mybatis开启MapperScannerConfigurer致使properties不生效

时间 2019-11-11

标签 mybatis 开启 mapperscannerconfigurer 致使 properties 生效栏目 MyBatis 繁體版

原文原文链接

背景

spring和mybatis集成过程当中，咱们能够经过MapperFactoryBean的方式配置Mapper接口。可是这样须要在配置文件中，为每一个mapper配置相同的代码块，浪费时间。关键对于代码洁癖的人来讲，一点不能忍。html

<bean id="userMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
  <property name="mapperInterface" value="org.mybatis.spring.sample.mapper.UserMapper" />
  <property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>

使用MapperScannerConfigurer进行自动转换Mapper的方式，让代码更加简洁优雅。java

可是，当我在项目中，按照文文档配置bean后，仍旧出现properties文件中jdbc的参数没法正常解析。spring

相关配置文件信息

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:jaxws="http://cxf.apache.org/jaxws" xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jdbc="http://www.springframework.org/schema/jdbc"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
      http://cxf.apache.org/jaxws http://cxf.apache.org/schemas/jaxws.xsd
      http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
      http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
      http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc.xsd
      http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd
      http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd"
      default-autowire="byName">

    <context:property-placeholder location="conf/*.properties"/>
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource" lazy-init="true">
        <property name="driverClassName" value="${jdbc.driver}"/>
        <property name="url" value="${jdbc.url}"/>
        <property name="username" value="${jdbc.user}"/>
        <property name="password" value="${jdbc.pwd}"/>
    </bean>

    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="mapperLocations" value="mapper/*.xml"/>
        <property name="dataSource" ref="dataSource"/>
    </bean>

    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.yanmushi.**.mapper"/>
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
    </bean>
	
</beans>

PS：请原谅在spring-boot，注解方式盛行的年代，还纠结xml中解决方法。sql

依赖版本

参考依赖apache

<dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-context-support</artifactId>
            <version>4.1.1-RELEASE</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis</artifactId>
            <version>3.2.8</version>
        </dependency>
        <dependency>
            <groupId>org.mybatis</groupId>
            <artifactId>mybatis-spring</artifactId>
            <version>1.2.2</version>
        </dependency>

分析过程

在搜索引擎中，找到了一种解决方法。session

原理：使用sqlSessionFactoryBeanName注入，不会当即初始化sqlSessionFactory, 因此不会引起提早初始化问题。
同时还应注意在配置org.mybatis.spring.SqlSessionFactoryBean这个Bean时，id不能为sqlSessionFactory，若是为这样的话会致使MapperScannerConigurer在bean定义加载时，加载PropertyPlaceholderConfigurer还没来得及替换定义中的变量mybatis

以上方法，可以正常解决问题，可是为何呢？app

为何sqlsessionfactorybeanname注入呢？

打开MapperScannerConfigurer，会发现它实现了spring的四个接口：ide

BeanDefinitionRegistryPostProcessor
InitializingBean
ApplicationContextAware
BeanNameAware

问题的关键在于第一个接口，它是干什么的呢？主要是容许代码像xml同样，注册自定义Bean到BeanFactory中。spring-boot

经过这个接口，MapperScannerConfigurer在spring初始化过程当中，将扫描basePackage中的自定义mapper接口转换为MapperFactoryBean，并注册到BeanFactory中。

/**
 * Extension to the standard {@link BeanFactoryPostProcessor} SPI, allowing for
 * the registration of further bean definitions <i>before</i> regular
 * BeanFactoryPostProcessor detection kicks in. In particular,
 * BeanDefinitionRegistryPostProcessor may register further bean definitions
 * which in turn define BeanFactoryPostProcessor instances.
 */

spring容器自己已经很好到解决了Bean管理问题。为何会致使提早初始化呢？

在AbstractApplicationContext#refresh()方法中，详细注明类初始化的流程。

@Override
	public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

			// Tell the subclass to refresh the internal bean factory.
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

			try {
				// Allows post-processing of the bean factory in context subclasses.
				postProcessBeanFactory(beanFactory);

				// Invoke factory processors registered as beans in the context.
				invokeBeanFactoryPostProcessors(beanFactory);

