Master Sentinel Flow Control and Circuit Breaking in Spring Cloud Alibaba

Custom Resource Points

Based on a project that already includes Spring Cloud Alibaba Sentinel, you first add annotation support in the main application class.

@SpringBootApplication
public class TestApplication {
    public static void main(String[] args) {
        SpringApplication.run(TestApplication.class, args);
    }

    // Annotation support bean
    @Bean
    public SentinelResourceAspect sentinelResourceAspect() {
        return new SentinelResourceAspect();
    }
}

Then annotate the method you want to protect with @SentinelResource and give it a resource name.

@Slf4j
@Service
public class TestService {
    @SentinelResource(value = "doSomeThing")
    public void doSomeThing(String str) {
        log.info(str);
    }
}

Implementing Flow Limiting

Expose the protected method through a REST controller.

@RestController
public class TestController {
    @Autowired
    private TestService testService;

    @GetMapping("/hello")
    public String hello() {
        testService.doSomeThing("hello " + new Date());
        return "didispace.com";
    }
}

Start the application and the Sentinel Dashboard, then send requests to /hello. The dashboard will display two resource points: the HTTP endpoint and the custom doSomeThing resource, where you can set a QPS limit (e.g., 2). When the limit is exceeded, Sentinel throws a FlowException and logs an error.

Handling Flow‑Limiting Exceptions

Define a blockHandler method to process blocked requests instead of returning a raw exception.

@Slf4j
@Service
public class TestService {
    @SentinelResource(value = "doSomeThing", blockHandler = "exceptionHandler")
    public void doSomeThing(String str) {
        log.info(str);
    }

    public void exceptionHandler(String str, BlockException ex) {
        log.error("blockHandler: " + str, ex);
    }
}

The block handler must have the same parameters as the original method plus a BlockException and return the same type.

Implementing Circuit Breaking (Degrade)

Use @SentinelResource with a fallback method to define degradation logic.

@Slf4j
@Service
public class TestService {
    @SentinelResource(value = "doSomeThing2", fallback = "fallbackHandler")
    public void doSomeThing2(String str) {
        log.info(str);
        throw new RuntimeException("exception occurred");
    }

    public void fallbackHandler(String str) {
        log.error("fallbackHandler: " + str);
    }
}

After configuring a degradation rule (e.g., 50% exception ratio, 2‑second window) on the Dashboard for the doSomeThing2 resource, frequent calls that exceed the rule will trigger the fallback method instead of propagating the exception.

More Annotation Attributes

value

: resource name (required). entryType: entry type, default EntryType.OUT. blockHandler / blockHandlerClass: method or class handling BlockException. fallback / fallbackClass: method or class handling business exceptions. defaultFallback: global fallback method (since 1.6.0). exceptionsToIgnore: exceptions excluded from fallback handling.

Reference

Sentinel official documentation and the sample project GitHub / Gitee .