多线程下载辅助类实现

如需转载，必须注明转自： http://blog.csdn.net/xiazdong/article/details/7738298

使用声明：

类名：MultiThreadDownloadUtil

API：

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

path：文件URL；

count：线程数量；

[java] view
plaincopy

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：

[java] view
plaincopy

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);

}

}

将此文件下载到工程目录后，运行可用；