Chapter 4: The Server Tier – Exam Revision Notes

1. Introduction

• The server tier is the backend of a web application that handles data processing, business logic, and communication with databases.
  
• It interacts with the client tier (front-end) to generate dynamic content and maintain state.
  

2. Web Server Concept

• A web server receives requests from clients (web browsers) and responds with HTML, JSON, or XML.
  
• Functions:
  
  • Serve static content (HTML, CSS, images)
    
  • Generate dynamic content (via scripts or server-side programs)
    
  • Manage sessions and authentication
    

3. Creating Dynamic Content

• Dynamic content changes based on user input or other runtime factors.
  
• Methods:
  
  • Server-side scripting: Java (JSP), PHP, ASP.NET
    
  • Template engines: Generate HTML dynamically
    
• Control flow structures (if-else, loops) determine how content is generated.
  

4. Sessions and State

• HTTP is stateless, so servers need mechanisms to track user interactions:
  
  • Sessions: Store data across multiple requests from the same user
    
  • Cookies: Store small pieces of data on the client
    
  • Hidden fields: Pass state info in forms
    

5. Error Handling

• Servers must handle errors gracefully:
  
  • Client errors (4xx): Bad request, unauthorized access
    
  • Server errors (5xx): Internal server errors
    
• Error handling techniques:
  
  • Try-catch blocks (for server-side scripts)
    
  • Custom error pages
    
  • Logging for debugging and monitoring
    

6. Architecting Web Applications

• Design patterns for server-side development:
  
  • MVC (Model-View-Controller): Separates logic, data, and presentation
    
  • Layered architecture: Presentation → Business logic → Data access
    
• Benefits:
  
  • Modular, maintainable, scalable, and testable applications
    

7. Tag Libraries

• Predefined collections of reusable server-side components.
  
• Examples in Java:
  
  • JSP Standard Tag Library (JSTL)
    
  • Custom tag libraries for common tasks (loops, conditionals, formatting)
    
• Advantages:
  
  • Simplifies coding
    
  • Reduces errors
    
  • Enhances code readability
    

8. Writing Tag Libraries

• Steps to create a custom tag library in Java:
  
  1. Define the tag in a Tag Library Descriptor (TLD) file
     
  2. Implement Java class for tag behavior
     
  3. Include the tag library in JSP using <%@ taglib %> directive
     

9. Key Takeaways

• The server tier executes business logic, handles requests, and manages communication with databases.
  
• Dynamic content, session management, and error handling are core responsibilities.
  
• Proper architecture and use of tag libraries improve maintainability and scalability.
  
• Understanding server-side processing is critical for building robust web applications.