spring mvc using interceptor

spring-boot-modules/spring-boot-libraries/src/main/java/com/baeldung/ratelimiting/bucket4japp/Bucket4jRateLimitingApp.java

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+package com.baeldung.ratelimiting.bucket4japp;
+
+import org.springframework.boot.autoconfigure.SpringBootApplication;
+import org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration;
+import org.springframework.boot.autoconfigure.security.servlet.SecurityAutoConfiguration;
+import org.springframework.boot.builder.SpringApplicationBuilder;
+import org.springframework.web.servlet.config.annotation.InterceptorRegistry;
+import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;
+
+import com.baeldung.ratelimiting.bucket4japp.interceptor.RateLimitingInterceptor;
+
+@SpringBootApplication(scanBasePackages = "com.baeldung.ratelimiting", exclude = { 
+        DataSourceAutoConfiguration.class,
+        SecurityAutoConfiguration.class
+})
+public class Bucket4jRateLimitingApp implements WebMvcConfigurer {
+
+    @Override
+    public void addInterceptors(InterceptorRegistry registry) {
+        registry.addInterceptor(new RateLimitingInterceptor())
+            .addPathPatterns("/api/v1/area/**");
+    }
+
+    public static void main(String[] args) {
+        new SpringApplicationBuilder(Bucket4jRateLimitingApp.class)
+            .properties("spring.config.location=classpath:ratelimiting/application-bucket4j.yml")
+            .run(args);
+    }
+}

spring-boot-modules/spring-boot-libraries/src/main/java/com/baeldung/ratelimiting/bucket4japp/interceptor/PricingPlan.java

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+package com.baeldung.ratelimiting.bucket4japp.interceptor;
+
+import java.time.Duration;
+
+import io.github.bucket4j.Bandwidth;
+import io.github.bucket4j.Refill;
+
+enum PricingPlan {
+
+    FREE {
+
+        @Override
+        Bandwidth getLimit() {
+            return Bandwidth.classic(20, Refill.intervally(20, Duration.ofHours(1)));
+        }
+    },
+
+    BASIC {
+
+        @Override
+        Bandwidth getLimit() {
+            return Bandwidth.classic(40, Refill.intervally(40, Duration.ofHours(1)));
+        }
+    },
+
+    PROFESSIONAL {
+
+        @Override
+        Bandwidth getLimit() {
+            return Bandwidth.classic(100, Refill.intervally(100, Duration.ofHours(1)));
+        }
+    };
+
+    abstract Bandwidth getLimit();
+
+    static PricingPlan resolvePlanFromApiKey(String apiKey) {
+        if (apiKey == null || apiKey.isEmpty()) {
+            return FREE;
+        
+        } else if (apiKey.startsWith("PX001-")) {
+            return PROFESSIONAL;
+            
+        } else if (apiKey.startsWith("BX001-")) {
+            return BASIC;
+        }
+        return FREE;
+    }
+}

spring-boot-modules/spring-boot-libraries/src/main/java/com/baeldung/ratelimiting/bucket4japp/interceptor/RateLimitingInterceptor.java

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+package com.baeldung.ratelimiting.bucket4japp.interceptor;
+
+import java.util.Map;
+import java.util.concurrent.ConcurrentHashMap;
+
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
+import org.springframework.http.HttpStatus;
+import org.springframework.web.servlet.HandlerInterceptor;
+
+import io.github.bucket4j.Bandwidth;
+import io.github.bucket4j.Bucket;
+import io.github.bucket4j.Bucket4j;
+import io.github.bucket4j.ConsumptionProbe;
+
+public class RateLimitingInterceptor implements HandlerInterceptor {
+
+    private static final String HEADER_API_KEY = "X-api-key";
+    private static final String HEADER_LIMIT_REMAINING = "X-Rate-Limit-Remaining";
+    private static final String HEADER_RETRY_AFTER = "X-Rate-Limit-Retry-After-Milliseconds";
+
+    private final Map<String, Bucket> cache = new ConcurrentHashMap<>();
+
+    @Override
+    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
+        
+        String apiKey = request.getHeader(HEADER_API_KEY);
+
+        if (apiKey == null || apiKey.isEmpty()) {
+            response.sendError(HttpStatus.BAD_REQUEST.value(), "Missing Header: " + HEADER_API_KEY);
+            return false;
+        }
+        
+        Bucket tokenBucket = cache.computeIfAbsent(apiKey, this::resolveBucket);
+
+        ConsumptionProbe probe = tokenBucket.tryConsumeAndReturnRemaining(1);
+
+        if (probe.isConsumed()) {
+
+            response.addHeader(HEADER_LIMIT_REMAINING, String.valueOf(probe.getRemainingTokens()));
+            return true;
+
+        } else {
+
+            long waitForRefillMilli = probe.getNanosToWaitForRefill() % 1_000_000;
+
+            response.sendError(HttpStatus.TOO_MANY_REQUESTS.value(), "You have exhausted your API Request Quota"); // 429
+            response.addHeader(HEADER_RETRY_AFTER, String.valueOf(waitForRefillMilli));
+
+            return false;
+        }
+    }
+
+    private Bucket resolveBucket(String apiKey) {
+        PricingPlan pricingPlan = PricingPlan.resolvePlanFromApiKey(apiKey);
+        return bucket(pricingPlan.getLimit());
+    }
+    
+    private Bucket bucket(Bandwidth limit) {
+        return Bucket4j.builder()
+            .addLimit(limit)
+            .build();
+    }
+}

spring-boot-modules/spring-boot-libraries/src/main/resources/ratelimiting/application-bucket4j.yml

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+server:
+  port: 9000
+
+spring:
+  application:
+    name: bucket4j-api-rate-limiting-app
+  mvc:
+    throw-exception-if-no-handler-found: true
+  resources:
+    add-mappings: false