Java EE architecture

The Java EE platform follows the four-tier architecture, the tiers being as follows:

• EIS tier: This is the enterprise information system (EIS) tier, where we store and retrieve all of our business data. Usually, it's a relational database system that's accessed using the Java Persistence API through our business tier, as will be discussed in detail in this book.
• Business tier: The business tier is responsible for managing business components that expose functionalities to other modules or separate systems. Enterprise JavaBeans, messaging, and other services are maintained in this tier, which will be discussed in detail in this book.
• Web tier: The web tier is where your web components/pages live. Although the Java's EE web profile is out of the scope of this book, we've used the web tier in many examples as well as in this chapter; therefore, basic knowledge about Servlets and JSP is essential.
• Client tier: Either a thin client (web browser) or a thick one (another Java application) that consumes the services we provide in our enterprise middleware solution.

Note that, in this book, we'll be focusing more on the EIS and business tier parts of an enterprise middleware solution, the web part being out of the scope of this book.