h2. servicemix-bean

h3. Overview
The ServiceMix Bean component provides integration with beans (POJOs) with the JBI bus to make it easy to use POJOs to process JBI message exchanges. Like in an Message Driven Bean in J2EE a POJO will receive a message from the NMR and process it in any way it likes. Unlike in a JMS component where the coding is already done the Bean component gives the developer the freedom to create any type of message handling but it must be hand coded all the way.

h4. Namespace and xbean.xml
The namespace URI for the servicemix-bean JBI component is {{http://servicemix.apache.org/bean/1.0}}.  This is an example of an {{xbean.xml}} file with a namespace definition with prefix {{bean}}.
{pygmentize:lang=xml}
<beans xmlns:bean="http://servicemix.apache.org/bean/1.0">
  <bean:endpoint service="test:service" endpoint="endpoint" bean="#listenerBean"/>
  <bean id="listenerBean" class="org.apache.servicemix.bean.beans.ListenerBean"/>
</beans></beans>
{pygmentize}

h4. Endpoint types
The servicemix-bean component only defines one endpoint, called {{bean:endpoint}}.  It can be used to receive and send message exchanges from/to the NMR.

h3. {{Endpoint bean:endpoint}}
There are two ways to configure the bean endpoint. The first is using the fully qualified name of the class and the second is by passing to the endpoint a reference to an existing bean.
h4. Using a Java class
When definining a {{bean:endpoint}} specifying a Java class name, a new instance of this class will be created for handling a single message exchange.

{pygmentize:lang=xml}
<beans xmlns:bean="http://servicemix.apache.org/bean/1.0"
       xmlns:my="urn:org:servicmix:docs:examples">

  <bean:endpoint service="my:service" endpoint="endpoint"
                 class="org.apache.servicemix.docs.bean.MyHandlerBean"/>

</beans>
{pygmentize}
h4. Using a spring bean
Alternative, a reference to an existing bean can be passed to the bean endpoint.
{pygmentize:lang=xml}
<beans xmlns:bean="http://servicemix.apache.org/bean/1.0">
    <bean:endpoint service="test:service" endpoint="endpoint" bean="#listenerBean"/>
    <bean id="listenerBean" class="org.apache.servicemix.bean.beans.ListenerBean"/>
</beans>
{pygmentize}
\\
*Attention*: The Bean Endpoint schema allows to set a Bean or a Bean Name. The Bean will create a *single* instance of the POJO per endpoint whereas the Bean Name will create an instance per request (message exchange).

h4. Endpoint properties
{include:jbi/components/_servicemix-bean-endpoint.conf}

h3. {{MessageExchangeListener}}
The first kind of POJOs you can deploy implement the [{{MessageExchagneListener}}|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/core/servicemix-core/apidocs/org/apache/servicemix/MessageExchangeListener.html] interface.  In such a case, {{servicemix-bean}} acts as a replacement of the lightweight container component.  This level offers the most control on the exchange received and sent.  This is usually used with the injected {{DeliveryChannel}} to send back the exchanges, or if the POJOs needs to act as a consumer (i.e. creating and sending exchanges to other services).

These POJOs are low-level POJOs: you need to understand the JBI Api and Message Exchange Patterns to correctly handle incoming exchanges.

Note that at this point (v 3.1), there is no base class that you can inherit to speed you in this process of implementing a POJO to handle JBI exchanges, but hopefully it will come in the future.

h3. Examples

This example on the right shows the most simple bean.  When it receives an exchange, it will print it to the console and set the status to DONE before sending the exchange back. This bean can not handle InOut exchanges, as it does not set any response (an exception would be thrown in such a case).

{pygmentize:lang=java}
import org.apache.servicemix.jbi.listener.MessageExchangeListener;

import javax.annotation.Resource;
import javax.jbi.messaging.DeliveryChannel;
import javax.jbi.messaging.ExchangeStatus;
import javax.jbi.messaging.MessageExchange;
import javax.jbi.messaging.MessagingException;

public class ListenerBean implements MessageExchangeListener {

    @Resource
    private DeliveryChannel channel;

    public void onMessageExchange(MessageExchange exchange) throws MessagingException {
        System.out.println("Received exchange: " + exchange);
        exchange.setStatus(ExchangeStatus.DONE);
        channel.send(exchange);
    }

}
{pygmentize}

This example will handle an InOut exchange and will send back the input as the response.
Note that this example would fail if receiving an InOnly exchange, as setting a response on an InOnly exchange is not a legal operation.

{pygmentize:lang=java}
import org.apache.servicemix.jbi.listener.MessageExchangeListener;
import org.apache.servicemix.jbi.util.MessageUtil;

import javax.annotation.Resource;
import javax.jbi.messaging.DeliveryChannel;
import javax.jbi.messaging.ExchangeStatus;
import javax.jbi.messaging.MessageExchange;
import javax.jbi.messaging.MessagingException;

public class ListenerBean implements MessageExchangeListener {

    @Resource
    private DeliveryChannel channel;

    public void onMessageExchange(MessageExchange exchange) throws MessagingException {
        if (exchange.getStatus() == ExchangeStatus.ACTIVE) {
            MessageUtil.transferInToOut(exchange, exchange);
            channel.send(exchange);
        }
    }

