Re: [JBoss-user] Can an ejb function as a daemon?

Ulf Schröter Thu, 26 Sep 2002 04:09:44 -0700

Here is my EJB2.1 conformal solution to the 'ejb fuction as daemon' problem. Until availability of EJB2.1 timer services the basic functionality is emulated via JBoss scheduler service an some helper code. Later code migration to EJB2.1 based timer service should be quite simple:

Here is the concept:

Step 1: Define EJB2.1 compatible interface TimedObject

Step 2: Create a generic schedulable object that creates and calls a configurable session

bean implementing TimedObject interface. The schedulable object is controlled by JBoss scheduler service

Step 3: Implement your timed session bean that implements TimedObject interface.

A Local/LocalHome EJB interface is required for object creation.

The schedulable object will invoke the ejbTimeout() method

Step 4: Configure a schedulable object MBean instance in your JBoss deployment

directory that invokes your timed session bean.

And here is the source code:

Step 1:

package de.mobilcom.eai.timerservice;

import java.util.Timer;

/**
* This definition of'TimedObject' is a temporary workaround
* until availability of EJB2.1 specification compatible
* application server with standard javax.ejb.TimedObject
* definition.
*
* @author      Ulf Schroeter
* @version     1.0
*
*/
public interface TimedObject
{
    public void ejbTimeout( Timer timer );
}

Step 2: Create a schedulable object that is controlled by JBoss scheduler service

package de.mobilcom.eai.timerservice.jboss;

import java.util.Date;
import java.lang.reflect.Method;

import javax.naming.Context;
import javax.naming.InitialContext;

import org.jboss.varia.scheduler.Schedulable;

import de.mobilcom.eai.timerservice.TimedObject;

/**
* The TimedObjectSchedulable class is a JBoss application server
* specific implementation for time interval based invocation
* of a controlled EJB.
*
* The controlled EJB class must implement a LocalHome interface
* with create() method for EJB object instance creation.
*
* The controlled EJB class must implement the TimedObject
* callback interface for time interval based EJB invocation.
*
* Object instances of TimedObjectSchedulabe will be created and
* controlled by the JBoss scheduler service.
*
* @author Ulf Schroeter
* @version 1.0
*
*/

public class TimedObjectSchedulable implements Schedulable
{
    /**
     * Attribute declaration
    */
    private String          m_TimedObjectJNDILocalHomeName ;
    private TimedObject     m_TimedObject                   ;


    /**
     * constructor ( will be called by JBoss scheduler service )
     *
     * @param JNDILocalHomeName JNDI lookup name of the local
     *                           home interface of the controlled
     *                           EJB object implementing TimedObject
     *                           interface
     */
    public TimedObjectSchedulable( String JNDILocalHomeName )
    {
        // store JNDI local home name
        m_TimedObjectJNDILocalHomeName = JNDILocalHomeName ;
    }

    /**
     * Schedulable callback method that will be called by
     * JBoss scheduler service when configured time interval
     * has elapsed.
     *
     * The method simply calls the ejbTimeout() methode of the
     * controlled EJB object implementing TimedObject interface.
     *
     * The lookup of the LocalHome interface of the controlled
     * EJB class within this function ensures that the timed
     * callback of the EJB class will continue even after EJB
     * redeployment ( e.g. due to maintenance reasons )
     *
     * @see org.jboss.varia.scheduler.Schedulable#perform(Date, long)
     */

    public void perform( Date arg0, long arg1 )
    {
        // get TimedObject interface
        try
        {
            if( m_TimedObject == null )
            {
                /**
                 * get initial context and lookup local home interface
                 *
                 * remark:     will throw exception if EJB object hasn't
                 *              been deployed ( e.g. while app server boot
                 *              sequence or due to undeployment of EJB for
                 *              update ) and causes a new EJB object lookup
                 *              attemp on the next timed perform() call.
                 */
                Context ctx = new InitialContext();

