java多线程批量下载文件

多线程下载文件

平时开发中有时会用到文件下载，为了提高文件的下载速率，采用多线程下载能够达到事半功倍的效果：

package test;

/**

* 文件下载类

* @author luweicheng

*

*/

import java.io.FileInputStream;

import java.io.FileNotFoundException;

import java.io.IOException;

import java.io.InputStream;

import java.io.RandomAccessFile;

import java.net.HttpURLConnection;

import java.net.URL;

import java.net.URLConnection;

public class DownFile {

private URL fileUrl;// 文件下载路径

private int threadCount;// 文件下载的线程数

private int startPos;// 每个线程下载文件的开始位置

private int size;// 每个线程下载文件的长度

private int fileLength;// 文件总程度

private String pathName;// 下载的文件路径（包含文件名）

private Downthread[] tDownthreads;// 线程数组

public DownFile(URL url, int threadCount, String pathName) throws IOException {

fileUrl = url;

this.threadCount = threadCount;

this.pathName = pathName;

init();

}

/**

* 初始化

*

* @throws IOException

*/

private void init() throws IOException {

tDownthreads = new Downthread[threadCount];

HttpURLConnection conn = (HttpURLConnection) fileUrl.openConnection();

conn.setConnectTimeout(5000);

conn.setRequestMethod("GET");

conn.setRequestProperty("connection", "keep-alive");

fileLength = conn.getContentLength();

System.out.println("文件长度" + fileLength);

size = fileLength / threadCount;

System.out.println("每个下载量==" + size);

conn.disconnect();// 断开链接

}

public URL getFileUrl() {

return fileUrl;

}

public int getThreadCount() {

return this.threadCount;

}

/**

* 开始下载

*/

public void startDown() {

for (int i = 0; i < threadCount; i++) {

try {

RandomAccessFile raFile = new RandomAccessFile(pathName, "rw");

tDownthreads[i] = new Downthread(i * size, raFile, i);

tDownthreads[i].start();

} catch (FileNotFoundException e) {

e.printStackTrace();

}

}

}

/**

* 下载线程类

*

* @author luweicheng

*

*/

class Downthread extends Thread {

private int startPos;// 开始的位置

private InputStream is;

private RandomAccessFile raFile;

private int length;// 下载的文件长度

private int flag;// 线程标志

public Downthread(int startPos, RandomAccessFile raFile, int i) {

this.startPos = startPos;

this.raFile = raFile;

flag = i;

}

@Override

public void run() {

try {

HttpURLConnection connection = (HttpURLConnection) fileUrl.openConnection();

connection.setRequestMethod("GET");

connection.setRequestProperty("connection", "keep-alive");

connection.setConnectTimeout(5 * 1000);

is = connection.getInputStream();

is.skip(startPos);

raFile.seek(startPos);

byte[] buf = new byte[8 * 1024];

int hasread = 0;// 读出的字节数

// 将位置在 startPos - startPos 位置的数据读出写入

while (length < size && (hasread = is.read(buf)) != -1) {

raFile.write(buf, 0, hasread);

length += hasread;

System.out.println("*****线程" + flag + "下载了*********" + length);

}

System.out.println("*******线程" + flag + "下载完成*********");

} catch (IOException e) {

} finally {

try {

is.close();

raFile.close();

} catch (IOException e) {

e.printStackTrace();

}

}

}

}

}

效果展示：

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详细配置信息可以参考这篇文章：

http://blog.ncmem.com/wordpress/2019/08/28/java%e6%89%b9%e9%87%8f%e4%b8%8b%e8%bd%bd/