报错日志
在搭建 spring 4.3 + mybatis 3.4 的开发框架时，启动报错
启动报错如下：
nested exception is java.sql.SQLException: ${jdbc.driver}
配置都是大同小异，唯一的区别是加了这个更便捷的配置
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="com.taro.dao"/>
<property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property>
</bean>
有了这个配置就不需要再写一大堆繁琐的Dao配置，spring会自动为我们把这些 dao 写入到 内部维护的BeanDefinitions 中去。
解决方法
- 一.如果有配置 default-autowire 将这个配置去掉
- 二.spring 配置文件中org.mybatis.spring.SqlSessionFactoryBean 的命名不要命名成
sqlSessionFactory， 另外MapperScannerConfigurer中的sqlSessionFactoryBeanName也改成相应的名字
正确的配置:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.springframework.org/schema/beans"
xmlns:p="http://www.springframework.org/schema/p"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd"
default-autowire="byName" default-lazy-init="true">
<!-- DataSource数据 -->
<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close">
<property name="name" value="souchecar"/>
<property name="driverClassName" value="${jdbc.driver}"/>
<property name="url" value="${jdbc.url}"/>
<property name="username" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
<property name="maxActive" value="20"/>
<property name="minIdle" value="2"/>
<property name="initialSize" value="2"/>
<property name="validationQuery" value="SELECT 1"/>
<property name="testOnBorrow" value="false"/>
<property name="testOnReturn" value="false"/>
<property name="testWhileIdle" value="true"/>
<property name="timeBetweenEvictionRunsMillis" value="60000"/>
<property name="minEvictableIdleTimeMillis" value="300000"/>
<property name="defaultAutoCommit" value="true"/>
<property name="removeAbandoned" value="true"/>
<property name="removeAbandonedTimeout" value="6000"/>
<property name="logAbandoned" value="true"/>
<property name="filters" value="stat"/>
</bean>
<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="dataSource"/>
</bean>
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="mapperLocations">
<list>
<value>classpath*:sqlmap/**/*.xml</value>
</list>
</property>
<property name="dataSource" ref="dataSource"/>
</bean>
<!-- DAO接口所在包名，Spring会自动查找其下的类 -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="com.taro.dao"/>
<property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property>
</bean>
</beans>
分析原因
看报错可知配置信息没有加载进去
配置信息我是配置了的，配置没有任何问题
<bean id="propertyConfigurer" class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
<property name="locations">
<list>
<value>classpath*:*.properties</value>
</list>
</property>
</bean>
那么是什么原因呢，让我们来看源码
可知 PropertyPlaceholderConfigurer 是实现了 BeanFactoryPostProcessor 接口的
而 MapperScannerConfigurer 实现了 BeanDefinitionRegistryPostProcessor 接口
要想知道这几个接口含义,以及是在spring 加载的哪个过程执行的，还是得一步步的看源码
- 回到spring最经典的入口代码
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// 一,Prepare this context for refreshing.
prepareRefresh();
// 二,重启容器,并载入BeanDefinitions
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// 三,Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// 四,Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// 五,执行BeanFactoryPostProcessor接口和BeanDefinitionRegistryPostProcessor接口的地方
invokeBeanFactoryPostProcessors(beanFactory);
// 六,Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// 七,Initialize message source for this context.
initMessageSource();
// 八,Initialize event multicaster for this context.
initApplicationEventMulticaster();
// 九,Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory);
// Last step: publish corresponding event.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
- 我们重点来看第5步，进入invokeBeanFactoryPostProcessors方法
PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
- invokeBeanFactoryPostProcessors
public static void invokeBeanFactoryPostProcessors(
ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
// 先执行 BeanDefinitionRegistryPostProcessors // processedBeans 存放已经执行过的 FactoryPostProcessor
Set<String> processedBeans = new HashSet<String>();
// 先判断beanFactory 是不是 BeanDefinitionRegistry 类型
if (beanFactory instanceof BeanDefinitionRegistry) {
BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
List<BeanDefinitionRegistryPostProcessor> registryProcessors = new LinkedList<BeanDefinitionRegistryPostProcessor>();
// 把手动加入的 BeanFactoryPostProcessor 分类型分别放入regularPostProcessors ,registryProcessors 中
for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
BeanDefinitionRegistryPostProcessor registryProcessor =
(BeanDefinitionRegistryPostProcessor) postProcessor;
registryProcessor.postProcessBeanDefinitionRegistry(registry);
registryProcessors.add(registryProcessor);
}
else {
regularPostProcessors.add(postProcessor);
}
}
// Do not initialize FactoryBeans here: We need to leave all regular beans
// uninitialized to let the bean factory post-processors apply to them!
