Android多线程断点续传下载实现代码

学习了多线程下载，而且可以断点续传的逻辑，线程数量可以自己选择，但是线程数量过多手机就承受不起，导致闪退，好在有断点续传。

步骤写在了代码的注释里。大概就是获取服务器文件的大小，在本地新建一个相同大小的文件用来申请空间，然后将服务器的文件读下来写到申请的文件中去。若开多线程，将文件分块，计算每个线程下载的开始位置和结束位置。若断点传输，则保存断开后下载的位置，下次将此位置赋给开始下载的位置即可。细节见代码。

下面是效果图：

布局文件activity_main.xml:

<?xml version="1.0" encoding="utf-8"?>
<android.support.constraint.ConstraintLayout xmlns:android="http://schemas.android.com/apk/res/android"
  xmlns:tools="http://schemas.android.com/tools"
  android:layout_width="match_parent"
  android:layout_height="match_parent"
  tools:context=".MainActivity">

  <LinearLayout
    android:layout_width="match_parent"
    android:layout_height="match_parent"
    android:orientation="vertical">

    <EditText
      android:id="@+id/et_path"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:hint="请输入下载路径"
      android:text="http://10.173.29.234/test.exe" />

    <EditText
      android:id="@+id/et_threadCount"
      android:layout_width="match_parent"
      android:layout_height="wrap_content"
      android:hint="请输入线程数量" />

    <Button
      android:layout_width="wrap_content"
      android:layout_height="wrap_content"
      android:onClick="click"
      android:text="下载" />

    <LinearLayout
      android:id="@+id/ll_pb"
      android:layout_width="match_parent"
      android:layout_height="match_parent"
      android:background="#455eee"
      android:orientation="vertical">

    </LinearLayout>
  </LinearLayout>

</android.support.constraint.ConstraintLayout>

创建布局文件，用来动态显示每个线程的进度条

layout.xml:

<?xml version="1.0" encoding="utf-8"?>
<ProgressBar xmlns:android="http://schemas.android.com/apk/res/android"
  android:id="@+id/progressBar"
  style="?android:attr/progressBarStyleHorizontal"
  android:layout_width="match_parent"
  android:layout_height="wrap_content" />

MainActivity.java:

import...;

public class MainActivity extends AppCompatActivity {

  private EditText et_path;
  private EditText et_threadCount;
  private LinearLayout ll_pb;
  private String path;

  private static int runningThread;// 代表正在运行的线程
  private int threadCount;
  private List<ProgressBar> pbList;//集合存储进度条的引用

  @Override
  protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);

    et_path = findViewById(R.id.et_path);
    et_threadCount = findViewById(R.id.et_threadCount);
    ll_pb = findViewById(R.id.ll_pb);
    //添加一个进度条的引用
    pbList = new ArrayList<ProgressBar>();
  }

  //点击按钮实现下载逻辑
  public void click(View view) {
    //获取下载路径
    path = et_path.getText().toString().trim();
    //获取线程数量
    String threadCounts = et_threadCount.getText().toString().trim();
    //移除以前的进度条添加新的进度条
    ll_pb.removeAllViews();
    threadCount = Integer.parseInt(threadCounts);
    pbList.clear();
    for (int i = 0; i < threadCount; i++) {
      ProgressBar v = (ProgressBar) View.inflate(getApplicationContext(), R.layout.layout, null);

      //把v添加到几何中
      pbList.add(v);

      //动态获取进度条
      ll_pb.addView(v);
    }

    //java逻辑移植
    new Thread() {
      @Override
      public void run() {
        /*************/
        System.out.println("你好");
        try {
          URL url = new URL(path);
          HttpURLConnection conn = (HttpURLConnection) url.openConnection();
          conn.setRequestMethod("GET");
          conn.setConnectTimeout(5000);
          int code = conn.getResponseCode();
          if (code == 200) {
            int length = conn.getContentLength();
            // 把运行线程的数量赋值给runningThread
            runningThread = threadCount;

            System.out.println("length=" + length);
            // 创建一个和服务器的文件一样大小的文件，提前申请空间
            RandomAccessFile randomAccessFile = new RandomAccessFile(getFileName(path), "rw");
            randomAccessFile.setLength(length);
            // 算出每个线程下载的大小
            int blockSize = length / threadCount;
            // 计算每个线程下载的开始位置和结束位置
            for (int i = 0; i < length; i++) {
              int startIndex = i * blockSize;// 开始位置
              int endIndex = (i + 1) * blockSize;// 结束位置
              // 特殊情况就是最后一个线程
              if (i == threadCount - 1) {
                // 说明是最后一个线程
                endIndex = length - 1;
              }
              // 开启线程去服务器下载
              DownLoadThread downLoadThread = new DownLoadThread(startIndex, endIndex, i);
              downLoadThread.start();

