Add file/classpath support in Spring Cloud Gateway

FileSchemeGlobalFilter.java

import org.springframework.cloud.gateway.filter.GatewayFilterChain;
import org.springframework.cloud.gateway.filter.GlobalFilter;
import org.springframework.cloud.gateway.route.Route;
import org.springframework.cloud.gateway.support.ServerWebExchangeUtils;
import org.springframework.core.io.FileSystemResource;
import org.springframework.core.io.Resource;
import org.springframework.core.io.buffer.DataBufferUtils;
import org.springframework.http.server.reactive.ServerHttpResponse;
import org.springframework.stereotype.Component;
import org.springframework.web.server.ServerWebExchange;
import reactor.core.publisher.Mono;

/**
 * Static resource using the {@code classpath:} or {@code file:} URI schemes.
 */
@Component
public class FileSchemeGlobalFilter implements GlobalFilter {

    @Override
    public Mono<Void> filter(ServerWebExchange exchange, GatewayFilterChain chain) {
        final Route route = exchange.getAttribute(ServerWebExchangeUtils.GATEWAY_ROUTE_ATTR);
        assert route != null;
        if (!route.getUri().getScheme().equals("file")) {
            return chain.filter(exchange);
        }
        final Resource resource = new FileSystemResource(route.getUri().getPath());

        ServerWebExchangeUtils.setAlreadyRouted(exchange);
        return chain.filter(exchange).then(Mono.defer(() -> {
            final ServerHttpResponse response = exchange.getResponse();
            return response.writeWith(DataBufferUtils.read(resource, response.bufferFactory(), 1024));
        }));
    }
}