A static web filter

StaticWebFilter.java

import org.springframework.stereotype.Component;
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 StaticWebFilter implements WebFilter {
    @Override
    public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
        if (exchange.getRequest().getURI().getPath().equals("/")) {
            return chain.filter(exchange
                    .mutate()
                    .request(exchange.getRequest()
                            .mutate()
                            .path("/index.html")
                            .build())
                    .build());
        }

        return chain.filter(exchange);
    }
}