Lecture Notes: Filters versus Interceptors in Spring Boot

Introduction

• Instructor: Shan
• Previous video covered Spring Boot interceptors.
• Topic: Differences between Filters and Interceptors.
• Goal: Clarify doubts and help decide when to use a filter or an interceptor.

Definitions

• Filter: Intercepts HTTP requests and responses before they reach the servlet.
• Interceptor: Specific to Spring framework; intercepts HTTP requests and responses after servlet but before reaching the controller.

Request Handling in Spring Boot

• Request flow:
  1. Servlet container (e.g., Tomcat) catches the request.
  2. Filters are applied in a chain before reaching the servlet.
  3. Dispatcher servlet determines the appropriate controller.
  4. Interceptors apply logic before reaching the controller.

Servlets

• Servlet: A Java class accepting requests and returning responses.
• Used for different tasks like handling REST APIs, SOAP APIs, etc.
• In microservices (Spring Boot), need for multiple servlets is reduced.
• Dispatcher servlet often handles all requests (/ mapping).

When to Use Filters vs. Interceptors

• Filters:
  • Applied to all HTTP requests and responses, regardless of servlet.
  • Ideal for generic logic (e.g., security).
• Interceptors:
  • Specific to Spring Boot's dispatcher servlet.
  • Ideal for logic specific to a particular servlet or application.

Implementation Details

Filters

• Implement by creating a filter class with methods init, doFilter, and destroy.
• Use doFilter to process requests and responses.
• Sequence maintained via doFilter method.

Interceptors

• Implement custom interceptors by configuring them in Spring Boot.
• Methods include preHandle, postHandle, and afterCompletion.
• preHandle can prevent further processing if it returns false.
• Sequence is preHandle -> controller logic -> postHandle -> afterCompletion.

Code Examples

• Demonstrated creating multiple filters and interceptors.
• Showed how to control the order of execution and how requests and responses flow.

Conclusion

• Filters and interceptors, though having access to request and response, should be chosen based on use case.
• Filters are used for generic purposes, interceptors for application-specific logic.
• Encourage further discussion for scenarios or additional insights on the topic.