Why do i get an InvalidClassException 'no valid constructor' when inherit from an abstract Serializable?

Question

Hi,

here's the code (simplified):

public abstract class PageBase implements Serializable {
     private static final long serialVersionUID = -31905358958878336L;
}

public abstract class ListPage extends PageBase {

    public Controller getController() {
         // Controller is a class
         // that implements Serializable and does have an def. constr.
         return new Controller() {
              @Override
              public void someMethod() {
                  // DoSomething
              }
         };
    }
}

public class ProjectList extends ListPage {
}

and through deserialization it throws:

java.io.InvalidClassException: de.edeka.plive.page.ListPage$1; no valid constructor

The deserialization is taking place somewhere in the IBM JSF-Code.

Any ideas? Thanks!

Answer 1

You are trying to serialize an abstract class which, by definition, cannot be instantiated. That is, with your definition of ListPage, you cannot do:

ListPage l = new ListPage();

Remove the abstract qualifier from ListPage and ProjectList, and everything will be ok.

Answer 2

One serializes objects, not classes, no? All of the classes you've shown are abstract, so can't be instantiatiated, so what is it that you're (de)serializing?

The error references the class as "ListPage$1" -- an anonymous inner class. I think we'd need to see more of the code to understand what's going on.

Answer 3

de.edeka.plive.page.ListPage$1 will be an anonymous inner classes. Serialisaing nested classes isn't a good idea at the best of times (poor mapping to full JVM name and handling of "outer this" references).

The exception looks as if it is trying to find the no-arg constructor of the most derived non-Serializable base class, which must be accessible to the least derived Serializable class.

Answer 4

I'd suggest defining the anonymous Controller as a separate class.

Answer 5

I think that the problem is that subclass of Controller is a non-static inner class, and as such its constructor has an implicit argument that refers to the instance of the enclosing class. This makes the constructor unusable for object deserialization.

It is a bad idea to try to serialize these objects, but if you change the inner class so that it is static deserialization may work.