url.openConnection();
        conn.setRequestMethod("GET");
        if(conn.getResponseCode()==200){
            return conn.getContentLength();
        }
        else{
            return 0;
        }
    }
}
测试类：

package org.xiazdong.download;

import org.xiazdong.multidownload.util.MultiThreadDownloadUtil;


public class MultiThreadDownloader {

    public static void main(String[] args) throws Exception {
        int threadCount = 3;    //指定线程数量
        String path = "http://dlc2.pconline.com.cn/filedown_61761_6694063/drivethelife2010_pconline_setup.exe"; //指定下载文件路径
        MultiThreadDownloadUtil.download(path, threadCount);
    }
}

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