				// Register bean processors that intercept bean creation.
				registerBeanPostProcessors(beanFactory);

				// Initialize message source for this context.
				initMessageSource();

				// Initialize event multicaster for this context.
				initApplicationEventMulticaster();

				// 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) {
				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;
			}
		}
	}

MapperScannerConfigurer和PropertySourcesPlaceholderConfigurer两个类，都是BeanFactoryPostProcessor的实现类。可是MapperScannerConfigurer实现了BeanFactoryPostProcessor的子接口，BeanDefinitionRegistryPostProcessor。

在执行invokeBeanFactorPostProcessors(beanFacotry)方法时，是调用到PostProcessorRegistrationDelegate#invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory, List<BeanFactoryPostProcessor>)方法，在这个方法中，BeanDefinitionRegistryPostProcessor被优先执行。因此，在执行MapperScannerConfigurer中不能关联须要读取properties文件的Bean，由于Properties没有被初始化。

public static void invokeBeanFactoryPostProcessors(
			ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {

		// Invoke BeanDefinitionRegistryPostProcessors first, if any.
		Set<String> processedBeans = new HashSet<String>();

		if (beanFactory instanceof BeanDefinitionRegistry) {
			BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
			List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
			List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
					new LinkedList<BeanDefinitionRegistryPostProcessor>();

			for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
					BeanDefinitionRegistryPostProcessor registryPostProcessor =
							(BeanDefinitionRegistryPostProcessor) postProcessor;
					registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
					registryPostProcessors.add(registryPostProcessor);
				}
				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.
			String[] postProcessorNames =
					beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);

			// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
			List<BeanDefinitionRegistryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanDefinitionRegistryPostProcessor>();
			for (String ppName : postProcessorNames) {
				if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
					priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
					processedBeans.add(ppName);
				}
			}
			OrderComparator.sort(priorityOrderedPostProcessors);
			registryPostProcessors.addAll(priorityOrderedPostProcessors);
			// 此时去执行：postProcessor.postProcessBeanFactory(beanFactory)方法
			invokeBeanDefinitionRegistryPostProcessors(priorityOrderedPostProcessors, registry);

			// ……
	}

为何咱们使用sqlSessionFacotryBeanName，可是依旧会出现properties没有被引用的问题呢？

这是由于在spring.xml文件中，beans节点，咱们配置了**default-autowire="byName"**属性。开启后，使得BeanFacotry在实例化bean的时候，会自动根据bean名字和属性名字进行自动匹配。从而在实例化MapperScannerConfigurer的时候，自动匹配到sqlSessionFactory属性，触发sqlSessionFactory的实例化，引起dataSource进行实例化，而此时properties属性并无进行解析。

总结

关闭default-autowire属性；不然，须要更改SqlSessionFactory这个bean的id，避免自动关联。
若是只有一个数据源，MapperScannerConfigurer会自动关联的；若是有多个，能够经过sqlSessionFactoryBeanName来配置bean的名字。

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns:jaxws="http://cxf.apache.org/jaxws" xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop"
       xmlns:tx="http://www.springframework.org/schema/tx" xmlns:jdbc="http://www.springframework.org/schema/jdbc"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="
      http://cxf.apache.org/jaxws http://cxf.apache.org/schemas/jaxws.xsd
      http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd
      http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
      http://www.springframework.org/schema/jdbc http://www.springframework.org/schema/jdbc/spring-jdbc.xsd
      http://www.springframework.org/schema/tx http://www.springframework.org/schema/tx/spring-tx.xsd
      http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop.xsd">

    <context:property-placeholder location="conf/*.properties"/>
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource" lazy-init="true">
        <property name="driverClassName" value="${jdbc.driver}"/>
        <property name="url" value="${jdbc.url}"/>
        <property name="username" value="${jdbc.user}"/>
        <property name="password" value="${jdbc.pwd}"/>
    </bean>

    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="mapperLocations" value="mapper/*.xml"/>
        <property name="dataSource" ref="dataSource"/>
    </bean>

    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.yanmushi.**.mapper"/>
        <!-- <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>-->
    </bean>
</beans>