Count active requests with Spring Boot

package hoge;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.actuate.metrics.CounterService;
import org.springframework.boot.autoconfigure.EnableAutoConfiguration;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.servlet.*;
import java.io.IOException;

@EnableAutoConfiguration
@ComponentScan
@RestController
public class Application {
    @RequestMapping("/")
    String hoge() throws Exception {
        Thread.sleep(5000);
        return "hoge";
    }

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

    @Configuration
    static class Config {
        @Autowired
        CounterService counterService;

        @Bean
        Filter counterFilter() {
            return new Filter() {
                @Override
                public void init(FilterConfig filterConfig) throws ServletException {
                }

                @Override
                public void doFilter(ServletRequest servletRequest, ServletResponse servletResponse, FilterChain filterChain) throws IOException, ServletException {
                    try {
                        counterService.increment("active-http-sessions");
                        filterChain.doFilter(servletRequest, servletResponse);
                    } finally {
                        counterService.decrement("active-http-sessions");
                    }
                }

                @Override
                public void destroy() {
                }
            };
        }

    }
}