问题如下：

2021-01-08 16:12:23.936  WARN 12420 --- [           main] ConfigServletWebServerApplicationContext : Exception encountered during context initialization - cancelling refresh attempt: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'documentationPluginsBootstrapper' defined in URL [jar:file:/D:/Maven/apache-maven-3.6.3/repository/io/springfox/springfox-spring-web/2.9.2/springfox-spring-web-2.9.2.jar!/springfox/documentation/spring/web/plugins/DocumentationPluginsBootstrapper.class]: Unsatisfied dependency expressed through constructor parameter 1; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'webMvcRequestHandlerProvider' defined in URL [jar:file:/D:/Maven/apache-maven-3.6.3/repository/io/springfox/springfox-spring-web/2.9.2/springfox-spring-web-2.9.2.jar!/springfox/documentation/spring/web/plugins/WebMvcRequestHandlerProvider.class]: Unsatisfied dependency expressed through constructor parameter 1; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'requestMappingHandlerMapping' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Unsatisfied dependency expressed through method 'requestMappingHandlerMapping' parameter 2; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mvcResourceUrlProvider' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.resource.ResourceUrlProvider]: Factory method 'mvcResourceUrlProvider' threw exception; nested exception is java.lang.NoSuchFieldError: defaultInstance
Related cause: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'requestMappingHandlerMapping' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Unsatisfied dependency expressed through method 'requestMappingHandlerMapping' parameter 2; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mvcResourceUrlProvider' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.resource.ResourceUrlProvider]: Factory method 'mvcResourceUrlProvider' threw exception; nested exception is java.lang.NoSuchFieldError: defaultInstance
2021-01-08 16:12:23.939  INFO 12420 --- [           main] o.apache.catalina.core.StandardService   : Stopping service [Tomcat]
2021-01-08 16:12:23.946  INFO 12420 --- [           main] ConditionEvaluationReportLoggingListener : 

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-01-08 16:12:23.957 ERROR 12420 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'documentationPluginsBootstrapper' defined in URL [jar:file:/D:/Maven/apache-maven-3.6.3/repository/io/springfox/springfox-spring-web/2.9.2/springfox-spring-web-2.9.2.jar!/springfox/documentation/spring/web/plugins/DocumentationPluginsBootstrapper.class]: Unsatisfied dependency expressed through constructor parameter 1; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'webMvcRequestHandlerProvider' defined in URL [jar:file:/D:/Maven/apache-maven-3.6.3/repository/io/springfox/springfox-spring-web/2.9.2/springfox-spring-web-2.9.2.jar!/springfox/documentation/spring/web/plugins/WebMvcRequestHandlerProvider.class]: Unsatisfied dependency expressed through constructor parameter 1; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'requestMappingHandlerMapping' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Unsatisfied dependency expressed through method 'requestMappingHandlerMapping' parameter 2; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mvcResourceUrlProvider' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.resource.ResourceUrlProvider]: Factory method 'mvcResourceUrlProvider' threw exception; nested exception is java.lang.NoSuchFieldError: defaultInstance
	......
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'webMvcRequestHandlerProvider' defined in URL [jar:file:/D:/Maven/apache-maven-3.6.3/repository/io/springfox/springfox-spring-web/2.9.2/springfox-spring-web-2.9.2.jar!/springfox/documentation/spring/web/plugins/WebMvcRequestHandlerProvider.class]: Unsatisfied dependency expressed through constructor parameter 1; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'requestMappingHandlerMapping' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Unsatisfied dependency expressed through method 'requestMappingHandlerMapping' parameter 2; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mvcResourceUrlProvider' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.resource.ResourceUrlProvider]: Factory method 'mvcResourceUrlProvider' threw exception; nested exception is java.lang.NoSuchFieldError: defaultInstance
	......
Caused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'requestMappingHandlerMapping' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Unsatisfied dependency expressed through method 'requestMappingHandlerMapping' parameter 2; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mvcResourceUrlProvider' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.resource.ResourceUrlProvider]: Factory method 'mvcResourceUrlProvider' threw exception; nested exception is java.lang.NoSuchFieldError: defaultInstance
	......
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'mvcResourceUrlProvider' defined in class path resource [org/springframework/boot/autoconfigure/web/servlet/WebMvcAutoConfiguration$EnableWebMvcConfiguration.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.resource.ResourceUrlProvider]: Factory method 'mvcResourceUrlProvider' threw exception; nested exception is java.lang.NoSuchFieldError: defaultInstance
	......
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.web.servlet.resource.ResourceUrlProvider]: Factory method 'mvcResourceUrlProvider' threw exception; nested exception is java.lang.NoSuchFieldError: defaultInstance
	.....
Caused by: java.lang.NoSuchFieldError: defaultInstance
	.....

可能存在的问题如下：
① controller的接口地址有重复(比如两个接口都是“/api”)，修改为不同的接口名称。
② 检查pom.xml依赖是否有重复(我的问题所在，有两个web)，去掉下面那个。