Apache Camel: Spring Remoting

Spring Remoting

We support Spring Remoting in Camel. The implementing of Spring Remoting uses Camel as the underlying transport mechanism. The nice thing about this approach is we can use any of the Camel transport Components to communicate between beans.

It also means we can use Content Based Router and the other Enterprise Integration Patterns in between the beans; in particular we can use Message Translator to be able to convert what the on-the-wire messages look like in addition to adding various headers and so forth.

Using Camel Spring Remoting

In your Spring XML just use the CamelProxyFactoryBean to create a client side proxy implementing some interface which then sends messages to some remote Camel Endpoint such as ActiveMQ, JMS, File, HTTP, XMPP etc.

Then to implement the service you use CamelServiceExporter

The following example shows how to create a proxy which when invoked with fire a message to the direct:say endpoint

<!--  Creates a proxy to the direct:say endpoint. -->
<bean id="sayProxy" class="org.apache.camel.spring.remoting.CamelProxyFactoryBean">
  <property name="serviceUrl" value="direct:say"/>
  <property name="serviceInterface" value="org.apache.camel.spring.remoting.ISay"/>
</bean>

Then we expose the service on an endpoint so that messages from direct:sayImpl will be dispatched to the service (note that we have a route in between these two endpoints).

<!--  Exposes the above bean as via the pojo:say endpoint -->
<bean id="say" class="org.apache.camel.spring.remoting.CamelServiceExporter">
  <property name="uri" value="direct:sayImpl"/>
  <property name="service">
    <bean class="org.apache.camel.spring.remoting.SayService"/>
  </property>
  <property name="serviceInterface" value="org.apache.camel.spring.remoting.ISay"/>
</bean>

Using Custom Namespaces

In this example we use the Camel custom namespaces to make the XML much more concise. First, create a proxy via the proxy element

<!--  Creates a proxy to the direct:say endpoint. -->
<camel:proxy id="sayProxy" serviceUrl="direct:say"
                    serviceInterface="org.apache.camel.spring.remoting.ISay"/>

Then we expose the service via the export element

<bean id="sayService" class="org.apache.camel.spring.remoting.SayService"/>

<camel:export id="say" uri="direct:sayImpl" serviceRef="sayService"
                       serviceInterface="org.apache.camel.spring.remoting.ISay"/>

Its much cleaner - use whichever approach you prefer as they are both equivalent.

ServiceExporter is Optional

Note that the service is not mandatory; since the Bean component and the various other forms of Bean Integration can be used to route any message exchange to a bean, so you can miss out the serviceExporter if you prefer. The main value of the service exporter is its a single XML element to bind a URI to a bean and it allows the full API of the bean to be restricted by a serviceInterface.

Working with InOnly method calls

As of 1.5 Camel supports the @InOnly and @Pattern annotations to let you specify which methods are not InOut (Request Reply) but are InOnly (oneway or fire and forget Event Message).

For more details see Using Exchange Pattern Annotations

Bean Binding

The Bean Binding in Camel defines both which methods are invoked and also how the Message is converted into the parameters of the method when it is invoked.

Choosing the method to invoke

The binding of a Camel Message to a bean method call can occur in different ways

the method name can be specified explicitly in the DSL or when using POJO Consuming
if the bean can be converted to a Processor using the Type Converter mechanism then this is used to process the message. This mechanism is used by the ActiveMQ component to allow any JMS MessageListener to be invoked directly by Camel without having to write any integration glue code. You can use the same mechanism to integrate Camel into any other messaging/remoting frameworks.
if the body of the message can be converted to a BeanInvocation (the default payload used by the ProxyHelper) - then that its used to invoke the method and pass the arguments
if the message contains the header org.apache.camel.MethodName then that method is invoked, converting the body to whatever the argument is to the method
otherwise the type of the method body is used to try find a method which matches; an error is thrown if a single method cannot be chosen unambiguously.
you can also use Exchange as the parameter itself, but then the return type must be void.

By default the return value is set on the outbound message body.

Binding Annotations

You can use the Parameter Binding Annotations to customize how parameter values are created from the Message

Examples

For example a Bean such as:

public class Bar {

    public String doSomething(String body) {
      // process the in body and return whatever you want
      return "Bye World";
   }

Or the Exchange example. Notice that the return type must be void:

public class Bar {

    public void doSomething(Exchange exchange) {
      // process the exchange
      exchange.getIn().setBody("Bye World");
   }

For example you could use POJO Consuming to write a bean like this

@MessageDriven requires camel-spring

Using the @MessageDriven annotations requires camel-spring that uses the org.apache.camel.spring.CamelBeanPostProcessor to perform the setup for this consumer and the needed bean bindings.

public class Foo {

    @MessageDriven(uri = "activemq:my.queue")
    public void doSomething(String body) {
		// process the inbound message here
    }

}

Here Camel with subscribe to an ActiveMQ queue, then convert the message payload to a String (so dealing with TextMessage, ObjectMessage and BytesMessage in JMS), then process this method.

Spring Remoting

Using Camel Spring Remoting

Using Custom Namespaces

ServiceExporter is Optional

Working with InOnly method calls

Bean Binding

Choosing the method to invoke

Binding Annotations

Examples

Overview

Documentation

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