Java NIO内存映射文件可以实现多线程下载

首先，使用Firefox下载一个Tomcat

Java多线程下载程序

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.nio.MappedByteBuffer;

import java.nio.channels.FileChannel.MapMode;

class Worker implements Runnable {

//多线程下载的数量

private static int THREADS = 4;

//每个线程下载开始的位置

private int startIndex;

//每个线程下载内容的长度

private int length;

//文件保存位置

private String localFile;

//远程文件的流

InputStream in;

private Worker(String urlFile, String localFile, int startIndex, int length) throws IOException {

this.startIndex = startIndex;

this.length = length;

this.localFile = localFile;

init(urlFile);

}

/**

* 主线程打开网络文件,先分割为指定的大小，然后开启多线程下载

*/

public Worker(String urlFile, String localFile) throws IOException {

this.localFile = localFile;

int contentLength = init(urlFile);

int step = contentLength / THREADS;

int index = 0;

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

if (i == 0) {

this.startIndex = 0;

this.length = step;

new Thread(this).start();

} else if (i == THREADS - 1) {

Worker worker = new Worker(urlFile, localFile, index, contentLength - index);

new Thread(worker).start();

} else {

Worker worker = new Worker(urlFile, localFile, index, step);

new Thread(worker).start();

}

index = index + step;

}

}

private int init(String urlFile) throws IOException {

URL url;

url = new URL(urlFile);

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

connection.setConnectTimeout(5 * 1000);

connection.setRequestMethod("GET");

connection.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, " + "application/x-shockwave-flash, application/xaml+xml, "

+ "application/vnd.ms-xpsdocument, application/x-ms-xbap, " + "application/x-ms-application, application/vnd.ms-excel, " + "application/vnd.ms-powerpoint, application/msword, */*");

connection.setRequestProperty("Accept-Language", "zh-CN");

connection.setRequestProperty("Charset", "UTF-8");

connection.setRequestProperty("Connection", "Keep-Alive");

InputStream in = connection.getInputStream();

this.in = in;

return connection.getContentLength();

}

@Override

public void run() {

System.out.println(this);

try {

RandomAccessFile localRandomFile = new RandomAccessFile(localFile, "rw");

MappedByteBuffer buffer = localRandomFile.getChannel().map(MapMode.READ_WRITE, startIndex, length);

int i = 0;

in.skip(startIndex);

while (i < length) {

buffer.put((byte) in.read());

i++;

}

buffer.force();

in.close();

localRandomFile.close();

} catch (FileNotFoundException e) {

e.printStackTrace();

} catch (IOException e) {

e.printStackTrace();

}

}

@Override

public String toString() {

return "Worker [localFile=" + localFile + ", startIndex=" + startIndex + ", length=" + length + "]";

}

public static void main(String[] args) throws IOException {

new Worker("http://mirrors.cnnic.cn/apache/tomcat/tomcat-7/v7.0.53/bin/apache-tomcat-7.0.53.zip", "tomcat.zip");

}

}