網路許可權：

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

MainActivity

downloadAPK(bean.getData().getApkUrl(),"APK");

private void downloadAPK(String versionUrl, String versionName) {
    //建立下載任務
DownloadManager.Request request = new DownloadManager.Request(Uri.parse(versionUrl));
    request.setAllowedOverRoaming(false);//漫遊網路是否可以下載
//設定檔案型別，可以在下載結束後自動開啟該檔案
 
MimeTypeMap mimeTypeMap = MimeTypeMap.getSingleton();
    String mimeString = mimeTypeMap.getMimeTypeFromExtension(MimeTypeMap.getFileExtensionFromUrl(versionUrl));
    request.setMimeType(mimeString);

    //在通知欄中顯示，預設就是顯示的
request.setNotificationVisibility(DownloadManager.Request.VISIBILITY_VISIBLE);
    request.setVisibleInDownloadsUi
 
(true);

    //sdcard的目錄下的download資料夾，必須設定
request.setDestinationInExternalPublicDir("/download/", versionName);
    //request.setDestinationInExternalFilesDir(),也可以自己制定下載路徑
//將下載請求加入下載佇列
downloadManager = (DownloadManager) MainActivity.this.getSystemService(MainActivity.this.DOWNLOAD_SERVICE);
    //加入下載佇列後會給該任務返回一個long型的id，
//通過該id可以取消任務，重啟任務等等，看上面原始碼中框起來的方法
mTaskId = downloadManager.enqueue(request);

    //註冊廣播接收者，監聽下載狀態
MainActivity.this.registerReceiver(receiver,new IntentFilter(DownloadManager.ACTION_DOWNLOAD_COMPLETE));
}

private BroadcastReceiver receiver = new BroadcastReceiver() {
    @Override
public void onReceive(Context context, Intent intent) {
        checkDownloadStatus();//檢查下載狀態
}
};

private void checkDownloadStatus() {
    DownloadManager.Query query = new DownloadManager.Query();
    query.setFilterById(mTaskId);//篩選下載任務，傳入任務ID，可變引數
Cursor c = downloadManager.query(query);
    if (c.moveToFirst()) {
        int status = c.getInt(c.getColumnIndex(DownloadManager.COLUMN_STATUS));
        switch (status) {
            case DownloadManager.STATUS_PAUSED:
                Log.i("zzz",">>>下載暫停");
            case DownloadManager.STATUS_PENDING:
                Log.i("zzz",">>>下載延遲");
            case DownloadManager.STATUS_RUNNING:
                Log.i("zzz",">>>正在下載");
                break;
            case DownloadManager.STATUS_SUCCESSFUL:
                Log.i("zzz",">>>下載完成");
                File file = Environment.getExternalStorageDirectory();
                installAPK(new File(file+"/Download"));
                break;
            case DownloadManager.STATUS_FAILED:
                Log.i("zzz",">>>下載失敗");
                break;
        }
    }
}

protected void installAPK(File file) {
    if (!file.exists()) return;
    Intent intent = new Intent(Intent.ACTION_VIEW);
    Uri uri = Uri.parse("file://" + file.toString());
    intent.setDataAndType(uri, "application/vnd.android.package-archive");
    //在服務中開啟activity必須設定flag,後面解釋
intent.setFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
    MainActivity.this.startActivity(intent);
}