android使用AsyncTask实现多线程下载实例

asynctask不仅方便我们在子线程中对ui进行更新操作，还可以借助其本身的线程池来实现多线程任务。下面是一个使用asynctask来实现的多线程下载例子。

01 效果图

02 核心类 - downloadtask.class

public class downloadtask extends asynctask<string, integer, integer> {
  public static final int type_success = 0;
  public static final int type_failure = 1;
  public static final int type_pause = 2;
  public static final int type_cancel = 3;

  public int positiondownload;

  private boolean ispaused = false;
  private boolean iscancelled = false;

  private downloadlistener downloadlistener;
  private int lastprogress;

  public downloadtask(downloadlistener downloadlistener){
    this.downloadlistener = downloadlistener;
  }

  public void setdownloadlistener(downloadlistener downloadlistener){
    this.downloadlistener = downloadlistener;
  }

  @override
  protected integer doinbackground(string... params) {
    inputstream is = null;
    randomaccessfile savedfile = null;
    file file = null;

    long downloadlength = 0;
    string downloadurl = params[0];
    positiondownload = integer.parseint(params[1]);
    string filename = downloadurl.substring(downloadurl.lastindexof("/"));
    string directory = environment.getexternalstoragepublicdirectory(environment.directory_downloads).getpath();
    file = new file(directory + filename);

    if(file.exists()){
      downloadlength = file.length();
    }

    long contentlength = getcontentlength(downloadurl);
    if(contentlength == 0){
      return type_failure;
    } else if(contentlength == downloadlength){
      return type_success;
    }

    okhttpclient client = new okhttpclient();
    request request = new request.builder()
                  .addheader("range", "bytes="+downloadlength+"-")
                  .url(downloadurl)
                  .build();
    try {
      response response = client.newcall(request).execute();
      if(response != null){
        is = response.body().bytestream();
        savedfile = new randomaccessfile(file, "rw");
        savedfile.seek(downloadlength);
        byte[] buffer = new byte[1024];
        int total = 0;
        int length;

        while((length = is.read(buffer)) != -1){
          if(iscancelled){
            response.body().close();
            return type_cancel;
          } else if(ispaused) {
            response.body().close();
            return type_pause;
          }

          total += length;
          savedfile.write(buffer, 0, length);

          int progress = (int) ((total + downloadlength) * 100 / contentlength);
          int currentdownload = (int) (total + downloadlength);
          publishprogress(positiondownload, progress, currentdownload, (int) contentlength);
        }

        response.body().close();
        return type_success;
      }
    } catch (ioexception e) {
      e.printstacktrace();
    } finally {
      try {
        if(is != null) is.close();
        if(savedfile != null) savedfile.close();
        if(iscancelled && file != null) file.delete();
      } catch (ioexception e) {
        e.printstacktrace();
      }
    }

    return type_failure;
  }

  @override
  protected void onprogressupdate(integer... values) {
    int progress = values[1];
    if(progress > lastprogress){
      downloadlistener.onprogress(values[0], progress, values[2], values[3]);
      lastprogress = progress;
    }
  }

  @override
  protected void onpostexecute(integer status) {
    switch (status){
      case type_success:
        downloadlistener.onsuccess(positiondownload);
        break;
      case type_failure:
        downloadlistener.onfailure();
        break;
      case type_pause:
        downloadlistener.onpause();
        break;
      case type_cancel:
        downloadlistener.oncancel();
        break;
    }
  }

  public void pausedownload(){
    ispaused = true;
  }

  public void canceldownload(){
    iscancelled = true;
  }

  private long getcontentlength(string downloadurl) {
    okhttpclient client = new okhttpclient();
    request request = new request.builder()
                  .url(downloadurl)
                  .build();
    response response = null;
    try {
      response = client.newcall(request).execute();
      if(response != null && response.issuccessful()){
        long contentlength = response.body().contentlength();
        response.body().close();
        return contentlength;
      }
    } catch (ioexception e) {
      e.printstacktrace();
    }

    return 0;
  }
}

03 核心类 - downloadservice.class

public class downloadservice extends service {
  private map<string, downloadtask> downloadtaskmap = new hashmap<>();

  private downloadbinder mbinder = new downloadbinder();

