Android 实现网络多线程APK文件下载

(转自：http://blog.csdn.net/mad1989/article/details/38421465)

实现原理

(1)首先获得下载文件的长度，然后设置本地文件的长度。

(2)根据文件长度和线程数计算每条线程下载的数据长度和下载位置。

如：文件的长度为6M，线程数为3，那么，每条线程下载的数据长度为2M，每条线程开始下载的位置如下图所示：

例如10M大小，使用3个线程来下载，

线程下载的数据长度   (10%3 == 0 ？ 10/3:10/3+1) ,第1，2个线程下载长度是4M，第三个线程下载长度为2M
下载开始位置：线程id*每条线程下载的数据长度 = ?
下载结束位置：（线程id+1）*每条线程下载的数据长度-1=?

之前练习时的一个demo，不多说了，直接上代码吧，有关断点续传，需要使用数据库，不再加了，网上有很多成熟的项目可以直接用。

实例

MainApp：

 package com.amos.app;

 import java.io.File;
 import java.io.IOException;
 import java.net.MalformedURLException;
 import java.net.URL;
 import java.net.URLConnection;
 import com.amos.download.R;
 import android.annotation.SuppressLint;
 import android.app.Activity;
 import android.os.Bundle;
 import android.os.Environment;
 import android.os.Handler;
 import android.os.Message;
 import android.util.Log;
 import android.view.View;
 import android.view.View.OnClickListener;
 import android.widget.ProgressBar;
 import android.widget.TextView;
 import android.widget.Toast;

 /**
  * @author yangxiaolong
  * @2014-5-6
  */
 public class MainApp extends Activity implements OnClickListener {

     private static final String TAG = MainApp.class.getSimpleName();

     /** 显示下载进度TextView */
     private TextView mMessageView;
     /** 显示下载进度ProgressBar */
     private ProgressBar mProgressbar;

     @Override
     protected void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.progress_activity);
         findViewById(R.id.download_btn).setOnClickListener(this);
         mMessageView = (TextView) findViewById(R.id.download_message);
         mProgressbar = (ProgressBar) findViewById(R.id.download_progress);
     }

     @Override
     public void onClick(View v) {
         if (v.getId() == R.id.download_btn) {
             doDownload();
         }
     }

     /**
      * 使用Handler更新UI界面信息
      */
     @SuppressLint("HandlerLeak")
     Handler mHandler = new Handler() {
         @Override
         public void handleMessage(Message msg) {

             mProgressbar.setProgress(msg.getData().getInt("size"));

             float temp = (float) mProgressbar.getProgress()
                     / (float) mProgressbar.getMax();

             int progress = (int) (temp * 100);
             if (progress == 100) {
                 Toast.makeText(MainApp.this, "下载完成！", Toast.LENGTH_LONG).show();
             }
             mMessageView.setText("下载进度:" + progress + " %");

         }
     };

     /**
      * 下载准备工作，获取SD卡路径、开启线程
      */
     private void doDownload() {
         // 获取SD卡路径
         String path = Environment.getExternalStorageDirectory()
                 + "/amosdownload/";
         File file = new File(path);
         // 如果SD卡目录不存在创建
         if (!file.exists()) {
             file.mkdir();
         }
         // 设置progressBar初始化
         mProgressbar.setProgress(0);

         // 简单起见，我先把URL和文件名称写死，其实这些都可以通过HttpHeader获取到
         String downloadUrl = "http://gdown.baidu.com/data/wisegame/91319a5a1dfae322/baidu_16785426.apk";
         String fileName = "baidu_16785426.apk";
         int threadNum = 5;
         String filepath = path + fileName;
         Log.d(TAG, "download file  path:" + filepath);
         downloadTask task = new downloadTask(downloadUrl, threadNum, filepath);
         task.start();
     }

     /**
      * 多线程文件下载
      *
      * @author yangxiaolong
      * @2014-8-7
      */
     class downloadTask extends Thread {
         private String downloadUrl;// 下载链接地址
         private int threadNum;// 开启的线程数
         private String filePath;// 保存文件路径地址
         private int blockSize;// 每一个线程的下载量

         public downloadTask(String downloadUrl, int threadNum, String fileptah) {
             this.downloadUrl = downloadUrl;
             this.threadNum = threadNum;
             this.filePath = fileptah;
         }

         @Override
         public void run() {

             FileDownloadThread[] threads = new FileDownloadThread[threadNum];
             try {
                 URL url = new URL(downloadUrl);
                 Log.d(TAG, "download file http path:" + downloadUrl);
                 URLConnection conn = url.openConnection();
                 // 读取下载文件总大小
                 int fileSize = conn.getContentLength();
                 if (fileSize <= 0) {
                     System.out.println("读取文件失败");
                     return;
                 }
                 // 设置ProgressBar最大的长度为文件Size
                 mProgressbar.setMax(fileSize);

                 // 计算每条线程下载的数据长度
                 blockSize = (fileSize % threadNum) == 0 ? fileSize / threadNum
                         : fileSize / threadNum + 1;

                 Log.d(TAG, "fileSize:" + fileSize + "  blockSize:");

