33、多线程断点下载的实现&界面的更新

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

     <TextView
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:text="@string/down_load" />

     <EditText
         android:id="@+id/et"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:hint="@string/hint"
         android:text="http://192.168.1.247:8080/youdao.exe" />

     <ProgressBar
         android:id="@+id/pb"
         style="?android:attr/progressBarStyleHorizontal"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content" />

     <TextView
         android:id="@+id/tv_process"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content" />

     <Button
         android:id="@+id/bt"
         android:layout_width="fill_parent"
         android:layout_height="wrap_content"
         android:text="@string/download" />

 </LinearLayout>

 /**
  * 49_多线程断点下载的实现&界面的更新 DEMO
  * @author dr
  *
  */
 public class DemoActivity extends Activity implements OnClickListener {

     private ProgressBar pb;
     private Button bt;
     private TextView tv;
     private EditText et;
     boolean flag = true;
     boolean stopflag = false;
     int total = 0;

     private Handler handler = new Handler() {

         @Override
         public void handleMessage(Message msg) {
             pb.setProgress(total);
             // 文件总长度
             int max = pb.getMax();
             // total和max都是从0开始的。
             if (total >= (max - 1)) {
                 total = max;
                 flag = false;
             }
             int result = total * 100 / max;
             tv.setText("当前进度 :" + result + "%");

             super.handleMessage(msg);
         }
     };

     @Override
     public void onCreate(Bundle savedInstanceState) {
         super.onCreate(savedInstanceState);
         setContentView(R.layout.main);
         pb = (ProgressBar) this.findViewById(R.id.pb);
         bt = (Button) this.findViewById(R.id.bt);
         tv = (TextView) this.findViewById(R.id.tv_process);
         et = (EditText) this.findViewById(R.id.et);
         bt.setOnClickListener(this);

     }

     @Override
     public void onClick(View v) {
         switch (v.getId()) {
         case R.id.bt:
             // 创建一个子线程 定期的更新ui
             if ("开始下载".equals(bt.getText().toString())) {
                 bt.setText("暂停");
                 stopflag = false; // 开始下载
             } else {
                 bt.setText("开始下载");
                 stopflag = true;
             }
             new Thread() {
                 @Override
                 public void run() {
                     super.run();
                     while (flag) {
                         try {
                             sleep(1000);
                             // 如果total > = 文件长度
                             Message msg = new Message();
                             handler.sendMessage(msg);
                         } catch (InterruptedException e) {
                             e.printStackTrace();
                         }
                     }
                 }
             }.start();

             // 开始执行下载的操作
             String path = et.getText().toString().trim();
             if ("".equals(path)) {
                 Toast.makeText(this, "路径不能为空", 1).show();
                 return;
             }
             try {
                 URL url = new URL(path);
                 HttpURLConnection conn = (HttpURLConnection) url
                         .openConnection();
                 conn.setRequestMethod("GET");
                 conn.setConnectTimeout(5000);
                 conn.setRequestProperty("User-Agent",
                         "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
                 int code = conn.getResponseCode();
                 if (code == 200) {
                     int len = conn.getContentLength();
                     RandomAccessFile file = new RandomAccessFile("/mnt/sdcard/"
                             + getFilenName(path), "rwd");
                     // 1.设置本地文件大小跟服务器的文件大小一致
                     file.setLength(len);
                     // 设置进度条的最大值
                     pb.setMax(len);

                     // 2 .假设开启3 个线程
                     int threadnumber = 3;
                     int blocksize = len / threadnumber;
                     /**
                      * 线程1 0~ blocksize 线程2 1*bolocksize ~ 2*blocksize 线程3
                      * 2*blocksize ~ 文件末尾
                      */
                     for (int i = 0; i < threadnumber; i++) {
                         int startposition = i * blocksize;
                         int endpositon = (i + 1) * blocksize;
                         if (i == (threadnumber - 1)) {
                             // 最后一个线程
                             endpositon = len;
                         }

