Spring (Error creating bean, No visible constructors) for Singleton class with private constructor

Question

I have 4 singleton classes with private constructors and I'm trying to create bean property for all the 4 classes.

The main problem is, I'm able to create the bean for 3 classes and these 3 classes have similar structure with a getInstance method and a private constructor() (Singleton class) but the fourth and the last one is throwing an exception (Exception message is pasted below)

Please find below the getInstance method, the private constructor and the bean id declaration. Which is same across all the four bean declarations

But If I change the constructor from "Private" to "Public" then I dont get the error. Could anyone throw any light on what is happening? Since the other three classes have private constructors and they work perfectly fine

The getInstance() method

public static ApplicationConfiguration getInstance() throws IOException,
            IllegalArgumentException, InconsistentDataException {
        ApplicationConfiguration result = instance.get();
        if (result == null) {
            try {
                // Check again if already created
                result = instance.get();
                if (result == null) {
                    result = new ApplicationConfiguration();

                }
            } finally {
                // something here
            }
        } 
        return result;
    }

The private constructor

private ApplicationConfiguration() throws Exception {
        // call a method here
    }

The bean property declaration

<bean id="configManager" class="com.manager.ApplicationConfiguration" factory-method="getInstance" />

<bean id="configEnricher" class="com.enricher.ApplicationConfiguration" factory-method="getInstance" />

<bean id="configBussiness" class="com.validationservice.ApplicationConfiguration" factory-method="getInstance" />

The above three works

This bean property is throwing the error

<bean id="configEviction" class="com.evictionservice.ApplicationConfiguration" factory-method="getInstance" />

The Exception message

[#|2012-08-07 11:53:21,130|ERROR|RMI TCP Connection(226)-172.18.36.14|org.springframework.
web.context.ContextLoader||slodev-rhngp5.mblox.com|core-1|Context initialization failed|#]
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'co
nfigEviction' defined in ServletContext resource [/WEB-INF/camel-context.xml]: Initializat
ion of bean failed; nested exception is org.springframework.aop.framework.AopConfigExcepti
on: Could not generate CGLIB subclass of class [class com.evictionservice.ApplicationConfiguration]: 
Common causes of this problem include using
a final class or a non-visible class; nested exception is java.lang.IllegalArgumentExcepti
on: No visible constructors in class com.evictionservice.ApplicationConfiguration
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.do
CreateBean(AbstractAutowireCapableBeanFactory.java:526)
        at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.cr
eateBean(AbstractAutowireCapableBeanFactory.java:455)
        at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(Abstr
actBeanFactory.java:293)
        at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingl
eton(DefaultSingletonBeanRegistry.java:222)
        at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(Abstrac
tBeanFactory.java:290)
        at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractB
eanFactory.java:192)
        at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstant
iateSingletons(DefaultListableBeanFactory.java:585)
        at org.springframework.context.support.AbstractApplicationContext.finishBeanFactor
yInitialization(AbstractApplicationContext.java:895)
        at org.springframework.context.support.AbstractApplicationContext.refresh(Abstract
ApplicationContext.java:425)
:

Answer 1

The problem is not the bean creation itself (as you already noticed, that's not different from the other beans). The issue seems to be related to some AOP configuration that you're trying to use. If you want to create a proxy for that class, it cannot do it with CGLIB because the class cannot be subclassed (since it has a private constructor).

The only way to get around this (given your current design) is to create an interface that will be implemented by the ApplicationConfiguration class and then create the proxy for that interface instead of proxy-ing the class.