Tutorial on using Camel in a Web Application

Camel has been designed to work great with the Spring framework; so if you are already a Spring user you can think of Camel as just a framework for adding to your Spring XML files.

So you can follow the usual Spring approach to working with web applications; namely to add the standard Spring hook to load a /WEB-INF/applicationContext.xml file. In that file you can include your usual Camel XML configuration.

Step1: Edit your web.xml

To enable spring add a context loader listener to your /WEB-INF/web.xml file

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://java.sun.com/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
         version="2.5">

  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>

</web-app>

This will cause Spring to boot up and look for the /WEB-INF/applicationContext.xml file.

Step 2: Create a /WEB-INF/applicationContext.xml file

Now you just need to create your Spring XML file and add your camel routes or configuration.

For example

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
       http://www.springframework.org/schema/beans 
       http://www.springframework.org/schema/beans/spring-beans-2.5.xsd
       http://www.springframework.org/schema/context 
       http://www.springframework.org/schema/context/spring-context-2.5.xsd
       http://camel.apache.org/schema/spring 
       http://camel.apache.org/schema/spring/camel-spring.xsd">

  <camelContext xmlns="http://camel.apache.org/schema/spring">
    <route>
      <from uri="seda:foo"/>
      <to uri="mock:results"/>
    </route>
  </camelContext>

</beans>

Then boot up your web application and you're good to go!

Hints and Tips

If you use Maven to build your application your directory tree will look like this...

src/main/webapp/WEB-INF
  web.xml
  applicationContext.xml

You should update your Maven pom.xml to enable WAR packaging/naming like this...

<project>
    ...
    <packaging>war</packaging>
    ...
    <build>
	<finalName>[desired WAR file name]</finalName>
        ...
    </build>

To enable more rapid development we highly recommend the jetty:run maven plugin.

Please refer to the help for more information on using jetty:run - but briefly if you add the following to your pom.xml 

  <build>
    <plugins>
      <plugin>
        <groupId>org.mortbay.jetty</groupId>
        <artifactId>maven-jetty-plugin</artifactId>
        <configuration>
          <webAppConfig>
            <contextPath>/</contextPath>
          </webAppConfig>
          <scanIntervalSeconds>10</scanIntervalSeconds>
        </configuration>
      </plugin>
    </plugins>
  </build>

Then you can run your web application as follows

mvn jetty:run

Then Jetty will also monitor your target/classes directory and your src/main/webapp directory so that if you modify your spring XML, your web.xml or your java code the web application will be restarted, re-creating your Camel routes.

If your unit tests take a while to run, you could miss them out when running your web application via

mvn -Dtest=false jetty:run
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