Creating and Using Interceptors in Spring Boot

Introduction

• Instructor: Nilan from The Tech Mojo
• Topic: Creating and using interceptors in Spring Boot
• Video Structure:
  • Chapter 1: Introduction to Spring Interceptors
  • Chapter 2: Differences between Spring Interceptors and Servlet Filters
  • Chapter 3: Implementing and registering an Interceptor
  • Chapter 4: Interceptor execution order
  • Chapter 5: Creating an Interceptor for basic authentication checks

Chapter 1: Introduction to Spring Interceptors

• Purpose: Intercept client requests before the controller processes them
• Use Cases:
  • Logging HTTP requests and responses for debugging or tracking performance
  • Enforcing security policies (e.g., checking user authentication)
  • Caching HTTP requests and responses
  • Transforming HTTP requests and responses (e.g., converting JSON to XML)
• Workflow in Spring Boot:
  • Request received by web server and forwarded to Spring Boot application
  • Dispatcher servlet receives request and consults URL Handler mapping
  • Handler mapping determines the appropriate controller

Chapter 2: Difference Between Spring Interceptors and Servlet Filters

• Servlet Filters:
  • Part of Servlet API, operate at a lower level
  • Intercept request-response lifecycle, not specific to Spring Framework
• Spring Interceptors:
  • Part of Spring Web MVC, require Spring application context
• Deciding which to use:
  • Use Interceptors for tasks requiring Spring MVC
  • Use Filters for more generic tasks not requiring Spring

Chapter 3: Implementing and Registering an Interceptor

• Creating Interceptor Class: Implements HandlerInterceptor interface
  • Methods:
    • preHandle: Executed before the controller, returns a boolean
    • postHandle: Executed after the controller but before the response is sent
    • afterCompletion: Executed after the request completion (for cleanup tasks)
• Registering Interceptor:
  • Create a class implementing WebMvcConfigurer
  • Override addInterceptors method
  • Add Interceptor to InterceptorRegistry

Chapter 4: Interceptor Execution Order

• Execution Sequence:
  • Multiple interceptors can be added
  • Specifying order using @Order annotation
  • First on pre-handle, reverse on post-handle and after completion
  • Example provided on how order affects execution

Chapter 5: Creating an Interceptor for Basic Authentication Checks

• Objective: Ensure authenticated requests for certain endpoints
• Steps:
  • Extract and decode the Authorization header
  • Validate username and password against predefined values
  • Implement logic in preHandle method for authentication checks

Example: Adding and Testing Interceptor

• Creating LogHandlerInterceptor:
  • Implements HandlerInterceptor
  • Logs request flow in preHandle, postHandle, and afterCompletion methods
• Registering LogHandlerInterceptor
• Creating BasicAuthHandlerInterceptor:
  • Extends LogHandlerInterceptor
  • Performs basic authentication by validating against hardcoded credentials
• Testing Interceptors:
  • Use Postman to test endpoints with and without correct credentials
  • Observe logs for sequence of interceptor execution

Conclusion

• Summary of adding and using interceptors for various tasks in a Spring Boot application
• Encouragement to ask questions and provide feedback
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