Exposing a Java class as a POJO service (Provides mode)

Usage

The POJO that you want to develop must follow certain constraints :

• no specific interface implementation is required.
• if a public setComponentContext(ComponentContext context) setter method is defined, the component set its ComponentContext instance with this method at the initialization of the Service Unit.
• if a public setDeliveryChannel(DeliveryChannel channel) setter method is defined, the component set its DeliveryChannel instance with this method at the initialization of the Service Unit.
• if a public setJBIListener(AbstractJBIListener jbiListener) setter method is defined, the component set its JBIListener instance with this method at the initialization of the Service Unit.
• if a public setLogger(Logger logger) setter method is defined, the component set its Logger instance with this method at the initialization of the Service Unit.
• if a public void init() method is defined, the component invoke it at the initialization of the Service Unit.
• a public boolean onExchange(Exchange exchange) MUST be provided.
• an public boolean onAsyncExchange(Exchange exchange, AsyncContext asyncContext) CAN be provided, optionally.
• all methods can throw exceptions.
• only one instance of the POJO class is instanciated by the component, so the POJO must be thread-safe
• to prevent memory leak, using the singleton pattern is to prohibit

Process a service in the synchronous way

A sample class following the above rules for processing service in the synchronous way:

package test;
import java.util.logging.Level;
[...]
import org.ow2.petals.component.framework.listener.AbstractJBIListener;

public class SamplePojoService {
  AbstractJBIListener jbiListener;
  Logger logger;
  ComponentContext ctx;

  public void setJBIListener(AbstractJBIListener jbiListener) {
    this.jbiListener = jbiListener;
  }
  public void setComponentContext(ComponentContext ctx) {
    this.ctx = ctx;
  }
  public void setLogger(Logger logger) {
    this.logger = logger;
  }

  public boolean onExchange(Exchange exchange)
    throws MessagingException {
    [...]
    jbiListener.sendSync(anotherExchange);
    [...]
    return true;
  }

  public void init() {
    logger.log(Level.INFO, "Sample Pojo inits.");
  }
}

The method onExchange(Exchange exchange) is invoked when an exchange is received from the component that is addressed to the current POJO endpoint.
The POJO must process the service in that method.
The POJO can invoke any 'sub-service' during its processing by synchronous invocations using the jbiListener instance.
If the POJO service must reply with a message OUT or FAULT, according to the MEP, the method must build and set the message to the current exchange.
Then, the method must return true to delegate the effective send back of the response or acknowledgment (according to the MEP) to the CDK.
The exceptions should be handled properly during the processing of the method, and set accordingly as error or fault to the exchange.
However, mishandled exceptions will be handled by the CDK as generic exceptions.

Process a service in the asynchronous way

A sample class following the above rules for processing service in the asynchronous way:

package test;
import java.util.logging.Level;
[...]
import org.ow2.petals.component.framework.listener.AbstractJBIListener;

public class SamplePojoService {
  AbstractJBIListener jbiListener;
  Logger logger;
  ComponentContext ctx;

  public void setJBIListener(AbstractJBIListener jbiListener) {
    this.jbiListener = jbiListener;
  }
  public void setComponentContext(ComponentContext ctx) {
    this.ctx = ctx;
  }
  public void setLogger(Logger logger) {
    this.logger = logger;
  }

  public boolean onExchange(Exchange exchange)
    throws MessagingException {
    [...]
    MyAsyncContext myAsyncContext = new MyAsyncContext(...);
    [...]
    jbiListener.sendASync(anotherExchange, myAsyncContext);
    [...]
    return false;
  }

  public boolean onAsyncExchange(Exchange subExchange, AsyncContext asyncContext)
    throws MessagingException {
    [...]
    Exchange originalExchange = asyncContext.getOriginalExchange();
    [...]
    jbiListener.send(originalExchange);
    [...]
    return true;
  }

  public boolean onExpiredAsyncJBIMessage(Exchange subExchange, AsyncContext asyncContext)
    throws MessagingException {
    [...Handle here the subExchange timeout...]
    return false;
  }

  public void init() {
    logger.log(Level.INFO, "Sample Pojo Async inits.");
  }
}

Processing a service in asynchronous way is the best approach when targeting performance, but it's more tedious to develop, and demands an average level in Petals development.
Basically, all is in the data that permit to correlate asynchronous sent exchange and their asynchronous response.
The original exchange is the received by the component and the process of the service start in the onExchange(Exchange exchange) method.
The method create an asynchronous context, to set the data.
The method can create any 'sub-exchange' and send then asynchronously, with the asynchronous context as parameter.
Then the onExchange(Exchange exchange) returns false, as the response or the acknowledgment of the original exchange is not yet ready to be sent back.
Any asynchronous response from the 'sub-exchange' comes back in the onAsyncExchange(Exchange subExchange, AsyncContext asyncContext) method. During the process of this method, the 'sub-exchange' must be handled according to the MEP, and the returns true of the method let the CDK send the 'sub-exchange' to the partner.
Once all 'sub-exchanges' are received, the 'original' exchange can be retrieve from the asynchronous context and the response or acknowledgement send back explicitly.
If a 'sub-service' do not response at time, the onExpiredAsyncJBIMessage(...) method will be invoked by the CDK. You must handle the timeout of the 'sub-exchange' in this method.

