Dependency Injection not working?

[vShyam Sundar]

Hi all,
Dependency Injection in EJB3 is allowed only on manageable classes? What is meant by this?
I tried to execute program with JNDI lookup and same With Dependency Injection. Unfortunately the code with Dependency Injection doesn't work. When i tried to execute the program with DI. I got a null pointer exception

I have pasted the code below. Please provide your valuable inputs

import javax.naming.InitialContext;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.shyam.EJBInteface.Calculator;


public class ActionServlet extends HttpServlet{
	
	private Calculator calculator = null;
	public void doGet(HttpServletRequest request, 
			  HttpServletResponse response)
			  throws ServletException,IOException{
	try{
		
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out.print("Hurray!!!!!!!!!!In servlet");
		System.out.println("In servelt");
		int c=0;
		InitialContext ic = new InitialContext();
		calculator = (Calculator) ic.lookup("Sample1/CalculatorBean/remote");
		out.print("Hurray!!!!!!!!!!After calculation"+calculator.add(4, 5));
		RequestDispatcher rd = request.getRequestDispatcher("/sample2.jsp");
		rd.include(request, response);
	}catch (Exception e) {
		e.printStackTrace();
		// TODO: handle exception
	}
	}

}

and my business interface is:.

package com.shyam.EJBInteface;

import javax.ejb.Remote;

@Remote
public interface Calculator {
 public int add(int a,int b);
 public int sub(int a,int b);
 public int mult(int a,int b);
 public int div(int a,int b);
}

and stateless bean code is as follows:

package com.shyam.EJBBean;

import javax.ejb.Remote;
import javax.ejb.Stateless;

import com.shyam.EJBInteface.Calculator;
@Stateless(name="CalculatorBean")
@Remote(Calculator.class)  
public class CalculatorBean implements Calculator {
	public CalculatorBean(){
	
	}
	public int add(int a,int b){
		int c=0;
		c=a+b;
		System.out.println("The addition value is"+c);
		return c;
	}
	public int sub(int a,int b){
		int c=0;
		c=a-b;
		System.out.println("The subtraction  value is"+c);
		return c;
	}
	public int mult(int a,int b){
		int c=0;
		c=a*b;
		System.out.println("The multiplication value is"+c);
		return c;
	}
	public int div(int a,int b){
		int c=0;
		c=a/b;
		System.out.println("The divison value is"+c);
		return c;
	}
}

The above code executed well but when i changed the action servlet to achieve dependency injection, I got the null pointer exception.

 
import java.io.IOException;
import java.io.PrintWriter;

import javax.ejb.EJB;
import javax.servlet.RequestDispatcher;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.shyam.EJBInteface.Calculator;


public class ActionServlet extends HttpServlet{
	@EJB
	private Calculator calculator = null;
	public void doGet(HttpServletRequest request, 
			  HttpServletResponse response)
			  throws ServletException,IOException{
	try{
		
		response.setContentType("text/html");
		PrintWriter out = response.getWriter();
		out.print("Hurray!!!!!!!!!!In servlet");
		System.out.println("In servelt");
		int c=0;
		//InitialContext ic = new InitialContext();
		 //calculator = (Calculator) ic.lookup("Sample1/CalculatorBean/remote");
		out.print("Hurray!!!!!!!!!!After calculation"+calculator.add(4, 5));
		RequestDispatcher rd = request.getRequestDispatcher("/sample2.jsp");
		rd.include(request, response);
	}catch (Exception e) {
		e.printStackTrace();
		// TODO: handle exception
	}
	}

}

Thanks,
Shyam.

[Murali Ranga]

jndi name is missing to annotation.
@Stateless(name="CalculatorBean", mappedName="Sample1/CalculatorBean/remote")

[Jaikiran Pai]

Do you have a web.xml? What does it look like? The xsd version declaration should be 2.5 or 3.0 for injection to work.

[vShyam Sundar]

Thanks JaiKiran. It worked now. Previously i just had <web-app> tag in web.xml but now i replaced with

<web-app xmlns="http://java.sun.com/xml/ns/javaee"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/j2ee/web-app_2_5.xsd"
version="2.5">

Any idea on why we need this extra attributes?

and also Dependency Injection is allowed only on managable classes- What is meant by this?

Thanks,
Shyam.

[Jaikiran Pai]

vShyam Sundar wrote:
Any idea on why we need this extra attributes?

That's because prior to web-app version 2.5, dependency injection wasn't available.

vShyam Sundar wrote:
and also Dependency Injection is allowed only on managable classes- What is meant by this?

It means that dependency injection is supported on classes whose lifecycle is managed by the container(s). For example the servlets, EJBs etc...

[vShyam Sundar]

Thanks for your valuable reply