【问题】java.lang.ClassNotFoundException: org.apache.log4j.Logger异常问题引发的思考

文章目录1.问题描述2.分析原因3.问题解决方案一：结合Slf4j合并springboot默认自带日志框架(logback)方案二：保留filter中的log4j不变，引入其依赖即可4.知识拓展4.代码示例1.问题描述在使用springboot整合mybatis的时候，启动项目，出现如下问题。我们先观察下，主要的问题点：java.lang.ClassNotFoundException: org.a

你好洋一

13334人浏览 · 2021-04-02 00:35:37

你好洋一 · 2021-04-02 00:35:37 发布

文章目录

1.问题描述

在使用springboot整合mybatis的时候，启动项目，出现如下问题。我们先观察下，主要的问题点：

java.lang.ClassNotFoundException: org.apache.log4j.Logger
Failed to instantiate [javax.sql.DataSource]: Factory method ‘dataSource’ threw exception; nested exception is java.lang.NoClassDefFoundError: org/apache/log4j/Logger
Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name ‘dataSource’ defined in class path resource [com/daobili/config/DruidConfig.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.sql.DataSource]: Factory method ‘dataSource’ threw exception; nested exception is java.lang.NoClassDefFoundError: org/apache/log4j/Logger

Error starting ApplicationContext. To display the conditions report re-run your application with 'debug' enabled.
2021-04-01 22:54:10.326 ERROR 2201 --- [           main] o.s.boot.SpringApplication               : Application run failed

org.springframework.beans.factory.UnsatisfiedDependencyException: Error creating bean with name 'org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaConfiguration': Unsatisfied dependency expressed through constructor parameter 0; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [com/daobili/config/DruidConfig.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.sql.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.NoClassDefFoundError: org/apache/log4j/Logger
	at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:800) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.ConstructorResolver.autowireConstructor(ConstructorResolver.java:229) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.autowireConstructor(AbstractAutowireCapableBeanFactory.java:1354) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1204) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:564) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:524) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:410) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1334) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1177) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:564) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:524) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.context.support.AbstractApplicationContext.getBean(AbstractApplicationContext.java:1154) ~[spring-context-5.3.5.jar:5.3.5]
	at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:908) ~[spring-context-5.3.5.jar:5.3.5]
	at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:583) ~[spring-context-5.3.5.jar:5.3.5]
	at org.springframework.boot.web.servlet.context.ServletWebServerApplicationContext.refresh(ServletWebServerApplicationContext.java:144) ~[spring-boot-2.4.4.jar:2.4.4]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:769) [spring-boot-2.4.4.jar:2.4.4]
	at org.springframework.boot.SpringApplication.refresh(SpringApplication.java:761) [spring-boot-2.4.4.jar:2.4.4]
	at org.springframework.boot.SpringApplication.refreshContext(SpringApplication.java:426) [spring-boot-2.4.4.jar:2.4.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:326) [spring-boot-2.4.4.jar:2.4.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1313) [spring-boot-2.4.4.jar:2.4.4]
	at org.springframework.boot.SpringApplication.run(SpringApplication.java:1302) [spring-boot-2.4.4.jar:2.4.4]
	at com.daobili.SpringbootMybatisApplication.main(SpringbootMybatisApplication.java:21) [classes/:na]
Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in class path resource [com/daobili/config/DruidConfig.class]: Bean instantiation via factory method failed; nested exception is org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.sql.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.NoClassDefFoundError: org/apache/log4j/Logger
	at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:658) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.ConstructorResolver.instantiateUsingFactoryMethod(ConstructorResolver.java:486) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.instantiateUsingFactoryMethod(AbstractAutowireCapableBeanFactory.java:1334) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBeanInstance(AbstractAutowireCapableBeanFactory.java:1177) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:564) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:524) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:335) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:234) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:333) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:208) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.config.DependencyDescriptor.resolveCandidate(DependencyDescriptor.java:276) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:1380) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:1300) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.ConstructorResolver.resolveAutowiredArgument(ConstructorResolver.java:887) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.ConstructorResolver.createArgumentArray(ConstructorResolver.java:791) ~[spring-beans-5.3.5.jar:5.3.5]
	... 29 common frames omitted
Caused by: org.springframework.beans.BeanInstantiationException: Failed to instantiate [javax.sql.DataSource]: Factory method 'dataSource' threw exception; nested exception is java.lang.NoClassDefFoundError: org/apache/log4j/Logger
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:185) ~[spring-beans-5.3.5.jar:5.3.5]
	at org.springframework.beans.factory.support.ConstructorResolver.instantiate(ConstructorResolver.java:653) ~[spring-beans-5.3.5.jar:5.3.5]
	... 43 common frames omitted
Caused by: java.lang.NoClassDefFoundError: org/apache/log4j/Logger
	at com.alibaba.druid.filter.logging.Log4jFilter.<init>(Log4jFilter.java:26) ~[druid-1.1.10.jar:1.1.10]
	at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[na:1.8.0_191]
	at sun.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:62) ~[na:1.8.0_191]
	at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45) ~[na:1.8.0_191]
	at java.lang.reflect.Constructor.newInstance(Constructor.java:423) ~[na:1.8.0_191]
	at java.lang.Class.newInstance(Class.java:442) ~[na:1.8.0_191]
	at com.alibaba.druid.filter.FilterManager.loadFilter(FilterManager.java:124) ~[druid-1.1.10.jar:1.1.10]
	at com.alibaba.druid.pool.DruidAbstractDataSource.addFilters(DruidAbstractDataSource.java:1325) ~[druid-1.1.10.jar:1.1.10]
	at com.alibaba.druid.pool.DruidAbstractDataSource.setFilters(DruidAbstractDataSource.java:1314) ~[druid-1.1.10.jar:1.1.10]
	at com.daobili.config.DruidConfig.dataSource(DruidConfig.java:120) ~[classes/:na]
	at com.daobili.config.DruidConfig$$EnhancerBySpringCGLIB$$3997f063.CGLIB$dataSource$0(<generated>) ~[classes/:na]
	at com.daobili.config.DruidConfig$$EnhancerBySpringCGLIB$$3997f063$$FastClassBySpringCGLIB$$456c75a7.invoke(<generated>) ~[classes/:na]
	at org.springframework.cglib.proxy.MethodProxy.invokeSuper(MethodProxy.java:244) ~[spring-core-5.3.5.jar:5.3.5]
	at org.springframework.context.annotation.ConfigurationClassEnhancer$BeanMethodInterceptor.intercept(ConfigurationClassEnhancer.java:331) ~[spring-context-5.3.5.jar:5.3.5]
	at com.daobili.config.DruidConfig$$EnhancerBySpringCGLIB$$3997f063.dataSource(<generated>) ~[classes/:na]
	at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) ~[na:1.8.0_191]
	at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62) ~[na:1.8.0_191]
	at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) ~[na:1.8.0_191]
	at java.lang.reflect.Method.invoke(Method.java:498) ~[na:1.8.0_191]
	at org.springframework.beans.factory.support.SimpleInstantiationStrategy.instantiate(SimpleInstantiationStrategy.java:154) ~[spring-beans-5.3.5.jar:5.3.5]
	... 44 common frames omitted
Caused by: java.lang.ClassNotFoundException: org.apache.log4j.Logger
	at java.net.URLClassLoader.findClass(URLClassLoader.java:382) ~[na:1.8.0_191]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:424) ~[na:1.8.0_191]
	at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:349) ~[na:1.8.0_191]
	at java.lang.ClassLoader.loadClass(ClassLoader.java:357) ~[na:1.8.0_191]
	... 64 common frames omitted

