最近在写商城相关的项目，用到了Swagger2生成RESTAPI文档，启动项目时报错：

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FactoryBean threw exception on object creation; nested exception is java.lang.NullPointerException

具体报错放到后边了。其实就是SpringBoot2与Swagger2版本冲突了（当前SpringBoot版本是2.1.4，Swagger版本是2.2.2），修改成2.7.0即可：

    io.springfox
    springfox-swagger2
    2.7.0


    io.springfox
    springfox-swagger-ui
    2.7.0

具体错误细节：

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2019-05-02 15:50:15.742 ERROR 12312 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'leftItemController': Unsatisfied dependency expressed through field 'userClient'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.pie.shop.api.media.client.UserClient': FactoryBean threw exception on object creation; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:596) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.annotation.InjectionMetadata.inject(InjectionMetadata.java:90) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessProperties(AutowiredAnnotationBeanPostProcessor.java:374) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1411) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:592) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:515) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:320) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:318) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:849) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:877) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:549) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:142) ~[spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
    at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:775) [spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
    at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:397) [spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:316) [spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1260) [spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
    at org.springframework.boot.SpringApplication.run(SpringApplication.java:1248) [spring-boot-2.1.4.RELEASE.jar:2.1.4.RELEASE]
    at com.pie.shop.api.media.MediaApiApplication.main(MediaApiApplication.java:16) [classes/:na]
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'com.pie.shop.api.media.client.UserClient': FactoryBean threw exception on object creation; nested exception is java.lang.NullPointerException
    at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:178) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.getObjectFromFactoryBean(FactoryBeanRegistrySupport.java:101) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getObjectForBeanInstance(AbstractBeanFactory.java:1674) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.getObjectForBeanInstance(AbstractAutowireCapableBeanFactory.java:1249) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:257) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:277) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.addCandidateEntry(DefaultListableBeanFactory.java:1470) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1427) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1210) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1167) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:593) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    ... 19 common frames omitted
Caused by: java.lang.NullPointerException: null
    at springfox.documentation.schema.property.OptimizedModelPropertiesProvider.beanDescription(OptimizedModelPropertiesProvider.java:317) ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.property.OptimizedModelPropertiesProvider.propertiesFor(OptimizedModelPropertiesProvider.java:117) ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.property.OptimizedModelPropertiesProvider$$FastClassBySpringCGLIB$$cb306bb2.invoke() ~[springfox-schema-2.2.2.jar:2.2.2]
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) ~[spring-core-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:749) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:88) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at springfox.documentation.spring.web.caching.CachingAspect.cachedValue(CachingAspect.java:86) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at springfox.documentation.spring.web.caching.CachingAspect.operationsAndProperties(CachingAspect.java:69) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_201]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_201]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_201]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_201]
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:644) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:633) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:70) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:175) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:93) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at springfox.documentation.schema.property.OptimizedModelPropertiesProvider$$EnhancerBySpringCGLIB$$69a5bef1.propertiesFor() ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.ModelDependencyProvider.propertiesFor(ModelDependencyProvider.java:184) ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.ModelDependencyProvider.nonTrivialProperties(ModelDependencyProvider.java:132) ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.ModelDependencyProvider.resolvedPropertiesAndFields(ModelDependencyProvider.java:121) ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.ModelDependencyProvider.resolvedDependencies(ModelDependencyProvider.java:100) ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.ModelDependencyProvider.resolvedTypeParameters(ModelDependencyProvider.java:110) ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.ModelDependencyProvider.resolvedDependencies(ModelDependencyProvider.java:99) ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.ModelDependencyProvider.dependentModels(ModelDependencyProvider.java:62) ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.ModelDependencyProvider$$FastClassBySpringCGLIB$$ac0d0878.invoke() ~[springfox-schema-2.2.2.jar:2.2.2]
