Using Gson instead of Jackson in Spring Webflux

Question

We have many Spring MVC projects already, which all use gson instead of jackson for response body encode. Our bean classes are all written based on gson annotation. Now I am setting up a Spring Webflux restful server. It would save a lot of work if we can use the old bean classes from our Spring MVC projects.

I have tried spring.http.converters.preferred-json-mapper=gson property to no avail.

I have tried HttpMessageConverter bean, which is included in webflux packages, but that does not work as in the Spring MVC projects.

I googled a lot and the only thing helpful is to implement org.springframework.http.codec.HttpMessageEncoder class and set it to WebFluxConfigurer.configureHttpMessageCodecs() method:

@Configuration
public class WebConfiguration implements WebFluxConfigurer {
    @Override
    public void configureHttpMessageCodecs(ServerCodecConfigurer configurer) {
        configurer.customCodecs().decoder(new GsonHttpMessageDecoder());
        configurer.customCodecs().encoder(new GsonHttpMessageEncoder());
    }

    private static class GsonHttpMessageEncoder implements HttpMessageEncoder {
        ...
    }

    private static class GsonHttpMessageDecoder implements HttpMessageDecoder {
        ...
    }
}

I haven't try this out yet, since it is a little complex. Is there some easy way to replace jackson with gson in Spring Webflux?

Any help is appreciated.

Not sure if this will work, but have you tried excluding the transitive Jackson dependency? That might force WebFlux to use the configuration you've provided (GSON). — Mario Ishac, Oct 15 '19 at 05:47
@ThomasAndolf Because we already have many beans written with gson annotation like `@Expose` `@SerializedName` in SpringMVC projects, and these beans are shared across our projects by a jar as a common api definition between services. If we use jackson, we must rewrite these beans and logic along with them. I think it is not a good practice to have two code implementation represent one fact, since it violates Single-Point-of-Truth rule. Apart from that, no big deal indeed. If solving the problem cost too much, I will surrender and use jackson~. — Lyux, Oct 15 '19 at 06:42
looks like WebConfiguration is the only way to go. webflux does not support gson out of box. — ozkanpakdil, Oct 19 '19 at 09:21
@ThomasAndolf - One reason would be that Gson is a better platform for highly customized serialization of generic types. Jackson is battle-hardened and widely-used, but its design is incoherent when it comes to handling generic types. — Doradus, Aug 30 '20 at 14:56

score 2 · Accepted Answer · answered Jul 14 '21 at 12:21

Spring Framework doesn't support GSON as a WebFlux Encoder / Decoder for now. Feel free to follow up on the dedicated issue.

Note that as far as I know, GSON doesn't support non-blocking parsing so even if the support is implemented in Framework, it won't be complete and should not cover streaming input use cases.

Using Gson instead of Jackson in Spring Webflux

1 Answers1