Archive for March, 2009

ActiveMQ NullPointer exceptions when creating objectmessages.

Posted on March 24, 2009. Filed under: Java |

At the moment, I’m working with Flex, BlazeDS en ActiveMQ in a Spring application. I’m using Flex to display some of my database contents, and for direct communication, I use BlazeDS, and for updating the view, I use JMS (ActiveMQ) in combation with BlazeDS. It works by publishing information to topics, which can be easily done using the following code:

    private void sendJmsUpdate() {
        this.jmsTemplate.send(this.destination, new MessageCreator() {
            public Message createMessage(Session session) throws JMSException {
                return session.createObjectMessage(new ArrayList<TodoItem>(getList()));
            }
        });
    }

The above code uses the Spring JmsTemplate to created messages and send them to the topic. However, when I tried this, I got this exception:


java.lang.NullPointerException
at org.apache.activemq.ActiveMQMessageTransformation.copyProperties(ActiveMQMessageTransformation.java:188)
at org.apache.activemq.ActiveMQMessageTransformation.transformMessage(ActiveMQMessageTransformation.java:173)
at org.apache.activemq.ActiveMQSession.send(ActiveMQSession.java:1606)
at org.apache.activemq.ActiveMQMessageProducer.send(ActiveMQMessageProducer.java:227)
at org.apache.activemq.ActiveMQMessageProducerSupport.send(ActiveMQMessageProducerSupport.java:241)
at org.springframework.jms.core.JmsTemplate.doSend(JmsTemplate.java:572)
at org.springframework.jms.core.JmsTemplate.doSend(JmsTemplate.java:549)
at org.springframework.jms.core.JmsTemplate$3.doInJms(JmsTemplate.java:516)
at org.springframework.jms.core.JmsTemplate.execute(JmsTemplate.java:447)
at org.springframework.jms.core.JmsTemplate.send(JmsTemplate.java:514)
at org.epseelon.samples.todolist.business.TodoServiceImpl.sendJmsUpdate(TodoServiceImpl.java:77)
at org.epseelon.samples.todolist.business.TodoServiceImpl.save(TodoServiceImpl.java:39)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)


After a lot of Googling, I found nothing (well, a bug report somewhere, which was totally unrelated to what I had here). Why did I get this error?? I know my remoting was working (String were send), my objects were fine since I could get the list manually by doing a Refresh with the flex client itself (which used ≶mx:RemoteObject>) to call the Spring service…. And then it occured to me that the explanation was already here. I just overlooked it (hate it when that happens): the BlazeDS service apparently doesn’t require the objects (TodoItem) to be Serializable…. JMS ofcourse does! Argh! I forgot to implement Serializable here!

So, if you ever encounter this message, which is hardly descriptive at all, check your objects to see if they are all serializable. It saves a lot of debugging!