compile 'com.loopj.android:android-async-http:1.4.9'

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

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
 xmlns:tools="http://schemas.android.com/tools"
 android:id="@+id/activity_main"
 android:layout_width="match_parent"
 android:layout_height="match_parent"
 android:paddingBottom="@dimen/activity_vertical_margin"
 android:paddingLeft="@dimen/activity_horizontal_margin"
 android:paddingRight="@dimen/activity_horizontal_margin"
 android:paddingTop="@dimen/activity_vertical_margin"
 tools:context="com.lv.mama.test004.MainActivity">


 <ProgressBar
  style="?android:attr/progressBarStyleHorizontal"
  android:layout_width="match_parent"
  android:layout_height="20dp"
  android:layout_marginTop="15dp"
  android:id="@+id/pb"
  android:layout_alignParentTop="true"
  android:layout_alignParentLeft="true"
  android:layout_alignParentStart="true"
  />

 <TextView
  android:text="TextView"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_below="@+id/pb"
  android:layout_alignParentLeft="true"
  android:layout_alignParentStart="true"
  android:layout_marginLeft="20dp"
  android:layout_marginStart="20dp"
  android:layout_marginTop="13dp"
  android:id="@+id/tv_info" />

 <Button
  android:text="暫停"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_marginTop="17dp"
  android:id="@+id/bt_pause"
  android:onClick="pause"
  android:layout_below="@+id/tv_info"
  android:layout_alignParentLeft="true"
  android:layout_alignParentStart="true"
  android:layout_marginLeft="11dp"
  android:layout_marginStart="11dp" />

 <Button
  android:text="開始"
  android:layout_width="wrap_content"
  android:layout_height="wrap_content"
  android:layout_marginRight="24dp"
  android:layout_marginEnd="24dp"
  android:id="@+id/bt_download"
  android:onClick="download"
  android:layout_alignBaseline="@+id/bt_pause"
  android:layout_alignBottom="@+id/bt_pause"
  android:layout_alignParentRight="true"
  android:layout_alignParentEnd="true" />
</RelativeLayout>

public class MainActivity extends AppCompatActivity {
 protected static final String TAG = "OtherActivity";

 //下載線程的數(shù)量
 private final static int threadsize = 3;

 protected static final int SET_MAX = 0;
 public static final int UPDATE_VIEW = 1;


 private ProgressBar pb;
 private Button bt_download;

 private Button bt_pause;
 private TextView tv_info;
 //顯示進(jìn)度和更新進(jìn)度
 private Handler mHandler = new Handler() {
  public void handleMessage(android.os.Message msg) {
   switch (msg.what) {
    case SET_MAX://設(shè)置進(jìn)度條的最大值
     int filelength = msg.arg1;
     pb.setMax(filelength);
     break;
    case UPDATE_VIEW://更新進(jìn)度條 和 下載的比率
     int len = msg.arg1;//新下載的長(zhǎng)度
     pb.setProgress(pb.getProgress() + len);//設(shè)置進(jìn)度條的刻度

     int max = pb.getMax();//獲取進(jìn)度的最大值
     int progress = pb.getProgress();//獲取已經(jīng)下載的數(shù)據(jù)量
     // 下載：30 總：100
     int result = (progress * 100) / max;

     tv_info.setText("下載:" + result + "%");

     break;

    default:
     break;
   }
  }

  ;
 };

 String uri = "http://c.hiphotos.baidu.com/image/pic/item/b90e7bec54e736d1e51217c292504fc2d46269f3.jpg";

 @Override
 protected void onCreate(Bundle savedInstanceState) {
  super.onCreate(savedInstanceState);
  setContentView(R.layout.activity_main);
  //找到控件
  pb = (ProgressBar) findViewById(R.id.pb);
  tv_info = (TextView) findViewById(R.id.tv_info);

  bt_download = (Button) findViewById(R.id.bt_download);
  bt_pause = (Button) findViewById(R.id.bt_pause);

  //數(shù)據(jù)的回顯
  //確定下載的文件
  String name = getFileName(uri);
  File file = new File(Environment.getExternalStorageDirectory(), name);
  if (file.exists()) {//文件存在回顯
   //獲取文件的大小
   int filelength = (int) file.length();
   pb.setMax(filelength);
   try {
    //統(tǒng)計(jì)原來(lái)所有的下載量
    int count = 0;
    //讀取下載記錄文件
    for (int threadid = 0; threadid < threadsize; threadid++) {
     //獲取原來(lái)指定線程的下載記錄
     int existDownloadLength = readDownloadInfo(threadid);
     count = count + existDownloadLength;
    }
    //設(shè)置進(jìn)度條的刻度
    pb.setProgress(count);

    //計(jì)算比率
    int result = (count * 100) / filelength;
    tv_info.setText("下載:" + result + "%");
   } catch (Exception e) {
    e.printStackTrace();
   }
  }
 }
 //暫停
 private boolean flag = false;//是否在下載

 public void pause(View v){
  flag = false;
  bt_download.setEnabled(true);
  bt_pause.setEnabled(false);
 }
 //下載
 public void download(View v){
  flag = true; //是在下載
  bt_download.setEnabled(false);//一點(diǎn)擊變成不可點(diǎn)擊
  bt_pause.setEnabled(true);//一點(diǎn)擊變成可點(diǎn)擊
  new Thread(){//子線程
   public void run() {
    try {
     //獲取服務(wù)器上文件的大小
     HttpClient client = new DefaultHttpClient();
     HttpHead request = new HttpHead(uri);
     HttpResponse response = client.execute(request);
     //response 只有響應(yīng)頭 沒(méi)有響應(yīng)體
     if(response.getStatusLine().getStatusCode() == 200){
      Header[] headers = response.getHeaders("Content-Length");
      String value = headers[0].getValue();
      //文件大小
      int filelength = Integer.parseInt(value);
      Log.i(TAG, "filelength:"+filelength);

