John Alden

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since Jan 09, 2004
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Recent posts by John Alden

The following are excerpts from the J2EE Design Patterns book published by O'reilly:

Business delegates can be staeful or stateless. To use a stateful business delegate, generate an instance of the business delegate class. To create a stateless business delegate, declare the business delegate methods as static.


Here's a rule of thumb: if a business delegate requires a resource that is both expensive to create and that must be created specifically for the current user (such as a JAAS security principal), and if that resource will be used multiple times within the same delegate by the same thread, use a stateful delegate. You should also use a stateful delegate if the delegate needs complex configuration specifically for the current invocation, rather than trying to pass in all configuration information with each method call. Otherwise, look for opportunities to use a stateless delegate.
I was planning to show a Composite Entity Bean but then leave it at that. I struggle with where architecture ends and design begins?
Why did you choose to use BMP/DAO instead of CMP?

I am thinking of calling the web service from a DAO. Anyone else doing that?
This is confusing to me. It isn't the JSP that calls the controller but rather the browser. I was thinking of the following:

Browser makes HTTP request to controller; Controller does it's work and forwards the request to JSP; JSP produces HTML and sends HTTP response back to browser.

Browser ---> Controller
Controller ---> JSP
JSP ---> Browser

I know Cade did this differently but he doesn't show forwarding to a JSP to produce the output for the browser.
Are you able to bring your design for reference to Part III of the exam?
Fom the Sun site.

Client Tier

This tier represents all device or system clients accessing the system or the application. A client can be a web browser, a Java or other application, a Java applet, a WAP phone, a network application, or some device introduced in the future.

Presentation Tier

This tier encapsulates all presentation logic required to service the clients that access the system. The presentation tier intercepts the client requests, provides single sign-on, session management and accesses business services, constructs the response, and delivers the response to the client. Servlets and JSPs reside in this tier.

Business Tier

This tier provides the business services required by the application clients. The tier contains the business data and business logic. All business processing for the application is centralized into this tier. The enterprise bean components are the usual choice for implementing the business objects in the business tier.

Integration Tier

This tier is responsible for communicating with external resources and systems, such as data stores and legacy applications. The business tier is coupled with the integration tier whenever the business objects require data or services that reside in the resource tier. The components in this tier can use JDBC, J2EE connector technology, or some proprietary middleware to work with the resource tier.

Resource Tier

This is the tier that contains the business data and external resources such as mainframes and legacy systems and business-to-business (B2B) systems, and services such as credit card authorization.
An applet is limited to the security manager within the browser. It does not automatically have access to external browser resources such as network, printers, files system, file servers, etc.

You can however sign your applet so it is trusted by the browser. A trusted applet has access to to the file system, etc.