最新版本的Spring需要reactor 2.0，看看你的POM有一個明確的1.1.6依賴。

解決：

<dependency>
    <groupId>org.projectreactor</groupId>
    <artifactId>reactor-core</artifactId>
    <version>1.1.6.RELEASE</version>
</dependency>

<dependency>
    <groupId>org.projectreactor</
 
groupId>
    <artifactId>reactor-net</artifactId>
    <version>1.1.6.RELEASE</version>
</dependency>


<dependency>
    <groupId>org.projectreactor</groupId>
    <artifactId>reactor-tcp</artifactId>
    <version>1.0.1.RELEASE</version>
 

</dependency>

<dependency>
    <groupId>org.projectreactor</groupId>
    <artifactId>reactor-spring</artifactId>
    <version>1.0.1.RELEASE</version>
</dependency>