Question

I am developing a desktop application using Swing, but with this I want to use Spring framework to use IOC, and that I want to do using Interface technique. But I am getting nullPointerException when I call a function by instance of an Interface and that interface is implemented by a class in which called function is declared.

Here is my simple app code:

Interface:

public interface IEmpMasterService {    
    public InternalResultsResponse<EmpMaster> maintainEmpMaster(
            EmpMaster empMaster);
}

Implementer class:

public class EmpMasterService implements IEmpMasterService {    
    private IEmpMasterDAO empMasterDAO; 
    public IEmpMasterDAO getEmpMasterDAO() {
        return empMasterDAO;
    }
    public void setEmpMasterDAO(IEmpMasterDAO empMasterDAO) {
        this.empMasterDAO = empMasterDAO;
    }
    @Override
    public InternalResultsResponse<EmpMaster> maintainEmpMaster(
            EmpMaster empMaster) {
        InternalResultsResponse<EmpMaster> response = new InternalResultsResponse<EmpMaster>();
        //some logic her...
        response = getEmpMasterDAO().maintainEmpMaster(request);
        return response;
    }}

DAO Interface:

public interface IEmpMasterDAO {
    InternalResultsResponse<EmpMaster> maintainEmpMaster(
            EmpMasterRequest request);
}
class Implementing DAO:
public class EmpMasterDAO extends HibernateDaoSupport implements IEmpMasterDAO{
    @Override
    public InternalResultsResponse<EmpMaster> maintainEmpMaster(
            EmpMasterRequest empMasterRequest) {
//hibernate code goes here...       
        return resultsResponse;
    }
} 

Main Class:

public class EmpManager extends javax.swing.JFrame {    
    private IEmpMasterService empMasterService;
    private static ApplicationContext context;  
    public IEmpMasterService getEmpMasterService() {
        return empMasterService;
    }
    public void setEmpMasterService(IEmpMasterService empMasterService) {
        this.empMasterService = empMasterService;
    }
public static void main(String args[]) {
        context = new ClassPathXmlApplicationContext(new String[]{"ApplicationContext.xml"});
empMasterService = (EmpMasterService)context.getBean("empMasterService");
}
private void jButton1ActionPerformed(java.awt.event.ActionEvent evt) {
        String name = jTextField1.getText();
        String salary = jTextField2.getText();
        EmpMaster empMaster = new EmpMaster();
        empMaster.setEmpName(name);
        empMaster.setSalary(Double.parseDouble(salary));  
//***** getting Error at this line *****//    
        InternalResultsResponse<EmpMaster> response = getEmpMasterService().maintainEmpMaster(empMaster);       
    }

my ApplicationContext.xml :

<?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">
    <import resource="dataSource.xml"/>
       <bean id="mainFrame" class="org.UI.EmpManager">
        <property name="title"> <value>Spring Example</value></property>    
        <property name="empMasterService" ref="empMasterServiceImpl"></property>    
    </bean>     
    <bean id="empMasterServiceImpl" class="org.service.EmpMasterService">
        <property name="empMasterDAO" ref="empMasterDAOTarget"></property>      
    </bean> 
    <bean id="empMasterDAOTarget" class="org.DAO.EmpMasterDAO">
        <property name="hibernateTemplate" ref="matrixHibernateTemplate"/>
    </bean> 
</beans>

And when i click on button an error that i am getting.

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at org.UI.EmpManager.jButton1ActionPerformed(EmpManager.java:140)
    at org.UI.EmpManager.access$0(EmpManager.java:132)
    at org.UI.EmpManager$1.actionPerformed(EmpManager.java:67)
    at javax.swing.AbstractButton.fireActionPerformed(Unknown Source)
    at javax.swing.AbstractButton$Handler.actionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.fireActionPerformed(Unknown Source)
    at javax.swing.DefaultButtonModel.setPressed(Unknown Source)
    at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(Unknown Source)
    at java.awt.Component.processMouseEvent(Unknown Source)
    at javax.swing.JComponent.processMouseEvent(Unknown Source)
    at java.awt.Component.processEvent(Unknown Source)
    at java.awt.Container.processEvent(Unknown Source)
    at java.awt.Component.dispatchEventImpl(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.LightweightDispatcher.retargetMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.processMouseEvent(Unknown Source)
    at java.awt.LightweightDispatcher.dispatchEvent(Unknown Source)
    at java.awt.Container.dispatchEventImpl(Unknown Source)
    at java.awt.Window.dispatchEventImpl(Unknown Source)
    at java.awt.Component.dispatchEvent(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Answer 1

How are you creating EmpManager, there is a bean in your application xml for the manager, but it also contains your main method. Then within your main method you’re getting the application context, and setting the service bean, so your EmpManager bean is not doing anything in your application context.

I’d recommend extracting the main method into a different class in which you load the Application Context and use getBean only on the UI manager. The way you currently have it set up ignores a lot of the IoC capabilities of Spring by directly grabbing beans from the Application Context, rather than letting Spring do that for you.

This might not solve your problem directly, but it will at least allow Spring to have a single point of entry, and keep DI in the hands of Spring, rather than relying on you to set them yourself.