[OWB-1234] generic classes are not correctly proxied when bridge methods are involved

• Type: Bug
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 2.0.4
• Component/s: Interceptor and Decorators
• Assignee: Mark Struberg
• Reporter: Alexander Zapletal
• Created: 01/Mar/18 16:52
• Updated: 12/Mar/21 09:28

Description

Proxies generated by NormalScopeProxyFactory do not contain (overriding) proxy methods for bridge methods, because bridge methods are generally ignored by the proxy generation, see AbstractProxyFactory.unproxyableMethod() and ClassUtil.addNonPrivateMethods() .

(See also OWB-923)

But this can lead to wrong proxies:

interface Contract {
  void doIt(Integer param);
}

public class BaseBean<T extends Number> {
  public void doIt(T param) {
  }
}

@ApplicationScoped
public class MyBean extends BaseBean<Integer> implements Contract { 
}

When compiling this code the compiler performs type erasure and needs to generate a bridge method. The generated byte code corresponds (roughly) to the following code:

public class BaseBean {
  public void doIt(Number param) {
  }
}

public class MyBean {

  // bridge method!
  public void doIt(Integer param) {
	super.doIt(param);
  }
}

NormalScopeProxyFactory generates a proxy class that (roughly) corresponds to the following code:

public class MyBean$$OwbNormalScopeProxy extends MyBean {
  
  public void doIt(Number var1) {
    ((MyBean)this.owbContextualInstanceProvider.get()).doIt(var1);
  }
}

But when we now call, for instance, doIt(4711) on an injected instance of Contract , we actually call MyBean.doIt(Integer) and thereby we bypass the proxy!

  @Inject Contract handler;
  handler.doIt(4711) 

Reason: When NormalScopeProxyFactory generated the proxy for MyBean, it found the following two methods (amongst others):

void doIt(Number var1)  // inherited from BaseBean
void doIt(Integer var1) // bridge method

Since NormalScopeProxyFactory ignores bridge methods, it only generated a proxy method for doIt(Number) . This method overloads MyBean.doIt(Integer) , it does not override it. So, handler.doIt(4711) actually calls MyBean.doIt(Integer) .

 

IMPORTANT NOTE: There is a quite simple workaround for this problem: Just implement the bridge method yourself. I.e. in the example above use the following implementation

@ApplicationScoped
public class MyBean extends BaseBean<Integer> implements Contract { 
  @Override
  public void doIt(Integer param) {
    super.doIt(param);
  }
}

Now, the method doIt(Integer) is not a bridge method anymore and NormalScopeProxyFactory will generate a proxy method for it.