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) ~[spring-core-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:749) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.aspectj.MethodInvocationProceedingJoinPoint.proceed(MethodInvocationProceedingJoinPoint.java:88) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at springfox.documentation.spring.web.caching.CachingAspect.cachedValue(CachingAspect.java:86) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at springfox.documentation.spring.web.caching.CachingAspect.modelsAndDependencies(CachingAspect.java:80) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_201]
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_201]
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_201]
    at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_201]
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethodWithGivenArgs(AbstractAspectJAdvice.java:644) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.aspectj.AbstractAspectJAdvice.invokeAdviceMethod(AbstractAspectJAdvice.java:633) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.aspectj.AspectJAroundAdvice.invoke(AspectJAroundAdvice.java:70) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:175) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:93) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at springfox.documentation.schema.ModelDependencyProvider$$EnhancerBySpringCGLIB$$6748c103.dependentModels() ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.DefaultModelProvider.dependencies(DefaultModelProvider.java:113) ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.schema.DefaultModelProvider$$FastClassBySpringCGLIB$$2c8f6146.invoke() ~[springfox-schema-2.2.2.jar:2.2.2]
    at org.springframework.cglib.proxy.MethodProxy.invoke(MethodProxy.java:218) ~[spring-core-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$CglibMethodInvocation.invokeJoinpoint(CglibAopProxy.java:749) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:163) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.interceptor.ExposeInvocationInterceptor.invoke(ExposeInvocationInterceptor.java:93) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.ReflectiveMethodInvocation.proceed(ReflectiveMethodInvocation.java:186) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.aop.framework.CglibAopProxy$DynamicAdvisedInterceptor.intercept(CglibAopProxy.java:688) ~[spring-aop-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at springfox.documentation.schema.DefaultModelProvider$$EnhancerBySpringCGLIB$$882ebc2d.dependencies() ~[springfox-schema-2.2.2.jar:2.2.2]
    at springfox.documentation.spring.web.scanners.ApiModelReader.populateDependencies(ApiModelReader.java:131) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at springfox.documentation.spring.web.scanners.ApiModelReader.read(ApiModelReader.java:75) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at springfox.documentation.spring.web.scanners.ApiListingScanner.scan(ApiListingScanner.java:91) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at springfox.documentation.spring.web.scanners.ApiDocumentationScanner.scan(ApiDocumentationScanner.java:62) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.scanDocumentation(DocumentationPluginsBootstrapper.java:101) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.onApplicationEvent(DocumentationPluginsBootstrapper.java:87) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at springfox.documentation.spring.web.plugins.DocumentationPluginsBootstrapper.onApplicationEvent(DocumentationPluginsBootstrapper.java:50) ~[springfox-spring-web-2.2.2.jar:2.2.2]
    at org.springframework.context.event.SimpleApplicationEventMulticaster.doInvokeListener(SimpleApplicationEventMulticaster.java:172) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.context.event.SimpleApplicationEventMulticaster.invokeListener(SimpleApplicationEventMulticaster.java:165) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.context.event.SimpleApplicationEventMulticaster.multicastEvent(SimpleApplicationEventMulticaster.java:139) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:402) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:408) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.publishEvent(AbstractApplicationContext.java:359) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.finishRefresh(AbstractApplicationContext.java:896) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:552) ~[spring-context-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    at org.springframework.cloud.context.named.NamedContextFactory.createContext(NamedContextFactory.java:136) ~[spring-cloud-context-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.cloud.context.named.NamedContextFactory.getContext(NamedContextFactory.java:101) ~[spring-cloud-context-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.cloud.context.named.NamedContextFactory.getInstance(NamedContextFactory.java:145) ~[spring-cloud-context-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.cloud.openfeign.FeignClientFactoryBean.get(FeignClientFactoryBean.java:220) ~[spring-cloud-openfeign-core-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.cloud.openfeign.FeignClientFactoryBean.feign(FeignClientFactoryBean.java:84) ~[spring-cloud-openfeign-core-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.cloud.openfeign.FeignClientFactoryBean.getTarget(FeignClientFactoryBean.java:257) ~[spring-cloud-openfeign-core-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.cloud.openfeign.FeignClientFactoryBean.getObject(FeignClientFactoryBean.java:247) ~[spring-cloud-openfeign-core-2.1.1.RELEASE.jar:2.1.1.RELEASE]
    at org.springframework.beans.factory.support.FactoryBeanRegistrySupport.doGetObjectFromFactoryBean(FactoryBeanRegistrySupport.java:171) ~[spring-beans-5.1.6.RELEASE.jar:5.1.6.RELEASE]
    ... 30 common frames omitted

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