Java / Android 基于Http的多线程下载的实现

jopen 9年前

转载请标明出处:http://blog.csdn.net/lmj623565791/article/details/26994463

有个朋友需要个多线程现在的例子,就帮忙实现了,在此分享下~

先说下原理,原理明白了,其实很简单:

a、对于网络上的一个资源,首先发送一个请求,从返回的Content-Length中回去需要下载文件的大小,然后根据文件大小创建一个文件。

this.fileSize = conn.getContentLength();// 根据响应获取文件大小  File dir = new File(dirStr);  this.localFile = new File(dir, filename);  RandomAccessFile raf = new RandomAccessFile(this.localFile, "rw");  raf.setLength(fileSize);  raf.close();

b、根据线程数和文件大小,为每个线程分配下载的字节区间,然后每个线程向服务器发送请求,获取这段字节区间的文件内容。

conn.setRequestProperty("Range", "bytes=" + startPos + "-"        + endPos);// 设置获取实体数据的范围

c、利用RandomAccessFile的seek方法,多线程同时往一个文件中写入字节。

raf.seek(startPos);  while ((len = is.read(buf)) != -1)  {   raf.write(buf, 0, len);  }
分析完了原理就很简单了,我封装了一个类,利用这个类的实例进行下载,所需参数:下载资源的URI, 本地文件路径,线程的数量。

package com.zhy.mutilthread_download;    import java.io.File;  import java.io.IOException;  import java.io.InputStream;  import java.io.RandomAccessFile;  import java.net.HttpURLConnection;  import java.net.URL;    public class MultipartThreadDownloador  {     /**    * 需要下载资源的地址    */   private String urlStr;   /**    * 下载的文件    */   private File localFile;   /**    * 需要下载文件的存放的本地文件夹路径    */   private String dirStr;   /**    * 存储到本地的文件名    */   private String filename;     /**    * 开启的线程数量    */   private int threadCount;   /**    * 下载文件的大小    */   private long fileSize;     public MultipartThreadDownloador(String urlStr, String dirStr,     String filename, int threadCount)   {    this.urlStr = urlStr;    this.dirStr = dirStr;    this.filename = filename;    this.threadCount = threadCount;   }     public void download() throws IOException   {    createFileByUrl();      /**     * 计算每个线程需要下载的数据长度     */    long block = fileSize % threadCount == 0 ? fileSize / threadCount      : fileSize / threadCount + 1;      for (int i = 0; i < threadCount; i++)    {     long start = i * block;     long end = start + block >= fileSize ? fileSize : start + block - 1;       new DownloadThread(new URL(urlStr), localFile, start, end).start();    }     }     /**    * 根据资源的URL获取资源的大小,以及在本地创建文件    */   public void createFileByUrl() throws IOException   {    URL url = new URL(urlStr);    HttpURLConnection conn = (HttpURLConnection) url.openConnection();    conn.setConnectTimeout(15 * 1000);    conn.setRequestMethod("GET");    conn.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, */*");    conn.setRequestProperty("Accept-Language", "zh-CN");    conn.setRequestProperty("Referer", urlStr);    conn.setRequestProperty("Charset", "UTF-8");    conn.setRequestProperty(      "User-Agent",      "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");    conn.setRequestProperty("Connection", "Keep-Alive");    conn.connect();      if (conn.getResponseCode() == 200)    {     this.fileSize = conn.getContentLength();// 根据响应获取文件大小     if (fileSize <= 0)      throw new RuntimeException(        "the file that you download has a wrong size ... ");     File dir = new File(dirStr);     if (!dir.exists())      dir.mkdirs();     this.localFile = new File(dir, filename);     RandomAccessFile raf = new RandomAccessFile(this.localFile, "rw");     raf.setLength(fileSize);     raf.close();       System.out.println("需要下载的文件大小为 :" + this.fileSize + " , 存储位置为: "       + dirStr + "/" + filename);      } else    {     throw new RuntimeException("url that you conneted has error ...");    }   }     private class DownloadThread extends Thread   {    /**     * 下载文件的URI     */    private URL url;    /**     * 存的本地路径     */    private File localFile;    /**     * 是否结束     */    private boolean isFinish;    /**     * 开始的位置     */    private Long startPos;    /**     * 结束位置     */    private Long endPos;      public DownloadThread(URL url, File savefile, Long startPos, Long endPos)    {     this.url = url;     this.localFile = savefile;     this.startPos = startPos;     this.endPos = endPos;    }      @Override    public void run()    {     System.out.println(Thread.currentThread().getName() + "开始下载...");     try     {      HttpURLConnection conn = (HttpURLConnection) url        .openConnection();      conn.setConnectTimeout(15 * 1000);      conn.setRequestMethod("GET");      conn.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, */*");      conn.setRequestProperty("Accept-Language", "zh-CN");      conn.setRequestProperty("Referer", url.toString());      conn.setRequestProperty("Charset", "UTF-8");      conn.setRequestProperty("Range", "bytes=" + startPos + "-"        + endPos);// 设置获取实体数据的范围        conn.setRequestProperty(        "User-Agent",        "Mozilla/4.0 (compatible; MSIE 8.0; Windows NT 5.2; Trident/4.0; .NET CLR 1.1.4322; .NET CLR 2.0.50727; .NET CLR 3.0.04506.30; .NET CLR 3.0.4506.2152; .NET CLR 3.5.30729)");      conn.setRequestProperty("Connection", "Keep-Alive");      conn.connect();        /**       * 代表服务器已经成功处理了部分GET请求       */      if (conn.getResponseCode() == 206)      {       InputStream is = conn.getInputStream();       int len = 0;       byte[] buf = new byte[1024];         RandomAccessFile raf = new RandomAccessFile(localFile,         "rwd");       raf.seek(startPos);       while ((len = is.read(buf)) != -1)       {        raf.write(buf, 0, len);       }       raf.close();       is.close();       System.out.println(Thread.currentThread().getName()         + "完成下载  : " + startPos + " -- " + endPos);       this.isFinish = true;      } else      {       throw new RuntimeException(         "url that you conneted has error ...");      }     } catch (IOException e)     {      e.printStackTrace();     }    }     }         }

createFileByUrl方法,就是我们上述的原理的步骤1,得到文件大小和创建本地文件。我在程序使用了一个内部类DownloadThread继承Thread,专门负责下载。download()方法,根据线程数量和文件大小计算每个线程需要下载的字节区间,然后开启线程去下载。

服务器端:我就扔了几个文件在Tomcat根目录做实验,下面是测试代码:

package com.zhy.mutilthread_download;    import java.io.IOException;    public class Test  {     public static void main(String[] args)   {    try    {     new MultipartThreadDownloador("http://localhost:8080/nexus.zip",       "f:/backup/nexus", "nexus.zip", 2).download();    } catch (IOException e)    {     e.printStackTrace();    }     }  }

输出结果:

需要下载的文件大小为 :31143237 , 存储位置为: f:/backup/nexus/nexus.zip  Thread-1开始下载...  Thread-2开始下载...  Thread-3开始下载...  Thread-4开始下载...  Thread-4完成下载  : 23357430 -- 31143237  Thread-2完成下载  : 7785810 -- 15571619  Thread-1完成下载  : 0 -- 7785809  Thread-3完成下载  : 15571620 -- 23357429

截图:



ok,多线程下载介绍完毕,如果代码设计不合理,以及方法使用错误,欢迎各位留言,,,



源码点击下载



来自: http://blog.csdn.net//lmj623565791/article/details/26994463