Re: Proxy null poiter exception with bad references

Hi Martin,

Martin Heyer wrote:
> Hello Ojb-Users.
> 
> I have a Cocoon + OJB installation running. For performance reasons 
> there is a dynamic Proxy configured with class B. For example let's
> have two classes A and B:
> 
> Class A: (has no proxy) - uid - link  -> points to uid of class B - B
> (foreign key, holds the instance of B associated with link)
> 
> Class B: (has a proxy) - uid - data
> 
> Everything works fine without the proxy. But when proxy is turned on
> and A points to an ID that has no B in the DB, it throws a NPE:
> 
> ... Caused by: org.apache.ojb.broker.PersistenceBrokerException:
> Error invoking method getIndirectionHandler at 
> org.apache.ojb.broker.core.proxy.AbstractIndirectionHandler.invoke(AbstractIndirectionHandler.java:363)
>  at $Proxy29.getIndirectionHandler(Unknown Source) ... 61 more Caused
> by: java.lang.NullPointerException at 
> org.apache.ojb.broker.core.proxy.AbstractIndirectionHandler.invoke(AbstractIndirectionHandler.java:347)
>  ... 62 more
> 
> Is there a way to catch this? I can load A so it has a proxy instance
> of B associated with it. ATM there is no way for me to know if the
> proxy will find a real object of B. When I access this reference, it
> crashes..

This should be fixed in SVN:
http://www.mail-archive.com/ojb-dev%40db.apache.org/msg03485.html

The only "workaround" I know is to patch method
AbstractIndirectionHandler.invoke(Object proxy, Method method, Object[] 
args)

replace:
return method.invoke(subject, args);

with:
if("toString".equals(methodName) && subject == null)
{
     return null;
}
if(subject == null)
{
     log.warn("Real object of this proxy object doesn't exist, all 
method will return 'null': " + getIdentity());
     return null;
}
else
{
     return method.invoke(subject, args);
}

OR use your own IndirectionHandler implementation class e.g.
public class IndirectionHandlerCGLIBPatchedImpl extends 
IndirectionHandlerCGLIBImpl
{
...
}
and override the invoke-method in same way described above and declare 
it in OJB.properties file (IndirectionHandlerClass=...). But in this 
case you have use the reflection-API to get access to a private member 
"_realSubject" in AbstractIndirectionHandler.

regards,
Armin

> 
> I really would appreciate help,
> 
> Martin
> 
> 
> 
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