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; //顯示進度和更新進度 private Handler mHandler = new Handler() {  public void handleMessage(android.os.Message msg) {   switch (msg.what) {    case SET_MAX://設置進度條的最大值     int filelength = msg.arg1;     pb.setMax(filelength);     break;    case UPDATE_VIEW://更新進度條 和 下載的比率     int len = msg.arg1;//新下載的長度     pb.setProgress(pb.getProgress() + len);//設置進度條的刻度     int max = pb.getMax();//獲取進度的最大值     int progress = pb.getProgress();//獲取已經下載的數據量     // 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);  //數據的回顯  //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 {    //統計原來所有的下載量    int count = 0;    //讀取下載記錄文件    for (int threadid = 0; threadid < threadsize; threadid++) {     //獲取原來指定線程的下載記錄     int existDownloadLength = readDownloadInfo(threadid);     count = count + existDownloadLength;    }    //設置進度條的刻度    pb.setProgress(count);    //計算比率    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);//一點擊變成不可點擊  bt_pause.setEnabled(true);//一點擊變成可點擊  new Thread(){//子線程   public void run() {    try {     //獲取服務器上文件的大小     HttpClient client = new DefaultHttpClient();     HttpHead request = new HttpHead(uri);     HttpResponse response = client.execute(request);     //response 只有響應頭 沒有響應體     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);      //設置進度條的最大值      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++){       //對應的下載記錄文件       File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");       //判斷文件是否存在       if(!file.exists()){        //創建文件        file.createNewFile();       }      }      //在sdcard創建和服務器大小一樣的文件      String name = getFileName(uri);      File file = new File(Environment.getExternalStorageDirectory(),name);      //隨機訪問文件      RandomAccessFile raf = new RandomAccessFile(file, "rwd");      //設置文件的大小      raf.setLength(filelength);      //關閉      raf.close();      //計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;   //計算下載的開始位置和結束位置   start = threadid * block;   end = (threadid + 1) * block - 1;   try {    //讀取該條線程原來的下載記錄    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 點擊暫停 false 就直接return 點擊下載true接著下載      if(!flag){       return;//標準線程結束      }      //寫數據      raf.write(buffer, 0, len);      //讀取原來下載的數據量 這里讀取是為了更新下載記錄      int existDownloadLength = readDownloadInfo(threadid);//原來下載的數據量      //計算最新的下載      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 看到進度條動的效果      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據量  * @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));  //讀取一行數據  String content = br.readLine();  int downlength = 0;  //如果該文件第一次創建去執行讀取操作 文件里面的內容是 null  if(!TextUtils.isEmpty(content)){   downlength = Integer.parseInt(content);  }  //關閉流  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); }}