Friday, November 2, 2007

classpath*:BeanRefFactory.xml not found when instantiating a singleton Spring application context inside EJB2.x running on Sun application server 8.2

For the project I'm currently working on, we use Spring's EJB support. In order to share application context among all EJB instances, SingletonBeanFactoryLocator is used to locate or load the shared application context. And we used the default "classpath*:beanRefFactory.xml" selector key.

However, when the EJB is deployed and invoked, a FatalBeanException is thrown stating
Unable to find resource for specified definition. Group resource name
[classpath*:beanRefFactory.xml], factory key [...]

Looking into the implementation of SingletonBeanFactoryLocator, we found that it delegates to PathMatchingResourcePatternResolver to load the XML file. If the resource starts with "classpath*:" prefix, it uses ClassLoader's getResources(String) method to load the resource; otherwise, a ClasspathResource is returned, which eventually uses ClassLoader's getResource(String) method to load the resource. Pay attention to the plural form of the method name.

In the base java.lang.ClassLoader, both getResource(String) and getResources(String) delegate to its parent first. If the resource is not found by the parent, it invokes findResource(String) and findResources(String) methods, both of which simply return null. The Javadoc of ClassLoader recommends that, for both finder methods:
Class loader implementations should override this method to specify where to
load resources from.

However, when tracing the execution in debug mode, we found that the EJBClassLoader used by Sun Application Server 8.2 only overrides findResource(String) method and searches for the resource in the expanded directory of the EJB Jar file; it does not override findResources(String), which remains returning null, against their own advice.

Now it's obvious, this is due to a defect in Sun Application Server 8.2. The simplest solution is to specify the selector key as "classpath:beanRefFactory.xml" instead of the default value.