Java多线程下载

通过多线程对文件分段进行下载，废话不多说，直接上代码

package com.download.test;

 
import java.io.File;
import java.net.HttpURLConnection;
import java.net.URL;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
 
/*
 * 多线程下载
 */
public class DownloadTest {
    //初始一个带缓存的线程池
    public static ExecutorService executorService = Executors.newCachedThreadPool();
    
	public static void main(String[] args) throws Exception {
        String path = "http://csdn-app.youkuaiyun.com/csdn.apk";
        new DownloadTest().download(path,3);
    }
     
    public void download (String path,int threadsize) throws Exception{
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setConnectTimeout(3000);
        conn.setRequestMethod("GET");
        if(conn.getResponseCode() == 200){
            //获取网络文件长度,文件的大小（单位是字节）
            int length = conn.getContentLength();   
            //新建本地文件保存下载数据
            File file = new File("D:/"+getFilename(path));
            //计算每条线程负责下载的数据量
            int block = length%threadsize==0 ? length/threadsize : length/threadsize+1;
            //开启指定数目的线程同时下载
            for(int threadid = 0; threadid < threadsize; threadid++){
            	executorService.execute(new DownloadThread(threadid,block,url,file,length));
                //new DownloadThread(threadid,block,url,file,length).start();
            }
        }else{
            System.out.println("下载失败！");
        }
    }
     
    private String getFilename(String path) {
        return path.substring(path.lastIndexOf("/")+1);
    }
}

下载线程类

package com.download.test;

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

public class DownloadThread extends Thread{
	private static int finished;
    private int threadid;   //线程编号
    private int block;      //下载块大小
    private URL url;        //下载链接
    private File file;      //下载数据保存文件
    private int length;		//文件长度
    
    public DownloadThread(int threadid, int block, URL url, File file,int length) {
        this.threadid = threadid;
        this.block = block;
        this.url = url;
        this.file = file;
        this.length = length;
    }

    public void run() {
        int start = threadid * block;       //本线程下载数据写入文件开始位置
        int end = (threadid+1) * block - 1; //本线程下载数据写入文件结束位置
        try {
            //创建一个随机访问文件流对象
            RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
            //文件指针偏移至正确写入位置
            accessFile.seek(start);
            HttpURLConnection conn = (HttpURLConnection) url.openConnection();
            conn.setConnectTimeout(3000);
            conn.setRequestMethod("GET");
            //设置请求数据的范围
            conn.setRequestProperty("Range", "bytes="+start+"-"+end);
            if(conn.getResponseCode() == 206){//状态码206:（部分内容） 服务器成功处理了部分 GET 请求
                InputStream inStream = conn.getInputStream();
                long time = System.currentTimeMillis();
                byte[] buffer = new byte[1024];
                int len = 0;
                while((len = inStream.read(buffer)) != -1){
                    accessFile.write(buffer, 0, len);
                    finished += len;
                    int i = finished * 100 / length;
                    //System.out.println(finished+"----------"+length);
                    if(System.currentTimeMillis()-time>500 || finished>=length){
                    	time = System.currentTimeMillis();
                    	System.out.println("下载进度："+i+"%");
                    }
                }
                accessFile.close();
                inStream.close();
            }
            System.out.println("第"+(threadid+1)+"部分下载完成");
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}