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The validateField method also uses reflection to load the validation object associated with the field being validated. For example, the email
field has an EmailValidation class. This class would be responsible for using some basic rules to determine whether the field entered resembles an email
address -- if the at symbol (@) is present, for instance. I have not elaborated on this validation in this article because
it is fairly self-explanatory.
This validation framework reduces the interdependencies of the teams developing the business objects and those developing the presentation layer. The development teams must agree upon a naming convention for all the fields used in the HTML in order to ensure proper application behavior. It is important that your development team agree on the field names early in order to proceed with development. As more actions are added to the system, you would only need to develop additional rules (which will likely be contained in property files anyway) and any additional validation rules, if necessary. In other words, little development would be necessary.
SUBHEAD_BREAK: Error handling
Perhaps the most important aspect of this servlet framework is its support for a unified error-handling scheme. With such a scheme, it is possible to build a sophisticated scheme to handle errors around the main proxy.
As described above, the proxy servlet calls the business objects. The business objects are then initialized and begin performing
their associated processes. The call to initialize the business object is present within a try-catch block that will catch
the ExampleException. This exception will result in a call to the exception handler to perform the necessary processes associated with the exception.
For example, should a database exception occur, an email could be sent to the party responsible for database support. In fact, exceptions could be given classifications ranging from warning to critical, with behaviors attached to each category.
Let's assume that the database failure category is classified as critical. The DatabaseFailureException would extend the CriticalException, which would then extend the ExampleException. In this manner, the more specific behavior could build upon the generic error handling.
The following code samples show the progression from generic error handling to the specific handling of the database failure.
Public abstract class ExampleExceptionHandler
{
public abstract void handleException
throws ExampleException(ExampleException e);
}
The ExampleExceptionHandler class is an abstract class; it is used as a base exception handler that you can extend. This class may contain functionality,
should your application require it.
public class CriticalExceptionHandler extends ExampleExceptionHandler {
public void handleException throws ExampleException(CriticalException e) {
// Send email to the application support team
sendMail("mcymerman", "error", e.getMessage() );
}
public void sendMail(String to, String subject, String message) {
// normal commands to send email
...
}
}
The critical exception handler by default sends an exception to the application support team to ensure that the application is monitored.