                         DownLoadTask task = new DownLoadTask(i, path,
                                 startposition, endpositon);
                         task.start();
                     }

                 }
             } catch (Exception e) {
                 Toast.makeText(this, "下载出现异常", 0).show();
                 e.printStackTrace();
             }

             break;
         }

     }

     class DownLoadTask extends Thread {

         int threadid;
         String filepath;
         int startposition;
         int endpositon;

         public DownLoadTask(int threadid, String filepath, int startposition,
                 int endpositon) {
             this.threadid = threadid;
             this.filepath = filepath;
             this.startposition = startposition;
             this.endpositon = endpositon;

         }

         @Override
         public void run() {
             try {
               File postionfile = new File("/mnt/sdcard/" + threadid + ".txt");
                 URL url = new URL(filepath);
                 HttpURLConnection conn = (HttpURLConnection) url
                         .openConnection();
                 System.out.println("线程" + threadid + "正在下载 " + "开始位置 : "
                         + startposition + "结束位置 " + endpositon);

                 if (postionfile.exists()) {
                     FileInputStream fis = new FileInputStream(postionfile);
                     byte[] result = StreamTool.getBytes(fis);
                     String str = new String(result);
                     if (!"".equals(str)) {
                         int newstartposition = Integer.parseInt(str);
                         if (newstartposition > startposition) {
                             startposition = newstartposition;
                         }
                     }
                 }

                 // "Range", "bytes=2097152-4194303")
                 conn.setRequestProperty("Range", "bytes=" + startposition + "-"
                         + endpositon);
                 conn.setRequestMethod("GET");
                 conn.setConnectTimeout(5000);
                 conn.setRequestProperty("User-Agent",
                         "Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1; SV1)");
                 InputStream is = conn.getInputStream();
                 RandomAccessFile file = new RandomAccessFile("/mnt/sdcard/"
                         + getFilenName(filepath), "rwd");
                 // 设置 数据从文件哪个位置开始写
                 file.seek(startposition);
                 byte[] buffer = new byte[1024];
                 int len = 0;
                 // 代表当前读到的服务器数据的位置 ,同时这个值已经存储的文件的位置
                 int currentPostion = startposition;
                 // 创建一个文件对象 ,记录当前某个文件的下载位置

                 while ((len = is.read(buffer)) != -1) {
                     if (stopflag) {   // 暂停下载
                         return;
                     }
                     file.write(buffer, 0, len);

                     synchronized (DemoActivity.this) { // 同步当前的
                         total += len;
                     }

                     currentPostion += len;
                     // 需要把currentPostion 信息给持久化到存储设备
                     String position = currentPostion + "";
                     FileOutputStream fos = new FileOutputStream(postionfile);
                     fos.write(position.getBytes());
                     fos.flush();
                     fos.close();
                 }

                 file.close();
                 System.out.println("线程" + threadid + "下载完毕");
                 // 当线程下载完毕后 把文件删除掉
                 if (postionfile.exists()) {
                     postionfile.delete();
                 }
             } catch (Exception e) {
                 e.printStackTrace();
             }
             super.run();
         }
     }

     public String getFilenName(String path) {
         int start = path.lastIndexOf("/") + 1;
         return path.substring(start, path.length());
     }
 }

 public class StreamTool {
     /**
      * 把一个inputstream里面的内容转化成一个byte[]
      */
     public static byte[] getBytes(InputStream is) throws Exception{
         ByteArrayOutputStream bos = new ByteArrayOutputStream();
         byte[] buffer = new byte[1024];
         int len = 0;
         while((len = is.read(buffer))!=-1){
             bos.write(buffer, 0, len);
         }
         is.close();
         bos.flush();
         byte[] result = bos.toByteArray();
         System.out.println(new String(result));
         return  result;
     }
 }

     <uses-permission android:name="android.permission.MOUNT_UNMOUNT_FILESYSTEMS"/>
     <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>
     <uses-permission android:name="android.permission.INTERNET"/>