项目启动报错：Unable to start EmbeddedWebApplicationContext due to missing EmbeddedServletContainerFactory bean.

org.springframework.context.ApplicationContextException: Unable to start embedded container; nested exception is org.springframework.context.ApplicationContextException: Unable to start EmbeddedWebApplicationContext due to missing EmbeddedServletContainerFactory bean.
	at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.onRefresh(EmbeddedWebApplicationContext.java:137) ~[spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:537) ~[spring-context-4.3.13.RELEASE.jar:4.3.13.RELEASE]
	at org.springframework.boot.context.embedded.EmbeddedWebApplicationContext.refresh(EmbeddedWebApplicationContext.java:122) ~[spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:693) ~[spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:360) ~[spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) ~[spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
	at org.springframework.boot.builder.SpringApplicationBuilder.run(SpringApplicationBuilder.java:134) [spring-boot-1.5.9.RELEASE.jar:1.5.9.RELEASE]
	at com.wukong.atp.registrycenter.RegistryCenterApplication.main(RegistryCenterApplication.java:26) [classes/:na]

　　背景：新公司，入职后跑工程的时候；项目是springboot的，是有内置容器的；查看pom，发现排除了

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

　　问题是为什么要排除呢？后面发现pom中还有另外一个依赖

                 <dependency>
			<groupId>org.springframework.boot</groupId>
			<artifactId>spring-boot-starter-undertow</artifactId>
			<scope>provided</scope>
		</dependency>

　　这个是undertow的依赖，undertow是一个高性能的web容器；像上面的，排除了tomcat，用undertow；那应该没问题啊；后面发现问题：

<scope>provided</scope>  这里，scope是provided。  改成compile就可以了；或者删掉，因为默认就是compile