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Professional EJB : The EJB 2.0 Entity Model

The measurement entity "bean" class has implementations for both the methods in the component interface and the methods in the home interface:

	package measurements;

	import java.util.Date;
	import java.util.Collection;
	import java.util.LinkedList;
	import java.sql.Connection;
	import java.sql.ResultSet;
	import java.sql.PreparedStatement;
	import javax.sql.DataSource;
	import javax.ejb.FinderException;
	import javax.ejb.ObjectNotFoundException;
	import javax.naming.InitialContext;
	import javax.ejb.EntityBean;
	import javax.ejb.CreateException;
	import javax.ejb.EntityContext;

	import javax.ejb.EJBException;

	public class MeasurementEJB implements EntityBean {
		private EntityContext ctx;
		private long id;
		private Date eventTimestamp;
		private String eventName;
		private double eventMagnitude;

	public long getId() {
		return id;
	}

	public Date getEventTimestamp() {
		return eventTimestamp;
	}

	public String getEventName() {
		return eventName;
	}

	public double getEventMagnitude() {
		return eventMagnitude;
	}

This is the implementation for the home business method. The totalMagnitudeForRange() method in the home interface becomes ejbHomeTotalMagnitudeForRange() in the implementation class. Notice that we don't use anything in this method that depends on the identity of the instance:

	public double ejbHomeTotalMagnitudeForRange
	(Date from, Date to) {
		Connection con = null;
		try {
		InitialContext initial = new InitialContext();
		DataSource ds =
			(DataSource) initial.lookup
			("java:comp/env/jdbc/DefaultDS");
		con = ds.getConnection();
		PreparedStatement ps =
			con.prepareStatement
			("SELECT sum(eventMagnitude) " +
				"FROM measurements WHERE " +
				"eventTimestamp >= ? 
				AND eventTimestamp <= ?");
		ps.setTimestamp
		(1, new java.sql.Timestamp(from.getTime()));
		ps.setTimestamp
		(2, new java.sql.Timestamp(to.getTime()));
		ResultSet rs = ps.executeQuery();
		if (rs.next()) {
			return rs.getDouble(1);
		} else {
		  throw new EJBException("Unknown error");
		}

	} catch (java.sql.SQLException sqle) {
		sqle.printStackTrace();
		throw new EJBException(sqle);
	} catch (javax.naming.NamingException ne) {
		ne.printStackTrace();
		throw new EJBException(ne);
	} finally {
		if (con != null) {
			try {
				con.close();
			} catch (Exception ex) {}
		}
	}
}

With bean-managed persistence, the bean is responsible for providing the implementation of the finder methods, including the mandatory findByPrimaryKey():

public Long ejbFindByPrimaryKey(Long measurementId)
		throws FinderException {
	Connection con = null;
	try {
		InitialContext initial = new InitialContext();
		DataSource ds =
			(DataSource) initial.lookup
			("java:comp/env/jdbc/DefaultDS");
		con = ds.getConnection();
		PreparedStatement ps =
			con.prepareStatement
			("SELECT id FROM measurements 
			WHERE id = ?");
		ps.setLong(1, measurementId.longValue());
		ResultSet rs = ps.executeQuery();
		if (!rs.next()) {
			throw new ObjectNotFoundException();
		}
		return measurementId;
	} catch (java.sql.SQLException sqle) {
		sqle.printStackTrace();
		throw new EJBException(sqle);
	} catch (javax.naming.NamingException ne) {
		ne.printStackTrace();
		throw new EJBException(ne);
	} finally {
		if (con != null) {
			try {
				con.close();
			} catch (Exception ex) {}
		}
	}
}

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