Question

I have a problem with injecting a bean into a helper class. It works basically like this: I create an object in the page constructor that does some work, returns some data and I show these on the page. In this helper object, a service should be injected via @Autowired annotation. However, I always get a null pointer exception when I use it. I also tried @SpringBean but it didn’t help. On the other hand, when I inject this service directly into the page with @SpringBean, it’s accessible and works fine. Do you know where the problem is?

This is the page:

public class Page extends BasePage {
    public Page() {
        HelperObject object = new HelperObject(new Application("APP_NAME"));
        String result = object.getData();

        add(new Label("label", result));
    }
}

Helper object:

public class HelperObject {
    private Application app;

    @Autowired
    private Service service;

    public HelperObject(Application app) {
        this.app = app;
    }

    public String getData() {
        // use service, manipulate data, return a string
    }
}

Answer 1

@SpringBean only injects dependencies into classes that inherit from Wicket’s Component. @Autowired only injects dependencies into classes created by Spring itself. That means you can’t automatically inject a dependency into an object you create with new.

(Edit: you can also add a @SpringBean injection to your class by injecting in the constructor:
InjectorHolder.getInjector().inject(this);)

My normal workaround for this is to use my application class to help. (I’m a little puzzled by your use of new Application(...). I assume this isn’t actually org.apache.wicket.Application.) For example:

public class MyApplication extends AuthenticatedWebApplication implements
    ApplicationContextAware {

    private ApplicationContext ctx;

    public void setApplicationContext(ApplicationContext applicationContext)
        throws BeansException {
        this.ctx = applicationContext;
    }

    public static MyApplication get() {
        return (MyApplication) WebApplication.get();
    }

    public static Object getSpringBean(String bean) {
        return get().ctx.getBean(bean);
    }

    public static <T> T getSpringBean(Class<T> bean) {
        return get().ctx.getBean(bean);
    }

    ....
}

In my Spring application context:

<!-- Set up wicket application -->
<bean id="wicketApplication" class="uk.co.humboldt.Project.MyApplication"/>

My helper object then looks up the service on demand:

public class HelperObject {

    private Service getService() {
        return MyApplication.getSpringBean(Service.class);
    }