SpringMvc Instantiating Beans – Singleton-Collection of common programming errors

11 years ago
admin
3 minutes

In the under mentioned code i created this because i was getting java.lang.NullPointerException see my error log under. When i implemented this it was fixed and it worked perfectly. However i was told by one of the members here that –

“you are creating new beans for every call to getOfficerRegistrationValidation. this includes recreating the database objects which are every expensive and can cost error if some object are supposed to be created only once (singleton). you should find a way to make OfficerRegistrationValidation reusable and threadsafe so that you can have only one of it and inject this to wherever you want using only IoC”

and i think hes right can someone tell me whats the best way to do this without having to instantiate all my beans again. I just want to instantiate only the certain beans and not run into this problem.

public final class BeanFactory() {

    private static ClassPathXmlApplicationContext context;

    private static ClassPathXmlApplicationContext getContext() {
        if (context== null) {
            context = new ClassPathXmlApplicationContext("applicationContext.xml");
        }
        return context;
    }

    public static OfficerRegistrationValidation getOfficerRegistrationValidation() {
        return (OfficerRegistrationValidation) getContext().getBean("officerRegistrationValidation");
    }
}

In the controller make a call like : `BeanFactory.getOfficerRegistrationValidation().validate(….)

Error Log:

java.lang.NullPointerException
    at com.crimetrack.service.OfficerRegistrationValidation.validate(OfficerRegistrationValidation.java:51)
    at org.springframework.validation.DataBinder.validate(DataBinder.java:725)
    at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.doBind(HandlerMethodInvoker.java:815)
    at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.resolveHandlerArguments(HandlerMethodInvoker.java:367)
    at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:171)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:436)
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:424)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:789)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:637)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
    at java.lang.Thread.run(Unknown Source)

  1. I’m going to hazard a guess at what you are asking about (as your question doesn’t provide your motivation for using a beanfactory and doesn’t provide enough code to give a complete picture)…

    Spring beans are by default instantiated as singletons. So you should be able to configure Spring to create your OfficerRegistrationValidation object using either XML or annotation (@Component) and then get it injected into your controller by using the @Inject annotation.

    Annotations are the way to go – just make sure you have the following in your Spring config XML (applicationContext.xml):

    Then simply add the @Component annotation to the class declaration of your OfficerRegistrationValidation class:

    @Component
public class OfficerRegistrationValidation {

    and then in your controller, declare a field for your OfficerRegistrationValidation and annotate it thus:

    @Controller
pubic class MyController {
     @Inject
     private OfficerRegistrationValidation officerRegistrationValidation;

    Now you will have access to the OfficerRegistrationValidation singleton bean in your controller – only ~4 lines of code needed!