(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：
1 package com.amos.app; 2 3 import java.io.File; 4 import java.io.IOException; 5 import java.net.MalformedURLException; 6 import java.net.URL; 7 import java.net.URLConnection; 8 import com.amos.download.R; 9 import android.annotation.SuppressLint; 10 import android.app.Activity; 11 import android.os.Bundle; 12 import android.os.Environment; 13 import android.os.Handler; 14 import android.os.Message; 15 import android.util.Log; 16 import android.view.View; 17 import android.view.View.OnClickListener; 18 import android.widget.ProgressBar; 19 import android.widget.TextView; 20 import android.widget.Toast; 21 22 /** 23 * @author yangxiaolong 24 * @2014-5-6 25 */ 26 public class MainApp extends Activity implements OnClickListener { 27 28 private static final String TAG = MainApp.class.getSimpleName(); 29 30 /** 显示下载进度TextView */ 31 private TextView mMessageView; 32 /** 显示下载进度ProgressBar */ 33 private ProgressBar mProgressbar; 34 35 @Override 36 protected void onCreate(Bundle savedInstanceState) { 37 super.onCreate(savedInstanceState); 38 setContentView(R.layout.progress_activity); 39 findViewById(R.id.download_btn).setOnClickListener(this); 40 mMessageView = (TextView) findViewById(R.id.download_message); 41 mProgressbar = (ProgressBar) findViewById(R.id.download_progress); 42 } 43 44 @Override 45 public void onClick(View v) { 46 if (v.getId() == R.id.download_btn) { 47 doDownload(); 48 } 49 } 50 51 /** 52 * 使用Handler更新UI界面信息 53 */ 54 @SuppressLint("HandlerLeak") 55 Handler mHandler = new Handler() { 56 @Override 57 public void handleMessage(Message msg) { 58 59 mProgressbar.setProgress(msg.getData().getInt("size")); 60 61 float temp = (float) mProgressbar.getProgress() 62 / (float) mProgressbar.getMax(); 63 64 int progress = (int) (temp * 100); 65 if (progress == 100) { 66 Toast.makeText(MainApp.this, "下载完成！", Toast.LENGTH_LONG).show(); 67 } 68 mMessageView.setText("下载进度:" + progress + " %"); 69 70 } 71 }; 72 73 /** 74 * 下载准备工作，获取SD卡路径、开启线程 75 */ 76 private void doDownload() { 77 // 获取SD卡路径 78 String path = Environment.getExternalStorageDirectory() 79 + "/amosdownload/"; 80 File file = new File(path); 81 // 如果SD卡目录不存在创建 82 if (!file.exists()) { 83 file.mkdir(); 84 } 85 // 设置progressBar初始化 86 mProgressbar.setProgress(0); 87 88 // 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 89 String downloadUrl = "http://gdown.baidu.com/data/wisegame/91319a5a1dfae322/baidu_16785426.apk"; 90 String fileName = "baidu_16785426.apk"; 91 int threadNum = 5; 92 String filepath = path + fileName; 93 Log.d(TAG, "download file path:" + filepath); 94 downloadTask task = new downloadTask(downloadUrl, threadNum, filepath); 95 task.start(); 96 } 97 98 /** 99 * 多线程文件下载100 * 101 * @author yangxiaolong102 * @2014-8-7103 */104 class downloadTask extends Thread {105 private String downloadUrl;// 下载链接地址106 private int threadNum;// 开启的线程数107 private String filePath;// 保存文件路径地址108 private int blockSize;// 每一个线程的下载量109 110 public downloadTask(String downloadUrl, int threadNum, String fileptah) {111 this.downloadUrl = downloadUrl;112 this.threadNum = threadNum;113 this.filePath = fileptah;114 }115 116 @Override117 public void run() {118 119 FileDownloadThread[] threads = new FileDownloadThread[threadNum];120 try {121 URL url = new URL(downloadUrl);122 Log.d(TAG, "download file http path:" + downloadUrl);123 URLConnection conn = url.openConnection();124 // 读取下载文件总大小125 int fileSize = conn.getContentLength();126 if (fileSize <= 0) {127 System.out.println("读取文件失败");128 return;129 }130 // 设置ProgressBar最大的长度为文件Size131 mProgressbar.setMax(fileSize);132 133 // 计算每条线程下载的数据长度134 blockSize = (fileSize % threadNum) == 0 ? fileSize / threadNum135 : fileSize / threadNum + 1;136 137 Log.d(TAG, "fileSize:" + fileSize + " blockSize:");138 139 File file = new File(filePath);140 for (int i = 0; i < threads.length; i++) {141 // 启动线程，分别下载每个线程需要下载的部分142 threads[i] = new FileDownloadThread(url, file, blockSize,143 (i + 1));144 threads[i].setName("Thread:" + i);145 threads[i].start();146 }147 148 boolean isfinished = false;149 int downloadedAllSize = 0;150 while (!isfinished) {151 isfinished = true;152 // 当前所有线程下载总量153 downloadedAllSize = 0;154 for (int i = 0; i < threads.length; i++) {155 