Interceptor in Spring 5 WebFlux - spring

Question

I am using Spring WebFlux in my project. I want to create an interceptor to calculate the time taken by each API. In Spring MVC we have HandlerInterceptor which is not present in spring-boot-starter-webflux. I tried adding spring-boot-starter-web and wrote my interceptor but it didn't work. Here is the code:
#Component
public class TimeInterceptor implements HandlerInterceptor {
public static Logger logger = Logger.getLogger(TimeInterceptor.class);
#Override
public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
long startTime = System.currentTimeMillis();
request.setAttribute("startTime", startTime);
return true;
}
#Override
public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
long totaltime = System.currentTimeMillis() - (long) request.getAttribute("startTime");
request.setAttribute("totaltime", totaltime);
logger.info("Logging total time" + totaltime);
}
...
...
I want to add similar functionality to my application and intercept time taken by each call.
Thanks in advance.

Answer 1

If you want to handle a request when it starts and when it completes, you can use WebFilter.
Try something like this
#Component
public class CustomWebFilter implements WebFilter {
#Override
public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
long startTime = System.currentTimeMillis();
return chain.filter(exchange).doFinally(signalType -> {
long totalTime = System.currentTimeMillis() - startTime;
exchange.getAttributes().put("totalTime", totalTime);
System.out.println(totalTime);
});
}
}
When request processing starts all defined filters are called. Mono is returned from filter. It indicates when request processing is complete.

Answer 2

There is no concept of HandlerInterceptor in Spring WebFlux, but you can use your own WebFilter for that instead.
The feature you're describing sounds a lot like the metrics support provided by Actuator and Micrometer. If you'd like to try it:
Add the actuator dependency to your project
Expose the relevant endpoints (here, metrics)
Go to "/actuator/metrics and select the metric for server HTTP requests (see the reference documentation).
Micrometer offers way more and helps you to get your metrics right, like: taking into account GC pauses when measuring time, providing histograms/percentiles/..., and more.
Note: adding spring-boot-starter-web to your application will turn it into a Spring MVC application.

Answer 3

Use the following project as dependency as jar / ant / maven / gradle
https://github.com/TurquoiseSpace/spring-webflux-http-interceptor
<dependency>
<groupId>com.github.TurquoiseSpace</groupId>
<artifactId>spring-webflux-http-interceptor</artifactId>
<version>0.0.7</version>
</dependency>
It provides ReactiveApiInterceptor which is a custom implementation of WebFilter

Answer 4

If required, you can override ReactiveApiInterceptor as well, to add your own custom logic, besides having the default logic, by calling
#Override
public Mono<Void> filter(ServerWebExchange serverWebExchange, WebFilterChain webFilterChain) {
// Your custom implementation, when api is hit and the request lands
super.filter(serverWebExchange, webFilterChain)
.doFinally(signalType -> {
// Your custom implementation, when request-response exchange gets completed
});
}