Unable to start web server; nested exception is org.springframework.context.ApplicationContextException: Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean.
SpringBoot启动时的异常信息如下：
1 "C:\Program Files\Java\jdk1.8.0_161\bin\java" ......... com.fangxing.javalearning.annotationlearning.ComponentScanApp
2 hello world
3
4 . ____ _ __ _ _
5 /\\ / ___'_ __ _ _(_)_ __ __ _ \ \ \ \
6 ( ( )\___ | '_ | '_| | '_ \/ _` | \ \ \ \
7 \\/ ___)| |_)| | | | | || (_| | ) ) ) )
8 ' |____| .__|_| |_|_| |_\__, | / / / /
9 =========|_|==============|___/=/_/_/_/
10 :: Spring Boot :: (v2.0.0.RELEASE)
11
12 2018-04-03 22:25:07.232 INFO 4976 --- [ main] c.f.j.a.ComponentScanApp : Starting ComponentScanApp on DESKTOP-BHGM3HS with PID 4976 (started by hasee in D:\test\projects\java-learning)
13 2018-04-03 22:25:07.237 INFO 4976 --- [ main] c.f.j.a.ComponentScanApp : No active profile set, falling back to default profiles: default
14 2018-04-03 22:25:07.321 INFO 4976 --- [ main] ConfigServletWebServerApplicationContext : Refreshing org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext@45f45fa1: startup date [Tue Apr 03 22:25:07 CST 2018]; root of context hierarchy
15 2018-04-03 22:25:07.664 WARN 4976 --- [ main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.context.ApplicationContextException: Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean.
16 2018-04-03 22:25:08.238 ERROR 4976 --- [ main] o.s.boot.SpringApplication : Application run failed
17
18 org.springframework.context.ApplicationContextException: Unable to start web server; nested exception is org.springframework.context.ApplicationContextException: Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean.
19 at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:155) ~[spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
20 at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:543) ~[spring-context-5.0.4.RELEASE.jar:5.0.4.RELEASE]
21 at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
22 at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:752) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
23 at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:388) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
24 at org.springframework.boot.SpringApplication.run(SpringApplication.java:327) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
25 at org.springframework.boot.SpringApplication.run(SpringApplication.java:1246) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
26 at org.springframework.boot.SpringApplication.run(SpringApplication.java:1234) [spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
27 at com.fangxing.javalearning.annotationlearning.ComponentScanApp.main(ComponentScanApp.java:15) [classes/:na]
28 Caused by: org.springframework.context.ApplicationContextException: Unable to start ServletWebServerApplicationContext due to missing ServletWebServerFactory bean.
29 at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.getWebServerFactory(ServletWebServerApplicationContext.java:204) ~[spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
30 at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.createWebServer(ServletWebServerApplicationContext.java:178) ~[spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
31 at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.onRefresh(ServletWebServerApplicationContext.java:152) ~[spring-boot-2.0.0.RELEASE.jar:2.0.0.RELEASE]
32 ... 8 common frames omitted
33
34
35 Process finished with exit code 1
Spring Boot启动出现错误，错误内容大概的意思是：未能加载嵌入的供web应用加载的空间，是因为缺少ServletWebServerFactory bean，在stackflow上面看到了这个错误的解决办法，原文如下：
The scheduling guide isn't a web app so you probably have some mouldy stuff in your pom.xml from the REST guide? If you follow the instructions closely it should work. Another potential issue with the code you posted above is that your @EnableAutoConfiguration class is not used in the context, only as a main method (which may not be a problem for the scheduling guide but it probably is for a bunch of others).
这里，添加了一个@EnableAutoConfiguration注解来解决问题。
参考文档：
https://blog.csdn.net/u010429286/article/details/52636753
http://stackoverflow.com/questions/21783391/spring-boot-unable-to-start-embeddedwebapplicationcontext-due-to-missing-embedd
