ClassCastException when casting to the same class

Question

I have 2 different Java projects, one has 2 classes: dynamicbeans.DynamicBean2 and dynamic.Validator.

On the other project, I load both of

Answer 1

I had the same issue, and I finally found a workaround on java.net :

Copy all org.eclipse.persistence jar files from glassfish4/glassfish/modules to WEB-INF/lib. Then go in your glassfish-web.xml, and set class-delegate to false.

Worked for me !

Answer 2

Another option:

Happened to me in weblogic, but I guess it can happen in other servers as well - if you do (just) "Publish" and therefor some of your classes are re-loaded. Instead do "Clean" so all the classes will re-loaded together.

Answer 3

The class objects were loaded in different classloaders, therefore the instances created from in each of classes are seen as 'incompatible'. This is a common issue in a an environment where there are many different classloaders being used and objects are being passed around. These issues can easily arise in Java EE and portal environments.

Casting an instance of a class requires that the Class linked to the object being casted is the same as the one loaded by the current thread context classloader.

Answer 4

I got the A2AClassCastException problem when trying to create a List of objects from XML using Apache Commons Digester.

List<MyTemplate> templates = new ArrayList<MyTemplate>();
Digester digester = new Digester();
digester.addObjectCreate("/path/to/template", MyTemplate.class);
digester.addSetNext("/path/to/template", "add");
// Set more rules...
digester.parse(f); // f is a pre-defined File

for(MyTemplate t : templates) { // ClassCastException: Cannot cast mypackage.MyTemplate to mypackage.MyTemplate
    // Do stuff
}

As stated above, the cause is that the digester doesn't use the same ClassLoader as the rest of the program. I ran this in JBoss, and it turned out that commons-digester.jar was not in JBoss's lib directory, but rather in a webapp's lib directory. Copying the jar into mywebapp/WEB-INF/lib also solved the problem. Another solution was to casll digester.setClassLoader(MyTemplate.class.getClassLoader()), but that feels like quite an ugly solution in this context.

Answer 5

Had the same my.package.MyClass cannot be cast to my.package.MyClass on WildFly 10.1 and, as I understand, I did the opposite to what @Emil Lundberg described in his answer.

I have added the module (which contains my.package.MyClass) to my.war/WEB-INF/jboss-deployment-structure.xml as a dependency

<dependencies>
    ...
    <module name="my.package"/>
</dependencies>

and removed the corresponding jar from my.war/WEB-INF/lib, re-deployed the WAR and then the code worked as expected.

Thus, we made sure it solves the issue. Now, we need to make sure the issue won't come back, for example, when the updated version of WAR will be assembled and deployed.

For this, in the sources of those WAR, it is required to add <scope>provided</scope> for those jar in pom.xml, so that when my.war is re-assembled next time with the fix/enhancement code injected, it will not bundle this jar into my.war/WEB-INF/lib.