Enterprise JavaBeans, Third Edition

Web Components and EJB

Together, servlets and JSP provide a powerful platform for generating web pages dynamically. Servlets and JSP, which are collectively called web components, can access resources like JDBC and enterprise beans. Because web components can access databases using JDBC, they can provide a powerful platform for e-commerce by allowing an enterprise to expose its business systems to the Web through an HTML interface. HTML has several advantages over more conventional client applications, in Java or any other language. The most important advantages have to do with distribution and firewalls. Conventional clients need to be distributed and installed on client machines, which is their biggest limitation: they require additional work for deployment and maintenance. Applets, which are dynamically downloaded, can be used to eliminate the headache of installation, but applets have other limitations, such as sandbox restrictions and heavyweight downloads. In contrast, HTML is extremely lightweight, does not require prior installation, and does not suffer from security restrictions. In addition, HTML interfaces can be modified and enhanced at their source without having to update the clients.

Firewalls present another significant problem in e-commerce. HTTP, the protocol over which web pages are requested and delivered, can pass through most firewalls without a problem, but other protocols such as IIOP or JRMP cannot. This restriction has proven to be a significant barrier ...