                 File file = new File(filePath);
                 for (int i = 0; i < threads.length; i++) {
                     // 启动线程，分别下载每个线程需要下载的部分
                     threads[i] = new FileDownloadThread(url, file, blockSize,
                             (i + 1));
                     threads[i].setName("Thread:" + i);
                     threads[i].start();
                 }

                 boolean isfinished = false;
                 int downloadedAllSize = 0;
                 while (!isfinished) {
                     isfinished = true;
                     // 当前所有线程下载总量
                     downloadedAllSize = 0;
                     for (int i = 0; i < threads.length; i++) {
                         downloadedAllSize += threads[i].getDownloadLength();
                         if (!threads[i].isCompleted()) {
                             isfinished = false;
                         }
                     }
                     // 通知handler去更新视图组件
                     Message msg = new Message();
                     msg.getData().putInt("size", downloadedAllSize);
                     mHandler.sendMessage(msg);
                     // Log.d(TAG, "current downloadSize:" + downloadedAllSize);
                     Thread.sleep(1000);// 休息1秒后再读取下载进度
                 }
                 Log.d(TAG, " all of downloadSize:" + downloadedAllSize);

             } catch (MalformedURLException e) {
                 e.printStackTrace();
             } catch (IOException e) {
                 e.printStackTrace();
             } catch (InterruptedException e) {
                 e.printStackTrace();
             }

         }
     }

 }

FileDownloadThread:

 package com.amos.app;

 import java.io.BufferedInputStream;
 import java.io.File;
 import java.io.IOException;
 import java.io.RandomAccessFile;
 import java.net.URL;
 import java.net.URLConnection;
 import android.util.Log;

 /**
  * 文件下载类
  *
  * @author yangxiaolong
  * @2014-5-6
  */
 public class FileDownloadThread extends Thread {

     private static final String TAG = FileDownloadThread.class.getSimpleName();

     /** 当前下载是否完成 */
     private boolean isCompleted = false;
     /** 当前下载文件长度 */
     private int downloadLength = 0;
     /** 文件保存路径 */
     private File file;
     /** 文件下载路径 */
     private URL downloadUrl;
     /** 当前下载线程ID */
     private int threadId;
     /** 线程下载数据长度 */
     private int blockSize;

     /**
      *
      * @param url:文件下载地址
      * @param file:文件保存路径
      * @param blocksize:下载数据长度
      * @param threadId:线程ID
      */
     public FileDownloadThread(URL downloadUrl, File file, int blocksize,
             int threadId) {
         this.downloadUrl = downloadUrl;
         this.file = file;
         this.threadId = threadId;
         this.blockSize = blocksize;
     }

     @Override
     public void run() {

         BufferedInputStream bis = null;
         RandomAccessFile raf = null;

         try {
             URLConnection conn = downloadUrl.openConnection();
             conn.setAllowUserInteraction(true);

             int startPos = blockSize * (threadId - 1);//开始位置
             int endPos = blockSize * threadId - 1;//结束位置
             //设置当前线程下载的起点、终点
             conn.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos);
             System.out.println(Thread.currentThread().getName() + "  bytes="
                     + startPos + "-" + endPos);

             byte[] buffer = new byte[1024];
             bis = new BufferedInputStream(conn.getInputStream());

             raf = new RandomAccessFile(file, "rwd");
             raf.seek(startPos);
             int len;
             while ((len = bis.read(buffer, 0, 1024)) != -1) {
                 raf.write(buffer, 0, len);
                 downloadLength += len;
             }
             isCompleted = true;
             Log.d(TAG, "current thread task has finished,all size:"
                     + downloadLength);

         } catch (IOException e) {
             e.printStackTrace();
         } finally {
             if (bis != null) {
                 try {
                     bis.close();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
             }
             if (raf != null) {
                 try {
                     raf.close();
                 } catch (IOException e) {
                     e.printStackTrace();
                 }
             }
         }
     }

     /**
      * 线程文件是否下载完毕
      */
     public boolean isCompleted() {
         return isCompleted;
     }

     /**
      * 线程下载文件长度
      */
     public int getDownloadLength() {
         return downloadLength;
     }

 }

补充:.xml文件：

 <?xml version="1.0" encoding="utf-8"?>
 <LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
     android:layout_width="match_parent"
     android:layout_height="match_parent"
     android:background="@android:color/white"
     android:orientation="vertical" >

     <Button
         android:id="@+id/download_btn"
         android:layout_width="match_parent"
         android:layout_height="60dp"
         android:layout_gravity="center"
         android:layout_marginLeft="10dp"
         android:layout_marginRight="10dp"
         android:layout_marginTop="50dp"
         android:text="Download"
         android:textSize="18sp" />

     <ProgressBar
         android:id="@+id/download_progress"
         style="?android:attr/progressBarStyleHorizontal"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:layout_marginLeft="10dip"
         android:layout_marginRight="10dip"
         android:layout_marginTop="20dp"
         android:indeterminate="false"
         android:max="100" />

     <TextView
         android:id="@+id/download_message"
         android:layout_width="wrap_content"
         android:layout_height="wrap_content"
         android:layout_gravity="center"
         android:layout_marginTop="10dp"
         android:maxLines="1"
         android:text="50%"
         android:textSize="18dip" />

 </LinearLayout>

效果图：