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在 Spring Boot 2.0.6.RELEASE 及之前的版本中，如果使用了 JPA 可能会在启动应用时出现一个 NullPointerException 导致启动失败，详细信息类似于这样
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'entityManagerFactory' defined in class path resource [org/springframework/boot/autoconfigure/orm/jpa/HibernateJpaConfiguration.class]: Invocation of init method failed; nested exception is javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory; nested exception is org.hibernate.MappingException: Could not get constructor for org.hibernate.persister.entity.SingleTableEntityPersister
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1694) ~[spring-beans-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:573) ~[spring-beans-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:495) ~[spring-beans-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317) ~[spring-beans-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222) ~[spring-beans-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315) ~[spring-beans-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199) ~[spring-beans-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1087) ~[spring-context-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:857) ~[spring-context-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:548) ~[spring-context-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:140) ~[spring-boot-2.0.6.RELEASE.jar:2.0.6.RELEASE]
at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:754) ~[spring-boot-2.0.6.RELEASE.jar:2.0.6.RELEASE]
at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:386) ~[spring-boot-2.0.6.RELEASE.jar:2.0.6.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:307) ~[spring-boot-2.0.6.RELEASE.jar:2.0.6.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1242) ~[spring-boot-2.0.6.RELEASE.jar:2.0.6.RELEASE]
at org.springframework.boot.SpringApplication.run(SpringApplication.java:1230) ~[spring-boot-2.0.6.RELEASE.jar:2.0.6.RELEASE]
at org.demo.DemoApplication.main(DemoApplication.java:12) ~[classes/:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[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:566) ~[na:na]
at org.springframework.boot.devtools.restart.RestartLauncher.run(RestartLauncher.java:49) ~[spring-boot-devtools-2.0.6.RELEASE.jar:2.0.6.RELEASE]
Caused by: javax.persistence.PersistenceException: [PersistenceUnit: default] Unable to build Hibernate SessionFactory; nested exception is org.hibernate.MappingException: Could not get constructor for org.hibernate.persister.entity.SingleTableEntityPersister
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:402) ~[spring-orm-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.afterPropertiesSet(AbstractEntityManagerFactoryBean.java:377) ~[spring-orm-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.afterPropertiesSet(LocalContainerEntityManagerFactoryBean.java:341) ~[spring-orm-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1753) ~[spring-beans-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1690) ~[spring-beans-5.0.10.RELEASE.jar:5.0.10.RELEASE]
... 21 common frames omitted
Caused by: org.hibernate.MappingException: Could not get constructor for org.hibernate.persister.entity.SingleTableEntityPersister
at org.hibernate.persister.internal.PersisterFactoryImpl.createEntityPersister(PersisterFactoryImpl.java:123) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.persister.internal.PersisterFactoryImpl.createEntityPersister(PersisterFactoryImpl.java:77) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.metamodel.internal.MetamodelImpl.initialize(MetamodelImpl.java:129) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.internal.SessionFactoryImpl.(SessionFactoryImpl.java:300) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.boot.internal.SessionFactoryBuilderImpl.build(SessionFactoryBuilderImpl.java:462) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.jpa.boot.internal.EntityManagerFactoryBuilderImpl.build(EntityManagerFactoryBuilderImpl.java:892) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.springframework.orm.jpa.vendor.SpringHibernateJpaPersistenceProvider.createContainerEntityManagerFactory(SpringHibernateJpaPersistenceProvider.java:57) ~[spring-orm-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean.createNativeEntityManagerFactory(LocalContainerEntityManagerFactoryBean.java:365) ~[spring-orm-5.0.10.RELEASE.jar:5.0.10.RELEASE]
at org.springframework.orm.jpa.AbstractEntityManagerFactoryBean.buildNativeEntityManagerFactory(AbstractEntityManagerFactoryBean.java:390) ~[spring-orm-5.0.10.RELEASE.jar:5.0.10.RELEASE]
... 25 common frames omitted
Caused by: org.hibernate.HibernateException: Unable to instantiate default tuplizer [org.hibernate.tuple.entity.PojoEntityTuplizer]
at org.hibernate.tuple.entity.EntityTuplizerFactory.constructTuplizer(EntityTuplizerFactory.java:91) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.tuple.entity.EntityTuplizerFactory.constructDefaultTuplizer(EntityTuplizerFactory.java:116) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.tuple.entity.EntityMetamodel.(EntityMetamodel.java:382) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.persister.entity.AbstractEntityPersister.(AbstractEntityPersister.java:519) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.persister.entity.SingleTableEntityPersister.(SingleTableEntityPersister.java:124) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:na]
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490) ~[na:na]
at org.hibernate.persister.internal.PersisterFactoryImpl.createEntityPersister(PersisterFactoryImpl.java:96) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
... 33 common frames omitted
Caused by: java.lang.reflect.InvocationTargetException: null
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:na]
at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:na]
at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:na]
at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:490) ~[na:na]
at org.hibernate.tuple.entity.EntityTuplizerFactory.constructTuplizer(EntityTuplizerFactory.java:88) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
... 42 common frames omitted
Caused by: java.lang.NullPointerException: null
at javassist.util.proxy.SecurityActions.setAccessible(SecurityActions.java:103) ~[javassist-3.22.0-GA.jar:na]
at javassist.util.proxy.DefineClassHelper.toClass3(DefineClassHelper.java:151) ~[javassist-3.22.0-GA.jar:na]
at javassist.util.proxy.DefineClassHelper.toClass2(DefineClassHelper.java:134) ~[javassist-3.22.0-GA.jar:na]
at javassist.util.proxy.DefineClassHelper.toClass(DefineClassHelper.java:95) ~[javassist-3.22.0-GA.jar:na]
at javassist.util.proxy.FactoryHelper.toClass(FactoryHelper.java:131) ~[javassist-3.22.0-GA.jar:na]
at javassist.util.proxy.ProxyFactory.createClass3(ProxyFactory.java:530) ~[javassist-3.22.0-GA.jar:na]
at javassist.util.proxy.ProxyFactory.createClass2(ProxyFactory.java:515) ~[javassist-3.22.0-GA.jar:na]
at javassist.util.proxy.ProxyFactory.createClass1(ProxyFactory.java:451) ~[javassist-3.22.0-GA.jar:na]
at javassist.util.proxy.ProxyFactory.createClass(ProxyFactory.java:422) ~[javassist-3.22.0-GA.jar:na]
at org.hibernate.proxy.pojo.javassist.JavassistProxyFactory.postInstantiate(JavassistProxyFactory.java:75) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.tuple.entity.PojoEntityTuplizer.buildProxyFactory(PojoEntityTuplizer.java:162) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.tuple.entity.AbstractEntityTuplizer.(AbstractEntityTuplizer.java:156) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
at org.hibernate.tuple.entity.PojoEntityTuplizer.(PojoEntityTuplizer.java:58) ~[hibernate-core-5.2.17.Final.jar:5.2.17.Final]
... 47 common frames omitted
可以很轻易看到很多 javassist 相关的内容。这个 BUG 由低版本的 javassist 库引起，在 Spring Boot 2.1.0.RELEASE 中修复了这个问题，如果可以升级，推荐升级到最新版本的 Spring Boot 解决。如果无法升级版本，可以显式引入新版的 javassist 依赖即可
org.javassist
javassist
3.23.1-GA