Android使用Handler实现下载文件功能

本文实例为大家分享了Android实现下载文件的具体代码，供大家参考，具体内容如下

1.实现效果

直接上图：

2.代码实现

在AndroidManifest.xml文件中声明申请的权限，如下所示：

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

新建一个名为DownloadDemo的项目，activity_main.xml代码如下：

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout 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"
android:gravity="center_horizontal"
android:orientation="vertical"
tools:context=".MainActivity">

<Button
 android:id="@+id/button"
 android:layout_width="wrap_content"
 android:layout_height="wrap_content"
 android:layout_marginTop="10dp"
 android:text="下载" />

<ProgressBar
 android:id="@+id/progressBar"
 style="?android:attr/progressBarStyleHorizontal"
 android:layout_width="match_parent"
 android:layout_height="wrap_content"
 android:layout_margin="10dp"
 android:max="100"
 android:progress="0" />
</LinearLayout>

MainActivity.class代码如下：

public class MainActivity extends AppCompatActivity implements View.OnClickListener {

public static final String APP_URL = "http://download.sj.qq.com/upload/connAssitantDownload/upload/MobileAssistant_1.apk";
public static final int DOWNLOAD_MESSAGE_CODE = 100001;
private static final int DOWNLOAD_MESSAGE_FAIL_CODE = 100002;
public static final int REQUEST_CODE = 1;
private Button button;
private ProgressBar progressBar;
private MyHandler mHandler;

@Override
protected void onCreate(Bundle savedInstanceState) {
 super.onCreate(savedInstanceState);
 setContentView(R.layout.activity_main);
 initView();
 askPermission();
 mHandler = new MyHandler(this);
}

public static class MyHandler extends Handler {
 final WeakReference<MainActivity> mWeakReference;

public MyHandler(MainActivity activity) {
  this.mWeakReference = new WeakReference<>(activity);
 }

@Override
 public void handleMessage(Message msg) {
  MainActivity activity = mWeakReference.get();
  super.handleMessage(msg);
  switch (msg.what) {
   case DOWNLOAD_MESSAGE_CODE:
    activity.progressBar.setProgress((Integer) msg.obj);
    if (((Integer) msg.obj) == 100) {
     Toast.makeText(activity, "文件下载已完成！", Toast.LENGTH_SHORT).show();
    }
    break;
   case DOWNLOAD_MESSAGE_FAIL_CODE:
    Toast.makeText(activity, "文件下载失败！", Toast.LENGTH_SHORT).show();
    break;
  }
 }
}

/**
 * 申请权限
 */
private void askPermission() {
 //将所需申请的权限添加到List集合中
 List<String> permissionList = new ArrayList<>();
 if (ContextCompat.checkSelfPermission(MainActivity.this,
   Manifest.permission.WRITE_EXTERNAL_STORAGE) != PackageManager.PERMISSION_GRANTED) {
  permissionList.add(Manifest.permission.WRITE_EXTERNAL_STORAGE);
 }
 //判断权限列表是否为空，若不为空，则向用户申请权限，否则则直接执行操作
 if (!permissionList.isEmpty()) {
  String[] permissions = permissionList.toArray(new String[permissionList.size()]);
  ActivityCompat.requestPermissions(MainActivity.this, permissions, REQUEST_CODE);
 } else {
  //TODO
  button.setOnClickListener(this);
 }
}

/**
 * 用户对请求权限的dialog做出响应之后,会处理请求权限的响应
 *
 * @param requestCode 请求码
 * @param permissions 权限的集合
 * @param grantResults 权限授予的结果
 */
@Override
public void onRequestPermissionsResult(int requestCode, @NonNull String[] permissions, @NonNull int[] grantResults) {
 super.onRequestPermissionsResult(requestCode, permissions, grantResults);
 switch (requestCode) {
  case REQUEST_CODE:
   if (grantResults.length > 0) {
    for (int result : grantResults) {
     if (result != PackageManager.PERMISSION_GRANTED) {
      Toast.makeText(this, "必须同意所有权限才能使用本程序", Toast.LENGTH_SHORT).show();
      finish();
      return;
     }
    }
    //TODO
    button.setOnClickListener(this);
   } else {
    Toast.makeText(this, "权限申请失败！", Toast.LENGTH_SHORT).show();
    finish();
   }
   break;
  default:
   break;
 }
}

/**
 * 点击事件
 *
 * @param v
 */
@Override
public void onClick(View v) {
 switch (v.getId()) {
  case R.id.button:
   new Thread(new Runnable() {
    @Override
    public void run() {
     download(APP_URL);
    }
   }).start();
   break;
 }
}

/**
 * 下载
 *
 * @param appUrl
 */
private void download(String appUrl) {
 try {
  //实例化一个url对象
  URL url = new URL(appUrl);
  //获取URLConnection对象
  URLConnection urlConnection = url.openConnection();
  //获取输入流
  InputStream inputStream = urlConnection.getInputStream();
  //获取文件的总长度
  int contentLength = urlConnection.getContentLength();
  //设置软件下载到手机存储的位置文件夹名称
  String downloadFolderName = Environment.getExternalStorageDirectory()
    + File.separator + "MyApp" + File.separator;
  File file = new File(downloadFolderName);
  //若文件夹不存在则进行创建
  if (!file.exists()) {
   file.mkdir();
  }
  String fileName = downloadFolderName + "chaixingsi.apk";
  File apkFile = new File(fileName);
  if (apkFile.exists()) {
   apkFile.delete();
  }
  int downloadContentLength = 0;
  int length = 0;
  byte[] bytes = new byte[1024];
  OutputStream outputStream = new FileOutputStream(fileName);
  while ((length = inputStream.read(bytes)) != -1) {
   outputStream.write(bytes, 0, length);
   downloadContentLength += length;
   /**
    * 发送消息通知主线程去更新UI
    */
   Message message = Message.obtain();
   message.obj = downloadContentLength * 100 / contentLength;
   message.what = DOWNLOAD_MESSAGE_CODE;
   mHandler.sendMessage(message);
  }
  inputStream.close();
  outputStream.close();
 } catch (MalformedURLException e) {
  //下载失败的话也发送消息
  notifyDownloadFailed();
  e.printStackTrace();
 } catch (IOException e) {
  notifyDownloadFailed();
  e.printStackTrace();
 }
}

/**
 * 通知下载失败
 */
private void notifyDownloadFailed() {
 Message message = Message.obtain();
 message.what = DOWNLOAD_MESSAGE_FAIL_CODE;
 mHandler.sendMessage(message);
}

/**
 * 初始化视图
 */
private void initView() {
 button = findViewById(R.id.button);
 progressBar = findViewById(R.id.progressBar);
}
}

3.快捷键总结

提取方法：Ctrl+Alt+M；
提取变量：Ctrl+Alt+V；
提取常量：Ctrl+Alt+C；

来源：https://blog.csdn.net/qingjianduoyun/article/details/80628571