JAVA記憶體對映檔案實現多執行緒下載

壹頁書發表於2014-05-15
Java記憶體執行緒
JAVA NIO記憶體對映檔案可以實現多執行緒下載
首先，使用firefox下載一個tomcat


JAVA多執行緒下載程式

  1. import java.io.FileNotFoundException;
  2. import java.io.IOException;
  3. import java.io.InputStream;
  4. import java.io.RandomAccessFile;
  5. import java.net.HttpURLConnection;
  6. import java.net.URL;
  7. import java.nio.MappedByteBuffer;
  8. import java.nio.channels.FileChannel.MapMode;

  10. class Worker implements Runnable {
  11.     //多執行緒下載的數量
  12.     private static int THREADS = 4;
  13.     //每個執行緒下載開始的位置
  14.     private int startIndex;
  15.     //每個執行緒下載內容的長度
  16.     private int length;
  17.     //檔案儲存位置
  18.     private String localFile;
  19.     //遠端檔案的流
  20.     InputStream in;

  22.     private Worker(String urlFile, String localFile, int startIndex, int length) throws IOException {
  23.         this.startIndex = startIndex;
  24.         this.length = length;
  25.         this.localFile = localFile;
  26.         init(urlFile);
  27.     }

  29.     /**
  30.      *    主執行緒開啟網路檔案,先分割為指定的大小，然後開啟多執行緒下載
  31.      */
  32.     public Worker(String urlFile, String localFile) throws IOException {
  33.         this.localFile = localFile;
  34.         int contentLength = init(urlFile);
  35.         int step = contentLength / THREADS;
  36.         int index = 0;
  37.         for (int i = 0; i < THREADS; i++) {
  38.             if (i == 0) {
  39.                 this.startIndex = 0;
  40.                 this.length = step;
  41.                 new Thread(this).start();
  42.             } else if (i == THREADS - 1) {
  43.                 Worker worker = new Worker(urlFile, localFile, index, contentLength - index);
  44.                 new Thread(worker).start();
  45.             } else {
  46.                 Worker worker = new Worker(urlFile, localFile, index, step);
  47.                 new Thread(worker).start();
  48.             }
  49.             index = index + step;
  50.         }
  51.     }

  53.     private int init(String urlFile) throws IOException {
  54.         URL url;

  56.         url = new URL(urlFile);

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

  60.         connection.setConnectTimeout(5 * 1000);
  61.         connection.setRequestMethod("GET");
  62.         connection.setRequestProperty("Accept", "image/gif, image/jpeg, image/pjpeg, image/pjpeg, " + "application/x-shockwave-flash, application/xaml+xml, "
  63.                 + "application/vnd.ms-xpsdocument, application/x-ms-xbap, " + "application/x-ms-application, application/vnd.ms-excel, " + "application/vnd.ms-powerpoint, application/msword, */*");
  64.         connection.setRequestProperty("Accept-Language", "zh-CN");
  65.         connection.setRequestProperty("Charset", "UTF-8");
  66.         connection.setRequestProperty("Connection", "Keep-Alive");
  67.         InputStream in = connection.getInputStream();
  68.         this.in = in;
  69.         return connection.getContentLength();
  70.     }

  72.     @Override
  73.     public void run() {
  74.         System.out.println(this);
  75.         try {
  76.             RandomAccessFile localRandomFile = new RandomAccessFile(localFile, "rw");
  77.             MappedByteBuffer buffer = localRandomFile.getChannel().map(MapMode.READ_WRITE, startIndex, length);
  78.             int i = 0;
  79.             in.skip(startIndex);
  80.             while (i < length) {
  81.                 buffer.put((byte) in.read());
  82.                 i++;
  83.             }
  84.             buffer.force();
  85.             in.close();
  86.             localRandomFile.close();
  87.         } catch (FileNotFoundException e) {
  88.             e.printStackTrace();
  89.         } catch (IOException e) {
  90.             e.printStackTrace();
  91.         }
  92.     }

  94.     @Override
  95.     public String toString() {
  96.         return "Worker [localFile=" + localFile + ", startIndex=" + startIndex + ", length=" + length + "]";
  97.     }

  99.     public static void main(String[] args) throws IOException {
  100.         new Worker("http://mirrors.cnnic.cn/apache/tomcat/tomcat-7/v7.0.53/bin/apache-tomcat-7.0.53.zip", "tomcat.zip");
  101.     }

  103. }

比對下載的檔案

來自 “ ITPUB部落格 ” ，連結：http://blog.itpub.net/29254281/viewspace-1162157/，如需轉載，請註明出處，否則將追究法律責任。

相關文章