<parent>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-parent</artifactId>
    <version>2.2.3.RELEASE</version>
    <relativePath/> <!-- lookup parent from repository -->
</parent>

<dependencyManagement>
    <dependencies>
        <dependency>
            <groupId>org.springframework.cloud</groupId>
            <artifactId>spring-cloud-dependencies</artifactId>
            <version>Hoxton.SR9</version>
            <type>pom</type>
            <scope>import</scope>
        </dependency>
    </dependencies>
</dependencyManagement>

以上是springboot和SpringCloud的所使用的版本，

在使用gateway，啟動服務時出現如下報錯。

***************************
APPLICATION FAILED TO START
***************************

Description:

An attempt was made to call a method that does not exist. The attempt was made from the following location:

    org.springframework.cloud.gateway.config.GatewayAutoConfiguration$NettyConfiguration.reactorNettyWebSocketClient(GatewayAutoConfiguration.java:
 
803)

The following method did not exist:

    org.springframework.web.reactive.socket.client.ReactorNettyWebSocketClient.setHandlePing(Z)V

The method's class, org.springframework.web.reactive.socket.client.ReactorNettyWebSocketClient, is available from the following locations:

    jar:file:/E:/codes/maven_reps/org/springframework/spring-webflux/5.2.3.RELEASE/spring-webflux-5.2.3.RELEASE.jar!/org/springframework/web/reactive/socket/client/ReactorNettyWebSocketClient.class
 


It was loaded from the following location:

    file:/E:/codes/maven_reps/org/springframework/spring-webflux/5.2.3.RELEASE/spring-webflux-5.2.3.RELEASE.jar


Action:

Correct the classpath of your application so that it contains a single, compatible version of org.springframework.web.reactive.socket.client.ReactorNettyWebSocketClient


Process finished with exit code 1

搜尋資料看到有人說是由於依賴衝突，spring-cloud-starter-gateway與spring-boot-starter-web和spring-boot-starter-webflux依賴衝突

我這裡在引入gateway時去掉webflux就能正常啟動了

<dependency>
    <groupId>org.springframework.cloud</groupId>
    <artifactId>spring-cloud-starter-gateway</artifactId>
    <exclusions>
        <exclusion>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </exclusion>
    </exclusions>
</dependency>