                Object obj = ctx.lookup( m_TimedObjectJNDILocalHomeName );

                // use java refection to call create() method for
                // obtaining EJB instance
                Method method = obj.getClass().getDeclaredMethod( "create",
                                                                   new Class[0] );

                // create EJB instance and cast to TimedObject reference
                m_TimedObject = (TimedObject) method.invoke( obj, new Object[0] );
            }

            /**
             * call timed object EJB callback method
             *
             * remark:     will throw exception if EJB object has been
             *              undeployed or redeployed and causes a new
             *              EJB object lookup attemp on the next timed
             *              perform() call.
             */

            m_TimedObject.ejbTimeout( null );
        }
        catch( Exception e )
        {
            System.err.println("TimedObjectSchedulable(" +
                                m_TimedObjectJNDILocalHomeName +
                                ")::perform() failed with Exception '" +
                               e.getMessage() + "' !" );

            // reset invalid timed object reference
            m_TimedObject = null;
        }
    }

}

Step 3: Implement your timed session bean that implements TimedObject interface.

A Local/LocalHome EJB interface is required for object creation.

The schedulable object will invoke the ejbTimeout() method

package de.mobilcom.eai.adapter.mcbs.event;

import java.util.Timer;

.....

import de.mobilcom.eai.timerservice.TimedObject;

/**
* .....

* It implements a EJB2.1 specification compatible TimedObject
* interface for time based invocation of ejbTimeout() method
* by the application server timer service.
*
* Until availability of a EJB2.1 compatible application server
* timer service a JBoss specific timer service emulation based
* on the provided scheduler service is used.
*
*
* @author Ulf Schroeter
* @version 1.0
*
*/

public class MCBSEventAdapterTDB implements SessionBean,
                                            TimedObject
{
    /**
     * Attribute declaration
    */

    private SessionContext m_Ctx           ;

    public void setSessionContext(SessionContext ctx) { }

    public void ejbCreate()    {}
    public void ejbActivate() {}
    ......
    ......

    /**
     * Called by the application server timer service when the
     * defined timer interval has elapsed. All required event
     * processing will be handled within this method.
     *
     * @param timer     triggering timer object ( will allways
     *                  be null for timer service emulation )
     */

    public void ejbTimeout( Timer timer )
    {
        System.out.println( "MCBSEventAdapterTDB::ejbTimeout(" +
                            Thread.currentThread().getName() + ")");
    }

}

Step 4: Configure the schedulable object in your JBoss deployment directory

* To set up timed EJB method invovation create an appropriate
* scheduler service xml-file in the JBoss deploy directory, e.g
*
* <?xml version="1.0" encoding="UTF-8"?>
* <!DOCTYPE server>
* 
*
* <server>
*
*    <classpath codebase="lib" archives="scheduler-plugin.jar, JMSTimerService.jar"/>
*
* 
* 
* 
*
*   
*
*   <mbean code="org.jboss.varia.scheduler.Scheduler"
*          name=":service=Scheduler,schedule=MCBSEventAdapterTDB">
*      <attribute name="StartAtStartup">true</attribute>
*      <attribute name="SchedulableClass">de.mobilcom.eai.timerservice.jboss.TimedObjectSchedulable</attribute>
*      <attribute name="SchedulableArguments">local/MCBSEventAdapterTDB</attribute>
*      <attribute name="SchedulableArgumentTypes">java.lang.String</attribute>
*      <attribute name="InitialStartDate">0</attribute>
*      <attribute name="SchedulePeriod">10000</attribute>
*      <attribute name="InitialRepetitions">-1</attribute>
*   </mbean>
*
* </server>
*
* for timed EJB callback invocation of MCBSEventAdapterTBD every 10 seconds
*

Best Regards

Ulf Schroeter

MobilCom Communicationstechnik GmbH

IT Business Unit Consumer / Projekte und Prozesse
mailto:[EMAIL PROTECTED]