Understanding Multi-Tier Architecture and Java EE Containers

Posted on Mar 30, 2025 in Computers

Understanding Multi-Tier Architecture

Multi-tier architecture separates application functionality into distinct logical and physical layers. This approach enhances maintainability, scalability, and flexibility.

Tiers in Multi-Tier Architecture

  1. Client Tier: This tier represents all devices or system clients accessing the system or application. A client can be a web browser, a Java or other application, a Java applet, a WAP phone, a network application, or any future device. It could even be a batch process.
  2. Presentation Tier: This tier encapsulates all presentation logic required to service the clients accessing the system. It intercepts client requests, provides single sign-on, conducts session management, controls access to business services, constructs responses, and delivers them to the client. Servlets and JavaServer Pages (JSP) typically reside in this tier. Note that servlets and JSP are not UI elements themselves but generate UI elements.
  3. Business Tier: This tier provides the business services required by the application clients, containing the business data and business logic. Typically, most business processing for the application is centralized here. However, due to legacy systems, some business processing might occur in the resource tier. Enterprise JavaBeans (EJB) components are the usual and preferred solution for implementing business objects in this tier.
  4. 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 business objects require data or services residing in the resource tier. Components in this tier can use JDBC, Java EE Connector Architecture (JCA), or proprietary middleware to interact with the resource tier.
  5. Resource Tier: This tier contains the business data and external resources, such as mainframes, legacy systems, business-to-business (B2B) integration systems, and services like credit card authorization.

Benefits of Layered Architecture

  • Easier to understand and traceable code for developers.
  • Easier to write applications.
  • Easier to test applications.
  • Easier to extend business rules on a particular domain object.

Java EE Containers Explained

Java EE containers act as the interface between a component (like a servlet or EJB) and the lower-level functionality provided by the application server platform to support that component and its APIs. The container’s functionality, defined by the platform, aims to enhance productivity and varies for each component type. The server enables different component types to collaborate, enhancing the functionality of an enterprise application.

Web Container

The web container serves as the interface between web components (or APIs) and the web server. Web components include JavaServer Pages (JSP), JavaServer Faces (JSF) Facelets pages, and servlets. It manages the request and response processes within the component’s lifecycle, dispatches requests to application components, and provides interfaces to context data (e.g., current request information).

Application Client Container

The application client container acts as the interface between Java EE application clients and the Java EE server. These clients are typically special Java SE applications that utilize Java EE server components and additional APIs. Running on the client machine, this container serves as the gateway between the client application and the Java EE server components it uses.

Key Container Features

  • Security: Java EE security models allow configuration of web components or Enterprise JavaBeans (EJB) to ensure system resources are accessed only by authorized users.
  • Transactions: The Java EE transaction model defines relationships among methods that constitute a single transaction, ensuring all methods within that transaction are treated as a single atomic unit.
  • Remote Connectivity: The Java EE remote connectivity model manages low-level communication protocols between clients and EJBs.

Z