WebFlux 中form data获取不到参数问题

Spring WebFlux 中, request.queryParams 只能获取到 查询参数, 对于 form 提交的参数无法进行参数自动装载

处理方式有两种:

一. 自定义 ArgumentResolver, 具体如下:

1. 实现接口 org.springframework.web.reactive.config.WebFluxConfigurer
2. 重载 configureArgumentResolvers, 自定义 ArgumentResolver
3. 从 ServerWebExchange.formData中查找参数值返回

@Configuration
class WebConfig : WebFluxConfigurer {

    @Autowired
    private lateinit var applicationContext: ConfigurableApplicationContext

    override fun configureArgumentResolvers(configurer: ArgumentResolverConfigurer) {

        class RequestFormDataMethodArgumentResolver(
                beanFactory: ConfigurableBeanFactory,
                registry: ReactiveAdapterRegistry,
                useDefaultResolution: Boolean
        ): RequestParamMethodArgumentResolver(beanFactory, registry, useDefaultResolution) {

            override fun resolveNamedValue(name: String, parameter: MethodParameter, exchange: ServerWebExchange): Any? {
                var result: Any? = null
                val formData = exchange.formData.block()
                val values = formData[name]
                if( null != values ){
                    result = values.takeUnless { it.size == 1 } ?: values[0]
                }
                return result
            }
        }
        configurer.addCustomResolver(RequestFormDataMethodArgumentResolver(applicationContext.beanFactory, ReactiveAdapterRegistry.getSharedInstance(), true))
    }
}

该方法无法绑定 @RequestParam标记的参数
查看org.springframework.web.reactive.result.method.annotation.ControllerResolver
我们的自定义参数处理器是位于列表末尾的, 对于 @RequestParam标记的参数已经有前面的处理器处理过了

二. 将参数封装在对象中

例如:

@PostMapping
fun create(name: String, password: String) { ... }

可以改成为:

@PostMapping
fun create(user: User) {println("$user.name - $user.password") }

作为对象封装将会触发spring的databinder机制
WebFlux 中实现了org.springframework.web.bind.support.WebExchangeDataBinder
在检测到不是基本参数的时候, 需要进行参数绑定动作

	/**
	 * Combine query params and form data for multipart form data from the body
	 * of the request into a {@code Map} of values to use for
	 * data binding purposes.
	 * @param exchange the current exchange
	 * @return a {@code Mono} with the values to bind
	 * @see org.springframework.http.server.reactive.ServerHttpRequest#getQueryParams()
	 * @see ServerWebExchange#getFormData()
	 * @see ServerWebExchange#getMultipartData()
	 */
	public static Mono> extractValuesToBind(ServerWebExchange exchange) {
		MultiValueMap queryParams = exchange.getRequest().getQueryParams();
		Mono> formData = exchange.getFormData();
		Mono> multipartData = exchange.getMultipartData();

		return Mono.zip(Mono.just(queryParams), formData, multipartData)
				.map(tuple -> {
					Map result = new TreeMap<>();
					tuple.getT1().forEach((key, values) -> addBindValue(result, key, values));
					tuple.getT2().forEach((key, values) -> addBindValue(result, key, values));
					tuple.getT3().forEach((key, values) -> addBindValue(result, key, values));
					return result;
				});
	}

这里可以看见, 进行参数绑定是从 queryParams, formData, multipartData 三个地方读取, 所以, 对象中的参数是可以正常绑定的

注意问题

WebFlux 官方文档中提到, formdata数据来自于 application/x-www-form-urlencoded, 所以使用以上方式实现 form data 参数绑定的, 注意了, 提交方式一定为: application/x-www-form-urlencoded, 否则, 请使用 request body