Mule returning a MessageCollection from component

Question

I'm having difficulty returning a collection of MuleMessage instances from a component.

Mule 3.3.1.

The following code works (i.e., after the component, a foreach component with a logger dumps out "abc" and "def" as I expect).

public Object onCall( MuleEventContext eventContext ) throws Exception 
{
    MuleMessage message = eventContext.getMessage();

    MuleMessageCollection collection = new DefaultMessageCollection( message.getMuleContext() );

    String s1 = "abc";
    String s2 = "def";
    DefaultMuleMessage m1 = new DefaultMuleMessage( s1, message.getMuleContext() );
    DefaultMuleMessage m2 = new DefaultMuleMessage( s2, message.getMuleContext() );
    List<MuleMessage> list = new ArrayList<MuleMessage>();
    list.add( m1 );
    list.add( m2 );

    collection.addMessages( list );

    return collection;
}

If, however, I substitute a class of my own in place of the Strings, like so:

public Object onCall( MuleEventContext eventContext ) throws Exception 
{
    MuleMessage message = eventContext.getMessage();

    MuleMessageCollection collection = new DefaultMessageCollection( message.getMuleContext() );

    LicenseRequest s1 = new LicenseRequest();
    LicenseRequest s2 = new LicenseRequest();
    DefaultMuleMessage m1 = new DefaultMuleMessage( s1, message.getMuleContext() );
    DefaultMuleMessage m2 = new DefaultMuleMessage( s2, message.getMuleContext() );
    List<MuleMessage> list = new ArrayList<MuleMessage>();
    list.add( m1 );
    list.add( m2 );

    collection.addMessages( list );

    return collection;
}

I get an exception:

org.mule.transport.http.HttpsConnector Work caused exception on 'workCompleted'. Work being executed was: org.mule.transport.http.HttpsMessageReceiver$HttpsWorker@7b921c57
org.mule.exception.DefaultSystemExceptionStrategy Caught exception in Exception Strategy: Payload was invalidated calling setPayload and the message is not collection anymore.
java.lang.IllegalStateException: Payload was invalidated calling setPayload and the message is not collection anymore.
    at org.mule.DefaultMessageCollection.checkValidPayload(DefaultMessageCollection.java:107)
    at org.mule.DefaultMessageCollection.newThreadCopy(DefaultMessageCollection.java:312)
    at org.mule.DefaultMuleEvent.newThreadCopy(DefaultMuleEvent.java:779)
    at org.mule.RequestContext.newEvent(RequestContext.java:140)
    at org.mule.RequestContext.setExceptionPayload(RequestContext.java:121)
    at org.mule.exception.AbstractSystemExceptionStrategy.handleException(AbstractSystemExceptionStrategy.java:54)
    at org.mule.exception.AbstractSystemExceptionStrategy.handleException(AbstractSystemExceptionStrategy.java:77)
    at org.mule.transport.http.HttpMessageReceiver$HttpWorker.run(HttpMessageReceiver.java:220)
    at org.mule.work.WorkerContext.run(WorkerContext.java:311)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)
Exception in thread "[license-generation].HTTPSConnector.receiver.02" java.lang.IllegalStateException: Payload was invalidated calling setPayload and the message is not collection anymore.
    at org.mule.DefaultMessageCollection.checkValidPayload(DefaultMessageCollection.java:107)
    at org.mule.DefaultMessageCollection.newThreadCopy(DefaultMessageCollection.java:312)
    at org.mule.DefaultMuleEvent.newThreadCopy(DefaultMuleEvent.java:779)
    at org.mule.RequestContext.newEvent(RequestContext.java:140)
    at org.mule.RequestContext.setExceptionPayload(RequestContext.java:121)
    at org.mule.exception.AbstractSystemExceptionStrategy.handleException(AbstractSystemExceptionStrategy.java:54)
    at org.mule.exception.AbstractSystemExceptionStrategy.handleException(AbstractSystemExceptionStrategy.java:77)
    at org.mule.transport.AbstractConnector.handleWorkException(AbstractConnector.java:2099)
    at org.mule.transport.AbstractConnector.workCompleted(AbstractConnector.java:2067)
    at org.mule.work.WorkerContext.run(WorkerContext.java:338)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1110)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:603)
    at java.lang.Thread.run(Thread.java:722)

At this point in my testing, LicenseRequest is just an empty class whose toString() method returns "ghi".

What am I doing wrong?

I should add that my goal is to return a collection of objects which are created from the incoming payload. I can then iterate over those objects in the calling flow and take appropriate action for each.

EDIT: It appears I can do what I want in a transformer, just not a component. Why is this?

Answer 1

I guess it is not required to wrap each of LicenseRequest object into a mule message and the adding it to the collection. Make a collection directly and return it from the onCall method.

public Object onCall( MuleEventContext eventContext ) throws Exception 
{
    MuleMessage message = eventContext.getMessage();

    LicenseRequest s1 = new LicenseRequest();
    LicenseRequest s2 = new LicenseRequest();

    List<LicenseRequest> list = new ArrayList<LicenseRequest>();
    list.add( s1 );
    list.add( s2 );

    return list;
}

Hope this helps.