}
{pygmentize}

This is similar example as the one from above (also works only for InOut exchange) but it shows how you can extract message from an exchange in order to process it and send back.
{pygmentize:lang=java}
import org.apache.servicemix.jbi.listener.MessageExchangeListener;
import org.apache.servicemix.jbi.util.MessageUtil;
import org.apache.servicemix.jbi.jaxp.SourceTransformer;

import javax.annotation.Resource;
import javax.jbi.messaging.DeliveryChannel;
import javax.jbi.messaging.ExchangeStatus;
import javax.jbi.messaging.MessageExchange;
import javax.jbi.messaging.MessagingException;
import javax.jbi.messaging.NormalizedMessage;
import javax.xml.transform.Source;

public class ListenerBean implements MessageExchangeListener {

    @Resource
    private DeliveryChannel channel;

    public void onMessageExchange(MessageExchange exchange) throws MessagingException {
        if (exchange.getStatus() == ExchangeStatus.ACTIVE) {
                        NormalizedMessage message = exchange.getMessage("in");
		        Source content = message.getContent();
			//process content according to your logic
			//e.g. to access the message body as a String use
			String body = (new SourceTransformer()).toString(content);

			message.setContent(content);
			exchange.setMessage(message, "out");
			channel.send(exchange);
        }
    }

}
{pygmentize}

h3. Disclaimer

In versions 3.1 to 3.1.2 the ServiceMix Bean component will not handle asynchronous messages correctly because the final send of the message marked as DONE back to the NMR will be handled as a consumer message and that fails because there is no corresponding provider message. The only workaround is to send the messages synchronously.

Note: This was resolved in 3.1.3, 3.2.x and later via [SM-1110|https://issues.apache.org/jira/browse/SM-1110].

h3. MessageExchange dispatching

If the POJO deployed implements the {{org.apache.servicemix.MessageExchangeListener}}, every message received for this POJO will be dispatched to the {{onMessageExchange}} method.

In other cases, exchanges in a provider role will be dispatched according to the {{MethodInvocationStrategy}} configured on the endpoint.  The default one try to find the method according to the operation name defined on the exchange.  If there is only a single method acting as an operation, it will always be used.

h3. Annotations

The {{servicemix-bean}} component can accept different kind of POJOs.  These POJOs may be annotated to customize their behavior.  All the following annotations belong to the {{org.apache.servicemix.bean}} package.
|| Annotation || Target || Description ||
| [Callback|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/apidocs/org/apache/servicemix/bean/Callback.html] | Method | |
| [Content|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/apidocs/org/apache/servicemix/bean/Content.html] | Parameter | |
| [Correlation|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/apidocs/org/apache/servicemix/bean/Correlation.html] | Type | |
| [Endpoint|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/apidocs/org/apache/servicemix/bean/Endpoint.html] | Type | This annotation is mandatory if the bean is automatically searched from a list of packages. |
| [ExchangeTarget|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/apidocs/org/apache/servicemix/bean/ExchangeTarget.html] | Field | |
| [Operation|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/apidocs/org/apache/servicemix/bean/Operation.html] | Method | |
| [Property|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/apidocs/org/apache/servicemix/bean/Property.html] | Parameter | |
| [XPath|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/apidocs/org/apache/servicemix/bean/XPath.html] | Parameter | |

In addition, standard annotations can be used:

|| Annotation || Target || Description ||
| [Resource|http://java.sun.com/javase/6/docs/api/javax/annotation/Resource.html] | Field | The Resource annotation marks a resource that is needed by the application.  Currently, this annotation is only supported on fields of type {{ComponentContext}} and {{DeliveryChannel}}. The component will inject the specified resource when the POJO is instantiated. |
| [PostConstruct|http://java.sun.com/javase/6/docs/api/javax/annotation/PostConstruct.html] | Method | The PostConstruct annotation is used on a method that needs to be executed after dependency injection is done to perform any initialization. |
| [PreDestroy|http://java.sun.com/javase/6/docs/api/javax/annotation/PreDestroy.html] | Method | The PreDestroy annotation is used on methods as a callback notification to signal that the instance is in the process of being removed by the container. |

The following interfaces are part of this API:

|| Interface || Description ||
| [MessageExchangeListener|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/core/servicemix-core/apidocs/org/apache/servicemix/MessageExchangeListener.html] | When the POJO implements this interface, *all* exchanges will be dispatched to the {{onMessageExchange}} method. |
| [Destination|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/apidocs/org/apache/servicemix/bean/Destination.html] | This interface can be used to define a property on the bean, annotated with the {{@ExchangeTarget}} annotation.  This is a very simple API to send exchanges from a POJO.  More complex use cases can use an injected {{DeliveryChannel}} directly or to create a ServiceMix [client|Client API]. |

h3. More Examples

* [AnnotatedBean|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/xref-test/org/apache/servicemix/bean/beans/AnnotatedBean.html]
* [AutoDeployedBean|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/xref-test/org/apache/servicemix/bean/beans/AutoDeployedBean.html]
* [ConsumerBean|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/xref-test/org/apache/servicemix/bean/beans/ConsumerBean.html]
* [ListenerBean|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/xref-test/org/apache/servicemix/bean/beans/ListenerBean.html]
* [PlainBean|http://incubator.apache.org/servicemix/dist/servicemix-3.1-incubating/site/deployables/serviceengines/servicemix-bean/xref-test/org/apache/servicemix/bean/beans/PlainBean.html]