Mybatis + Spring 時出錯 java.lang.NoClassDefFoundError

一、首先項目中使用的是Mybatis3.2.2 + Spring3.2.2，同時使用了mybatis-spring-1.2.0.jar來做Mybatis與Spring的整合。

二、使用了Mybatis推薦的mapper加載方式：

<!-- mybatis配置 -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="writeDataSource" />
        <property name="mapperLocations" value="classpath*:com/baofoo/admin/dao/**/impl/*Mapper.xml" />
    </bean>
                                                                                                                                                                                         
    <!-- mybatis自動掃描包下的mapper -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.baofoo.admin.dao" />
        <!-- <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" /> -->
    </bean>

值得需要注意的是，在配置MapperScannerConfigurer時，這裏並沒有指定sqlSessionFactoryName以及sqlTemplateName。在沒有指定的情況下，spring就會指定默認的查找規則進行查詢，如分別查找到默認的sqlSessionFactory實現和sqlSessionTemplate實現，並注入到MapperFactoryBean中。

這種配置方式，在一個數據源時，沒有問題，但是在如果存在多個數據源時，上面的配置就存在問題了。在多個數據源時，如果配置不正確，或者配置的步驟不正確，將直接產生莫名奇妙的問題

最初從tomcat啓動一切正常，然後後面突然啓動服務時報出如下異常：

java.lang.NoClassDefFoundError: Could not initialize class org.springframework.beans.factory.BeanCreationException
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:532)
    at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:461)
    at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:295)
    at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:223)
    at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:292)
    at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
    at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:626)
    at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:932)
    at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:479)
    at org.springframework.web.servlet.FrameworkServlet.configureAndRefreshWebApplicationContext(FrameworkServlet.java:651)
    at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:599)
    at org.springframework.web.servlet.FrameworkServlet.createWebApplicationContext(FrameworkServlet.java:665)
    at org.springframework.web.servlet.FrameworkServlet.initWebApplicationContext(FrameworkServlet.java:518)
    at org.springframework.web.servlet.FrameworkServlet.initServletBean(FrameworkServlet.java:459)
    at org.springframework.web.servlet.HttpServletBean.init(HttpServletBean.java:136)
    at javax.servlet.GenericServlet.init(GenericServlet.java:160)
    at org.apache.catalina.core.StandardWrapper.initServlet(StandardWrapper.java:1274)
    at org.apache.catalina.core.StandardWrapper.loadServlet(StandardWrapper.java:1186)
    at org.apache.catalina.core.StandardWrapper.load(StandardWrapper.java:1081)
    at org.apache.catalina.core.StandardContext.loadOnStartup(StandardContext.java:5033)
    at org.apache.catalina.core.StandardContext.startInternal(StandardContext.java:5320)
    at org.apache.catalina.util.LifecycleBase.start(LifecycleBase.java:150)
    at org.apache.catalina.core.ContainerBase.addChildInternal(ContainerBase.java:901)
    at org.apache.catalina.core.ContainerBase.addChild(ContainerBase.java:877)
    at org.apache.catalina.core.StandardHost.addChild(StandardHost.java:633)
    at org.apache.catalina.startup.HostConfig.deployDescriptor(HostConfig.java:657)
    at org.apache.catalina.startup.HostConfig$DeployDescriptor.run(HostConfig.java:1637)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
    at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
    at java.util.concurrent.FutureTask.run(FutureTask.java:138)
    at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
    at java.lang.Thread.run(Thread.java:619)

我的解決方案是在“MapperScannerConfigurer”配置爲其指定“sqlSessionFactoryBeanName”，於是修改配置如下：

<!-- mybatis自動掃描包下的mapper -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.baofoo.admin.dao" />
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" /> <!-- 指定sqlSessionFactoryName -->
    </bean>

注：以上問題爲本人在實戰項目中解決問題的理解