How to convert payload and headers on JMS outbound message?

[davison]

hi,

We're trying to send a file via an si:channel which will be converted to a JMS message. We'd rather not use the s-i API's directly in our code. The following code/config works exactly as we'd like;

Message<byte[]> m = MessageBuilder.withPayload("this could be a real file".getBytes())
    .setHeader("file.name", "target/file/name.txt")
    .build();
        
MessageChannel out = (MessageChannel) context.getBean("gw-out");
out.send(m);

<si:channel id="gw-out"/>
<jms:outbound-channel-adapter
    connection-factory="connectionFactory"
    channel="gw-out"        
    destination-name="queue.dataupload.new"/>

In the above example, a JMS BytesMessage with an appropriate JMSProperty for the 'file.name' header is placed on the queue. So far, so good - the consumer on that queue gets exactly what it needs from the above setup.

Now, when I try to further this by removing the dependencies on Spring API's, I create a gateway interface..

public interface Gateway {
    void send(Object o);
}

.. add the following XML snippet..

<si:gateway 
    id="gateway"
    service-interface="test.Gateway" 
    default-request-channel="gw-out"/>

.. and begin to amend the client code..

Gateway g = (Gateway) context.getBean("gateway");
Object o = ?? // what goes here to replace the Spring MessageBuilder above?
g.send(o);

What do I replace the MessageBuilder with?

Cheers!
Darren.


NB:
Even if I leave the MessageBuilder in place, but still use the gateway, I have a new problem in that the actual GenericMessage instance gets serialized through the gateway. No longer do I have a BytesMessage on my JMS queue with a JMSProperty set with the 'file.name' value.. I have an ObjectMessage and a classname that the consumer knows nothing about. This appears to contradict the current ref docs that suggest the payload should be extracted.. I may have read this bit wrong of course.

[Mark Fisher]

For the line to replace the builder, you should be able to do something like this:

g.send("this could be a real file".getBytes(), "target/file/name.txt");

Where the gateway's interface defines a method like this:

void send(byte[] payload, @Header("file.name") String fileName);

Let me know if that works.

(I might need a bit more clarification on the question in your NB)

[davison]

thanks for the quick reply Mark.

Yes, your solution works, but I still have a Spring API in the code (the @Header annotation). Is this unavoidable? Any way, say, to pass a Map that will be treated as headers automagically?

Cheers,
Darren.

[Mark Fisher]

You can use @Headers and a map:

void send(byte[] payload, @Headers Map headerMap);

Yes, either annotation (@Header or @Headers) is going to introduce a Spring import. I guess we could consider auto-detecting 2 arguments where one is a Map and therefore headers. The only problem is that you could pass a Map payload as well (e.g. send(Map payload, Map headers)) in which case we would have to rely on the order, and that seems pretty ugly.

[davison]

yes, reflection's inability to access parameters by name curses us again

No better in many ways than the solution you proposed, but an alternative might be to check a Map for a key named "payload", treating all other keys as headers.

We'll go with the annotation for now I guess.

Cheers!
Darren.