Database Calls

Table 5-1 summarizes the database access calls in the SavingsAccountBean class. The business methods of the SavingsAccountBean class are absent from the preceding table because they do not access the database. Instead, these business methods update the instance variables, which are written to the database when the EJB container calls ejbStore. Another developer might have chosen to access the database in the business methods of the SavingsAccountBean class. This choice is one of those design decisions that depend on the specific needs of your application.

Before accessing a database, you must connect to it.

Table 5-1 SQL Statements in SavingsAccountBean 

Method	SQL Statement
ejbCreate	INSERT
ejbFindByPrimaryKey	SELECT
ejbFindByLastName	SELECT
ejbFindInRange	SELECT
ejbLoad	SELECT
ejbRemove	DELETE
ejbStore	UPDATE

Home Methods

A home method contains the business logic that applies to all entity beans of a particular class. In contrast, the logic in a business method applies to a single entity bean, an instance with a unique identity. During a home method invocation, the instance has neither a unique identity nor a state that represents a business object. Consequently, a home method must not access the bean's persistence state (instance variables). (For container-managed persistence, a home method also must not access relationships.)

Typically, a home method locates a collection of bean instances and invokes business methods as it iterates through the collection. This approach is taken by theejbHomeChargeForLowBalance method of the SavingsAccountBean class. The ejbHomeChargeForLowBalance method applies a service charge to all savings accounts with balances less than a specified amount. The method locates these accounts by invoking the findInRange method. As it iterates through the collection of SavingsAccount instances, theejbHomeChargeForLowBalance method checks the balance and invokes the debit business method. Here is the source code of the ejbHomeChargeForLowBalance method:

public void ejbHomeChargeForLowBalance(
    BigDecimal minimumBalance, BigDecimal charge) 
    throws InsufficientBalanceException {

   try {
       SavingsAccountHome home =
       (SavingsAccountHome)context.getEJBHome();
       Collection c = home.findInRange(new BigDecimal("0.00"),
           minimumBalance.subtract(new BigDecimal("0.01")));

       Iterator i = c.iterator();

       while (i.hasNext()) {
          SavingsAccount account = (SavingsAccount)i.next();
          if (account.getBalance().compareTo(charge) == 1) {
             account.debit(charge);
          }
       }

   } catch (Exception ex) {
       throw new EJBException("ejbHomeChargeForLowBalance: " 
           + ex.getMessage());
   } 
} 
 

The home interface defines a corresponding method named chargeForLowBalance. Since the interface provides the client view, the SavingsAccountClientprogram invokes the home method as follows:

SavingsAccountHome home;
...
home.chargeForLowBalance(new BigDecimal("10.00"), 
   new BigDecimal("1.00"));
 

In the entity bean class, the implementation of a home method must adhere to these rules:

• A home method name must start with the prefix ejbHome.
• The access control modifier must be public.
• The method modifier cannot be static.

The throws clause may include exceptions that are specific to your application; it must not throw the java.rmi.RemoteException.