Implementing Filters in Spring Web and Spring WebFlux

Introduction

Team is proactively working on spring boot 3.x upgrade and java 17. this post guide you how to migrate those Filters in both Spring Web and Spring WebFlux.

Filters are a fundamental aspect of web development, allowing developers to intercept and manipulate incoming requests and outgoing responses. In Spring applications, filters can be implemented to perform tasks such as logging, authentication, authorization, and request/response modification. This guide will demonstrate how to implement filters in both Spring Web and Spring WebFlux applications.

Implementing Filters in Spring Web

In Spring Web, filters are implemented by extending the javax.servlet.Filter interface and registering the filter with the servlet container using either web.xml or Servlet 3.0+ annotations.

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

@Component
public class MyFilter implements Filter {

    @Override
    public void init(FilterConfig filterConfig) throws ServletException {
        // Initialization logic
    }

    @Override
    public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
            throws IOException, ServletException {
        // Filter logic
        chain.doFilter(request, response); // Proceed with the filter chain
    }

    @Override
    public void destroy() {
        // Cleanup logic
    }
}

In the latest Java 17 release, the Jakarta EE namespace (jakarta.servlet) replaces the previous javax.servlet namespace.

import jakarta.servlet.*;
import jakarta.servlet.http.HttpServletRequest;

1. Create a Filter Class
2. Register the Filter: You can register the filter using either web.xml or Servlet 3.0+ annotations. With annotations, simply annotate the filter class with @Component.
3. Configure Filter Order (Optional): If you have multiple filters, you can specify their order using the @Order annotation or by implementing the Ordered interface.

Implementing Filters in Spring WebFlux

In Spring WebFlux, filters are implemented as WebFilter beans, which are registered with the WebFilterChain in the application configuration.

import org.springframework.web.server.ServerWebExchange;
import org.springframework.web.server.WebFilter;
import org.springframework.web.server.WebFilterChain;
import reactor.core.publisher.Mono;

@Component
public class MyWebFilter implements WebFilter {

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        // Filter logic
        return chain.filter(exchange); // Proceed with the filter chain
    }
}

1. Register the WebFilter Bean: The WebFilter bean is automatically registered with the WebFilterChain when the application starts.

Conclusion

Implementing filters in Spring Web and Spring WebFlux applications allows developers to intercept and manipulate HTTP requests and responses. Whether you're working with traditional servlet-based applications or reactive applications, Spring provides flexible mechanisms for implementing filters to meet your application's requirements. By following the guidelines outlined in this guide, you can effectively implement filters in your Spring applications to perform various tasks such as logging, authentication, and request/response modification.