Caused by: java.lang.ClassNotFoundException: javax.validation.constraints.Size

完整报错如下：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sizePlugin' defined in class path resource [springfox/bean/validators/configuration/BeanValidatorPluginsConfiguration.class]: Post-processing of merged bean definition failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [springfox.bean.validators.plugins.schema.SizeAnnotationPlugin] from ClassLoader [sun.misc.Launcher$AppClassLoader@18b4aac2]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:571) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:516) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:324) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:322) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:202) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:897) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:879) ~[spring-context-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:551) ~[spring-context-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:143) ~[spring-boot-2.3.7.RELEASE.jar:2.3.7.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:758) [spring-boot-2.3.7.RELEASE.jar:2.3.7.RELEASE]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:750) [spring-boot-2.3.7.RELEASE.jar:2.3.7.RELEASE]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:405) [spring-boot-2.3.7.RELEASE.jar:2.3.7.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:315) [spring-boot-2.3.7.RELEASE.jar:2.3.7.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1237) [spring-boot-2.3.7.RELEASE.jar:2.3.7.RELEASE]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1226) [spring-boot-2.3.7.RELEASE.jar:2.3.7.RELEASE]
	at com.hjt.SystemApplication.main(SystemApplication.java:9) [classes/:na]
Caused by: java.lang.IllegalStateException: Failed to introspect Class [springfox.bean.validators.plugins.schema.SizeAnnotationPlugin] from ClassLoader [sun.misc.Launcher$AppClassLoader@18b4aac2]
	at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:481) ~[spring-core-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.util.ReflectionUtils.doWithLocalMethods(ReflectionUtils.java:321) ~[spring-core-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.buildLifecycleMetadata(InitDestroyAnnotationBeanPostProcessor.java:232) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.findLifecycleMetadata(InitDestroyAnnotationBeanPostProcessor.java:210) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(InitDestroyAnnotationBeanPostProcessor.java:149) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(CommonAnnotationBeanPostProcessor.java:294) ~[spring-context-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyMergedBeanDefinitionPostProcessors(AbstractAutowireCapableBeanFactory.java:1093) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:568) ~[spring-beans-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	... 16 common frames omitted
Caused by: java.lang.NoClassDefFoundError: javax/validation/constraints/Size
	at java.lang.Class.getDeclaredMethods0(Native Method) ~[na:1.8.0_291]
	at java.lang.Class.privateGetDeclaredMethods(Class.java:2701) ~[na:1.8.0_291]
	at java.lang.Class.getDeclaredMethods(Class.java:1975) ~[na:1.8.0_291]
	at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:463) ~[spring-core-5.2.12.RELEASE.jar:5.2.12.RELEASE]
	... 23 common frames omitted
Caused by: java.lang.ClassNotFoundException: javax.validation.constraints.Size
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382) ~[na:1.8.0_291]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:418) ~[na:1.8.0_291]
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:355) ~[na:1.8.0_291]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:351) ~[na:1.8.0_291]
	... 27 common frames omitted

原因分析：没有引入某个类。

解决方案：引入以下依赖即可

   <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-validation</artifactId>
        </dependency>