Capturing the Handle of a related entity during the ejbCreate method of a containing entity.

• By Grant Holland
• May 24, 2001

This example improves upon example 2 of Part 1 by replacing the related key String “productName” by the byte array (byte[]) productSerHandle, which contains the serialized Handle of the related Product entity. This Handle will be persisted to the database, rather than the String productName.

public LineItemPK ejbCreate (
		int		lineItemID,
		int		orderID,
		int		quantity,
		Product	product	)

    throws CreateException,RemoteException
{
LineItemPK pk;

    try
    {
	  // capture all 3 field types
	  this.lineItemID = lineItemID;	// persistent data
	  this.orderID = orderID;		     // persistent data
	  this.quantity = quantity;	    // persistent data
	  this.product = product;		   // related EJB object
	  this.productName = 		       // related key
		((ProductPK)product.getPrimaryKey()).productName;

     // serialize the Handle
     byte[] productSerHandle = serialize(product.getHandle( ));

	 /*
	 // persist persistent data
	 < write “lineItemID” 	     to persistent store >
	 < write “orderID” 		to persistent store >
	 < write “quantity”   	     to persistent store >
	
	 // persist related key
	 < write “ productSerhandle”   to persistent store >
	 */

	 // create and initialize Primary Key object
	 LineItemPK pk = new LineItemPK(); 	// make PK
	 pk.lineItemID = lineItemID;		         // capture identity field
	 pk. orderID = orderID;			       // capture identity field
   }
    catch(Exception e)
  {
	throw new CreateException(e.getMessage());
  }

    return pk;
}

byte[] serialize( Handle hndl )throws IOException
{
    ByteArrayOutputStream bs = new ByteArrayOutputStream();
    ObjectOutputStream os = new ObjectOutputStream(bs);
    os.writeObject( hndl );
    return bs.toByteArray();
}

public void ejbActivate() throws RemoteException
{
    // get containing entity’s primary key from EntityContext
    LineItemPK lineItemPK = entityContext.getPrimaryKey();

    // get key from PK
    lineItemID = lineItemPK.lineItemID;
    orderID = pk.orderID;

    // use key to read persistent data and related key
    < read persistent data from persistent store >

    < read related key “productserhandle” from persistent store >
    byte[]productSerHandle
            = resultSet.getByteArray(“productserhandle”);

    // deserialize the Handle and use it to
    // reconstitute the related EJBObject
    Handle prodHandle = deserialize(productSerHandle);
    product = (Product)prodHandle.getEJBObject();
}

Handle deserialize( byte[] serHandle )
        throws IOException, ClassNotFoundException
{
ByteArrayInputStream is = new ByteArrayInputStream( serHandle );
ObjectInputStream os = new ObjectInputStream (is);
return (Handle)os.readObject();
}