Reviews : Java Books :
Professional EJB : The EJB 2.0 Entity Model

Deployment Descriptor

This deployment descriptor does not differ at all from an EJB 1.1 deployment descriptor.

<?xml version="1.0"?>
<ejb-jar>

<enterprise-beans>
<entity>

  <ejb-name>Measurement</ejb-name>
  <home>measurements.MeasurementHome</home>
  <remote>measurements.Measurement</remote>
  <ejb-class>measurements.MeasurementEJB</ejb-class>
  <persistence-type>Bean</persistence-type>
  <prim-key-class>java.lang.Long</prim-key-class>
  <reentrant>False</reentrant>
  <resource-ref>
	<res-ref-name>jdbc/DefaultDS</res-ref-name>
	<res-type>javax.sql.DataSource</res-type>
	<res-auth>Container</res-auth>
  </resource-ref>

</entity>

</enterprise-beans>


<assembly-descriptor>
	<container-transaction>
		<method>
			<ejb-name>Measurement</ejb-name>
			<method-name>*</method-name>
		</method>
	<trans-attribute>Required</trans-attribute>
	</container-transaction>
</assembly-descriptor>
</ejb-jar>

Client

This client creates some sample measurements, and then retrieves some summary data using two methods. First, it uses a finder method and iterates through the bean instances. Second, it uses the home business method that delegates the summary functionality to the database:

	package measurements;

	import java.util.Date;
	import java.util.Random;
	import java.util.Collection;
	import java.util.Iterator;
	import java.rmi.RemoteException;
	import javax.naming.InitialContext;
	import javax.rmi.PortableRemoteObject;
	import javax.ejb.CreateException;

	public class Client {
		private static long currentId = 1;
		private static Random random = new Random();

private static long getNextId() {
	return currentId++;
}

private static void createSampleMeasurements(MeasurementHome mh,
		Date timestamp, String eventName,
		int quantity) throws 
		CreateException, RemoteException {
	for (int iter = 0; iter < quantity; iter++) {
		mh.create(getNextId(), 
		  timestamp, eventName, random.nextDouble());
	}
}

public static void main(String[] args) {
	try {
		InitialContext initial = new InitialContext();
 
		MeasurementHome measurementHome =
		  (MeasurementHome) PortableRemoteObject
			.narrow(initial.lookup("Measurement"), 
		  MeasurementHome.class);

		Date currentTimestamp = new Date();
		createSampleMeasurements(measurementHome, 
			currentTimestamp,
			"TestEvent", 25);

With the first method, we use a finder to iterate through the measurements we care about:

	
	Collection measurements = 
	measurementHome.findInDate(currentTimestamp,
			currentTimestamp);

	double total = 0.0;
	Iterator iter = measurements.iterator();
	while (iter.hasNext()) {
		Measurement measurement =
			(Measurement) 
  		  PortableRemoteObject.narrow(iter.next(),
					Measurement.class);
		total += measurement.getEventMagnitude();
	}
	System.out.println("Results from method one: " + total);

With the second method, we use our home interface method:

		System.out.println("Results from method two: "
		  + measurementHome.totalMagnitudeForRange
			(currentTimestamp,
					currentTimestamp));
		} catch (Exception e) {
			e.printStackTrace();
	}
}
}

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