Spring - Weird Error in Bean Creation

Question

Any idea why I am getting this exception?

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'myService' defined in class path resource [context.xml]: Initialization of bean failed; nested exception is org.springframework.beans.TypeMismatchException: Failed to convert property value of type [$Proxy54 implementing org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised,net.sf.cglib.proxy.Factory,org.springframework.beans.factory.InitializingBean] to required type [com.mycompany.service.dao.MyDAO] for property 'myDAO'; nested exception is java.lang.IllegalArgumentException: Cannot convert value of type [$Proxy54 implementing org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised,net.sf.cglib.proxy.Factory,org.springframework.beans.factory.InitializingBean] to required type [com.mycompany.service.dao.MyDAO] for property 'myDAO': no matching editors or conversion strategy found
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:480)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
    at java.security.AccessController.doPrivileged(Native Method)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:671)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:610)
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredMethodElement.inject(AutowiredAnnotationBeanPostProcessor.java:499)
    ... 36 more
Caused by: java.lang.IllegalArgumentException: Cannot convert value of type [$Proxy54 implementing org.springframework.aop.SpringProxy,org.springframework.aop.framework.Advised,net.sf.cglib.proxy.Factory,org.springframework.beans.factory.InitializingBean] to required type [com.mycompany.service.dao.MyDAO] for property 'myDAO': no matching editors or conversion strategy found
    at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:231)
    at org.springframework.beans.TypeConverterDelegate.convertIfNecessary(TypeConverterDelegate.java:138)
    at org.springframework.beans.BeanWrapperImpl.convertForProperty(BeanWrapperImpl.java:386)
... 62 more

Answer 1

I suspect that if ProdMiscDAO was an interface (is it?) you would not have this error. I believe you probably have a class that is getting proxied using cglib under the hood, performing magic, etc. and in the end it cannot be safely cast to a paramter in a setter or constructor. Try programming to an interface and see if the error goes away.

Update: ProdMiscDAO is not an interface. It is a class that extends SqlMappedClientDaoSupport.

Given this, I recommend trying this:

1. Rename ProdMiscDAO to SqlMappedProdMiscDAO.
2. Extract an interface from SqlMappedProdMiscDAO named ProdMiscDAO (e.g. "class SqlMappedProdMiscDAO implements ProdMiscDAO")
3. Go through all your code that uses SqlMappedProdMiscDAO and change it to use ProdMiscDAO.
4. Configure spring to instantiate a SqlMappedProdMiscDAO, wiring it all the classes that need it.

This allows your DAO implementation to still extend SqlMappedClientDaoSupport but also to have an interface. After switching over all classes to use the interface instead of the class, Spring will not have to use cglib to proxy your DAO and the error should go away.

Answer 2

Spring uses proxies, generated at run-time from interfaces, to do things like transactions, aspects, etc. The proper Spring idiom for objects like DAOs, services, etc. is to start with an interface and create a concrete implementation. Once you have that, you're free to generate proxies from the interface as needed.

So of course you'll have a concrete DAO implementation, and that's free to extend SqlMapClientDaoSupport if you wish, but also create an interface that has your methods.

Be sure that you really need to extend SqlMapClientDaoSupport. It could be that composition and delegation is a better way to go.