sentinel/sentinel-adapter/sentinel-spring-webmvc-adapter

Sentinel Spring MVC Adapter

Introduction

Sentinel provides integration for Spring Web to enable flow control for web requests.

Add the following dependency in pom.xml (if you are using Maven):

<dependency>
    <groupId>com.alibaba.csp</groupId>
    <artifactId>sentinel-spring-webmvc-adapter</artifactId>
    <version>x.y.z</version>
</dependency>

Then we could add a configuration bean to configure the interceptor:

@Configuration
public class InterceptorConfig implements WebMvcConfigurer {

    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        SentinelWebMvcConfig config = new SentinelWebMvcConfig();
        // Enable the HTTP method prefix.
        config.setHttpMethodSpecify(true);
        // Add to the interceptor list.
        registry.addInterceptor(new SentinelWebInterceptor(config)).addPathPatterns("/**");
    }
}

Then Sentinel will extract URL patterns defined in Web Controller as the web resource (e.g. /foo/{id}).

Configuration

Block handling

Sentinel Spring Web adapter provides a BlockExceptionHandler interface to handle the blocked requests. We could set the handler via SentinelWebMvcTotalConfig#setBlockExceptionHandler() method.

By default the interceptor will throw out the BlockException. We need to set a global exception handler function in Spring to handle it. An example:

@ControllerAdvice
@Order(0)
public class SentinelBlockExceptionHandlerConfig {
    private Logger logger = LoggerFactory.getLogger(this.getClass());

    @ExceptionHandler(BlockException.class)
    @ResponseBody
    public String sentinelBlockHandler(BlockException e) {
        AbstractRule rule = e.getRule();
        logger.info("Blocked by Sentinel: {}", rule.toString());
        return "Blocked by Sentinel";
    }
}

We’ve provided a DefaultBlockExceptionHandler. When a request is blocked, the handler will return a default page indicating the request is rejected (Blocked by Sentinel (flow limiting)). The HTTP status code of the default block page is 429 (Too Many Requests).

We could also implement our implementation of the BlockExceptionHandler interface and set to the config object. An example:

SentinelWebMvcConfig config = new SentinelWebMvcConfig();
config.setBlockExceptionHandler((request, response, e) -> {
    String resourceName = e.getRule().getResource();
    // Depending on your situation, you can choose to process or throw
    if ("/hello".equals(resourceName)) {
        // Do something ......
        response.getWriter().write("Blocked by Sentinel");
    } else {
        // Handle it in global exception handling
        throw e;
    }
});

Customized configuration

• Common configuration in SentinelWebMvcConfig and SentinelWebMvcTotalConfig:

name	description	type	default value
blockExceptionHandler	The handler that handles the block request	BlockExceptionHandler	null (throw out the BlockException)
originParser	Extracting request origin (e.g. IP or appName from HTTP Header) from HTTP request	RequestOriginParser	-

• SentinelWebMvcConfig configuration:

name	description	type	default value
urlCleaner	The UrlCleaner interface is designed for clean and unify the URL resource.	UrlCleaner	-
requestAttributeName	Attribute key in request used by Sentinel (internal)	String	$$sentinel_spring_web_entry_attr
httpMethodSpecify	Specify whether the URL resource name should contain the HTTP method prefix (e.g. POST:).	boolean	false
webContextUnify	Specify whether unify web context(i.e. use the default context name).	boolean	true

• SentinelWebMvcTotalConfig configuration:

name	description	type	default value
totalResourceName	The resource name in SentinelTotalInterceptor	String	spring-mvc-total-url-request
requestAttributeName	Attribute key in request used by Sentinel (internal)	String	$$sentinel_spring_web_total_entry_attr