Keeping Track of Requests and Responses on Spring WebFlux

Introduction:

In today's world of reactive programming, Spring WebFlux has gained significant popularity for building highly scalable and responsive web applications. One crucial aspect of developing and debugging such applications is keeping track of requests and responses. In this blog post, we'll explore various techniques to monitor and log requests and responses in Spring WebFlux, along with code samples to help you implement these practices effectively.

Table of Contents:

1. Introduction to Spring WebFlux

2. Monitoring and Logging Requests

   a. Using WebFilter

   b. Interceptor-Based Logging

   c. Custom Logging Middleware

3. Tracking and Logging Responses

   a. Using ResponseFilter

   b. Custom Response Logging Middleware

4. Conclusion

1. Introduction to Spring WebFlux:

Spring WebFlux is a reactive web framework built on top of the Spring Framework, offering non-blocking, event-driven programming models for building scalable and high-performance applications. It leverages the power of reactive streams and provides excellent support for handling asynchronous and concurrent operations.

2. Monitoring and Logging Requests:

a. Using WebFilter:

One way to track requests is by utilizing the WebFilter interface provided by Spring WebFlux. You can create a custom filter that intercepts incoming requests and logs the relevant information such as HTTP method, URI, headers, and request body. Here's an example:

@Component

public class RequestLoggingFilter implements WebFilter {

    private static final Logger LOGGER = LoggerFactory.getLogger(RequestLoggingFilter.class);

    @Override

    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {

        ServerHttpRequest request = exchange.getRequest();

        LOGGER.info("Received request: {} {}", request.getMethod(), request.getURI());

        // Log headers, request body, or any additional information as needed

        return chain.filter(exchange);

    }

}

b. Interceptor-Based Logging:

Spring WebFlux provides an interceptor mechanism similar to traditional Spring MVC. You can create an interceptor that implements the HandlerInterceptor interface and overrides the necessary methods. This approach allows you to log requests and perform additional processing before and after request handling. Here's an example:

@Component

public class RequestLoggingInterceptor implements HandlerInterceptor {

    private static final Logger LOGGER = LoggerFactory.getLogger(RequestLoggingInterceptor.class);

    @Override

    public boolean preHandle(ServerWebExchange exchange, HandlerFunction<?> handler) {

        ServerHttpRequest request = exchange.getRequest();

        LOGGER.info("Received request: {} {}", request.getMethod(), request.getURI());

        // Log headers, request body, or any additional information as needed

        return true;

    }

    // Implement other methods like postHandle and afterCompletion as per your requirements

}

c. Custom Logging Middleware:

If you prefer a more centralized logging approach, you can create a custom middleware that intercepts requests globally. This middleware can capture and log request information for all incoming requests. Here's a sample code snippet:

@Component

public class RequestLoggingMiddleware implements WebFilter {

    private static final Logger LOGGER = LoggerFactory.getLogger(RequestLoggingMiddleware.class);

    @Override

    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {

        ServerHttpRequest request = exchange.getRequest();

        LOGGER.info("Received request: {} {}", request.getMethod(), request.getURI());

        // Log headers, request body, or any additional information as needed

        return chain.filter(exchange);

    }

}

3. Tracking and Logging Responses:

a. Using ResponseFilter:

Similar to monitoring requests, you can utilize the ResponseFilter interface provided by Spring WebFlux to track and log responses. This filter allows you to capture and log response status, headers, and body.

 Here's an example:

@Component

public class ResponseLoggingFilter implements WebFilter {

    private static final Logger LOGGER = LoggerFactory.getLogger(ResponseLoggingFilter.class);

    @Override

    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {

        ServerHttpResponse response = exchange.getResponse();

        return chain.filter(exchange)

            .doOnSuccessOrError((unused, throwable) -> {

                LOGGER.info("Sent response with status: {}", response.getStatusCode());

                // Log headers, response body, or any additional information as needed

            });

    }

}

b. Custom Response Logging Middleware:

Similar to custom request logging middleware, you can create a custom middleware to intercept responses globally and log the relevant information. Here's an example:

@Component

public class ResponseLoggingMiddleware implements WebFilter {

    private static final Logger LOGGER = LoggerFactory.getLogger(ResponseLoggingMiddleware.class);

    @Override

    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {

        ServerHttpResponse response = exchange.getResponse();

        return chain.filter(exchange)

            .doOnSuccessOrError((unused, throwable) -> {

                LOGGER.info("Sent response with status: {}", response.getStatusCode());

                // Log headers, response body, or any additional information as needed

            });

    }

}

4. Conclusion:

Monitoring and logging requests and responses are crucial for effective debugging, performance analysis, and auditing in Spring WebFlux applications. By leveraging the provided interfaces and implementing custom filters or middleware, you can easily track and log relevant information. These techniques ensure transparency and visibility into the flow of requests and responses, enabling efficient troubleshooting and optimization of your WebFlux applications.