// Separate between BeanDefinitionRegistryPostProcessors that implement
// PriorityOrdered, Ordered, and the rest.
// 下面的代码会根据优先级情况先后执行 BeanDefinitionRegistryPostProcessor 和 BeanFactoryPostProcessors
List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
// 先执行实现了 PriorityOrdered （优先执行）的接口的BeanDefinitionRegistryPostProcessor.class
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// 再执行 Ordered 类型的BeanDefinitionRegistryPostProcessor.class
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
// 最后执行 剩下的BeanDefinitionRegistryPostProcessor
boolean reiterate = true;
while (reiterate) {
reiterate = false;
postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
for (String ppName : postProcessorNames) {
if (!processedBeans.contains(ppName)) {
currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
processedBeans.add(ppName);
reiterate = true;
}
}
sortPostProcessors(currentRegistryProcessors, beanFactory);
registryProcessors.addAll(currentRegistryProcessors);
invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
currentRegistryProcessors.clear();
}
// 执行手动加入的
invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);
invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
}
else {
// 直接执行
invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
}
// 根据排序顺序执行 BeanFactoryPostProcessor ,前面已经执行过的BeanDefinitionRegistryPostProcessor 不会执行
String[] postProcessorNames =
beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
// Ordered, and the rest.
List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
List<String> orderedPostProcessorNames = new ArrayList<String>();
List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
for (String ppName : postProcessorNames) {
if (processedBeans.contains(ppName)) {
// skip - already processed in first phase above
}
else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
}
else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
orderedPostProcessorNames.add(ppName);
}
else {
nonOrderedPostProcessorNames.add(ppName);
}
}
// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
for (String postProcessorName : orderedPostProcessorNames) {
orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
sortPostProcessors(orderedPostProcessors, beanFactory);
invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
// Finally, invoke all other BeanFactoryPostProcessors.
List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
for (String postProcessorName : nonOrderedPostProcessorNames) {
nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
}
invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
// Clear cached merged bean definitions since the post-processors might have
// modified the original metadata, e.g. replacing placeholders in values...
beanFactory.clearMetadataCache();
}
超级长的一堆代码,看着慌...
我们分几步来分析
- BeanDefinitionRegistryPostProcessor 优先执行，执行顺序 实现了么接口PriorityOrdered
最优先 Ordered其次 ,最后执行普通的 BeanDefinitionRegistryPostProcessor - 再执行手动加入的 BeanDefinitionRegistryPostProcessor 和BeanFactoryPostProcessor （由容器的 addBeanFactoryPostProcessor
方法加入的） - 之后执行 BeanFactoryPostProcessor ,执行顺序与BeanDefinitionRegistryPostProcessor类似
现在我们再来分析原因
通过查看MapperScannerConfigurer源码，可知其实现了BeanDefinitionRegistryPostProcessor接口，而PropertyPlaceholderConfigurer实现的是BeanFactoryPostProcessor接口。 那么这就说明MapperScannerConfigurer是优先于PropertyPlaceholderConfigurer执行的,那么要是MapperScannerConfigurer提前初始化了数据库连接,而相关配置属性还没被替换,就会报这个错了。
貌似问题找打了，可仔细一看，我MapperScannerConfigurer配置的注入属性不是sqlSessionFactoryBeanName吗（sqlSessionFactoryBeanName会在spring初始化完成后才会获取），这可只是String 类型,怎么就提前去初始化了sqlSessionFactory 呢?
这就得从spring的依赖注入规则去分析了
首先，我配置的是自动注入 default-autowire="byName" 意思就是说就算我不配各种property Spring 也会自动根据Name去容器里找然后注入给我。那么问题就出在这里，因为MapperScannerConfigurer 里有SqlSessionFactory 类型的属性，所以spring就自作主张给我们去容器里找根据名字sqlSessionFactory去找这个类型的 BeanDefinition，因为我们配置的sqlSessionFactory 名字恰好也是 sqlSessionFactory，结果就给找到了,一找到就立马调用getBean方法提前初始化sqlSessionFactory了,进而提前初始化了dataSource，导致了报错！
所以解决方法就是上文提到的这两种方式
Spring 系列
