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Walk through another example

Introduction

We continue Continuing the walk from Walk through an example. This time our first example, we take a closer look at the routing and explains explain a few pointers - so you wont won't walk into a bear trap, but can enjoy a walk an after-hours walk to the local pub for a large beer

First we take a moment to look at the Enterprise Integration Patterns that is - the base pattern catalog for integrationsintegration scenarios. In particular we focus on the Pipes and filters EIP pattern, that is - a central pattern. This is used for to route messages through a sequence of processing steps, each performing a specific function - much like the Java Servlet Filters.

...

In this sample we want to process a message in a sequence of steps where each steps can perform their specific function. In our example we have a JMS queue for receiving new orders. When an order is received we need to process it in several steps:

• validate
• register
• send confirm email

This can be created in a route like this:

...

<route>
   <from uri="jms:queue:order"/>
   <bean ref="validateOrder"/>
   <bean ref="registerOrder"/>
   <bean ref="sendConfirmEmail"/>
</route>

<route>
   <from uri="jms:queue:order"/>
   <multicast>
     <to uri="log:org.company.log.Category"/>
     <pipeline>
       <bean ref="validateOrder"/>
       <bean ref="registerOrder"/>
       <bean ref="sendConfirmEmail"/>
     </pipeline>
   </multicast>
</route>

<route>
   <from uri="jms:queue:order"/>
   <multicast>
     <to uri="log:org.company.log.Category"/>
     <bean ref="validateOrder"/>
     <bean ref="registerOrder"/>
     <bean ref="sendConfirmEmail"/>
   </multicast>
</route>

Where as the bean ref is a reference for a spring bean id, so we define our beans using regular Spring XML as:

...

So what happens in the route above. Well when an order is received from the JMS queue the message is routed like Pipes and filters:
1. payload from the JMS is sent as input to the validateOrder bean
2. the output from validateOrder bean is sent as input to the registerOrder bean
3. the output from registerOrder bean is sent as input to the sendConfirmOrder sendConfirmEmail bean

Using Camel Components

In the route lets imaging imagine that the registration of the order has to be done by sending data to a TCP socket that could be a big mainframe. As Camel has many Components we will use the camel-mina component that supports TCP connectivity. So we change the route to:

...

What we now have in the route is a to type that can be used as a direct replacement for the bean type. The steps is now:
1. payload from the JMS is sent as input to the validateOrder bean
2. the output from validateOrder bean is sent as text to the mainframe using TCP
3. the output from mainframe is sent back as input to the sendConfirmOrder sendConfirmEmai bean

What to notice here is that the to is not the end of the route (the world ) in this example it's used in the middle of the Pipes and filters. In fact we can change the bean types to to as well:

...

As the to is a generic type we must state in the uri scheme which component it is. So we must write bean: for the {Bean] component that we are using.

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This example was provided to demonstrate the Spring DSL (XML based) as opposed to the pure Java DSL from the first example. And as well to point about that the {{to]} doens doesn't have to be the last node in a route graph.

This example is also based on the in-only message exchange pattern. What you must understand as well is the in-out message exchange pattern, where the caller expects a response. We will look into this in another example.

See also

• Examples
• Tutorials
• User Guide