injection of @DataModelSelection fails with value() attribut

[frege]

I've encountered a problem in my application that I was eventually able to reproduce with a simple change to the messages example. If you add a value attribute to the @DataModelSelection annotation, e.g.

@DataModelSelection("message")

Seam will fail to inject the selected object (message) when select() is called, causing a null pointer exception at the first reference. The potential ambiguity with the 'message' context variable introduced by Message.java is not the cause. You will get the same behaviour if you rename MessageListBean.java's 'message ' attribute to 'message2' and use @DataModelSelection("message2") instead.

You may wonder why I am using the undocumented value() attribute on @DataModelSelection. This all started because I was attempting to use two @DataModels in my statefull session component (two different @DataModel attribute names, two different @DataModelSelection attribute names, no use of the value attribute). The component fails to deploy with the following error:

10:24:28,341 ERROR [[/seam-messages]] Exception sending context initialized event to listener instance of class org.jboss.seam.servlet.SeamListener
java.lang.IllegalStateException: Missing value() for @DataModelSelection with multiple @DataModels

The documentation doesn't list a value() attribute for the @DataModelSelection annotation. Adding the value attribute to the two @DataModelSelection annotations (same name as the attribute) fixes the deployment problem, but causes the injection failure/null pointer problem.

Is this a bug? Is there a way to employ two @DataModels without using the value() attribute on @DataModelSelection?

Thanks

[gavin.king]

Can you show me the stack trace of the NPE?

[frege]

