The Composed Message Processor EIP is a useful pattern for composing multiple message processors into a single processor in Apache Camel. It can be used to combine the processing of a message in a modular and reusable way and to improve the testability of a route by allowing the processing of a message to be tested in isolation.
This blog post will discuss how to use the Composed Message Processor EIP in Apache Camel. We will look at how to define a Composed Message Processor and use it in a Camel route.
Photo by Ashkan Forouzani on Unsplash
To use the Composed Message Processor EIP in a Camel route, we can define a processor class that implements the org.apache.camel.Processor interface and add multiple message processors. The processor class should define a process method that invokes the individual message processors on the message.
Use Case
Suppose you are building a system that processes orders for a retail store. The system receives orders from multiple channels, such as a website, a mobile app, and in-store kiosks. The orders are processed by a series of message processors that validate the order, check the availability of the items, calculate the total cost, and send an email confirmation to the customer.
To implement this system using Apache Camel, you could use the Composed Message Processor EIP to define a processor that combines all of the necessary message processors. Here is an example of how you might define the processor:
|
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 |
import org.apache.camel.Exchange; import org.apache.camel.Processor; public class OrderProcessor implements Processor { private final Processor validateProcessor; private final Processor availabilityProcessor; private final Processor costProcessor; private final Processor emailProcessor; public OrderProcessor(Processor validateProcessor, Processor availabilityProcessor, Processor costProcessor, Processor emailProcessor) { this.validateProcessor = validateProcessor; this.availabilityProcessor = availabilityProcessor; this.costProcessor = costProcessor; this.emailProcessor = emailProcessor; } @Override public void process(Exchange exchange) throws Exception { // Validate the order validateProcessor.process(exchange); if (exchange.getProperty("valid", Boolean.class)) { // Check the availability of the items availabilityProcessor.process(exchange); if (exchange.getProperty("available", Boolean.class)) { // Calculate the total cost costProcessor.process(exchange); // Send an email confirmation to the customer emailProcessor.process(exchange); } } } } |
This processor class defines four message processors and a process the method that invokes the processors in the correct order to process an order.
To use this processor in a Camel route, you can instantiate it and pass the individual processors as arguments like this:
|
1 2 3 4 5 6 7 8 9 10 |
import org.apache.camel.builder.RouteBuilder; public class OrderRoute extends RouteBuilder { @Override public void configure() throws Exception { from("direct:orders") .process(new OrderProcessor(new ValidateProcessor(), new AvailabilityProcessor(), new CostProcessor(), new EmailProcessor())) .to("direct:output"); } } |
This route reads a message from the direct:orders endpoint and processes it using the OrderProcessor, which invokes the ValidateProcessor, AvailabilityProcessor, CostProcessor, and EmailProcessor processors on the message. The processed message is then sent to the direct:output endpoint.
As you can see, there are significant advantages to using Composed Message Processor EIP.
Advantages
- Modularity: The Composed Message Processor EIP allows you to organize the processing of a message into smaller, reusable units. This can make it easier to understand and maintain the processing logic of a route, as well as reuse the processing logic in other routes.
- Reusability: It allows you to reuse message processors in multiple routes or contexts. This can reduce the amount of code duplication and improve the maintainability of your routes.
- Flexibility: Further, the Composed message processor EIP allows you to easily change the processing logic of a route by replacing or adding message processors to the composed processor. This can make it easier to adapt to changing requirements or to add new functionality to a route.
- Testability: Additionally, it allows you to test the processing of a message in isolation by testing the individual message processors separately. This can make it easier to ensure that the processing logic of a route is correct and to identify any issues with the processing of a message.
Inherently, there are some risks with Composed Message Processor EIP
- Complexity: If you use the Composed Message Processor EIP to combine a large number of message processors, the processing logic of your route may become complex and difficult to understand. It may be helpful to use additional EIPs, such as the Splitter EIP or the Aggregator EIP, to break up the processing logic into smaller, more manageable units.
- Performance: If you use the Composed Message Processor EIP to combine a large number of message processors, the processing of a message may become slower as the number of processors increases. It may be helpful to use a profiler or to measure the performance of your route to ensure that it is performing efficiently.
Thanks for reading!