为什么spring-webflux应用默认运行在tomcat上，而不是netty上？

Question

我使用下面的pom.xml创建了一个Spring-webflux项目，但是当我启动应用程序时，它是在Tomcat上启动的。它不应该在Netty上启动default吗？

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.3.5.RELEASE</version>
    </parent>
    <groupId>com.test</groupId>
    <artifactId>reactive-rest</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>reactive-rest</name>

    <properties>
        <java-version>1.8</java-version>
    </properties>

    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-data-r2dbc</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-rsocket</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-security</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-webflux</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-websocket</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-messaging</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-rsocket</artifactId>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-devtools</artifactId>
            <scope>runtime</scope>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-configuration-processor</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <optional>true</optional>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
            <exclusions>
                <exclusion>
                    <groupId>org.junit.vintage</groupId>
                    <artifactId>junit-vintage-engine</artifactId>
                </exclusion>
            </exclusions>
        </dependency>
        <dependency>
            <groupId>io.projectreactor</groupId>
            <artifactId>reactor-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.security</groupId>
            <artifactId>spring-security-test</artifactId>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-surefire-plugin</artifactId>
            </plugin>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
            </plugin>
        </plugins>
        <pluginManagement>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <configuration>
                        <source>${java-version}</source>
                        <target>${java-version}</target>
                    </configuration>
                </plugin>
            </plugins>
        </pluginManagement>
    </build>

</project>

主类：

@SpringBootApplication(exclude = {SecurityAutoConfiguration.class, WebMvcAutoConfiguration.class})
public class ReactiveRestApplication {

    public static void main(String[] args) {
        SpringApplication.run(ReactiveRestApplication.class, args);
    }

}

启动日志：

2020-11-09 18:29:26.311  INFO 80838 --- [  restartedMain] o.s.b.d.a.OptionalLiveReloadServer       : LiveReload server is running on port 35729
2020-11-09 18:29:26.375  INFO 80838 --- [  restartedMain] o.s.b.w.embedded.tomcat.TomcatWebServer  : Tomcat started on port(s): 8080 (http) with context path ''
2020-11-09 18:29:26.390  INFO 80838 --- [  restartedMain] c.o.r.ReactiveRestApplication            : Started ReactiveRestApplication in 18.256 seconds (JVM running for 25.2)

我甚至尝试删除对tomcat的依赖，但应用程序仍然在Tomcat上启动

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

甚至尝试设置spring.main.web-application-type: reactive，但仍然是tomcat。

更新:我只保留了spring-boot-starter-webflux，并删除了所有其他依赖项。这一次也在'Tomcat‘上启动了服务

Answer 1

如果您查找mvnrepository上包含的不同库，您可以看到该spring-boot-starter-websocket

依赖于spring-boot-starter-web，这反过来会强制默认启动您的应用程序作为springMVC应用程序，而不是webflux应用程序。

我的假设是websockets已经包含在webflux依赖中。