Question

我写了这段代码

    class DownloadFileFromURL extends AsyncTask<String, String, String>
{
    @Override
    protected void onPreExecute()
    {
        super.onPreExecute();
            pDialog = new ProgressDialog(getContext());
            pDialog.setMessage("Downloading file. Please wait...");
            pDialog.setIndeterminate(false);
            pDialog.setMax(100);
            pDialog.setProgressStyle(ProgressDialog.STYLE_HORIZONTAL);
            pDialog.setCancelable(true);
            pDialog.show();

    }

    @Override
    protected String doInBackground(String... f_url)
    {
        int count;
        try
        {
            URL url = new URL(f_url[0]);
            URLConnection conection = url.openConnection();
            conection.connect();          
            int lenghtOfFile = conection.getContentLength();
            InputStream input = new BufferedInputStream(url.openStream(), 8192);
            OutputStream output = new FileOutputStream("/sdcard/downloadedfile.mp3");
            byte data[] = new byte[1024];
            long total = 0;
            while ((count = input.read(data)) != -1)
            {
                total += count;
                publishProgress(""+(int)((total*100)/lenghtOfFile));
                output.write(data, 0, count);
            }
            output.flush();
            output.close();
            input.close();

        }
        catch (Exception e)
        {
            Log.e("Error: ", e.getMessage());
        }
        return null;
    }
    protected void onProgressUpdate(String... progress)
    {            
        ViewHolder.progressbar.setProgress(Integer.parseInt(progress[0]));
    }
    @Override
    protected void onPostExecute(String file_url) {

            Handler mHandler = new Handler();
            mHandler.postDelayed(new Runnable() {

                @Override
                public void run() {
                    Dismiss();
                }
            }, 1000L);
        }
    }
    public void Dismiss(){
        pDialog.dismiss();
    }

对于Web应用程序，我收到此错误java.lang.NullPointerException：null 在com.example.demo.Controller.StudentsController.create（StudentsController.java:27）〜[classes /：na] 当我尝试使用其功能访问页面时，它不起作用只是给我这个错误是什么问题？此外，当我初始化IStudent Repository界面时，IntelliJ告诉我，即使我用它来创建方法，studentRepository也没有分配。

Answer 1

您没有注入IStudentsRepository。使用@Autowired

您可以像这样使用Field Injection

@Autowired
private IStudentsRepository studentsRepository;

或者最好的方法是使用构造函数注入。

@Controller
public class StudentsController {

private ArrayList<student> students = new ArrayList<>();

private final IStudentsRepository studentsRepository;

@Autowired
public StudentsController(final IStudentsRepository studentsRepository) {
   this.studentsRepository = studentsRepository;
}

接口java / spring的问题

1 个答案: