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This component is used for bootstrapping Camel applications in web applications. For example beforehand people would have to find their own way of bootstrapping Camel, or rely on 3rd party frameworks such as Spring to do it.

There may be situations where you want a pure Camel based solution, without the extra overhead of Spring Framework.

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This component

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supports Servlet 2.x onwards, which mean it works also in

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older web containers; which is the goal of this component.
Though Servlet 2.x requires to use a web.xml file as configuration.

For Servlet 3.x containers you can use annotation driven configuration to boostrap Camel using the @WebListener, and implement your own class, where you boostrap Camel. Doing this still puts the challenge how to let end users easily configure Camel, which you get for free with the old school web.xml file.

Maven users will need to add the following dependency to their pom.xml for this component:

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Using

You would need to chose one of the following implementations of the abstract class org.apache.camel.component.servletlistener.CamelServletContextListener.

• JndiCamelServletContextListener which uses the JndiRegistry to leverage JNDI for its registry.
• SimpleCamelServletContextListener which uses the SimpleRegistry to leverage a java.util.Map as its registry.

TODO: Maven dependency

Using

To use this you need to configure the org.apache.camel.component.servletlistener.CamelServletContextListener in the WEB-INF/web.xml file as shown below: TODO:

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Options

The org.apache.camel.component.servletlistener.CamelServletContextListener supports the following options which can be configured as context-param in the web.xml file.

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Examples

See Servlet Tomcat No Spring Example.

Accessing the created CamelContext

Available as of Camel 2.14/2.13.3/2.12.5

The created CamelContext is stored on the ServletContext as an attribute with the key "CamelContext". You can get hold of the CamelContext if you can get hold of the ServletContext as shown below:

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Configuring routes

You need to configure which routes to use in the web.xml file. You can do this in a number of ways, though all the parameters must be prefixed with "routeBuilder".

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By default Camel will assume the param-value is a FQN classname for a Camel RouteBuilder class, as shown below:

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You can specify multiple classes in the same param-value as shown below:

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The name of the parameter does not have a meaning at runtime. It just need to be unique and start with "routeBuilder". In the example above we have "routeBuilder-routes". But you could just as well have named it "routeBuilder.foo".

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You can also tell Camel to use package scanning, which mean it will look in the given package for all classes of RouteBuilder types and automatic adding them as Camel routes. To do that you need to prefix the value with "packagescan:" as shown below:

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Using a XML file

You can also define Camel routes using XML DSL, though as we are not using Spring or Blueprint the XML file can only contain Camel route(s).
In the web.xml you refer to the XML file which can be from "classpath", "file" or a "http" url, as shown below:

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And the XML file is:

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Notice that in the XML file the root tag is <routes> which must use the namespace "http://camel.apache.org/schema/spring". This namespace is having the spring in the name, but that is because of historical reasons, as Spring was the first and only XML DSL back in the time. At runtime no Spring JARs is needed. Maybe in Camel 3.0 the namespace can be renamed to a generic name.

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Here is a snippet of a web.xml configuration for setting up property placeholders to load myproperties.properties from the classpath

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Configuring JMX

Here is a snippet of a web.xml configuration for configuring JMX, such as disabling JMX.

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JNDI or Simple as Camel Registry

This component uses either JNDI or Simple as the Registry.
This allows you to lookup Beans and other services in JNDI, and as well to bind and unbind your own Beans.

This is done from Java code by implementing the org.apache.camel.component.servletlistener.CamelContextLifecycle.

Using custom CamelContextLifecycle

In the code below we use the callbacks beforeStart and afterStop to enlist our custom bean in the Simple Registry, and as well to cleanup when we stop.

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Then we need to register this class in the web.xml file as shown below, using the parameter name "CamelContextLifecycle". The value must be a FQN which refers to the class implementing the org.apache.camel.component.servletlistener.CamelContextLifecycle interface.

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As we enlisted our HelloBean Bean using the name "myBean" we can refer to this Bean in the Camel routes as shown below:

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Important: If you use org.apache.camel.component.servletlistener.JndiCamelServletContextListener then the CamelContextLifecycle must use the JndiRegistry as well. And likewise if the servlet is org.apache.camel.component.servletlistener.SimpleCamelServletContextListener then the CamelContextLifecycle must use the SimpleRegistry

See Also

• SERVLET

See Also

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• Servlet Tomcat Example
• Servlet Tomcat No Spring Example