Spring Cloud Gateway 启动报错（因为web依赖）

报错信息：

Spring Cloud Gateway启动一直报错详细错误信息

Parameter 0 of method modifyRequestBodyGatewayFilterFactory in org.springframework.cloud.gateway.config.GatewayAutoConfiguration required a bean of type 'org.springframework.http.codec.ServerCodecConfigurer' that could not be found.

Action:

Consider defining a bean of type 'org.springframework.http.codec.ServerCodecConfigurer' in your configuration.

查看源码：

1、GatewayClassPathWarningAutoConfiguration.java

spring cloud Gateway网关本身是一个Spring Boot项目，在网关微服务启动时他会自动加载它的配置，其中其中有一个叫做GatewayClassPathWarningAutoConfiguration的配置类, 如下：

看到@ConditionalOnMissingClass({"org.springframework.web.reactive.DispatcherHandler"})

在没有DispatcherHandler的情况下提示添加 spring-boot-starter-webflux 依赖。

在有DispatcherHandler的情况下提示移除 spring-boot-starter-web 依赖。

@Configuration(
    proxyBeanMethods = false
)
@AutoConfigureBefore({GatewayAutoConfiguration.class})
public class GatewayClassPathWarningAutoConfiguration {
    private static final Log log = LogFactory.getLog(GatewayClassPathWarningAutoConfiguration.class);
    private static final String BORDER = "\n\n**********************************************************\n\n";

    public GatewayClassPathWarningAutoConfiguration() {
    }

    @Configuration(
        proxyBeanMethods = false
    )
    @ConditionalOnMissingClass({"org.springframework.web.reactive.DispatcherHandler"}) //重点注解
    protected static class WebfluxMissingFromClasspathConfiguration {
        public WebfluxMissingFromClasspathConfiguration() {
            GatewayClassPathWarningAutoConfiguration.log.warn("\n\n**********************************************************\n\nSpring Webflux is missing from the classpath, which is required for Spring Cloud Gateway at this time. Please add spring-boot-starter-webflux dependency.\n\n**********************************************************\n\n");
        }
    }

    @Configuration(
        proxyBeanMethods = false
    )
    @ConditionalOnClass(
        name = {"org.springframework.web.servlet.DispatcherServlet"}
    )
    protected static class SpringMvcFoundOnClasspathConfiguration {
        public SpringMvcFoundOnClasspathConfiguration() {
            GatewayClassPathWarningAutoConfiguration.log.warn("\n\n**********************************************************\n\nSpring MVC found on classpath, which is incompatible with Spring Cloud Gateway at this time. Please remove spring-boot-starter-web dependency.\n\n**********************************************************\n\n");
        }
    }
}

如果pom文件中添加了spring-boot-starter-web 依赖，项目中就会存在 org.springframework.web.servlet.DispatcherServlet过滤器，这样与Spring Cloud Gateway冲突不兼容。

2、GatewayAutoConfiguration.java

打开网关自动配置类中GatewayAutoConfiguration 这个类，看到如下几个方法中需要org.springframework.http.codec.ServerCodecConfigurer这个bean

@Bean
public ModifyRequestBodyGatewayFilterFactory modifyRequestBodyGatewayFilterFactory(ServerCodecConfigurer codecConfigurer) {
    return new ModifyRequestBodyGatewayFilterFactory(codecConfigurer.getReaders());
}

@Bean
public DedupeResponseHeaderGatewayFilterFactory dedupeResponseHeaderGatewayFilterFactory() {
    return new DedupeResponseHeaderGatewayFilterFactory();
}

@Bean
public ModifyResponseBodyGatewayFilterFactory modifyResponseBodyGatewayFilterFactory(ServerCodecConfigurer codecConfigurer, Set<MessageBodyDecoder> bodyDecoders, Set<MessageBodyEncoder> bodyEncoders) {
    return new ModifyResponseBodyGatewayFilterFactory(codecConfigurer.getReaders(), bodyDecoders, bodyEncoders);
}