Java NIO內存映射文件可以實現多線程下載
首先，使用Firefox下載一個Tomcat
Java多線程：一道阿裡面試題的分析與應對 http://www.linuxidc.com/Linux/2014-03/98715.htm
Java多線程下載程序
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 {
//多線程下載的數量
private static int THREADS = 4;
//每個線程下載開始的位置
private int startIndex;
//每個線程下載內容的長度
private int length;
//文件保存位置
private String localFile;
//遠程文件的流
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);
}
/**
* 主線程打開網絡文件,先分割為指定的大小，然後開啟多線程下載
*/
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");
}
}
比對下載的文件
Java1.5後的多線程框架 http://www.linuxidc.com/Linux/2014-02/96879.htm
Java多線程和同步的理解 http://www.linuxidc.com/Linux/2013-12/93691.htm
Java中兩種實現多線程方式的對比分析 http://www.linuxidc.com/Linux/2013-12/93690.htm
Java利用多線程計算目錄數據大小 http://www.linuxidc.com/Linux/2013-09/90715.htm
Java多線程向數據庫寫入數據 http://www.linuxidc.com/Linux/2013-09/90297.htm
