Re: [openejb-user] 3tier Tomcat access to remote EJB

[Mark Lybarger]

Juan M Wagner wrote:
Hi again.
Another question, I'm using an Entity Bean to make chances to certain 
registry of
a table (mysql and postgresql),  but if I want to obtain bulk data 
with SELECT its better to
use the Session (Stateless) Bean ?

Juan,
In ejb2.0 you can have home business methods that return anything from 
the database.  you can return a list of all customer's first names, a 
hash table perhaps of records, etc.

to answer you 2nd question, session beans only need ejb-jar.xml (and 
possibly the vendor's ejb-jar.xml if applicable).

I think that Entity Beans are only for point to exactly one row of the 
table...
That's why I do an Session Bean , because a want many records in a 
Hashtable.

Here's the files.
-- my home interface --
package libro;
import java.rmi.RemoteException;
import javax.ejb.CreateException;
import javax.ejb.EJBHome;
public interface LibroHome extends EJBHome {  Libro create() throws 
CreateException, RemoteException; }

-- my remote interface --
package libro;
import javax.ejb.EJBObject;
import java.rmi.RemoteException;
import java.util.Hashtable;
public interface Libro extends EJBObject {
 // This Method must to return a Hashtable with the result of the 
query (Select *)
 public Hashtable buscaPorTitulo (String titulo) throws RemoteException;
}

-- my BEAN ! --
package libro;
import javax.ejb.*;
import javax.naming.*;
import java.sql.*;
import javax.sql.DataSource;
import java.util.*;
import java.rmi.RemoteException;
public class LibroBean implements SessionBean  { // must implemet the 
sessionbean
 public EntityContext context;
 public void ejbCreate() {};
 public Hashtable buscaPorTitulo (String titulo) throws SQLException {
     Connection con = null;
     PreparedStatement ps = null;
     ResultSet result = null;

     try {
        con = this.getConnection ();  // Preparing the query statement
        ps = con.prepareStatement ("select isbn, titulo from libro 
where titulo = ?");
        ps.setString (1,titulo);
        result = ps.executeQuery ();

        Hashtable keys = new Hashtable ();  Vector datos = new Vector();
        while( result.next() )  {
           datos.addElement (result.getObject ("titulo"));
           keys.put(result.getString("isbn"),datos);
        }
        return keys; // Here's where we return the Hashtable
     } catch (SQLException se) {throw new EJBException (se);}
       finally {
        try { result.close (); } catch (Exception e) {}
        try { ps.close (); } catch (Exception e) {}
        try { con.close (); } catch (Exception e) {}
     }
  }//ejbFindByTitulo
 public void setSessionContext( SessionContext context )     throws 
EJBException, RemoteException  { }

 public void ejbActivate() throws EJBException, RemoteException { }
 public void ejbLoad() throws EJBException, RemoteException { }
 public void ejbPassivate() throws EJBException, RemoteException { }
 public void ejbRemove() throws EJBException, RemoteException { }
 public void ejbStore() throws EJBException, RemoteException { }
 private Connection getConnection () throws SQLException  {
   try {
    Context jndiCntx = new InitialContext ();
    DataSource ds = (DataSource)jndiCntx.lookup 
("java:comp/env/jdbc/libreria");
    return ds.getConnection ();
   } catch (NamingException ne)   {  throw new EJBException (ne); }
  }
}

Ok, here is where I got my doubts...
In ENTITY BEANS xml files we must to put information about the database.
But if we use a Session Bean that is necesary ??? I think we dont.
To use this Session Bean only we need the ejb-jar.xml ??
-- my ejb-jar.xml -- <ejb-jar>
   <enterprise-beans>
       <session>
           <description>
               Este SESSION Bean representa al objeto Libro.
           </description>
           <ejb-name>LibroBean</ejb-name>
           <home>libro.LibroHome</home>
           <remote>libro.Libro</remote>
           <ejb-class>libro.LibroBean</ejb-class>
           <session-type>Stateless</session-type>
           <resource-ref>
               <description>DataSource para la base de datos de 
libros</description>
               <res-ref-name>jdbc/mysql</res-ref-name>
               <res-type>javax.sql.DataSource</res-type>
               <res-auth>Container</res-auth>                         
</resource-ref>             </entity>
   </enterprise-beans>

   <assembly-descriptor>
       <method-permission>
           <role-name>everyone</role-name>
           <method>
               <ejb-name>LibroBean</ejb-name>
               <method-name>*</method-name>
           </method>
       </method-permission>
       <container-transaction>
           <method>
               <ejb-name>LibroBean</ejb-name>
               <method-name>*</method-name>
           </method>
           <trans-attribute>Supports</trans-attribute>
       </container-transaction>
   </assembly-descriptor>
</ejb-jar>

There is yet another way to connect to OpenEJB, which I think would 
be the best fit in your envrironment. Externalize OpenEJB 
configuration from the code using the OpenEJB Tomcat resource 
factory. Here's more info on that: 
http://www.openejb.org/tomcat.html#tomcat-resource-factory.

Also, make sure the latest OpenEJB is used - pre-1.0. Unfortunatelly, 
it needs to be built from the sources - it's not yet available anywhere.