JavaLessons/springboot2-request-logger/README.md

How to log every Request in SpringBoot

Prerequesites

Imagine we have an web SpringBoot application containing a Controller. It returns a template index containing two links: on css file and on js file.

So we want to log every request from client while opening index.html:

1. index.html
2. test.css
3. test.js

Enabling logging

We must set up the logging of our classes. Take a look at example of logback-spring.xml.

Build a Filter

Every Spring Web application have a chain on different filters. Every request flows through this filter chain before getting a controller.

So we can implement a logging filter and put it into Spring Filter Chain to achieve our goal.

@Slf4j
@Component
public class RequestLoggingFilter extends OncePerRequestFilter {
    @Override
    protected void doFilterInternal(HttpServletRequest request, HttpServletResponse response, FilterChain filterChain) throws ServletException, IOException {
        log.debug(
                String.format("FILTERED URL: %s", request.getRequestURI())
        );

        //continue filtering
        filterChain.doFilter(request, response);
    }
}

Using @Slf4j annotation get us to decrease boilerplate code to have a logger in a class.

We must annotate our class with @Component annotation to make SpringBoot to instantiate this class as spring bean in Singleton scope.

Our class extends OncePerRequestFilter abstract class so every request goes through our filter only once.

And we are able to log anything regarding the request inside doFilterInternal method.

Result

You may run testControllerLoggingWithFilter to see the result

    @Test(expected = HttpClientErrorException.NotFound.class)
    public void testControllerLoggingWithFilter() {
        restTemplate.getForObject("http://localhost:"+port+"/", String.class);
        restTemplate.getForObject("http://localhost:"+port+"/test.js", String.class);
        restTemplate.getForObject("http://localhost:"+port+"/test.css", String.class);
        restTemplate.getForObject("http://localhost:"+port+"/does-not-exist.file", String.class);
    }

So our goal is achieved. We can see all files we request and not existing file too.