Apache Camel: Integration Nirvana

•    Pluggable data formats and type converters for easy message transformation between Artix Data Services, CSV, EDI, Flatpack, HL7, JAXB, JSON, XmlBeans, XStream, Zip, Camel-bindy, etc.
•    Pluggable languages to create expressions or predicates for use in the DSL. Some of these languages include: EL, JXPath, Mvel, OGNL, BeanShell, JavaScript, Groovy, Python, PHP, Ruby, SQL, XPath, XQuery, etc.  
•    Support for the integration of beans and POJOs in various places in Camel.
•    Excellent support for testing distributed and asynchronous systems using a messaging approach
•    and much more...

Example

A motorcycle parts business, Rider Auto Parts, supplies parts to motorcycle manufacturers. Over the years they've changed the way they receive orders several times. Initially, orders were placed by uploading CSV files to an FTP server. The message format was later changed to XML. Currently they provide a web site to submit orders as XML messages over HTTP. All of these messages are converted to an internal POJO format before processing.

Rider Auto Parts states to any new customers to use the web interface to place orders. However, because of existing agreements with customers, they must keep all the old message formats and interfaces up and running.
Solution using EIPs

Rider Auto Parts faces a pretty common problem; over years of operation businesses acquire software baggage in the form of transports/data formats that are popular at the time. Using patterns from the EIP book we can envision the solution as something like Figure 2.

 
 

Figure 2: This shows the solution to Rider Auto Parts integration problem using notation from the Enterprise Integration Patterns book.

So we have several patterns in use here.

1. There are two Message Endpoints; one for FTP connectivity and another for HTTP.

2. Messages from these endpoints are fed into the incomingOrderQueue Message Channel

3. The messages are consumed from the incomingOrderQueue and routed by a Content-Based Router to one of two Message Translators. As the EIP name implies, the routing destination depends on the content of the message. In this case we need to route based on whether the content is a CSV or XML file.

4. Both Message Translators convert the message content into a POJO, which is fed into the orderQueue Message Channel.

The whole section that uses a Content-Based Router and several Message Translators is referred to as a Normalizer. This composite pattern has a unique graphic to depict it but was left out here in favor of its sub-patterns to make things clearer.

Implementation using Camel

As mentioned before, Camel has a small core set of components included by default. The rest of the components exist as separate modules. In applications that require many types of connectivity it is useful to figure out what Camel modules to include. Listing 1 shows the dependencies using Apache Maven for the Camel implementation of the Rider Auto Parts example. Of course, you don't need to use Apache Maven for dependencies - it is just the easiest way to rapidly add new dependencies to your applications. The list of dependencies includes support for core Camel, ActiveMQ, JAXB marshaling, CSV marshaling, and HTTP. To make the example easier to try out, I've opted to use the File endpoint instead of the FTP. If we were using the FTP endpoint we would need to add a dependency on the camel-ftp module as well.

Listing 1: Maven dependencies for the Camel implementation

  <dependencies>
    <!-- Core Camel support -->     
    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-core</artifactId>
      <version>${camel-version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-spring</artifactId>
      <version>${camel-version}</version>
    </dependency>
    
    <!-- ActiveMQ connectivity for Camel -->            
    <dependency>
      <groupId>org.apache.activemq</groupId>
      <artifactId>activemq-camel</artifactId>
      <version>${activemq-version}</version>
    </dependency>
    
    <!-- Add support for JAXB marshaling -->
    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-jaxb</artifactId>
      <version>${camel-version}</version>
    </dependency>
    
    <!-- Add support for CSV marshaling -->    
    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-csv</artifactId>
      <version>${camel-version}</version>
   </dependency>
    
    <!-- Add support for HTTP -->
    <dependency>
      <groupId>org.apache.camel</groupId>
      <artifactId>camel-jetty</artifactId>
      <version>${camel-version}</version>
    </dependency>

    <!-- Embedded ActiveMQ broker -->
    <dependency>
      <groupId>org.apache.activemq</groupId>
      <artifactId>activemq-core</artifactId>
      <version>${activemq-version}</version>
    </dependency>
    <dependency>
      <groupId>org.apache.xbean</groupId>
      <artifactId>xbean-spring</artifactId>
      <version>${xbean-spring-version}</version>
    </dependency>
  </dependencies>