Hi,

I get NullPointerException when I try to invoke session bean from my message driven bean onMessage() method.

Here is my MDB code.

public class MDB implements MessageDrivenBean, MessageListener{

 private WorkerHome workerHome = null;

 private MessageDrivenContext ctx = null;
 public MDB() {

 }
 public void setMessageDrivenContext(MessageDrivenContext ctx)
 throws EJBException {
 this.ctx = ctx;
 }

 public void ejbCreate() {}

 public void ejbRemove() {ctx=null;}

 public void onMessage(Message message) {
 try {
 Worker worker = workerHome.create();

 if (message instanceof TextMessage) {
 TextMessage m = (TextMessage)message;
 worker.doWork(m.getText());
 }

 } catch(Exception ex) {
 throw new EJBException("Could not call worker " + ex);
 }

 }
}

Here is my ejb-jar.xml file:

<?xml version="1.0"?>
<!DOCTYPE ejb-jar PUBLIC "-//Sun Microsystems, Inc.//DTD Enterprise JavaBeans 2.0//EN" "http://java.sun.com/j2ee/dtds/ejb-jar_2_0.dtd">
 <ejb-jar>
 <enterprise-beans>
 <message-driven>
 <ejb-name>MDB</ejb-name>
 <ejb-class>test.bean.MDB</ejb-class>
 <message-selector></message-selector>
 <transaction-type>Container</transaction-type>
 <ejb-ref>
 <description>The Workers home</description>
 <ejb-ref-name>ejb/worker</ejb-ref-name>
 <ejb-ref-type>Session</ejb-ref-type>
 <ejb-link>WorkerBean</ejb-link>
 <home>test.bean.WorkerHome</home>
 <remote>test.bean.Worker</remote>
 </ejb-ref>
 <message-driven-destination>
 <destination-type>javax.jms.Topic</destination-type>
 <subscription-durability>NonDurable</subscription-durability>
 </message-driven-destination>
 </message-driven>
 <session>
 <description>Worker bean</description>
 <display-name>Worker</display-name>
 <ejb-name>WorkerBean</ejb-name>
 <home>test.bean.WorkerHome</home>
 <remote>test.bean.Worker</remote>
 <ejb-class>test.bean.WorkerBean</ejb-class>
 <session-type>Stateless</session-type>
 <transaction-type>Container</transaction-type>
 </session>

 </enterprise-beans>
 <assembly-descriptor>
 <container-transaction>
 <method>
 <ejb-name>MDB</ejb-name>
 <method-name>*</method-name>
 </method>
 <trans-attribute>Required</trans-attribute>
 </container-transaction>
 <container-transaction>
 <method>
 <ejb-name>WorkerBean</ejb-name>
 <method-intf>Remote</method-intf>
 <method-name>*</method-name>
 </method>
 <trans-attribute>Required</trans-attribute>
 </container-transaction>

 </assembly-descriptor>
</ejb-jar>

When I use client code to invoke MDB's onMessage() method ( publish topic), I get the following exception on the server console:

15:44:16,453 ERROR [JMSContainerInvoker] Exception in JMSCI message listener
javax.ejb.TransactionRolledbackLocalException: Could not call worker java.lang.NullPointerException; CausedByException is:
 Could not call worker java.lang.NullPointerException
 at org.jboss.ejb.plugins.AbstractTxInterceptor.invokeNext(AbstractTxInterceptor.java:232)
....
.....
javax.ejb.EJBException: Could not call worker java.lang.NullPointerException
 at test.bean.MDB.onMessage(MDB.java:41)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke

Could any one please tell me why my MDB throws NullPointerException when trying to call session bean?

Ravi Prakash