Service Configuration

Service Unit descriptor

The POJO JBI descriptor must contain a Provides section for each POJO to expose in the JBI bus.

AN example of the POJO SU:

<?xml version="1.0" encoding="UTF-8"?>
<!-- JBI descriptor for PEtALS' "petals-se-pojo" (POJO), version 2.0 -->
<jbi:jbi version="1.0"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns:jbi="http://java.sun.com/xml/ns/jbi"
  xmlns:pojo="http://petals.ow2.org/components/pojo/version-2.0"
  xmlns:petalsCDK="http://petals.ow2.org/components/extensions/version-4.0"
  xmlns:generatedNs="http://POJO/test">
  <!-- Import a Service into PEtALS or Expose a PEtALS Service => use a BC. -->
  <jbi:services binding-component="false">
     <!-- Import a Service into PEtALS => provides a Service. -->
     <jbi:provides
       interface-name="generatedNs:POJO"
       service-name="generatedNs:POJOService"
       endpoint-name="POJOServiceEndpoint">
       <!-- CDK specific elements -->
       <petalsCDK:wsdl xsi:nil="true" />
       <!-- Component specific elements -->
       <pojo:class-name>test.SamplePojoService</pojo:class-name>
     </jbi:provides>
  </jbi:services>
</jbi:jbi>

Interceptor

Example of an interceptor configuration:

<?xml version="1.0" encoding="UTF-8"?>
<!--...-->
<petalsCDK:su-interceptors>
  <petalsCDK:send>
    <petalsCDK:interceptor name="myInterceptorName">
      <petalsCDK:param name="myParamName">myParamValue</petalsCDK:param>
      <petalsCDK:param name="myParamName2">myParamValue2</petalsCDK:param>
    </petalsCDK:interceptor>
  </petalsCDK:send>
  <petalsCDK:accept>
    <petalsCDK:interceptor name="myInterceptorName">
      <petalsCDK:param name="myParamName">myParamValue</petalsCDK:param>
    </petalsCDK:interceptor>
  </petalsCDK:accept>
  <petalsCDK:send-response>
    <petalsCDK:Interceptor name="myInterceptorName">
      <petalsCDK:param name="myParamName">myParamValue</petalsCDK:param>
    </petalsCDK:Interceptor>
  </petalsCDK:send-response>
  <petalsCDK:accept-response>
    <petalsCDK:Interceptor name="myInterceptorName">
      <petalsCDK:param name="myParamName">myParamValue</petalsCDK:param>
    </petalsCDK:Interceptor>
  </petalsCDK:accept-response>
</petalsCDK:su-interceptors>
<!--...-->

Service Unit content

The POJO class(es) and their depending libraries must be set as JAR(s) file(s) at the root directory of the POJO Service
Unit package.

The Service Unit must contain the following elements, packaged in an ZIP archive:

• The META-INF/jbi.xml descriptor file, has described above.
• At least one jar containing the POJO class to expose

  service-unit.zip
  + META-INF
    - jbi.xml (as defined above)
    - mypojoclasses.jar
  

Component Configuration

Definition of CDK parameter scope :

• Installation: The parameter can be set during the installation of the component, by using the installation MBean (see JBI specifications for details about the installation sequence). If the parameter is optional and has not been defined during the development of the component, it is not available at installation time.
• Runtime: The paramater can be set during the installation of the component and during runtime. The runtime configuration can be changed using the CDK custom MBean named RuntimeConfiguration. If the parameter is optional and has not been defined during the development of the component, it is not available at installation and runtime times.

Interceptor

Interceptors can be defined to inject some post or pre processing in the component during service processing.

Using interceptor is very sensitive and must be manipulate only by power users. An non properly coded interceptor engaged in a component can lead to uncontrolled behaviors, out of the standard process.

Example of an interceptor configuration:

<?xml version="1.0" encoding="UTF-8"?>
<!--...-->
<petalsCDK:component-interceptors>
  <petalsCDK:interceptor active="true" class="org.ow2.petals.myInterceptor" name="myInterceptorName">
    <petalsCDK:param name="myParamName">myParamValue</petalsCDK:param>
    <petalsCDK:param name="myParamName2">myParamValue2</petalsCDK:param>
  </petalsCDK:interceptor>
</petalsCDK:component-interceptors>
<!--...-->