java 37 lines · 7 steps

Building a Spring Boot rate-limiter auto-config

A Spring Boot auto-configuration wires up a token-bucket rate limiter and registers it as a web interceptor, all conditionally.

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Spring Intermediate auto-configuration conditional-beans rate-limiting interceptors dependency-injection
1@AutoConfiguration
2@EnableConfigurationProperties(RateLimiterProperties.class)
3@ConditionalOnClass(RateLimiter.class)
4public class RateLimiterAutoConfiguration {
5 
6 @Bean
7 @ConditionalOnMissingBean
8 public RateLimiter rateLimiter(RateLimiterProperties properties, ObjectProvider<MeterRegistry> meterRegistry) {
9 TokenBucketRateLimiter limiter = new TokenBucketRateLimiter(
10 properties.getCapacity(),
11 properties.getRefillTokens(),
12 properties.getRefillPeriod());
13 meterRegistry.ifAvailable(limiter::bindMetrics);
14 return limiter;
15 }
16 
17 @Bean
18 @ConditionalOnMissingBean
19 @ConditionalOnProperty(prefix = "app.rate-limiter", name = "enabled", havingValue = "true", matchIfMissing = true)
20 public RateLimitInterceptor rateLimitInterceptor(RateLimiter rateLimiter, RateLimiterProperties properties) {
21 return new RateLimitInterceptor(rateLimiter, properties.getKeyResolver());
22 }
23 
24 @Bean
25 @ConditionalOnMissingBean
26 @ConditionalOnWebApplication(type = ConditionalOnWebApplication.Type.SERVLET)
27 public WebMvcConfigurer rateLimiterWebMvcConfigurer(RateLimitInterceptor interceptor, RateLimiterProperties properties) {
28 return new WebMvcConfigurer() {
29 @Override
30 public void addInterceptors(InterceptorRegistry registry) {
31 registry.addInterceptor(interceptor)
32 .addPathPatterns(properties.getPathPatterns())
33 .order(Ordered.HIGHEST_PRECEDENCE);
34 }
35 };
36 }
37}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1Auto-configuration classes let a library contribute beans that back off gracefully when the app already defines its own.
  2. 2Layered @Conditional annotations make wiring depend on classpath, properties, and application type rather than hard assumptions.
  3. 3ObjectProvider lets you consume an optional dependency without forcing it to exist.

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