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Introduction

Enterprise applications often need to execute common logic before or after every request.

Examples include

• Authentication
• Authorization
• Request Logging
• Audit Logging
• Performance Monitoring
• API Rate Limiting
• Correlation IDs
• Metrics Collection

Instead of writing the same code inside every controller, Spring MVC provides Interceptors.

Interceptors execute around controller methods and allow centralized request processing.

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Spring MVC Interceptor Architecture

flowchart LR

Client --> DispatcherServlet

DispatcherServlet --> Interceptor

Interceptor --> Controller

Controller --> Service

Service --> Database

Database --> Response

Response --> Interceptor

Interceptor --> Client

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Q1. What is an Interceptor in Spring MVC?

Answer

An Interceptor is a Spring MVC component that executes before and after controller execution.

Typical use cases

• Authentication
• Authorization
• Logging
• Auditing
• Metrics
• Request tracing

Interceptors are executed by the DispatcherServlet.

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Q2. What is HandlerInterceptor?

HandlerInterceptor is the primary Spring MVC interceptor interface.

It provides three lifecycle methods.

preHandle()

postHandle()

afterCompletion()

Applications implement this interface to intercept requests.

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Q3. What is preHandle()?

preHandle() executes before the controller method.

Responsibilities

• Authentication
• Authorization
• Logging
• Validate headers
• Block requests

Example

public boolean preHandle(){

    return true;

}

Return

• true → Continue request
• false → Stop processing

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Q4. What is postHandle()?

postHandle() executes after controller execution but before the response is rendered.

Typical use cases

• Add model attributes
• Logging
• Modify response model
• Metrics collection

Interceptor Flow

sequenceDiagram
Client->>Interceptor: preHandle()
Interceptor->>Controller: Execute
Controller-->>Interceptor: postHandle()
Interceptor-->>Client: Response

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Q5. What is afterCompletion()?

afterCompletion() executes after the complete request finishes.

Even if an exception occurs,

afterCompletion() still executes.

Typical use cases

• Cleanup
• Close resources
• Final logging
• Execution time calculation

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Q6. How do you register an Interceptor?

Implement WebMvcConfigurer.

Example

@Configuration
public class WebConfig
implements WebMvcConfigurer{

}

Override

addInterceptors()

Spring automatically registers the interceptor.

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Q7. Interceptor vs Filter

Filter	Interceptor
Servlet API	Spring MVC
Executes before DispatcherServlet	Executes after DispatcherServlet
Works for all requests	Only controller requests
Container-managed	Spring-managed
Suitable for compression, CORS	Suitable for authentication, logging

Both are frequently used together.

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Q8. Can multiple Interceptors be used?

Yes.

Spring executes them in order.

Example

Logging

↓

Authentication

↓

Authorization

↓

Controller

Execution order is configurable.

Multiple Interceptors

flowchart TD

LoggingInterceptor --> AuthInterceptor

AuthInterceptor --> AuditInterceptor

AuditInterceptor --> Controller

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Q9. What are common production use cases?

Common enterprise interceptors

• JWT Authentication
• Request Logging
• API Metrics
• Correlation IDs
• Audit Logging
• Localization
• Request Timing

These avoid duplication across controllers.

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Q10. Interceptor Best Practices

Keep Logic Lightweight

Avoid heavy processing.

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Avoid Business Logic

Use services instead.

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Log Correlation IDs

Support distributed tracing.

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Keep Authentication Centralized

Don't repeat in controllers.

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Use Interceptors for Cross-Cutting Concerns

Avoid controller duplication.

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Banking Example

flowchart TD

MobileApp --> DispatcherServlet

DispatcherServlet --> JWTInterceptor

JWTInterceptor --> AuditInterceptor

AuditInterceptor --> PaymentController

PaymentController --> PaymentService

PaymentService --> PostgreSQL

PaymentService --> JSONResponse

JSONResponse --> MobileApp

JWT validation and auditing occur before business processing.

