Wicket @SpringBean and Spring @Autowired with injection via constructor

Question

I have a Wicket panel in which I want to inject bean using @SpringBean

public class SomePanel extends Panel {

  @SpringBean
  private BlogSummaryMailGenerator blogSummaryMailGenerator;

}

But this BlogSummaryMailGenerator has injection via constructor defined like this:

@Component
public class BlogSummaryMailGenerator {

  private BlogRepository blogRepository;
  private BlogPostRepository blogPostRepository;

  @Autowired
  public BlogSummaryMailGenerator(BlogRepository blogRepository,
                                BlogPostRepository blogPostRepository) {
    this.blogRepository = blogRepository;
    this.blogPostRepository = blogPostRepository;
  }
}

And when SomePanel is instantiated I am getting an exception

Caused by: java.lang.IllegalArgumentException: Superclass has no null constructors but no arguments were given
at net.sf.cglib.proxy.Enhancer.emitConstructors(Enhancer.java:721) ~[cglib-3.1.jar:na]
at net.sf.cglib.proxy.Enhancer.generateClass(Enhancer.java:499) ~[cglib-3.1.jar:na]
at net.sf.cglib.core.DefaultGeneratorStrategy.generate(DefaultGeneratorStrategy.java:25) ~[cglib-3.1.jar:na]
at net.sf.cglib.core.AbstractClassGenerator.create(AbstractClassGenerator.java:216) ~[cglib-3.1.jar:na]
at net.sf.cglib.proxy.Enhancer.createHelper(Enhancer.java:377) ~[cglib-3.1.jar:na]
at net.sf.cglib.proxy.Enhancer.create(Enhancer.java:285) ~[cglib-3.1.jar:na]
at org.apache.wicket.proxy.LazyInitProxyFactory.createProxy(LazyInitProxyFactory.java:191) ~[wicket-ioc-7.2.0.jar:7.2.0]

Adding empty no-args constructor to the BlogSummaryMailGenerator solves this issue but adding such code only to make injection work is wrong and I would like to avoid it.

Any suggestions how to make @SpringBean work with beans using injection via constructor?

Answer 1

The real problem is in CGLIB. It requires a default constructor to be able to create the proxy instance. The real Spring bean is created separately by Spring and has no such restrictions. The default constructor needed by CGLIB could be even private as far as I remember.

Update: Since Wicket 9.5.0 Wicket could also use ByteBuddy instead of CGLib.

Another solution is to use an interface for this bean. Then Wicket will use JDK Proxy instead of CGLIB and in this case there is no need of default constructor in the implementation.