            }

          }
        } catch (MalformedURLException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
        } catch (IOException e) {
          // TODO Auto-generated catch block
          e.printStackTrace();
        }
        /*************/
      }
    }.start();

  }

  private class DownLoadThread extends Thread {
    // 通过构造方法吧每个线程的开始位置和结束位置传进来
    private int startIndex;
    private int endIndex;
    private int threadID;
    private int PbMaxSize;//代表当前下载（进度条）的最大值
    private int pblastPosition;//如果中断过，这是进度条上次的位置

    public DownLoadThread(int startIndex, int endIndex, int threadID) {
      this.startIndex = startIndex;
      this.endIndex = endIndex;
      this.threadID = threadID;

    }

    @Override
    public void run() {
      // 实现去服务器下载文件
      try {
        //计算进度条最大值
        PbMaxSize = endIndex - startIndex;
        URL url = new URL(path);
        HttpURLConnection conn = (HttpURLConnection) url.openConnection();
        conn.setRequestMethod("GET");
        conn.setConnectTimeout(5000);
        // 如果中间断过，接着上次的位置继续下载，聪慧文件中读取上次下载的位置
        File file = new File(getFileName(path) + threadID + ".txt");
        if (file.exists() && file.length() > 0) {
          FileInputStream fis = new FileInputStream(file);
          BufferedReader bufr = new BufferedReader(new InputStreamReader(fis));
          String lastPosition = bufr.readLine();
          int lastPosition1 = Integer.parseInt(lastPosition);

          //赋值给进度条位置
          pblastPosition = lastPosition1 - startIndex;
          // 改变一下startIndex的值
          startIndex = lastPosition1 + 1;
          System.out.println("线程id：" + threadID + "真实下载的位置：" + lastPosition + "-------" + endIndex);

          bufr.close();
          fis.close();

        }

        conn.setRequestProperty("Range", "bytes=" + startIndex + "-" + endIndex);
        int code = conn.getResponseCode();
        if (code == 206) {
          // 随机读写文件对象
          RandomAccessFile raf = new RandomAccessFile(getFileName(path), "rw");
          // 每个线程从自己的位置开始写

          raf.seek(startIndex);
          InputStream in = conn.getInputStream();
          // 把数据写到文件中
          int len = -1;
          byte[] buffer = new byte[1024];
          int totle = 0;// 代表当前线程下载的大小
          while ((len = in.read(buffer)) != -1) {
            raf.write(buffer, 0, len);
            totle += len;

            // 实现断点续传就是把当前线程下载的位置保存起来，下次再下载的时候按照上次下载的位置继续下载
            int currentThreadPosition = startIndex + totle;// 存到一个txt文本中
            // 用来存储当前线程当前下载的位置
            RandomAccessFile raff = new RandomAccessFile(getFileName(path) + threadID + ".txt", "rwd");
            raff.write(String.valueOf(currentThreadPosition).getBytes());
            raff.close();

            //设置进度条当前的进度
            pbList.get(threadID).setMax(PbMaxSize);
            pbList.get(threadID).setProgress(pblastPosition + totle);
          }
          raf.close();
          System.out.println("线程ID:" + threadID + "下载完成");
          // 将产生的txt文件删除，每个线程下载完成的具体时间不知道
          synchronized (DownLoadThread.class) {
            runningThread--;
            if (runningThread == 0) {
              //说明线程执行完毕
              for (int i = 0; i < threadCount; i++) {

                File filedel = new File(getFileName(path) + i + ".txt");
                filedel.delete();
              }

            }

          }

        }
      } catch (MalformedURLException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
      } catch (IOException e) {
        // TODO Auto-generated catch block
        e.printStackTrace();
      }

    }
  }

  public String getFileName(String path) {
    int start = path.lastIndexOf("/") + 1;
    String subString = path.substring(start);
    String fileName = "/data/data/com.lgqrlchinese.heima76android_11_mutildownload/" + subString;
    return fileName;

  }
}

在清单文件中添加以下权限

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

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