@Inject instance is null on start up servlet

[vipinlal.tg]

Hello All,

am new in CDI, (Container Dependency Injection).

My problem is and injecting one bean class and using that injected bean class instance used in servlet constructor.

The servlet is call on start up  of server, on that time am getting null at the point of injected bean instance.

How can i resolve this issue

Am highlighting the Injecting bean part with red color

import java.io.IOException;

import java.util.Date;

import java.util.Timer;

import java.util.concurrent.TimeUnit;

import javax.inject.Inject;

import javax.servlet.ServletException;

import javax.servlet.annotation.WebServlet;

import javax.servlet.http.HttpServlet;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

import com.beo.udi.fda.access.MasAccess;

import com.beo.udi.util.ApplicationFilePath;

import com.beo.udi.util.AutoFileChecker;

/**

* Servlet implementation class InitialServlet

*/

@WebServlet("/InitialServlet")

public class InitialServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    int MIN_TIME= 1000 * 60;

    /**

     * @see HttpServlet#HttpServlet()

     */

   @Inject MasAccess mas;

    public InitialServlet() {

        super();

        new ApplicationFilePath();

        Timer time = new Timer();

        AutoFileChecker task = new AutoFileChecker();

        time.schedule(task, new Date(), TimeUnit.MINUTES.toMinutes(MIN_TIME));

        mas.checkCount(); //getting null pointer exception here

    }

    /**

     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

     */

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        // TODO Auto-generated method stub

        response.getWriter().append("Served at: ").append(request.getContextPath());

    }

    /**

     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

     */

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        // TODO Auto-generated method stub

        doGet(request, response);

    }

}

Thanks & Regards

Vipin

[jaysensharma]

Let the servlet initialized properly.

Servlets are initialized by the web container. servlets is not initialized unlike other java class. Constructor are used to initialize an explicitly created object while servlet use a different method 'init()' for their initialization.

Servlet Constructor is not the right place to put some initialization code rather put it  inside the   "init(ServletConfig config)" life-cycle method of Servlet.

See:  https://docs.oracle.com/javaee/6/api/javax/servlet/GenericServlet.html#init(javax.servlet.ServletConfig)

Example:

@Inject MasAccess mas;
    public InitialServlet() {
        super();
        new ApplicationFilePath();
        Timer time = new Timer();
        AutoFileChecker task = new AutoFileChecker();
        time.schedule(task, new Date(), TimeUnit.MINUTES.toMinutes(MIN_TIME));
        //  //////////      REMOVED   ->   mas.checkCount(); //getting null pointer exception here
    }

    public void init(ServletConfig servletConfig) {
          System.out.println("### **** [init(ServletConfig servletConfig)]: mas.checkCount() invoked Here");
          mas.checkCount();
    }

  /*
    Alternate approach by using @PostConstruct annotation as following:
    @javax.annotation.PostConstruct
    public void hello() {
          System.out.println("### **** [hello] PostConstruct() invoked.");
         mas.checkCount();
    }
   */

Or alternatively you may try "javax.annotation.PostConstruct" as demonstrated above.

https://docs.oracle.com/javaee/5/api/javax/annotation/PostConstruct.html

[vipinlal.tg]

Hello Jay SenSharma,

My requirement is that, on server start up i need to read some file from specific location also i need to check every 1 min to for any file came.

for that am created one TimerTask class AutoFileChecker and it will call on start of the server from servlet.

The issue is am using CDI concept for calling between beans. and these beans are also using for this read file handling,

on startup server am creating instance of requestscoped beans using @inject but it is getting null on start up

Sample code below

class InitialServlet.java calling on start up

public class InitialServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    int MIN_TIME= 1000 * 60;

    /**

     * @see HttpServlet#HttpServlet()

     */

    public InitialServlet() {

        super();

    }

    AutoFileChecker task;

    @Override

    public void init(ServletConfig config) throws ServletException {

        new ApplicationFilePath();

        Timer time = new Timer();

        //AutoFileChecker task = new AutoFileChecker();

        time.schedule(task, new Date(), TimeUnit.MINUTES.toMinutes(MIN_TIME));

    }

    /**

     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)

     */

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        // TODO Auto-generated method stub

        response.getWriter().append("Served at: ").append(request.getContextPath());

    }

    /**

     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)

     */

    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        // TODO Auto-generated method stub

        doGet(request, response);

    }

    @Inject

    public void setTask(AutoFileChecker task) {

        this.task = task;

    }

}

AutoFileChecker.java

public class AutoFileChecker extends TimerTask implements ApplicationFilePathInterface{

    @Override

    public void run() {

        readReplayMessageFiles(ApplicationFilePath.getApplicationPath().getFolderPath(udi_replay_message_location),

                ApplicationFilePath.getApplicationPath().getFolderPath(udi_replay_message_done_location));

        new AutoSend().doAutoSend();

    }

}

public class AutoSend implements ApplicationFilePathInterface{

@inject private MasAccess accesss;

    public AutoSend() {

        // TODO Auto-generated constructor stub

    }

    public void doAutoSend() {

       this.accesss.checkCount();//getting null pointer here

     }

}

@RequestScoped

public class MasAccess {

     //some code

}