downloadedAllSize += threads[i].getDownloadLength();156 if (!threads[i].isCompleted()) {157 isfinished = false;158 }159 }160 // 通知handler去更新视图组件161 Message msg = new Message();162 msg.getData().putInt("size", downloadedAllSize);163 mHandler.sendMessage(msg);164 // Log.d(TAG, "current downloadSize:" + downloadedAllSize);165 Thread.sleep(1000);// 休息1秒后再读取下载进度166 }167 Log.d(TAG, " all of downloadSize:" + downloadedAllSize);168 169 } catch (MalformedURLException e) {170 e.printStackTrace();171 } catch (IOException e) {172 e.printStackTrace();173 } catch (InterruptedException e) {174 e.printStackTrace();175 }176 177 }178 }179 180 }FileDownloadThread:
1 package com.amos.app; 2 3 import java.io.BufferedInputStream; 4 import java.io.File; 5 import java.io.IOException; 6 import java.io.RandomAccessFile; 7 import java.net.URL; 8 import java.net.URLConnection; 9 import android.util.Log; 10 11 /** 12 * 文件下载类 13 * 14 * @author yangxiaolong 15 * @2014-5-6 16 */ 17 public class FileDownloadThread extends Thread { 18 19 private static final String TAG = FileDownloadThread.class.getSimpleName(); 20 21 /** 当前下载是否完成 */ 22 private boolean isCompleted = false; 23 /** 当前下载文件长度 */ 24 private int downloadLength = 0; 25 /** 文件保存路径 */ 26 private File file; 27 /** 文件下载路径 */ 28 private URL downloadUrl; 29 /** 当前下载线程ID */ 30 private int threadId; 31 /** 线程下载数据长度 */ 32 private int blockSize; 33 34 /** 35 * 36 * @param url:文件下载地址 37 * @param file:文件保存路径 38 * @param blocksize:下载数据长度 39 * @param threadId:线程ID 40 */ 41 public FileDownloadThread(URL downloadUrl, File file, int blocksize, 42 int threadId) { 43 this.downloadUrl = downloadUrl; 44 this.file = file; 45 this.threadId = threadId; 46 this.blockSize = blocksize; 47 } 48 49 @Override 50 public void run() { 51 52 BufferedInputStream bis = null; 53 RandomAccessFile raf = null; 54 55 try { 56 URLConnection conn = downloadUrl.openConnection(); 57 conn.setAllowUserInteraction(true); 58 59 int startPos = blockSize * (threadId - 1);//开始位置 60 int endPos = blockSize * threadId - 1;//结束位置 61 //设置当前线程下载的起点、终点 62 conn.setRequestProperty("Range", "bytes=" + startPos + "-" + endPos); 63 System.out.println(Thread.currentThread().getName() + " bytes=" 64 + startPos + "-" + endPos); 65 66 byte[] buffer = new byte[1024]; 67 bis = new BufferedInputStream(conn.getInputStream()); 68 69 raf = new RandomAccessFile(file, "rwd"); 70 raf.seek(startPos); 71 int len; 72 while ((len = bis.read(buffer, 0, 1024)) != -1) { 73 raf.write(buffer, 0, len); 74 downloadLength += len; 75 } 76 isCompleted = true; 77 Log.d(TAG, "current thread task has finished,all size:" 78 + downloadLength); 79 80 } catch (IOException e) { 81 e.printStackTrace(); 82 } finally { 83 if (bis != null) { 84 try { 85 bis.close(); 86 } catch (IOException e) { 87 e.printStackTrace(); 88 } 89 } 90 if (raf != null) { 91 try { 92 raf.close(); 93 } catch (IOException e) { 94 e.printStackTrace(); 95 } 96 } 97 } 98 } 99 100 /**101 * 线程文件是否下载完毕102 */103 public boolean isCompleted() {104 return isCompleted;105 }106 107 /**108 * 线程下载文件长度109 */110 public int getDownloadLength() {111 return downloadLength;112 }113 114 }补充:.
1 <? 2 <LinearLayout 3 android:layout_width="match_parent" 4 android:layout_height="match_parent" 5 android:background="@android:color/white" 6 android:orientation="vertical" > 7 8 <Button 9 android:id="@+id/download_btn"10 android:layout_width="match_parent"11 android:layout_height="60dp"12 android:layout_gravity="center"13 android:layout_marginLeft="10dp"14 android:layout_marginRight="10dp"15 android:layout_marginTop="50dp"16 android:text="Download"17 android:textSize="18sp" />18 19 <ProgressBar20 android:id="@+id/download_progress"21 22 android:layout_width="fill_parent"23 android:layout_height="wrap_content"24 android:layout_marginLeft="10dip"25 android:layout_marginRight="10dip"26 android:layout_marginTop="20dp"27 android:indeterminate="false"28 android:max="100" />29 30 <TextView31 android:id="@+id/download_message"32 android:layout_width="wrap_content"33 android:layout_height="wrap_content"34 android:layout_gravity="center"35 android:layout_marginTop="10dp"36 android:maxLines="1"37 android:text="50%"38 android:textSize="18dip" />39 40 </LinearLayout>
效果图：
原标题：Android 实现网络多线程APK文件下载
关键词：Android
我知道了 