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" />

<?xml version="1.0" encoding="utf-8"?><LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"  xmlns:app="http://schemas.android.com/apk/res-auto"  xmlns:tools="http://schemas.android.com/tools"  android:layout_width="match_parent"  android:layout_height="match_parent"  android:orientation="vertical"  tools:context="com.five.fashion.duandianxuchuan.MainActivity"><ProgressBar  style="@style/Widget.AppCompat.ProgressBar.Horizontal"  android:layout_width="match_parent"  android:layout_height="100dp"  android:id="@+id/pb"  /><TextView  android:layout_width="wrap_content"  android:layout_height="wrap_content"  android:id="@+id/tv_info"  />  <Button    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="下載"    android:id="@+id/bt_download"    />  <Button    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="暫停"    android:id="@+id/bt_pause"    /></LinearLayout>

package com.five.fashion.duandianxuchuan;import android.os.Bundle;import android.os.Environment;import android.os.Handler;import android.os.Message;import android.os.SystemClock;import android.support.annotation.Nullable;import android.support.v7.app.AppCompatActivity;import android.text.TextUtils;import android.util.Log;import android.view.View;import android.widget.Button;import android.widget.ProgressBar;import android.widget.TextView;import com.loopj.android.http.HttpGet;import java.io.BufferedReader;import java.io.File;import java.io.FileReader;import java.io.FileWriter;import java.io.InputStream;import java.io.RandomAccessFile;import cz.msebera.android.httpclient.Header;import cz.msebera.android.httpclient.HttpResponse;import cz.msebera.android.httpclient.client.HttpClient;import cz.msebera.android.httpclient.client.methods.HttpHead;import cz.msebera.android.httpclient.impl.client.DefaultHttpClient;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(@Nullable 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();      }    }    bt_download.setOnClickListener(new View.OnClickListener() {      @Override      public void onClick(View v) {        download(v);      }    });    bt_pause.setOnClickListener(new View.OnClickListener() {      @Override      public void onClick(View v) {        pause(v);      }    });  }  //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);  }}