3.5.3   Example
@Entity
@EntityListeners(com.acme.AlertMonitor.class)
public class Account {
Long accountId;
Integer balance;
boolean preferred;
@Id
public Long getAccountId() { ... }
...
public Integer getBalance() { ... }
...
    @Transient // because status depends upon non-persistent context
    public boolean isPreferred() { ... }
...
    public void deposit(Integer amount) { ... }
    public Integer withdraw(Integer amount) throws NSFException {... }
    @PrePersist
    protected void validateCreate() {
        if (getBalance() < MIN_REQUIRED_BALANCE)
        throw new AccountException("Insufficient balance to open an 
account");
    }
    @PostLoad
    protected void adjustPreferredStatus() {
        preferred =
            (getBalance() >= AccountManager.getPreferredStatu-
sLevel());
    }
}
public class AlertMonitor {
    @PostPersist
    public void newAccountAlert(Account acct) {
        Alerts.sendMarketingInfo(acct.getAccountId(), acct.getBal-
ance());
}
}