Dynamic injection using #SpringBean in wicket - wicket

Question

I have a form that based on collected information generates a report. I have multiple sources from which to generate reports, but the form for them is the same. I tried to implement strategy pattern using an interface implementing report generator services, but that led to wicket complaining about serialization issues of various parts of the report generator. I would like to solve this without duplicating the code contained in the form, but I have not been able to find information on dynamic injection with #SpringBean.
Here is a rough mock up of what I have
public class ReportForm extends Panel {
private IReportGenerator reportGenerator;
public ReportForm(String id, IReportGenerator reportGenerator) {
super(id);
this.reportGenerator = reportGenerator;
final Form<Void> form = new Form<Void>("form");
this.add(form);
...
form.add(new AjaxButton("button1") {
private static final long serialVersionUID = 1L;
#Override
protected void onSubmit(AjaxRequestTarget target)
{
byte[] report = reportGenerator.getReport(...);
...
}
});
}
}
If I do it this way, wicket tries to serialize the concrete instance of reportGenerator. If I annotate the reportGenerator property with #SpringBean I receive Concrete bean could not be received from the application context for class: IReportGenerator
Edit: I have reworked implementations of IRerportGenerator to be able to annotate them with #Component and now I when I use #SpringBean annotation I get More than one bean of type [IReportGenerator] found, you have to specify the name of the bean (#SpringBean(name="foo")) or (#Named("foo") if using #javax.inject classes) in order to resolve this conflict. Which is exactly what I don't want to do.

Answer 1

I think the behavior you're trying to achieve can be done with a slight workaround, by introducing a Spring bean that holds all IReportGenerator instances:
#Component
public class ReportGeneratorHolder {
private final List<IReportGenerator> reportGenerators;
#Autowired
public ReportGeneratorHolder(List<IReportGenerator> reportGenerators) {
this.reportGenerators = reportGenerators;
}
public Optional<IReportGenerator> getReportGenerator(Class<? extends IReportGenerator> reportGeneratorClass) {
return reportGenerators.stream()
.filter(reportGeneratorClass::isAssignableFrom)
.findAny();
}
}
You can then inject this class into your Wicket page, and pass the desired class as a constructor-parameter. Depending on your Spring configuration you might need to introduce an interface for this as well.
public class ReportForm extends Panel {
#SpringBean
private ReportGeneratorHolder reportGeneratorHolder;
public ReportForm(String id, Class<? extends IReportGenerator> reportGeneratorClass) {
super(id);
IReportGenerator reportGenerator = reportGeneratorHolder
.getReportGenerator(reportGeneratorClass)
.orElseThrow(IllegalStateException::new);
// Form logic omitted for brevity
}
}

Answer 2

As far as I am able to find, looking through documentation and even the source for wicket #SpringBean annotation, this isn't possible. The closest I got is with explicitly creating a proxy for a Spring bean based on class passed. As described in 13.2.4 Using proxies from the wicket-spring project chapter in Wicket in Action.
public class ReportForm extends Panel {
private IReportGenerator reportGenerator;
private Class<? extends IReportGenerator> classType;
private static ISpringContextLocator CTX_LOCATOR = new ISpringContextLocator() {
public ApplicationContext getSpringContext() {
return ((MyApplication)MyApplication.get()).getApplicationContext();
}
};
public ReportForm(String id, Class<? extends IReportGenerator> classType) {
super(id);
this.classType = classType;
final Form<Void> form = new Form<Void>("form");
this.add(form);
...
form.add(new AjaxButton("button1") {
private static final long serialVersionUID = 1L;
#Override
protected void onSubmit(AjaxRequestTarget target)
{
byte[] report = getReportGenerator().getReport(...);
...
}
});
}
private <T> T createProxy(Class<T> classType) {
return (T) LazyInitProxyFactory.createProxy(classType, new
SpringBeanLocator(classType, CTX_LOCATOR));
}
private IReportGenerator getReportGenerator() {
if (reportGenerator = null) {
reportGenerator = createProxy(classType);
}
return reportGenerator;
}
}