Extending ADF's FacesPageLifecycle

Recently I've encountered strange exceptions while testing my application. I pressed the Submit button and sometimes everything was fine, while at times the action bound to the button was not invoked, but errors were reported:

JBO-29000: null
java.lang.NullPointerException

Unfortunately, there was no trace of this exception and I didn't even know where should I look for it. Then I came up with and idea: let's decorate the process of displaying errors and find out more about this exception. To achieve this, I had to extend ADF's FacesPageLifecycle:

package januszm.adf.util;

import javax.faces.context.FacesContext;

import oracle.adf.controller.faces.lifecycle.FacesPageLifecycle;

import oracle.binding.AttributeBinding;

public class MyPageLifecycle extends FacesPageLifecycle {
    protected void addMessage(FacesContext context, AttributeBinding binding,
                              Throwable error) {
        super.addMessage( context, binding, error );
        // the easiest thing we can do here
        error.printStackTrace();
    }
}

Another question is: how can we tell ADF to use our lifecycle? That's easy too - we extend ADFPhaseListener:

package januszm.adf.util;

import oracle.adf.controller.faces.lifecycle.ADFPhaseListener;
import oracle.adf.controller.v2.lifecycle.PageLifecycle;


public class MyPhaseListener extends ADFPhaseListener {
    protected PageLifecycle createPageLifecycle() {
        return new MyPageLifecycle();   
    }
}

Finally, we need to substitute the original ADFPhaseListener with our class in faces-config.xml:

  <lifecycle>
    <phase-listener>januszm.adf.util.MyPhaseListener</phase-listener>
  </lifecycle>

That allowed me to locate the problem - the exception was thrown in the line containing:

this.someField.toString()

because sometimes the field wasn't set...

The conclusion is simple - if a library throws a weird exception, don't blame the library, but check YOUR code first.