one question about Interceptor

[diyun2008]

When I run example "icefaces",I debug class LoggedInInterceptor.But I
found :

 Method method = invocation.getMethod();
 if ( method.getReturnType().equals(void.class) )
 {
 return null;
 }

Why "return null" not "return 'login'".I clicked link "http://localhost:8000/seam-registration/main.seam?cid=2" ,it did not return to "login" page.So I fixed "retrun null" above to "return 'login'",but it still did not return to "login" page.Through logging, I found if "Lifecycle.getPhaseId()!=PhaseId.INVOKE_APPLICATION",it will never be redirect to new page.How can I redirect to new page in Interceptor,and who can tell me how does Interceptor work?
Your appreciation!

[norman.richards]

You can't change the return type of a Java method. If the method doesn't return a value then you can't suddenly decide to return a string in an interceptor.

[diyun2008]

You probably misunderstand.
The comlete code is here:

import javax.faces.event.PhaseId;

import org.jboss.seam.annotations.Interceptor;
import org.jboss.seam.contexts.Contexts;
import org.jboss.seam.contexts.Lifecycle;
import org.jboss.seam.interceptors.BijectionInterceptor;
import org.jboss.seam.interceptors.BusinessProcessInterceptor;
import org.jboss.seam.interceptors.ConversationInterceptor;
import org.jboss.seam.interceptors.RemoveInterceptor;
import org.jboss.seam.interceptors.ValidationInterceptor;

@Interceptor(around={BijectionInterceptor.class, ValidationInterceptor.class,
 ConversationInterceptor.class, BusinessProcessInterceptor.class},
 within=RemoveInterceptor.class)
public class LoggedInInterceptor
{

 @AroundInvoke
 public Object checkLoggedIn(InvocationContext invocation) throws Exception
 {
 boolean isLoggedIn = Contexts.getSessionContext().get("loggedIn")!=null;
 if ( Lifecycle.getPhaseId()==PhaseId.INVOKE_APPLICATION )
 {
 if (isLoggedIn)
 {
 return invocation.proceed();
 }
 else
 {
 return "login";
 }
 }
 else
 {
 if ( isLoggedIn )
 {
 return invocation.proceed();
 }
 else
 {
 Method method = invocation.getMethod();
 if ( method.getReturnType().equals(void.class) )
 {
 return null;
 }
 else
 {
 return method.invoke( invocation.getTarget(), invocation.getParameters() );
 }
 }
 }
 }

}