WAS v8.5 > Reference > Developer examples

Example: Using a read-only entity bean

A usage scenario and example for writing an Enterprise JavaBeans 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:

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 concepts:

Enterprise beans
Concurrency control


Related


Develop applications that use JNDI


Reference:

WebSphere extensions to the Enterprise JavaBeans specification
Enterprise bean development best practices


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