Programming Jakarta Struts, 2nd Edition [Electronic resources] نسخه متنی

3.1 A Banking Account Example

This section introduces an online banking application that will be used
to familiarize you with Struts. The example presented here is not
complete, but it provides an overview of the major components that
are present in all Struts applications and shows how those components
fit together. A more comprehensive and thorough shopping- cart
example will be used throughout the rest of the book.

Most people are familiar with the concept of online banking, so we
won't spend too much time explaining the business
requirements. In short, the online banking application will allow an
end user to log in to the financial institution's
web site, view account information, and transfer funds from one
account to another (assuming the user has more than one account). The
user must present a valid set of credentials to enter the
sitein this case, an access number and a personal
identification number (PIN).

If the user leaves one or both fields blank, the application will
display a formatted message informing the user that both fields are
required. If the user enters values for both fields but the
authentication fails, the login screen will be redisplayed, along
with a formatted error message informing the user that the login has
failed. Figure 3-1 shows the online banking login
screen after an invalid login attempt has been detected.

Figure 3-1. Login screen for the online banking application

If the proper credentials are entered for an account, the user is
taken to the account information screen. This screen shows all of the
accounts that the user has with the financial institution, as well as
the current balance for each account.

For this example, we are not going to provide a robust, full-fledged
security service and security realm. Handling security in a web
application can be complicated, and there's no
reason to muddy the waters with it at the moment. For the purposes of
this chapter, we'll use a simple Java interface that
contains a single login() method to authenticate
users. The IAuthentication interface is shown in Example 3-1.

Example 3-1. The IAuthentication interface used by the banking application

package com.oreilly.struts.banking.service;
import com.oreilly.struts.banking.view.UserView;
/**
* Provides methods that the banking security service should implement.
*/
public interface IAuthentication {
/**
* The login method is called when a user wants to log in to
* the online banking application.
* @param accessNumber- The account access number.
* @param pin- The account private id number.
* @returns a DTO object representing the user's personal data.
* @throws InvalidLoginException if the credentials are invalid.
*/
public UserView login( String accessNumber, String pin )
throws InvalidLoginException;
}

The IAuthentication interface contains a very
simple login() method, which takes the
accessNumber and pin from the
login page. If the authentication is successful, a
com.oreilly.struts.banking.view.UserView
object is returned. If the login is unsuccessful, an
InvalidLoginException is thrown.

The UserView is a simple JavaBean that can be
stored within the user's session and used to display
customer-specific content in the application. Although
it's not completely relevant to the current
discussion, the source listing for the UserView
will be shown later in the chapter.

The com.oreilly.struts.banking.service.SecurityService
class is shown in Example 3-2. It implements the
IAuthentication interface from Example 3-1 and allows the application to authenticate
users. We are not going to authenticate against a security realm for
this example, so the SecurityService class will
contain hardcoded logic to authenticate users.

Example 3-2. The security service used by the example banking application

package com.oreilly.struts.banking.service;
import com.oreilly.struts.banking.view.UserView;
/**
* Used by the example banking application to simulate a security service.
*/
public class SecurityService implements IAuthentication {
public UserView login( String accessNumber, String pin ) 
throws InvalidLoginException {
// A real security service would check the login against a security realm.
// This example is hardcoded to let in only 123/456.
if( "123".equals(accessNumber) && "456".equals(pin) ){
/* Dummy a UserView for this example.
* This data/object would typically come from the business layer
* after proper authentication/authorization had been done.
*/
UserView userView = new UserView( "John", "Doe" );
userView.setId( "39017" );
return userView;
}
else {
// If the login method is invalid, throw an InvalidLoginException.
// Create a msg that can be inserted into a log file.
String msg = "Invalid Login Attempt by " + accessNumber + ":" + pin;
throw new InvalidLoginException( msg );
}
}
}

For this example application, we will authenticate the user only if
the accessNumber entered is
"123" and the
pin entered is
"456".

If the SecurityService were being used in a real application, it would have to check the credentials against some type of security realm, such as a relational database or an LDAP server.

Once the user has logged in successfully, she may perform two actions:

• View an account detail

• Log out

Figure 3-2 shows the account information screen to
which the user is taken after a successful login. The user can view
detailed information about an account by clicking on that account.
Figure 3-3 shows the account detail screen for the
checking account listed in Figure 3-2.

Figure 3-2. The account information screen

Figure 3-3. The account detail screen

In a typical online banking application, the user would also have the
ability to transfer funds from one account to another. As the purpose
of this chapter is to familiarize you with the components of the
Struts framework, not to teach you the correct functionality of a web
banking application, the funds-transfer functionality will not
actually be implemented here (feel free to implement it as a
practical exercise if you'd like!). Finally, the
user may log out of the application altogether by clicking on the
Logout button. When she does so, she will be logged out of the
application and returned to the login screen.