I have a Spring Boot library that adds autoconfiguration. I am already using @ConditionalOnClass successfully to only activate parts of the library if Spring Security is on the classpath for example.
Currently, my library requires spring-boot-starter-validation as a dependency, and I would like to make this optional. I added @ConditionalOnClass like this:
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@Bean @ConditionalOnClass(name = "javax.validation.ConstraintViolationException") public ConstraintViolationApiExceptionHandler constraintViolationApiExceptionHandler(ErrorHandlingProperties properties, HttpStatusMapper httpStatusMapper, ErrorCodeMapper errorCodeMapper, ErrorMessageMapper errorMessageMapper) { return new ConstraintViolationApiExceptionHandler(properties, httpStatusMapper, errorCodeMapper, errorMessageMapper); }But when running in an application, I get this error:
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2022-03-26 11:00:14.028 ERROR 3171 --- [ main] o.s.boot.SpringApplication : Application run failedorg.springframework.beans.factory.BeanCreationException: Error creating bean with name 'httpHandler' defined in class path resource [org/springframework/boot/autoconfigure/web/reactive/HttpHandlerAutoConfiguration$AnnotationConfig.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.http.server.reactive.HttpHandler]: Factory method 'httpHandler' threw exception; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'globalErrorWebExceptionHandler' defined in class path resource [io/github/wimdeblauwe/errorhandlingspringbootstarter/ReactiveErrorHandlingConfiguration.class]: Unsatisfied dependency expressed through method 'globalErrorWebExceptionHandler' parameter 7; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'constraintViolationApiExceptionHandler' defined in class path resource [io/github/wimdeblauwe/errorhandlingspringbootstarter/ReactiveErrorHandlingConfiguration.class]: Post-processing of merged bean definition failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [io.github.wimdeblauwe.errorhandlingspringbootstarter.handler.ConstraintViolationApiExceptionHandler] from ClassLoader [jdk.internal.loader.ClassLoaders$AppClassLoader@251a69d7] at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:658) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:638) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1352) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1195) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:953) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:918) ~[spring-context-5.3.16.jar:5.3.16] at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.16.jar:5.3.16] at org.springframework.boot.web.reactive.context.ReactiveWebServerApplicationContext.refresh(ReactiveWebServerApplicationContext.java:64) ~[spring-boot-2.6.4.jar:2.6.4] at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:740) ~[spring-boot-2.6.4.jar:2.6.4] at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:415) ~[spring-boot-2.6.4.jar:2.6.4] at org.springframework.boot.SpringApplication.run(SpringApplication.java:303) ~[spring-boot-2.6.4.jar:2.6.4] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1312) ~[spring-boot-2.6.4.jar:2.6.4] at org.springframework.boot.SpringApplication.run(SpringApplication.java:1301) ~[spring-boot-2.6.4.jar:2.6.4] at com.wimdeblauwe.examples.reactiveerrorhandling.ReactiveErrorHandlingApplication.main(ReactiveErrorHandlingApplication.java:10) ~[classes/:na]Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [org.springframework.http.server.reactive.HttpHandler]: Factory method 'httpHandler' threw exception; nested exception is org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'globalErrorWebExceptionHandler' defined in class path resource [io/github/wimdeblauwe/errorhandlingspringbootstarter/ReactiveErrorHandlingConfiguration.class]: Unsatisfied dependency expressed through method 'globalErrorWebExceptionHandler' parameter 7; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'constraintViolationApiExceptionHandler' defined in class path resource [io/github/wimdeblauwe/errorhandlingspringbootstarter/ReactiveErrorHandlingConfiguration.class]: Post-processing of merged bean definition failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [io.github.wimdeblauwe.errorhandlingspringbootstarter.handler.ConstraintViolationApiExceptionHandler] from ClassLoader [jdk.internal.loader.ClassLoaders$AppClassLoader@251a69d7] at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:653) ~[spring-beans-5.3.16.jar:5.3.16] 19 common frames omittedCaused by: org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'globalErrorWebExceptionHandler' defined in class path resource [io/github/wimdeblauwe/errorhandlingspringbootstarter/ReactiveErrorHandlingConfiguration.class]: Unsatisfied dependency expressed through method 'globalErrorWebExceptionHandler' parameter 7; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'constraintViolationApiExceptionHandler' defined in class path resource [io/github/wimdeblauwe/errorhandlingspringbootstarter/ReactiveErrorHandlingConfiguration.class]: Post-processing of merged bean definition failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [io.github.wimdeblauwe.errorhandlingspringbootstarter.handler.ConstraintViolationApiExceptionHandler] from ClassLoader [jdk.internal.loader.ClassLoaders$AppClassLoader@251a69d7] at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:800) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:541) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1352) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1195) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:582) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.DefaultListableBeanFactory$1.orderedStream(DefaultListableBeanFactory.java:481) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.web.server.adapter.WebHttpHandlerBuilder.applicationContext(WebHttpHandlerBuilder.java:178) ~[spring-web-5.3.16.jar:5.3.16] at org.springframework.boot.autoconfigure.web.reactive.HttpHandlerAutoConfiguration$AnnotationConfig.httpHandler(HttpHandlerAutoConfiguration.java:65) ~[spring-boot-autoconfigure-2.6.4.jar:2.6.4] at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na] at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:77) ~[na:na] at java.base/jdk.internal.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:na] at java.base/java.lang.reflect.Method.invoke(Method.java:568) ~[na:na] at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.3.16.jar:5.3.16] 20 common frames omittedCaused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'constraintViolationApiExceptionHandler' defined in class path resource [io/github/wimdeblauwe/errorhandlingspringbootstarter/ReactiveErrorHandlingConfiguration.class]: Post-processing of merged bean definition failed; nested exception is java.lang.IllegalStateException: Failed to introspect Class [io.github.wimdeblauwe.errorhandlingspringbootstarter.handler.ConstraintViolationApiExceptionHandler] from ClassLoader [jdk.internal.loader.ClassLoaders$AppClassLoader@251a69d7] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:597) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:542) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.DefaultListableBeanFactory.addCandidateEntry(DefaultListableBeanFactory.java:1607) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.DefaultListableBeanFactory.findAutowireCandidates(DefaultListableBeanFactory.java:1571) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveMultipleBeans(DefaultListableBeanFactory.java:1460) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1347) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1309) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:887) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:791) ~[spring-beans-5.3.16.jar:5.3.16] 37 common frames omittedCaused by: java.lang.IllegalStateException: Failed to introspect Class [io.github.wimdeblauwe.errorhandlingspringbootstarter.handler.ConstraintViolationApiExceptionHandler] from ClassLoader [jdk.internal.loader.ClassLoaders$AppClassLoader@251a69d7] at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:485) ~[spring-core-5.3.16.jar:5.3.16] at org.springframework.util.ReflectionUtils.doWithLocalMethods(ReflectionUtils.java:321) ~[spring-core-5.3.16.jar:5.3.16] at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.buildLifecycleMetadata(InitDestroyAnnotationBeanPostProcessor.java:232) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.findLifecycleMetadata(InitDestroyAnnotationBeanPostProcessor.java:210) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.annotation.InitDestroyAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(InitDestroyAnnotationBeanPostProcessor.java:149) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.context.annotation.CommonAnnotationBeanPostProcessor.postProcessMergedBeanDefinition(CommonAnnotationBeanPostProcessor.java:305) ~[spring-context-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyMergedBeanDefinitionPostProcessors(AbstractAutowireCapableBeanFactory.java:1116) ~[spring-beans-5.3.16.jar:5.3.16] at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:594) ~[spring-beans-5.3.16.jar:5.3.16] 50 common frames omittedCaused by: java.lang.NoClassDefFoundError: javax/validation/ConstraintViolation at java.base/java.lang.Class.getDeclaredMethods0(Native Method) ~[na:na] at java.base/java.lang.Class.privateGetDeclaredMethods(Class.java:3402) ~[na:na] at java.base/java.lang.Class.getDeclaredMethods(Class.java:2504) ~[na:na] at org.springframework.util.ReflectionUtils.getDeclaredMethods(ReflectionUtils.java:467) ~[spring-core-5.3.16.jar:5.3.16] 57 common frames omittedCaused by: java.lang.ClassNotFoundException: javax.validation.ConstraintViolation at java.base/jdk.internal.loader.BuiltinClassLoader.loadClass(BuiltinClassLoader.java:641) ~[na:na] at java.base/jdk.internal.loader.ClassLoaders$AppClassLoader.loadClass(ClassLoaders.java:188) ~[na:na] at java.base/java.lang.ClassLoader.loadClass(ClassLoader.java:520) ~[na:na] 61 common frames omittedAdvertisement
Answer
I think you have to put @ConditionalOnClass on the class level. Otherwise Spring Boot still has to load the configuration class to analyze it and this will fail if not all dependencies are on the classpath. If you put @ConditionalOnClass on the configuration class instead, Spring Boot can read this information without actually loading the class and skip class loading if the class declared in @ConditionalOnClass is not on the classpath.
In this case you could even reference the real class in @ConditionalOnClass instead of the class name as string. Just make sure that your dependency is optional so that it’s not included as transitive dependency of your library.
By the way, this was the short answer. The long version can be found here: https://youtu.be/N39hpGAT43s 😉 I really like this presentation. Learned a lot from it.