13:16:10,705 ERROR [[Faces Servlet]] Servlet.service() for servlet Faces Servlet threw exception
javax.faces.FacesException: Error calling action method of component with id _id0:_id2_0:_id8
at org.apache.myfaces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:74)
at javax.faces.component.UICommand.broadcast(UICommand.java:106)
at javax.faces.component.UIData.broadcast(UIData.java:338)
at javax.faces.component.UIViewRoot._broadcastForPhase(UIViewRoot.java:90)
at javax.faces.component.UIViewRoot.processApplication(UIViewRoot.java:164)
at org.apache.myfaces.lifecycle.LifecycleImpl.invokeApplication(LifecycleImpl.java:316)
at org.apache.myfaces.lifecycle.LifecycleImpl.execute(LifecycleImpl.java:86)
at javax.faces.webapp.FacesServlet.service(FacesServlet.java:106)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:252)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.jboss.web.tomcat.filters.ReplyHeaderFilter.doFilter(ReplyHeaderFilter.java:96)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:202)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:173)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:213)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:178)
at org.jboss.web.tomcat.security.CustomPrincipalValve.invoke(CustomPrincipalValve.java:54)
at org.jboss.web.tomcat.security.SecurityAssociationValve.invoke(SecurityAssociationValve.java:174)
at org.jboss.web.tomcat.security.JaccContextValve.invoke(JaccContextValve.java:74)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:126)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:105)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:107)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:148)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:868)
at org.apache.coyote.http11.Http11BaseProtocol$Http11ConnectionHandler.processConnection(Http11BaseProtocol.java:663)
at org.apache.tomcat.util.net.PoolTcpEndpoint.processSocket(PoolTcpEndpoint.java:527)
at org.apache.tomcat.util.net.MasterSlaveWorkerThread.run(MasterSlaveWorkerThread.java:112)
at java.lang.Thread.run(Unknown Source)
Caused by: javax.faces.el.EvaluationException: Exception while invoking expression #{messageList.select}
at org.apache.myfaces.el.MethodBindingImpl.invoke(MethodBindingImpl.java:153)
at org.apache.myfaces.application.ActionListenerImpl.processAction(ActionListenerImpl.java:63)
... 26 more
Caused by: javax.ejb.EJBException: java.lang.NullPointerException
at org.jboss.ejb3.tx.Ejb3TxPolicy.handleExceptionInOurTx(Ejb3TxPolicy.java:69)
at org.jboss.aspects.tx.TxPolicy.invokeInOurTx(TxPolicy.java:83)
at org.jboss.aspects.tx.TxInterceptor$Required.invoke(TxInterceptor.java:192)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
at org.jboss.aspects.tx.TxPropagationInterceptor.invoke(TxPropagationInterceptor.java:76)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
at org.jboss.ejb3.stateful.StatefulInstanceInterceptor.invoke(StatefulInstanceInterceptor.java:81)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
at org.jboss.aspects.security.AuthenticationInterceptor.invoke(AuthenticationInterceptor.java:78)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
at org.jboss.ejb3.ENCPropagationInterceptor.invoke(ENCPropagationInterceptor.java:47)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
at org.jboss.ejb3.asynchronous.AsynchronousInterceptor.invoke(AsynchronousInterceptor.java:106)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
at org.jboss.ejb3.stateful.StatefulContainer.localInvoke(StatefulContainer.java:190)
at org.jboss.ejb3.stateful.StatefulLocalProxy.invoke(StatefulLocalProxy.java:98)
at $Proxy69.select(Unknown Source)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.myfaces.el.MethodBindingImpl.invoke(MethodBindingImpl.java:129)
... 27 more
Caused by: java.lang.NullPointerException
at org.jboss.seam.example.messages.MessageListBean.select(MessageListBean.java:51)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:109)
at org.jboss.ejb3.interceptor.InvocationContextImpl.proceed(InvocationContextImpl.java:168)
at org.jboss.seam.interceptors.SeamInvocationContext.proceed(SeamInvocationContext.java:56)
at org.jboss.seam.interceptors.ValidationInterceptor.validateTargetComponent(ValidationInterceptor.java:65)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.jboss.seam.util.Reflections.invoke(Reflections.java:13)
at org.jboss.seam.interceptors.Interceptor.aroundInvoke(Interceptor.java:87)
at org.jboss.seam.interceptors.SeamInvocationContext.proceed(SeamInvocationContext.java:60)
at org.jboss.seam.interceptors.OutcomeInterceptor.interceptOutcome(OutcomeInterceptor.java:21)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.jboss.seam.util.Reflections.invoke(Reflections.java:13)
at org.jboss.seam.interceptors.Interceptor.aroundInvoke(Interceptor.java:87)
at org.jboss.seam.interceptors.SeamInvocationContext.proceed(SeamInvocationContext.java:60)
at org.jboss.seam.interceptors.RollbackInterceptor.rollbackIfNecessary(RollbackInterceptor.java:30)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.jboss.seam.util.Reflections.invoke(Reflections.java:13)
at org.jboss.seam.interceptors.Interceptor.aroundInvoke(Interceptor.java:87)
at org.jboss.seam.interceptors.SeamInvocationContext.proceed(SeamInvocationContext.java:60)
at org.jboss.seam.interceptors.BijectionInterceptor.bijectTargetComponent(BijectionInterceptor.java:32)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.jboss.seam.util.Reflections.invoke(Reflections.java:13)
at org.jboss.seam.interceptors.Interceptor.aroundInvoke(Interceptor.java:87)
at org.jboss.seam.interceptors.SeamInvocationContext.proceed(SeamInvocationContext.java:60)
at org.jboss.seam.interceptors.ConversationInterceptor.endOrBeginLongRunningConversation(ConversationInterceptor.java:58)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.jboss.seam.util.Reflections.invoke(Reflections.java:13)
at org.jboss.seam.interceptors.Interceptor.aroundInvoke(Interceptor.java:87)
at org.jboss.seam.interceptors.SeamInvocationContext.proceed(SeamInvocationContext.java:60)
at org.jboss.seam.interceptors.BusinessProcessInterceptor.manageBusinessProcessContext(BusinessProcessInterceptor.java:58)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.jboss.seam.util.Reflections.invoke(Reflections.java:13)
at org.jboss.seam.interceptors.Interceptor.aroundInvoke(Interceptor.java:87)
at org.jboss.seam.interceptors.SeamInvocationContext.proceed(SeamInvocationContext.java:60)
at org.jboss.seam.interceptors.RemoveInterceptor.removeIfNecessary(RemoveInterceptor.java:38)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.jboss.seam.util.Reflections.invoke(Reflections.java:13)
at org.jboss.seam.interceptors.Interceptor.aroundInvoke(Interceptor.java:87)
at org.jboss.seam.interceptors.SeamInvocationContext.proceed(SeamInvocationContext.java:60)
at org.jboss.seam.ejb.SeamInterceptor.aroundInvoke(SeamInterceptor.java:41)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.jboss.ejb3.interceptor.InvocationContextImpl.proceed(InvocationContextImpl.java:120)
at org.jboss.ejb3.interceptor.EJB3InterceptorsInterceptor.invoke(EJB3InterceptorsInterceptor.java:62)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
at org.jboss.ejb3.entity.ExtendedPersistenceContextPropagationInterceptor.invoke(ExtendedPersistenceContextPropagationInterceptor.java:71)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
at org.jboss.ejb3.AllowedOperationsInterceptor.invoke(AllowedOperationsInterceptor.java:47)
at org.jboss.aop.joinpoint.MethodInvocation.invokeNext(MethodInvocation.java:98)
at org.jboss.aspects.tx.TxPolicy.invokeInOurTx(TxPolicy.java:79)
... 47 more

