Example: Using a read-only entity bean
A usage scenario and example for writing an Enterprise JavaBeans (EJB) application that uses a 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 has read-only access to this data. 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 is 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
Deprecated feature: The reloadInterval
and reloadingEnabled attributes of the IBM deployment descriptor extensions,
including both the WAR file extension (WEB-INF/ibm-web-ext.xmi) and
the application extension (META-INF/ibm-application-ext.xmi) were
deprecated.depfeat
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.
Related: