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Sending a Message
The JmsTemplate
contains many convenience methods to send a message. Send
methods specify the destination by using a jakarta.jms.Destination
object, and others
specify the destination by using a String
in a JNDI lookup. The send
method
that takes no destination argument uses the default destination.
The following example uses the MessageCreator
callback to create a text message from the
supplied Session
object:
import jakarta.jms.ConnectionFactory;
import jakarta.jms.JMSException;
import jakarta.jms.Message;
import jakarta.jms.Queue;
import jakarta.jms.Session;
import org.springframework.jms.core.MessageCreator;
import org.springframework.jms.core.JmsTemplate;
public class JmsQueueSender {
private JmsTemplate jmsTemplate;
private Queue queue;
public void setConnectionFactory(ConnectionFactory cf) {
this.jmsTemplate = new JmsTemplate(cf);
}
public void setQueue(Queue queue) {
this.queue = queue;
}
public void simpleSend() {
this.jmsTemplate.send(this.queue, new MessageCreator() {
public Message createMessage(Session session) throws JMSException {
return session.createTextMessage("hello queue world");
}
});
}
}
In the preceding example, the JmsTemplate
is constructed by passing a reference to a
ConnectionFactory
. As an alternative, a zero-argument constructor and
connectionFactory
is provided and can be used for constructing the instance in
JavaBean style (using a BeanFactory
or plain Java code). Alternatively, consider
deriving from Spring’s JmsGatewaySupport
convenience base class, which provides
pre-built bean properties for JMS configuration.
The send(String destinationName, MessageCreator creator)
method lets you send a
message by using the string name of the destination. If these names are registered in JNDI,
you should set the destinationResolver
property of the template to an instance of
JndiDestinationResolver
.
If you created the JmsTemplate
and specified a default destination, the
send(MessageCreator c)
sends a message to that destination.
Using Message Converters
To facilitate the sending of domain model objects, the JmsTemplate
has
various send methods that take a Java object as an argument for a message’s data
content. The overloaded methods convertAndSend()
and receiveAndConvert()
methods in
JmsTemplate
delegate the conversion process to an instance of the MessageConverter
interface. This interface defines a simple contract to convert between Java objects and
JMS messages. The default implementation (SimpleMessageConverter
) supports conversion
between String
and TextMessage
, byte[]
and BytesMessage
, and java.util.Map
and MapMessage
. By using the converter, you and your application code can focus on the
business object that is being sent or received through JMS and not be concerned with the
details of how it is represented as a JMS message.
The sandbox currently includes a MapMessageConverter
, which uses reflection to convert
between a JavaBean and a MapMessage
. Other popular implementation choices you might
implement yourself are converters that use an existing XML marshalling package (such as
JAXB or XStream) to create a TextMessage
that represents the object.
To accommodate the setting of a message’s properties, headers, and body that can not be
generically encapsulated inside a converter class, the MessagePostProcessor
interface
gives you access to the message after it has been converted but before it is sent. The
following example shows how to modify a message header and a property after a
java.util.Map
is converted to a message:
public void sendWithConversion() {
Map map = new HashMap();
map.put("Name", "Mark");
map.put("Age", new Integer(47));
jmsTemplate.convertAndSend("testQueue", map, new MessagePostProcessor() {
public Message postProcessMessage(Message message) throws JMSException {
message.setIntProperty("AccountID", 1234);
message.setJMSCorrelationID("123-00001");
return message;
}
});
}
This results in a message of the following form:
MapMessage={ Header={ ... standard headers ... CorrelationID={123-00001} } Properties={ AccountID={Integer:1234} } Fields={ Name={String:Mark} Age={Integer:47} } }
Using SessionCallback
and ProducerCallback
While the send operations cover many common usage scenarios, you might sometimes
want to perform multiple operations on a JMS Session
or MessageProducer
. The
SessionCallback
and ProducerCallback
expose the JMS Session
and Session
/
MessageProducer
pair, respectively. The execute()
methods on JmsTemplate
run
these callback methods.