      //設(shè)置進(jìn)度條的最大值
      Message msg_setmax = Message.obtain(mHandler, SET_MAX, filelength, 0);
      msg_setmax.sendToTarget();


      //處理下載記錄文件
      for(int threadid=0;threadid<threadsize;threadid++){
       //對(duì)應(yīng)的下載記錄文件
       File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
       //判斷文件是否存在
       if(!file.exists()){
        //創(chuàng)建文件
        file.createNewFile();
       }
      }


      //在sdcard創(chuàng)建和服務(wù)器大小一樣的文件
      String name = getFileName(uri);
      File file = new File(Environment.getExternalStorageDirectory(),name);
      //隨機(jī)訪問(wèn)文件
      RandomAccessFile raf = new RandomAccessFile(file, "rwd");
      //設(shè)置文件的大小
      raf.setLength(filelength);
      //關(guān)閉
      raf.close();

      //計(jì)算每條線程的下載量
      int block = (filelength%threadsize == 0)?(filelength/threadsize):(filelength/threadsize+1);

      //開啟三條線程執(zhí)行下載
      for(int threadid=0;threadid<threadsize;threadid++){
       new DownloadThread(threadid, uri, file, block).start();
      }

     }
    } catch (Exception e) {
     e.printStackTrace();
    }
   };
  }.start();
 }
 //線程下載類
 private class DownloadThread extends Thread {
  private int threadid;//線程的id
  private String uri;//下載的地址
  private File file;//下載文件
  private int block;//下載的塊
  private int start;
  private int end;

  public DownloadThread(int threadid, String uri, File file, int block) {
   super();
   this.threadid = threadid;
   this.uri = uri;
   this.file = file;
   this.block = block;
   //計(jì)算下載的開始位置和結(jié)束位置
   start = threadid * block;
   end = (threadid + 1) * block - 1;

   try {
    //讀取該條線程原來(lái)的下載記錄
    int existDownloadLength = readDownloadInfo(threadid);

    //修改下載的開始位置 從新下載
    start = start + existDownloadLength;
   } catch (Exception e) {
    e.printStackTrace();
   }
  }
  //下載 狀態(tài)碼：200是普通的下載  206是分段下載  Range:范圍
  @Override
  public void run() {
   super.run();
   try {
    RandomAccessFile raf = new RandomAccessFile(file, "rwd");
    //跳轉(zhuǎn)到起始位置
    raf.seek(start);

    //分段下載
    HttpClient client = new DefaultHttpClient();
    HttpGet request = new HttpGet(uri);
    request.addHeader("Range", "bytes:"+start+"-"+end);//添加請(qǐng)求頭
    HttpResponse response = client.execute(request);
    if(response.getStatusLine().getStatusCode() == 200){
     InputStream inputStream = response.getEntity().getContent();
     //把流寫入到文件
     byte[] buffer = new byte[1024];
     int len = 0;
     while((len = inputStream.read(buffer)) != -1){
      //如果暫停下載 點(diǎn)擊暫停 false 就直接return 點(diǎn)擊下載true接著下載
      if(!flag){
       return;//標(biāo)準(zhǔn)線程結(jié)束
      }
      //寫數(shù)據(jù)
      raf.write(buffer, 0, len);

      //讀取原來(lái)下載的數(shù)據(jù)量 這里讀取是為了更新下載記錄
      int existDownloadLength = readDownloadInfo(threadid);//原來(lái)下載的數(shù)據(jù)量

      //計(jì)算最新的下載
      int newDownloadLength = existDownloadLength + len;

      //更新下載記錄 從新記錄最新下載位置
      updateDownloadInfo(threadid, newDownloadLength);

      //更新進(jìn)度條的顯示 下載的百分比
      Message update_msg = Message.obtain(mHandler, UPDATE_VIEW, len, 0);
      update_msg.sendToTarget();
      //模擬 看到進(jìn)度條動(dòng)的效果
      SystemClock.sleep(50);
     }
     inputStream.close();
     raf.close();
     Log.i(TAG, "第"+threadid+"條線程下載完成");
    }

   } catch (Exception e) {
    e.printStackTrace();
   }
  }
 }
 /**
  * 讀取指定線程的下載數(shù)據(jù)量
  * @param threadid 線程的id
  * @return
  * @throws Exception
  */
 public int readDownloadInfo(int threadid) throws Exception{
  //下載記錄文件
  File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
  BufferedReader br = new BufferedReader(new FileReader(file));
  //讀取一行數(shù)據(jù)
  String content = br.readLine();

  int downlength = 0;
  //如果該文件第一次創(chuàng)建去執(zhí)行讀取操作 文件里面的內(nèi)容是 null
  if(!TextUtils.isEmpty(content)){
   downlength = Integer.parseInt(content);
  }
  //關(guān)閉流
  br.close();
  return downlength;
 }
 /**
  * 更新下載記錄
  * @param threadid
  * @param newDownloadLength
  */
 public void updateDownloadInfo(int threadid,int newDownloadLength) throws Exception{
  //下載記錄文件
  File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
  FileWriter fw = new FileWriter(file);
  fw.write(newDownloadLength+"");
  fw.close();
 }

 /**
  * 獲取文件的名稱
  * @param uri
  * @return
  */
 private String getFileName(String uri){
  return uri.substring(uri.lastIndexOf("/")+1);
 }


}