How to modify query param in webflux filter - filter

Question

So any ideal how to modify query param in webflux filter, this code didn't work;
public class MyFilter implements WebFilter {
#Override
public Mono<Void> filter(ServerWebExchange exchange, WebFilterChain chain) {
ServerHttpRequest request = exchange.getRequest();
// didn't work, throw UnSupportOperationException
//request.getQueryParams().add("key1", "value1");
return chain.filter(exchange);
}
}

Answer 1

I am not sure about how you can modify the query param but the reason why you are not able to modify the params through the method getQueryParams() is because it returns a read only map. Check this link
https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/http/server/reactive/ServerHttpRequest.html#getQueryParams--

Answer 2

As #Prakher Jindal explained request.getQueryParams() returns a read-only map,
but you can add query params by writing a filter like this:
import lombok.AllArgsConstructor;
import lombok.Data;
import lombok.NoArgsConstructor;
import org.springframework.cloud.gateway.filter.GatewayFilter;
import org.springframework.cloud.gateway.filter.OrderedGatewayFilter;
import org.springframework.cloud.gateway.filter.RouteToRequestUrlFilter;
import org.springframework.cloud.gateway.filter.factory.AbstractGatewayFilterFactory;
import org.springframework.stereotype.Component;
import org.springframework.web.util.UriComponents;
import org.springframework.web.util.UriComponentsBuilder;
import java.net.URI;
import java.util.Optional;
import static org.springframework.cloud.gateway.support.ServerWebExchangeUtils.GATEWAY_REQUEST_URL_ATTR;
#Component
public class MyRewriteGatewayFilter extends AbstractGatewayFilterFactory<MyRewriteGatewayFilter.Config> {
public SecurityRewriteGatewayFilter() {
super(Config.class);
}
#Override
public GatewayFilter apply(Config config) {
return new OrderedGatewayFilter((exchange, chain) -> {
Optional.of(exchange)
.map(e -> (URI) e.getAttribute(GATEWAY_REQUEST_URL_ATTR))
.map(URI::toString)
.map(uri -> uri + "?key=" + "value")
.map(UriComponentsBuilder::fromUriString)
.map(UriComponentsBuilder::build)
.map(UriComponents::toUri)
.ifPresent(u -> exchange.getAttributes().put(GATEWAY_REQUEST_URL_ATTR, u));
return chain.filter(exchange.mutate().build());
}
, RouteToRequestUrlFilter.ROUTE_TO_URL_FILTER_ORDER + 1);
}
#Data
public static class Config {
}
}
Since this filter is not a global filter, make sure to add this to your application.yml file for the
routes on which you want to apply it. Something like this:
spring:
cloud:
gateway:
routes:
- id: my-routes
uri: http://localhost:8082
predicates:
- Path=/api/**
filters:
- name: MyRewriteGatewayFilter