Java多线程下载源码

IZZY

2011-11-29

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Java多线程下载源码，仅作参考之用

import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
public class MyThreadDownloader
{
public static void main(String args[])
{
// 下载连接
String downloadURL = "http://localhost:8080/cangjingkong.avi";
// 下载开启线程数
int threadSize = 3;
try
{
new MyThreadDownloader().download(downloadURL, threadSize);
}
catch (Exception e)
{
e.printStackTrace();
}
}
private void download(String downloadURL, int threadSize) throws Exception
{
String fileName = getFileName(downloadURL);
URL url = new URL(downloadURL);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
// 设置超时
connection.setConnectTimeout(5000);
// 设置请求方式
connection.setRequestMethod("GET");
// 获取文件长度
int fileLength = connection.getContentLength();
// 保存文件
File localFile = new File(fileName);
// 临时文件不存内存,直接进行数据读写"rwd"
RandomAccessFile randomAccessFile = new RandomAccessFile(localFile,"rwd");
// 直接创建与服务器获取长度相等的文件
randomAccessFile.setLength(fileLength);
// 文件操作over,关闭
randomAccessFile.close();
// 计算每条线程负责下载的数据量
int downblock = fileLength % threadSize == 0 ? fileLength / threadSize
: fileLength / threadSize + 1;
// 分配每条线程下载任务
for (int threadID = 0; threadID < threadSize; threadID++)
{
//开启多线程下载任务
new DownloadThread(threadID, url, localFile, downblock).start();
}
}
/**
* @param downloadURL
* 下载连接
* @return 返回下载文件名
*/
private String getFileName(String downloadURL)
{
return downloadURL.substring(downloadURL.lastIndexOf("/") + 1);
}
public final class DownloadThread extends Thread
{
private int threadID; // 当前下载线程ID
private URL url; // 下载连接
private File localFile; // 目标文件
private int downblock; // 分段下载长度
private int startPosition; // 开始下载位置
private int endPosition; // 结束下载位置
public DownloadThread(int threadID, URL url, File localFile,
int downblock)
{
this.threadID = threadID;
this.url = url;
this.localFile = localFile;
this.downblock = downblock;
}
public void run()
{
startPosition = threadID * downblock;
endPosition = (threadID + 1) * downblock;
try
{
RandomAccessFile randomAccessFile = new RandomAccessFile(localFile,"rwd");
randomAccessFile.seek(startPosition);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setReadTimeout(5000);
connection.setRequestMethod("GET");
connection.setRequestProperty("Range", "bytes="+startPosition+"-"+endPosition);
InputStream inputStream = connection.getInputStream();
byte[] buffer = new byte[1024];
int len = 0;
while ((len = inputStream.read(buffer)) != -1)
{
randomAccessFile.write(buffer, 0, len);
}
inputStream.close();
randomAccessFile.close();
System.out.println("第"+(threadID+1)+"条线程已经下载完成");
}
catch (FileNotFoundException e)
{
e.printStackTrace();
}
catch (IOException e)
{
e.printStackTrace();
}
}
}
}

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