Android实现简单断点续传和下载到本地功能

本文实例为大家分享了Android实现断点续传和下载的具体代码，供大家参考，具体内容如下

效果展示

导入依赖与权限

依赖

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

权限

 <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>

主MainActivity（布局）

<?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="暂停"
  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="开始"
  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>

主MainActivity

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

 //下载线程的数量
 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;
 //显示进度和更新进度
 private Handler mHandler = new Handler() {
  public void handleMessage(android.os.Message msg) {
   switch (msg.what) {
    case SET_MAX://设置进度条的最大值
     int filelength = msg.arg1;
     pb.setMax(filelength);
     break;
    case UPDATE_VIEW://更新进度条 和 下载的比率
     int len = msg.arg1;//新下载的长度
     pb.setProgress(pb.getProgress() + len);//设置进度条的刻度

     int max = pb.getMax();//获取进度的最大值
     int progress = pb.getProgress();//获取已经下载的数据量
     // 下载：30 总：100
     int result = (progress * 100) / max;

     tv_info.setText("下载:" + 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);

  //数据的回显
  //确定下载的文件
  String name = getFileName(uri);
  File file = new File(Environment.getExternalStorageDirectory(), name);
  if (file.exists()) {//文件存在回显
   //获取文件的大小
   int filelength = (int) file.length();
   pb.setMax(filelength);
   try {
    //统计原来所有的下载量
    int count = 0;
    //读取下载记录文件
    for (int threadid = 0; threadid < threadsize; threadid++) {
     //获取原来指定线程的下载记录
     int existDownloadLength = readDownloadInfo(threadid);
     count = count + existDownloadLength;
    }
    //设置进度条的刻度
    pb.setProgress(count);

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

 public void pause(View v){
  flag = false;
  bt_download.setEnabled(true);
  bt_pause.setEnabled(false);
 }
 //下载
 public void download(View v){
  flag = true; //是在下载
  bt_download.setEnabled(false);//一点击变成不可点击
  bt_pause.setEnabled(true);//一点击变成可点击
  new Thread(){//子线程
   public void run() {
    try {
     //获取服务器上文件的大小
     HttpClient client = new DefaultHttpClient();
     HttpHead request = new HttpHead(uri);
     HttpResponse response = client.execute(request);
     //response 只有响应头 没有响应体
     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);

      //设置进度条的最大值
      Message msg_setmax = Message.obtain(mHandler, SET_MAX, filelength, 0);
      msg_setmax.sendToTarget();

      //处理下载记录文件
      for(int threadid=0;threadid<threadsize;threadid++){
       //对应的下载记录文件
       File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
       //判断文件是否存在
       if(!file.exists()){
        //创建文件
        file.createNewFile();
       }
      }

      //在sdcard创建和服务器大小一样的文件
      String name = getFileName(uri);
      File file = new File(Environment.getExternalStorageDirectory(),name);
      //随机访问文件
      RandomAccessFile raf = new RandomAccessFile(file, "rwd");
      //设置文件的大小
      raf.setLength(filelength);
      //关闭
      raf.close();

      //计算每条线程的下载量
      int block = (filelength%threadsize == 0)?(filelength/threadsize):(filelength/threadsize+1);

      //开启三条线程执行下载
      for(int threadid=0;threadid<threadsize;threadid++){
       new DownloadThread(threadid, uri, file, block).start();
      }

     }
    } catch (Exception e) {
     e.printStackTrace();
    }
   };
  }.start();
 }
 //线程下载类
 private class DownloadThread extends Thread {
  private int threadid;//线程的id
  private String uri;//下载的地址
  private File file;//下载文件
  private int block;//下载的块
  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;
   //计算下载的开始位置和结束位置
   start = threadid * block;
   end = (threadid + 1) * block - 1;

   try {
    //读取该条线程原来的下载记录
    int existDownloadLength = readDownloadInfo(threadid);

    //修改下载的开始位置 从新下载
    start = start + existDownloadLength;
   } catch (Exception e) {
    e.printStackTrace();
   }
  }
  //下载 状态码：200是普通的下载  206是分段下载  Range:范围
  @Override
  public void run() {
   super.run();
   try {
    RandomAccessFile raf = new RandomAccessFile(file, "rwd");
    //跳转到起始位置
    raf.seek(start);

    //分段下载
    HttpClient client = new DefaultHttpClient();
    HttpGet request = new HttpGet(uri);
    request.addHeader("Range", "bytes:"+start+"-"+end);//添加请求头
    HttpResponse response = client.execute(request);
    if(response.getStatusLine().getStatusCode() == 200){
     InputStream inputStream = response.getEntity().getContent();
     //把流写入到文件
     byte[] buffer = new byte[1024];
     int len = 0;
     while((len = inputStream.read(buffer)) != -1){
      //如果暂停下载 点击暂停 false 就直接return 点击下载true接着下载
      if(!flag){
       return;//标准线程结束
      }
      //写数据
      raf.write(buffer, 0, len);

      //读取原来下载的数据量 这里读取是为了更新下载记录
      int existDownloadLength = readDownloadInfo(threadid);//原来下载的数据量

      //计算最新的下载
      int newDownloadLength = existDownloadLength + len;

      //更新下载记录 从新记录最新下载位置
      updateDownloadInfo(threadid, newDownloadLength);

      //更新进度条的显示 下载的百分比
      Message update_msg = Message.obtain(mHandler, UPDATE_VIEW, len, 0);
      update_msg.sendToTarget();
      //模拟 看到进度条动的效果
      SystemClock.sleep(50);
     }
     inputStream.close();
     raf.close();
     Log.i(TAG, "第"+threadid+"条线程下载完成");
    }

   } catch (Exception e) {
    e.printStackTrace();
   }
  }
 }
 /**
  * 读取指定线程的下载数据量
  * @param threadid 线程的id
  * @return
  * @throws Exception
  */
 public int readDownloadInfo(int threadid) throws Exception{
  //下载记录文件
  File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
  BufferedReader br = new BufferedReader(new FileReader(file));
  //读取一行数据
  String content = br.readLine();

  int downlength = 0;
  //如果该文件第一次创建去执行读取操作 文件里面的内容是 null
  if(!TextUtils.isEmpty(content)){
   downlength = Integer.parseInt(content);
  }
  //关闭流
  br.close();
  return downlength;
 }
 /**
  * 更新下载记录
  * @param threadid
  * @param newDownloadLength
  */
 public void updateDownloadInfo(int threadid,int newDownloadLength) throws Exception{
  //下载记录文件
  File file = new File(Environment.getExternalStorageDirectory(),threadid+".txt");
  FileWriter fw = new FileWriter(file);
  fw.write(newDownloadLength+"");
  fw.close();
 }

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

}

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