GOF Singelton class in Spring 3

[Praveen Kumar Singh]

Hi,
I am trying to built an GOF type (not spring DI singleton) Singleton class in spring.

public class PrivilegesMgr {

	private static PrivilegesMgr instance = new PrivilegesMgr();

	
	private PrivilegesMgr() {
	}

	private UserAuthenticationService userAuthenticationService;

	public void setUserAuthenticationService(UserAuthenticationService userAuthenticationService) {
		this.userAuthenticationService = userAuthenticationService;
	}

	public static PrivilegesMgr getInstance() {

		return PrivilegesMgr.instance;
	}




}

As, it is clear that to access the bean "userAuthenticationService", i need to fetch it from application context, hence i need to configure PrivilegesMgr in application context
After some R&D, i got the way

	ApplicationContext applicationContext = 
                WebApplicationContextUtils.
                      getWebApplicationContext(servletContextEvent.getServletContext());
 
		PrivilegesMgr privilegesMgr = (PrivilegesMgr)applicationContext.getBean("privilegesMgr");
		privilegesMgr.getInstance().populateUserPrivilages();


and


 <bean id="privilegesMgr" class="com.nokia.authgw.custweb.service.global.privilege.PrivilegesMgr" factory-method="getInstance" >
    <property name="userAuthenticationService" ref="userAuthenticationService" />
 </bean> 

My problem is
Singleton class, traditionally called as PrivilegesMgr.getInstance() and not privilegesMgr.getInstance()

when, try to do PrivilegesMgr.getInstance(), i get null pointer, which is logical, as their is no bean available.
Any suggestion ?

[Rob Spoor]

Moving to our Spring forum.

[Praveen Kumar Singh]

Any update guys?

[Praveen Kumar Singh]

GOF = Gang of four

[Nathan Pruett]

Singleton class, traditionally called as PrivilegesMgr.getInstance() and not privilegesMgr.getInstance()

Yes, it's considered bad form to call a static method through it's class rather than an object reference, but there is really no difference in Java - it works either way. There's also no need to call "getInstance()" explicitly in your code - Spring has already called "getInstance()" for you - you can just call it as:

PrivilegesMgr privilegesMgr = (PrivilegesMgr)applicationContext.getBean("privilegesMgr");  
privilegesMgr.populateUserPrivilages(); 

when, try to do PrivilegesMgr.getInstance(), i get null pointer, which is logical, as their is no bean available.

Why do you think there is no bean available? The code you posted looked OK - are you sure you're loading the beans XML configuration containing your "privilegesMgr" bean? Can you post relevant sections from your web.xml deployment descriptor?