Android快速实现断点续传的方法

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="下载"    android:id="@+id/bt_download"    />  <Button    android:layout_width="wrap_content"    android:layout_height="wrap_content"    android:text="暂停"    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(@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);    //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();      }    }    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);      }    });  }  //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);  }}