Example: read-only entity bean

 

Usage Scenario

A customer has a database of catalog pricing and shipping rate information that is updated daily no later than 10:00 PM local time (22:00 in 24-hour format). They want to write an EJB application that accesses this data in a read-only fashion. That is, this application never updates the pricing database. Updating is done through some other application.

 

Example

The customer's entity bean local interface might be:

  public interface ItemCatalogData extends EJBLocalObject {
   
    public int getItemPrice();
   
    public int getShippingCost(int destinationCode);
   
  }

The code in the stateless SessionBean method (assume it’s a TxRequired) that invokes this EntityBean to figure out the total cost including shipping, would look like:

  .....
  // Some transactional steps occur prior to this point, such as removing the item from 
  // inventory, etc.
  // Now obtain the price of this item and start to calculate the total cost to the purchaser
 
  ItemCatalogData theItemData = 
      (ItemCatalogData) ItemCatalogDataHome.findByPrimaryKey(theCatalogNumber);
 
  int totalcost = theItemData.getItemPrice();
   
  // ...     some other processing, etc. in the interim
  // ...
  // ...
   
  // Add the shipping costs
  totalcost = totalcost + theItemData.getShippingCost(theDestinationPostalCode);

At application assembly time, the customer sets the EJB caching parameters for this bean as follows:

• ActivateAt = ONCE

• LoadAt = DAILY

• ReloadInterval = 2200

On the first call to the getItemPrice() method after 22:00 each night, the EJB container reloads the pricing information from the database. If the clock strikes 22:00 between the call to getItemPrice() and getShippingCost(), the getShippingCost() method still returns the value it had prior to any changes to the database that might have occurred at 22:00, since the first method invocation in this transaction occurred prior to 22:00. Thus, the item price and shipping cost used remain in sync with each other.

 

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