[gavin.king]

P.S. I have now refreshed the documentation of the datamodel stuff. Thanks for pointing out it was missing.

[gavin.king]

OK, so no message is being injected into the DataModelSelection. (There is no NPE in Seam, the NPE is in the application.)

Please show me the code of the MessageList class.

[frege]

The only change from the original is line 37 for line 36:

//$Id: MessageListBean.java,v 1.2 2006/01/14 20:13:46 gavin Exp $
package org.jboss.seam.example.messages;

import static org.jboss.seam.ScopeType.SESSION;
import static javax.persistence.PersistenceContextType.EXTENDED;

import java.io.Serializable;
import java.util.List;

import javax.ejb.Interceptors;
import javax.ejb.Remove;
import javax.ejb.Stateful;
import javax.persistence.EntityManager;
import javax.persistence.PersistenceContext;

import org.jboss.seam.annotations.Destroy;
import org.jboss.seam.annotations.Factory;
import org.jboss.seam.annotations.Name;
import org.jboss.seam.annotations.Out;
import org.jboss.seam.annotations.Scope;
import org.jboss.seam.annotations.datamodel.DataModel;
import org.jboss.seam.annotations.datamodel.DataModelSelection;
import org.jboss.seam.ejb.SeamInterceptor;

@Stateful
@Scope(SESSION)
@Name("messageList")
@Interceptors(SeamInterceptor.class)
public class MessageListBean implements Serializable, MessageList
{

 @DataModel
 private List<Message> messages;

 @Out(required=false)
// @DataModelSelection
 @DataModelSelection("message")
 private Message message;

 @PersistenceContext(type=EXTENDED)
 private EntityManager em;

 @Factory("messages")
 public void findMessages()
 {
 messages = em.createQuery("from Message msg order by msg.datetime desc").getResultList();
 }

 public String select()
 {
 message.setRead(true);
 return "selected";
 }

 public String delete()
 {
 messages.remove(message);
 em.remove(message);
 message=null;
 return "deleted";
 }

 @Remove @Destroy
 public void destroy() {}

}

[gavin.king]

The value() of the @DataModelSelection must be the name of the DataModel context variable. Which in this case is "messages". If you want to change that, you need to have:

* @DataModel("foo")
* @DataModelSelection("foo")
* @Factory("foo")

[frege]

Ah ha! Since it was (previously) undocumented, I assumed it was named after its own attribute variable, like the doc says for @DataModel. I even tried naming it after the "var" in the JSF dataTable.

Thanks for the promt attention.

[gavin.king]

It was documented in the Javadoc:

http://docs.jboss.com/seam/api/org/jboss/seam/annotations/datamodel/DataModelSelection.html#value()