2.分析原因

这个问题很明显，说的意思是我们在配置数据源的时候需要log4j，但是我们没有引入它。那么问题来了,我们在哪里要求说，我需要你log4j。

通过查druid数据源连接池配置看到：

spring.datasource.filters=stat,wall,log4j

可以发现，我们在配置数据源的时候使用log4j。

3.问题解决

找到问题的出错点，我们就来解决它，我们可以看看druid框架中都能支持哪些日志框架的使用。如下图：

在这里插入图片描述

druid通过log4j跟slf4j进行绑定一起使用，我们知道springboot中默认自带的日志框架是logback。

了解slf4j、log4j、logback的关系

slf4j是日志框架的抽象(类似我们java提供一个通用的接口，但是具体通过什么方式实现，就有你来决定)，所有log4j和logback是日志框架具体的实现。

log4j和logback可以单独使用，调用自己的框架来按照自己的方式输出即可；
log4j和logback通过绑定slf4j，调用通用的api进行标准输出；

方案一：结合Slf4j合并springboot默认自带日志框架(logback)

因为，我们知道springboot默认支持logback日志框架，所以我们将数据库连接池中filter修改为slf4j可解决问题。

spring.datasource.filters=stat,wall,slf4j

方案二：保留filter中的log4j不变，引入其依赖即可

spring.datasource.filters=stat,wall,log4j

引入log4j依赖

<dependency>
    <groupId>log4j</groupId>
    <artifactId>log4j</artifactId>
    <version>1.2.17</version>
</dependency>

4.知识拓展

log4j跟slf4j如何进行绑定？
如果刚才你细心的话，会发现其实druid的pom文件中已经给我们做了很好的解答。

在这里插入图片描述

我们需要引入依赖：

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>1.7.9</version>
</dependency>

<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-log4j12</artifactId>
    <version>1.7.9</version>
</dependency>

<dependency>
   <groupId>org.apache.logging.log4j</groupId>
   <artifactId>log4j-api</artifactId>
   <version>2.5</version>
</dependency>

<dependency>             <groupId>org.apache.logging.log4j</groupId>
  <artifactId>log4j-core</artifactId>
  <version>2.5</version>
  <scope>provided</scope>
</dependency>