Customizing and Using Interceptors in Spring Boot to Prevent Duplicate Submissions

Introduction: The previous article covered basic Spring Boot web development; this article introduces how to customize and configure interceptors in Spring Boot.

Spring Boot version: The examples are based on Spring Boot 2.3.4.RELEASE .

What is an interceptor? In Spring MVC, an Interceptor is similar to a Servlet Filter and can be used for permission verification, logging, login checks, and other request‑preprocessing tasks.

How to create a custom interceptor? Implement the HandlerInterceptor interface, which defines three methods:

preHandle() : executed before the controller method; returning true continues processing, false aborts.

postHandle() : executed after the controller method but before view rendering.

afterCompletion() : executed after the entire request is completed, useful for resource cleanup.

How to enable the interceptor in Spring Boot? Define a configuration class that implements WebMvcConfigurer and override addInterceptors() to register the interceptor.

@Configuration
public class WebConfig implements WebMvcConfigurer {
    @Autowired
    private XXX xxx;

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        // URIs that should not be intercepted
        final String[] commonExclude = {};
        registry.addInterceptor(xxx).excludePathPatterns(commonExclude);
    }
}

Example scenario: Prevent rapid duplicate requests (e.g., caused by repeated clicks) within a short time window using an interceptor.

Idea: Before the controller method executes, check whether the same request has been made within a specified period (e.g., 5 seconds). If it has, reject the request; otherwise, allow it.

Determining the unique key can involve IP address, user identifier, request parameters, request URI, or any combination of these.

Because the data needs to expire quickly, Redis is a suitable storage medium.

Implementation steps:

Create a custom annotation @RepeatSubmit with a seconds attribute (default 5 seconds). @Target({ElementType.METHOD, ElementType.TYPE}) @Retention(RetentionPolicy.RUNTIME) public @interface RepeatSubmit { /** Default expiration time of 5 seconds */ long seconds() default 5; }

Create a RepeatSubmitInterceptor component that checks for the annotation on methods or classes, uses StringRedisTemplate to set a key with setIfAbsent , and throws RepeatSubmitException if the key already exists. @Component public class RepeatSubmitInterceptor implements HandlerInterceptor { @Autowired private StringRedisTemplate stringRedisTemplate; @Override public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception { if (handler instanceof HandlerMethod) { HandlerMethod method = (HandlerMethod) handler; // Annotation on method RepeatSubmit repeatSubmitByMethod = AnnotationUtils.findAnnotation(method.getMethod(), RepeatSubmit.class); // Annotation on class RepeatSubmit repeatSubmitByCls = AnnotationUtils.findAnnotation(method.getMethod().getDeclaringClass(), RepeatSubmit.class); if (repeatSubmitByMethod == null && repeatSubmitByCls == null) { return true; // No restriction, continue } // Example: use request URI as the key (in real projects combine more criteria) String uri = request.getRequestURI(); long timeout = (repeatSubmitByMethod != null) ? repeatSubmitByMethod.seconds() : repeatSubmitByCls.seconds(); Boolean ifAbsent = stringRedisTemplate.opsForValue() .setIfAbsent(uri, "", timeout, TimeUnit.SECONDS); // If the key already exists, reject the request if (ifAbsent != null && !ifAbsent) { throw new RepeatSubmitException(); } } return true; } }

Configure the interceptor in a WebConfig class that implements WebMvcConfigurer , injecting the interceptor and excluding certain paths. @Configuration public class WebConfig implements WebMvcConfigurer { @Autowired private RepeatSubmitInterceptor repeatSubmitInterceptor; @Override public void addInterceptors(InterceptorRegistry registry) { // URIs that should not be intercepted final String[] commonExclude = {"/error", "/files/**"}; registry.addInterceptor(repeatSubmitInterceptor).excludePathPatterns(commonExclude); } }

Apply the @RepeatSubmit annotation to a controller or specific methods to activate the duplicate‑submission protection.

@RestController
@RequestMapping("/user")
@RepeatSubmit // All endpoints in this controller are protected
public class LoginController {
    @RequestMapping("/login")
    public String login() {
        return "login success";
    }
}

Note: When both class‑level and method‑level annotations are present, the method‑level seconds value overrides the class‑level value.

Conclusion: Configuring an interceptor in Spring Boot is straightforward and provides an effective way to prevent duplicate submissions.