问题
I'm creating an MVC Spring webapp. Using: Jetty (servlet container), DataNucleus (dao platform), DB4O (embedded datastore).
When I persist an object (done from within a Spring Controller) using JDO from DataNucleus, it stores to the DB fine.
@PersistenceCapable
public class Test {
@Persistent
private String testString;
//getter-setters implemented
}
When I do a simple query for the objects I previously added I get a ClassCastException on my Test class (can't cast a.b.c.Test to a.b.c.Test).
The classloader of Test returned by JDO is (toString) [sun.misc.Launcher$AppClassLoader@5acac268], the classloader of the Test class before I persisted it to the DB is [WebAppClassLoader@1593275665]
I've gotten this far, but I don't really know what to do with a classloader issue like this, I've never spent much thought on classloaders before. Any direction is helpful.
回答1:
There doesn't need to be two different versions of the class for a class cast exception to appear. Even the same class definition is seen as two different classes when loaded by two distinct classloaders. Which seems to be the case here.
Unfortunately I am not familiar with the platforms you use, so I can't give more concrete advice than this: try to experiment with moving the jar containing your Test class to different places on your web app classpath, and/or reconfiguring the Spring and Jetty classloaders so that both delegate the loading of Test to the same parent classloader.
回答2:
I think that your problem might be similar to the one described here.
If so, the cure would appear to be to make sure that the jdo jarfile is loaded by a common ancestor of the classloaders.
来源：https://stackoverflow.com/questions/4013047/different-classloaders-cause-classcastexception-when-persisting-data-via-spring