Not able to understant object initialisation

[Rahul Shivsharan]

Performer.java file

package com.inter;

public interface Performer{
	public void perform();
}

Juggler.java file

package com.impl;
import com.inter.Performer;

public class Juggler implements Performer{
	private int beanbags = 3;

	public Juggler(int beanbags){		
		this.beanbags = beanbags;
	}
	
	@Override
	public void perform(){		
		System.out.println(" JUGGLING "+beanbags+" BEANBAGS ");
	}
}

bean-prac-cfg.xml file

<?xml version="1.0" encoding="UTF-8"?>
<beans	xmlns="http://www.springframework.org/schema/beans"
		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		xsi:schemaLocation="http://www.springframework.org/schema/beans
							http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
		
		<bean id="jgl-pojo" class="com.impl.Juggler">
			<constructor-arg  value="34" />
		</bean>
</beans>							

MainPractise04.java file, which i run ,

package com.main;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import org.springframework.beans.factory.BeanFactory; 
import com.inter.Performer; 


public class MainPractise04{
	public static void main(String [] args){
		BeanFactory beanFactory = null;
		Performer myObj = null;
		try{
			beanFactory = new ClassPathXmlApplicationContext("bean-prac-cfg.xml");
			myObj = (Performer) beanFactory.getBean("jgl-pojo");			
			myObj.perform();
		}catch(Exception e){
			e.printStackTrace();
		}
	}
}

When i run the above file, the program runs fine and prints the sop in method perform();

but when i switch the xml file to new xml ie. bean-cfg.xml as follows,

<?xml version="1.0" encoding="UTF-8"?>
<beans	xmlns="http://www.springframework.org/schema/beans"
		xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
		xsi:schemaLocation="http://www.springframework.org/schema/beans
							http://www.springframework.org/schema/beans/spring-beans-3.0.xsd">
		<bean id="contractEmp" class="com.impl.ContractEmpl" />
		<bean id="permanentEmp" class="com.impl.PermanentEmpl" />
		<bean id="logBean" class="com.jal.LoggerChk" />
		<bean id="dms" class="com.jal.ConnectionDMS" />
		
		<bean id="emplServiceObj" class="com.service.EmployeeService">
			<property name="emp" ref="contractEmp" />
		</bean>					
		
		<bean id="init-pojo" class="com.jal.LifeCycleBean">
			<property name="studentName" value="David Serverkartha Sankulichit" />
		</bean>
		
		<bean id="jgl-pojo" class="com.impl.Juggler">
			<constructor-arg  value="34" />
		</bean>
</beans>							

and in MainPractise04.java, i change the path of called xml to bean-cfg.xml,
the perform() method is not called and i get Nullpointerexception, ie. obj is still null, thought the constructor sop of Juggler.java is called

why so ?

[Rahul Shivsharan]

this the output, of the above code when i add bean-cfg.xml, and run MainPractise04.java from command prompt

D:\Rahul S Shivsharan\Practise\Spring Project>ant run -DclassnameParam=com.main.MainPractise04
Buildfile: D:\Rahul S Shivsharan\Practise\Spring Project\build.xml

run:
     [java] Aug 24, 2011 3:15:31 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
     [java] INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1c1c9dc: startup date [Wed Aug 24 15:15:31 I
     [java] Aug 24, 2011 3:15:32 PM org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
     [java] INFO: Loading XML bean definitions from class path resource [bean-cfg.xml]
     [java] 1> LifeCycleBean is initialised....
     [java] 2> in setter of StudentName
     [java] 3> set Bean Name init-pojo
     [java] 4> Set Bean Factory
     [java] 6> After properties set
     [java] Aug 24, 2011 3:15:32 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
     [java] INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1dbad5b: defining bea
-pojo,jgl-pojo]; root of factory hierarchy
     [java]  ContractEmpl initialised
     [java] 5> Post process before initialisation
     [java]  PermanentEmpl initialised
     [java] 5> Post process before initialisation
     [java]  LoggerChk initialised...
     [java] 5> Post process before initialisation
     [java]  ConnectionDMS initialised...
     [java] 5> Post process before initialisation
     [java]  EmployeeService initialised...
     [java]  in setter of Empoyee...
     [java] 5> Post process before initialisation
     [java]  JUGGLER INSTATIATED....
     [java] 5> Post process before initialisation
     [java] java.lang.NullPointerException
     [java]     at com.main.MainPractise04.main(Unknown Source)
     [java]     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     [java]     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
     [java]     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
     [java]     at java.lang.reflect.Method.invoke(Method.java:601)
     [java]     at org.apache.tools.ant.taskdefs.ExecuteJava.run(ExecuteJava.java:217)
     [java]     at org.apache.tools.ant.taskdefs.ExecuteJava.execute(ExecuteJava.java:152)
     [java]     at org.apache.tools.ant.taskdefs.Java.run(Java.java:771)
     [java]     at org.apache.tools.ant.taskdefs.Java.executeJava(Java.java:221)
     [java]     at org.apache.tools.ant.taskdefs.Java.executeJava(Java.java:135)
     [java]     at org.apache.tools.ant.taskdefs.Java.execute(Java.java:108)
     [java]     at org.apache.tools.ant.UnknownElement.execute(UnknownElement.java:291)
     [java]     at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
     [java]     at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
     [java]     at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
     [java]     at java.lang.reflect.Method.invoke(Method.java:601)
     [java]     at org.apache.tools.ant.dispatch.DispatchUtils.execute(DispatchUtils.java:106)
     [java]     at org.apache.tools.ant.Task.perform(Task.java:348)
     [java]     at org.apache.tools.ant.Target.execute(Target.java:390)
     [java]     at org.apache.tools.ant.Target.performTasks(Target.java:411)
     [java]     at org.apache.tools.ant.Project.executeSortedTargets(Project.java:1399)
     [java]     at org.apache.tools.ant.Project.executeTarget(Project.java:1368)
     [java]     at org.apache.tools.ant.helper.DefaultExecutor.executeTargets(DefaultExecutor.java:41)
     [java]     at org.apache.tools.ant.Project.executeTargets(Project.java:1251)
     [java]     at org.apache.tools.ant.Main.runBuild(Main.java:809)
     [java]     at org.apache.tools.ant.Main.startAnt(Main.java:217)
     [java]     at org.apache.tools.ant.launch.Launcher.run(Launcher.java:280)
     [java]     at org.apache.tools.ant.launch.Launcher.main(Launcher.java:109)
     [echo] Java running completed

BUILD SUCCESSFUL
Total time: 1 second

D:\Rahul S Shivsharan\Practise\Spring Project>

[Mark Spritzler]

Do me a favor and change the following.

Remove the try catch, no Idea why you need that there. It looks to me like you are trying things out, and the exception if thrown will be printed out anyway.

change

BeanFactory beanFactory = null;
beanFactory = new ClassPathXmlApplicationContext("bean-prac-cfg.xml");


so your code to start should look like this

public static void main(String[] args) {
    ApplicationContext context = new ClassPathXmlApplicationContext("bean-prac-cfg.xml");
    Performer myObj = (Performer)context.getBean("jgl-pojoj");
    myObj.perform();
}

That is much cleaner and what you should be doing using either Spring 2.5.6 or Spring 3.x

If you are trying to learn on an older version of Spring, I recommend using the latest.

Mark

[Mark Spritzler]

As far as your error, what is different. I would say the other beans, so I would say one of the other beans has a problem. And I am going to guess, because the stack trace is too short there to show the real error. (By the, way read exceptions in Spring from bottom up, looking for the true root cause of the exception) I would say it is the initBean that is the cause of the problems.

Mark