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Common Interview Questions

• What is an Interceptor?
• What is HandlerInterceptor?
• Explain preHandle().
• Explain postHandle().
• Explain afterCompletion().
• How do you register an Interceptor?
• Interceptor vs Filter?
• Multiple Interceptors?
• Production use cases?
• Interceptor best practices?

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Quick Revision

Topic	Summary
Interceptor	Cross-cutting request processing
HandlerInterceptor	Spring MVC interceptor interface
preHandle()	Before controller
postHandle()	After controller, before response
afterCompletion()	After response completion
WebMvcConfigurer	Register interceptors
Logging	Common use case
Authentication	Common use case
Auditing	Common use case
Metrics	Performance monitoring

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Complete Interceptor Lifecycle

sequenceDiagram
Client->>DispatcherServlet: HTTP Request
DispatcherServlet->>Interceptor: preHandle()
Interceptor-->>DispatcherServlet: Continue
DispatcherServlet->>Controller: Execute
Controller->>Service: Business Logic
Service-->>Controller: Result
Controller-->>DispatcherServlet: Return
DispatcherServlet->>Interceptor: postHandle()
DispatcherServlet-->>Client: HTTP Response
DispatcherServlet->>Interceptor: afterCompletion()

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Production Example – Banking Payment API

A banking platform exposes

POST /api/v1/payments

Requirements

• Authenticate JWT token.
• Generate correlation ID.
• Record request duration.
• Write audit logs.
• Capture exceptions.

Workflow

1. Client sends a payment request.
2. JWTInterceptor.preHandle() validates the access token.
3. A correlation ID is added to the logging context (MDC).
4. Controller processes the payment.
5. postHandle() records business metrics.
6. HTTP response is returned.
7. afterCompletion() logs execution time and clears MDC.

public class JwtInterceptor
implements HandlerInterceptor {

    @Override
    public boolean preHandle(
            HttpServletRequest request,
            HttpServletResponse response,
            Object handler) {

        // Validate JWT

        return true;
    }

}

flowchart LR

MobileApp --> DispatcherServlet

DispatcherServlet --> JwtInterceptor

JwtInterceptor --> CorrelationInterceptor

CorrelationInterceptor --> PaymentController

PaymentController --> PaymentService

PaymentService --> PostgreSQL

PaymentService --> PaymentResponse

PaymentResponse --> MobileApp

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Filter vs Interceptor vs ControllerAdvice

Feature	Filter	Interceptor	ControllerAdvice
Layer	Servlet Container	Spring MVC	Spring MVC
Runs Before DispatcherServlet	✅	❌	❌
Runs Before Controller	✅	✅	❌
Runs After Controller	❌	✅	❌
Handles Exceptions	Limited	Limited	✅
Typical Usage	CORS, Compression, Encoding	Authentication, Logging, Auditing	Global Exception Handling

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Interceptor Execution Order

flowchart TD

HTTPRequest --> Filter

Filter --> DispatcherServlet

DispatcherServlet --> InterceptorPreHandle

InterceptorPreHandle --> Controller

Controller --> InterceptorPostHandle

InterceptorPostHandle --> ViewRendering

ViewRendering --> InterceptorAfterCompletion

InterceptorAfterCompletion --> HTTPResponse

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Key Takeaways

• Interceptors provide centralized processing for requests before and after controller execution.
• HandlerInterceptor defines three lifecycle methods: preHandle(), postHandle(), and afterCompletion().
• preHandle() is commonly used for authentication, authorization, logging, and request validation.
• postHandle() executes after the controller but before the response is rendered, making it useful for metrics and model enrichment.
• afterCompletion() always executes after request completion, making it ideal for cleanup, execution time logging, and resource release.
• Interceptors are registered through WebMvcConfigurer and apply only to Spring MVC controller requests.
• Filters, Interceptors, and @ControllerAdvice serve different purposes and are often used together in enterprise applications.
• Interceptors are best suited for cross-cutting concerns, helping keep controllers clean, reusable, and maintainable.