Object Serialization Issue With Wicket

Question

I am trying to pass a searchService into a Form into Wicket to use. When I run this with out the searchService being final I get no issues but I have to make it final in order to use it inside the overwritten onSubmit.

    final SearchService searchService = new SearchService();

    Form<?> form = new Form("searchForm") {
        public void onSubmit() {
            List<File> results = searchService.getSearchResults();
            info("Found: " + results.size());
        }
    };

If I do that I receive an error:

org.apache.wicket.core.util.objects.checker.CheckingObjectOutputStream$ObjectCheckException: The object type is not Serializable!
A problem occurred while checking object with type: test.service.SearchService
Field hierarchy is:
  2 [class=test.webui.HomePage, path=2]
    private java.lang.Object org.apache.wicket.MarkupContainer.children [class=[Ljava.lang.Object;]
      private java.lang.Object org.apache.wicket.MarkupContainer.children[1] [class=org.apache.wicket.markup.html.form.Form, path=2:searchForm]
        private final test.service.SearchService test.webui.HomePage$1.val$searchService [class=test.service.SearchService] <----- field that is causing the problem

I'm new to wicket so I'm wondering if there is a correct way to do this?

Answer 1

Yes. It is expected behavior.

Wicket will serialize the whole page. In fact, the whole pageflow.

The error you are seeing is great because it helps you make your application work in a replicated session cluster.

To solve it you have several options. Off the top of my head:

• You could instantiate the SearchService inside the onSubmit form instead of passing it as an attribute.
• You could use some sort of dependency injection. Wicket supports Guice and Spring out of the box. But nothing stops you from using the injector proxies with other dependency injectors.
• You could store the SearchService on the Wicket Application instead of the page. The wicket application is a non-serializable singleton per cluster node, and it is available in the thread.

Answer 2

You can try to implement Serializable to your SearchService class and declare a variable serialVersionUID .

Eg:

public class SearchService implements Serializable {
    private static final long serialVersionUID = -1769512858853931584L;
    //your code
}