  @override
  public ibinder onbind(intent intent) {
    return mbinder;
  }

  private notification getnotification(string title, int progress) {
    intent intent = new intent(this, mainactivity.class);
    pendingintent pendingintent = pendingintent.getactivity(this, 0, intent, 0);

    notificationcompat.builder builder = new notificationcompat.builder(this);
    builder.setsmallicon(r.mipmap.ic_launcher);
    builder.setlargeicon(bitmapfactory.decoderesource(getresources(), r.mipmap.ic_launcher));
    builder.setcontentintent(pendingintent);
    builder.setcontenttitle(title);
    if(progress > 0){
      builder.setcontenttext(progress + "%");
      builder.setprogress(100, progress, false);
    }


    return builder.build();
  }

  private notificationmanager getnotificationmanager() {
    return (notificationmanager) getsystemservice(notification_service);
  }


  class downloadbinder extends binder {
    public void startdownload(string url, int position, downloadlistener listener){
      if(!downloadtaskmap.containskey(url)){
        downloadtask downloadtask = new downloadtask(listener);
        downloadtask.executeonexecutor(asynctask.thread_pool_executor, url, position+"");
        downloadtaskmap.put(url, downloadtask);
        if(downloadtaskmap.size() == 1){
          startforeground(1, getnotification("正在下载" + downloadtaskmap.size(), -1));
        } else{
          getnotificationmanager().notify(1, getnotification("正在下载" + downloadtaskmap.size(), -1));
        }
      }
    }

    public void updatedownload(string url, downloadlistener listener){
      if(downloadtaskmap.containskey(url)){
        downloadtask downloadtask = downloadtaskmap.get(url);
        if(downloadtask != null){
          downloadtask.setdownloadlistener(listener);
        }
      }

    }

    public void pausedownload(string url){
      if(downloadtaskmap.containskey(url)){
        downloadtask downloadtask = downloadtaskmap.get(url);
        if(downloadtask != null){
          downloadtask.pausedownload();
        }

        downloadtaskmap.remove(url);

        if(downloadtaskmap.size() > 0){
          getnotificationmanager().notify(1, getnotification("正在下载" + downloadtaskmap.size(), -1));
        } else {
          stopforeground(true);
          getnotificationmanager().notify(1, getnotification("全部暂停下载", -1));
        }
      }
    }

    public void downloadsuccess(string url){
      if(downloadtaskmap.containskey(url)){
        downloadtask downloadtask = downloadtaskmap.get(url);
        downloadtaskmap.remove(url);
        if(downloadtask != null){
          downloadtask = null;
        }

        if(downloadtaskmap.size() > 0){
          getnotificationmanager().notify(1, getnotification("正在下载" + downloadtaskmap.size(), -1));
        } else {
          stopforeground(true);
          getnotificationmanager().notify(1, getnotification("下载成功", -1));
        }

      }
    }

    public boolean isdownloading(string url){
      if(downloadtaskmap.containskey(url)){
        return true;
      }

      return false;
    }

    public void canceldownload(string url){
      if(downloadtaskmap.containskey(url)){
        downloadtask downloadtask = downloadtaskmap.get(url);
        if(downloadtask != null){
          downloadtask.canceldownload();
        }
        downloadtaskmap.remove(url);

        if(downloadtaskmap.size() > 0){
          getnotificationmanager().notify(1, getnotification("正在下载" + downloadtaskmap.size(), -1));
        } else {
          stopforeground(true);
          getnotificationmanager().notify(1, getnotification("全部取消下载", -1));
        }
      }

      if(url != null){
        string filename = url.substring(url.lastindexof("/"));
        string directory = environment.getexternalstoragepublicdirectory(environment.directory_downloads).getpath();
        file file = new file(directory + filename);

        if(file.exists()){
          file.delete();
          toast.maketext(downloadservice.this, "deleted", toast.length_short).show();
        }
      }
    }
  }
}

04 源码

下载地址

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