WebFilter

WebFilter is a core component in the reactive stack that intercepts and processes HTTP requests and responses.

The WebFilter interface looks like the following.

public interface WebFilter {

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

}

The filter method receives a ServerWebExchange that lets you inspect the request and perform cross-cutting operations before or after the request is handled.

The WebFilterChain is similar to the role of FilterChain in the Servlet Filter. At runtime, a series of WebFilter can be chained to execute in one web request.

The following is an example of WebFilter where it works as a security checker. If there is no user query parameter provided, then send a UNAUTHORIZED status code to the response.

@Component
public class SecurityWebFilter implements WebFilter{
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        if(!exchange.getRequest().getQueryParams().containsKey("user")){
            exchange.getResponse().setStatusCode(HttpStatus.UNAUTHORIZED);
        }
        return chain.filter(exchange);
    }
}

NOTE: In production applications prefer Spring Security for authentication and authorization. This example demonstrates how a simple WebFilter can be used for small checks or prototyping.

For the complete codes, check spring-reactive-sample/web-filter.