<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context="${relativePackage}.${activityClass}" >
 
  <ProgressBar
    android:id="@+id/progressBar"
    style="?android:attr/progressBarStyleHorizontal"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:max="100" />
 
  <TextView
    android:id="@+id/textView"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:layout_below="@+id/progressBar"
    android:layout_centerHorizontal="true"
    android:layout_marginTop="24dp"
    android:text="TextView" />
 
  <ImageView
    android:id="@+id/imageView"
    android:layout_marginTop="24dp"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:layout_alignParentBottom="true"
    android:layout_below="@+id/textView"
    android:contentDescription="@string/app_name"
    android:src="@drawable/ic_launcher" />
 
</RelativeLayout>

public class MainActivity extends Activity {
 
  ProgressBar pb; 
  TextView tv;
  ImageView imageView;
  int fileSize;  
  int downLoadFileSize;  
  String fileEx,fileNa,filename; 
  //用來接收線程發(fā)送來的文件下載量，進行UI界面的更新
  private Handler handler = new Handler(){  
    @Override  
    public void handleMessage(Message msg)  
    {//定義一個Handler，用于處理下載線程與UI間通訊
     if (!Thread.currentThread().isInterrupted())
     {  
      switch (msg.what)
      {  
       case 0:  
        pb.setMax(fileSize);
       case 1:  
        pb.setProgress(downLoadFileSize);  
        int result = downLoadFileSize * 100 / fileSize;  
        tv.setText(result + "%");  
        break;  
       case 2:  
        Toast.makeText(MainActivity.this, "文件下載完成", Toast.LENGTH_SHORT).show(); 
        FileInputStream fis = null;
        try {
          fis = new FileInputStream(Environment.getExternalStorageDirectory() + File.separator + "/ceshi/" + filename);
        } catch (FileNotFoundException e) {
          e.printStackTrace();
        }
        Bitmap bitmap = BitmapFactory.decodeStream(fis); ///把流轉(zhuǎn)化為Bitmap圖
        imageView.setImageBitmap(bitmap);
        break;  
   
       case -1:  
        String error = msg.getData().getString("error");
        Toast.makeText(MainActivity.this, error, Toast.LENGTH_SHORT).show();  
        break;  
      }  
     }  
     super.handleMessage(msg);  
    }  
   };
   
  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    pb=(ProgressBar)findViewById(R.id.progressBar);
    tv=(TextView)findViewById(R.id.textView);
    imageView = (ImageView) findViewById(R.id.imageView);
    tv.setText("0%");
    new Thread(){
      public void run(){
        try {
          //下載文件，參數(shù)：第一個URL，第二個存放路徑
          down_file("http://cdnq.duitang.com/uploads/item/201406/15/20140615203435_ABQMa.jpeg", Environment.getExternalStorageDirectory() + File.separator + "/ceshi/");
        } catch (ClientProtocolException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
        } catch (IOException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
        } 
      }  
    }.start();  
   
  }  
   
  /**
   * 文件下載
   * @param url：文件的下載地址
   * @param path：文件保存到本地的地址
   * @throws IOException
   */
  public void down_file(String url,String path) throws IOException{  
    //下載函數(shù)     
    filename=url.substring(url.lastIndexOf("/") + 1);
    //獲取文件名  
    URL myURL = new URL(url);
    URLConnection conn = myURL.openConnection();  
    conn.connect();  
    InputStream is = conn.getInputStream();  
    this.fileSize = conn.getContentLength();//根據(jù)響應(yīng)獲取文件大小  
    if (this.fileSize <= 0) throw new RuntimeException("無法獲知文件大小 ");  
    if (is == null) throw new RuntimeException("stream is null");
    File file1 = new File(path);
    File file2 = new File(path+filename);
    if(!file1.exists()){
      file1.mkdirs();
    }
    if(!file2.exists()){
      file2.createNewFile();
    }
    FileOutputStream fos = new FileOutputStream(path+filename);  
    //把數(shù)據(jù)存入路徑+文件名  
    byte buf[] = new byte[1024];
    downLoadFileSize = 0;  
    sendMsg(0);  
    do{  
      //循環(huán)讀取  
      int numread = is.read(buf);  
      if (numread == -1)  
      {  
       break;  
      }  
      fos.write(buf, 0, numread);  
      downLoadFileSize += numread;  
   
      sendMsg(1);//更新進度條  
    } while (true); 
     
    sendMsg(2);//通知下載完成  
     
    try{  
      is.close();  
    } catch (Exception ex) {  
      Log.e("tag", "error: " + ex.getMessage(), ex);  
    }  
   
  }  
   
  //在線程中向Handler發(fā)送文件的下載量，進行UI界面的更新
  private void sendMsg(int flag)  
  {  
    Message msg = new Message();  
    msg.what = flag;  
    handler.sendMessage(msg);  
  }    
   
}

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