mybatis-spring 启动报错ClassNotFoundException ${jdbc.driverClassName}

昨天按照mybatis-spring官网教程，将mybatis-spring整合到原来的spring-jdbc项目，启动时报错ClassNotFoundException

严重: dataSource init error
java.sql.SQLException: ${slave.jdbc.driverClassName}
    at com.alibaba.druid.util.JdbcUtils.createDriver(JdbcUtils.java:520)
    at com.alibaba.druid.pool.DruidDataSource.init(DruidDataSource.java:583)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeCustomInitMethod(AbstractAutowireCapableBeanFactory.java:1833)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1776)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1704)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:581)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503)
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:367)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:110)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.lambda$resolveManagedMap$1(BeanDefinitionValueResolver.java:426)
    at java.util.LinkedHashMap.forEach(LinkedHashMap.java:684)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveManagedMap(BeanDefinitionValueResolver.java:424)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:167)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1611)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1363)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:580)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503)
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:367)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:110)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1611)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1363)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:580)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503)
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:199)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:367)
    at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:110)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1611)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1363)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:580)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:503)
    at org.springframework.beans.factory.support.AbstractBeanFactory.lambda$doGetBean$0(AbstractBeanFactory.java:317)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:315)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:204)
    at org.springframework.context.support.PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(PostProcessorRegistrationDelegate.java:116)
    at org.springframework.context.support.AbstractApplicationContext.invokeBeanFactoryPostProcessors(AbstractApplicationContext.java:694)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:532)
    at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext(ContextLoader.java:409)
    at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:291)
    at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:103)
    at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:4643)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5109)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:742)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:718)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:703)
    at org.apache.catalina.startup.HostConfig.deployDirectory(HostConfig.java:1141)
    at org.apache.catalina.startup.HostConfig$DeployDirectory.run(HostConfig.java:1876)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:511)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)
    at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:112)
    at org.apache.catalina.startup.HostConfig.deployDirectories(HostConfig.java:1053)
    at org.apache.catalina.startup.HostConfig.deployApps(HostConfig.java:428)
    at org.apache.catalina.startup.HostConfig.start(HostConfig.java:1585)
    at org.apache.catalina.startup.HostConfig.lifecycleEvent(HostConfig.java:308)
    at org.apache.catalina.util.LifecycleBase.
fireLifecycleEvent(LifecycleBase.java:123)
    at org.apache.catalina.util.LifecycleBase.setStateInternal(LifecycleBase.java:424)
    at org.apache.catalina.util.LifecycleBase.setState(LifecycleBase.java:367)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:966)
    at org.apache.catalina.core.StandardHost.startInternal(StandardHost.java:839)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1427)
    at org.apache.catalina.core.ContainerBase$StartChild.call(ContainerBase.java:1417)
    at java.util.concurrent.FutureTask.run(FutureTask.java:266)
    at org.apache.tomcat.util.threads.InlineExecutorService.execute(InlineExecutorService.java:75)
    at java.util.concurrent.AbstractExecutorService.submit(AbstractExecutorService.java:134)
    at org.apache.catalina.core.ContainerBase.startInternal(ContainerBase.java:943)
    at org.apache.catalina.core.StandardEngine.startInternal(StandardEngine.java:258)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
    at org.apache.catalina.core.StandardService.startInternal(StandardService.java:422)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
    at org.apache.catalina.core.StandardServer.startInternal(StandardServer.java:770)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:183)
    at org.apache.catalina.startup.Catalina.start(Catalina.java:682)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:498)
    at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:350)
    at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:492)
Caused by: java.lang.ClassNotFoundException: ${slave.jdbc.driverClassName}
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1309)
    at org.apache.catalina.loader.WebappClassLoaderBase.loadClass(WebappClassLoaderBase.java:1138)
    at java.lang.Class.forName0(Native Method)
    at java.lang.Class.forName(Class.java:264)
    at com.alibaba.druid.util.JdbcUtils.createDriver(JdbcUtils.java:518)
    ... 95 more

看样子是加载不了properties里面的值

项目中applicationContext.xml的mybatis是如下配置

　　<bean id="dataSource" class="com.ace.common.DynamicDataSource">
        <property name="targetDataSources">
            <map>
                <entry key="slave" value-ref="slaveDataSource" />
            </map>
        </property>
        <property name="defaultTargetDataSource" ref="masterDataSource" />
    </bean>
    
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
      <property name="dataSource" ref="dataSource" />
      <property name="mapperLocations" value="classpath*:com/ace/mapper/*.xml" />
    </bean>
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
      <property name="basePackage" value="com.ace.dao" />
      <property name="sqlSessionFactoryBeanName" ref="sqlSessionFactory" />
    </bean>
    

在slaveDataSource配置中使用了properties中的值，这里没有加载进去。

参考了网上的很多方法，例如是否多加了空格造成的问题，还是使用了MapperScannerConfigurer过时的SqlSessionFactory属性，发现都不是。

在和官网一一对照代码时发现，在上面的MapperScannerConfigurer配置中指定SqlSessionFactoryName时使用了ref而不是value，改为value之后完美解决了此问题。

因为自己刚入手java和spring，对bean的理解不够。ref的作用是将目标bean定义的实例注入到属性或构造器中，一般作用于对象类型，而SqlSessionFactoryName是字符串类型，应该使用value。

上面就是过早的实例化SqlSessionFactory，然后在还没导入properties值时实例化dataSource时导致的错误。

关于使用SqlSessionFactoryName而不使用SqlSessionFactory可以参考传送门

官网有MapperScannerConfigurer的使用说明，自己没有看仔细，官网介绍如下

 

关于java中bean的用法还需要仔细研究才行。