java多线程下载文件

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import java.io.File;
import java.io.InputStream;
import java.io.RandomAccessFile;
import java.net.HttpURLConnection;
import java.net.URL;
public class MulThreadDownload {
public static void main(String[] args) throws Exception {
String path = "http://192.168.1.100:8080/Hello/Big.exe";
new MulThreadDownload().download(path, 3);
}
/**
* 下载文件
*
* @param path
* 网络文件路径
* @param threadSize
* 线程数
* @throws Exception
*/
private void download(String path, int threadSize) throws Exception {
URL url = new URL(path);
HttpURLConnection connection = (HttpURLConnection) url.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(5000);
if (connection.getResponseCode() == 200) {
int length = connection.getContentLength();// 获取网络文件长度
File file = new File(getFileName(path));
// 在本地生成一个长度与网络文件相同的文件
RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
accessFile.setLength(length);
accessFile.close();
// 计算每条线程负责下载的数据量
int block = length % threadSize == 0 ? length / threadSize : length
/ threadSize + 1;
for (int threadId = 0; threadId < threadSize; threadId++) {
new DownloadThread(threadId, block, url, file).start();
}
} else {
System.out.println("download fail");
}
}
private class DownloadThread extends Thread {
private int threadId;
private int block;
private URL url;
private File file;
public DownloadThread(int threadId, int block, URL url, File file) {
this.threadId = threadId;
this.block = block;
this.url = url;
this.file = file;
}
@Override
public void run() {
int start = threadId * block; // 计算该线程从网络文件什么位置开始下载
int end = (threadId + 1) * block - 1; // 计算下载到网络文件什么位置结束
try {
RandomAccessFile accessFile = new RandomAccessFile(file, "rwd");
accessFile.seek(start); //从start开始
HttpURLConnection connection = (HttpURLConnection) url
.openConnection();
connection.setRequestMethod("GET");
connection.setConnectTimeout(5000);
//设置获取资源数据的范围，从start到end
connection.setRequestProperty("Range", "bytes=" + start + "-"
+ end);
//注意多线程下载状态码是 206 不是200
if (connection.getResponseCode() == 206) {
InputStream inputStream = connection.getInputStream();
byte[] buffer = new byte[1024];
int len = 0;
while ((len = inputStream.read(buffer)) != -1) {
accessFile.write(buffer, 0, len);
}
accessFile.close();
inputStream.close();
}
System.out.println("第" + (threadId + 1) + "条线程已经下载完成");
} catch (Exception e) {
e.printStackTrace();
}
}
}
/**
* 获取文件名称
*
* @param path
* 网络文件路径
* @return
*/
private String getFileName(String path) {
return path.substring(path.lastIndexOf("/") + 1);
}
}

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