The Delayer Pattern allows you to delay the delivery of messages to some destination.
So the above example will delay all messages received on seda:b 1 second before sending them to mock:result.
You can of course use many different _expression_ languages such as XPath, XQuery, SQL or various Scripting Languages. You can just delay things a fixed amount of time from the point at which the delayer receives the message. For example to delay things 2 seconds
The above assume that the delivery order is maintained and that the messages are delivered in delay order. If you want to reorder the messages based on delivery time, you can use the Resequencer with this pattern. For example
from("activemq:someQueue").resequencer(header("MyDeliveryTime")).delay("MyRedeliveryTime").to("activemq:aDelayedQueue");
Camel 2.0 - Spring DSL
The sample below demonstrates the delay in Spring DSL:
<camelContext id="camel" xmlns="http://camel.apache.org/schema/spring">
<route>
<from uri="seda:a"/>
<delay>
<header>MyDelay</header>
</delay>
<to uri="mock:result"/>
</route>
<route>
<from uri="seda:b"/>
<delay>
<constant>1000</constant>
</delay>
<to uri="mock:result"/>
</route>
</camelContext>
Camel 1.x - Spring DSL
The delayer is using slightly different names in Camel 1.x:
<delayer>
<delayTime>3000</delayTime>
</_expression_>
</delayer>
The empty tag </_expression_> is needed to fulfill the XSD validation as its an optional element and we use JAXB annotations to generated the XSD in Camel and some combinations is hard to auto generate with optional elements.
For further examples of this pattern in use you could look at the junit test case
Asynchronous delaying
Available as of Camel 2.4
You can let the Delayer use non blocking asynchronous delaying, which means Camel will use a scheduler to schedule a task to be executed in the future. The task will then continue routing. This allows the caller thread to not block and be able to service other messages etc.
From Java DSL
You use the asyncDelay() to enable the async behavior.
from("activemq:queue:foo").delay(1000).asyncDelay().to("activemq:aDelayedQueue");
From Spring XML
You use the asyncDelay="true" attribute to enable the async behavior.
<route>
<from uri="activemq:queue:foo"/>
<delay asyncDelay="true">
<constant>1000</constant>
</delay>
<to uri="activemq:aDealyedQueue"/>
</route>
Creating a custom delay
You can use an _expression_ to determine when to send a message using something like this
from("activemq:foo").
delay().method("someBean", "computeDelay").
to("activemq:bar");
then the bean would look like this...
public class SomeBean {
public long computeDelay() {
long delay = 0;
return delay;
}
}
Using This Pattern
If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.
