spring4+mybatis3无法读取properties解决办法

当把数据源配置信息改成从properties文件读取时错误提示：

Caused by: org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'sqlSessionFactory' defined in URL [file:/D:/java/apache-tomcat-7.0.64/webapps/spring_mybatis/WEB-INF/classes/config/applicationContext.xml]: Cannot resolve reference to bean 'dataSource' while setting bean property 'dataSource'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'dataSource' defined in URL [file:/D:/java/apache-tomcat-7.0.64/webapps/spring_mybatis/WEB-INF/classes/config/applicationContext.xml]: Error setting property values; nested exception is org.springframework.beans.PropertyBatchUpdateException; nested PropertyAccessExceptions (1) are:
PropertyAccessException 1: org.springframework.beans.MethodInvocationException: Property 'driverClassName' threw exception; nested exception is java.lang.IllegalStateException: Could not load JDBC driver class [${driver}]
at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:359)
at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveValueIfNecessary(BeanDefinitionValueResolver.java:108)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.applyPropertyValues(AbstractAutowireCapableBeanFactory.java:1477)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1222)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:537)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:476)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:303)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:230)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:299)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:194)
at org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:351)

db.properties

driver=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mybatis
username=root
password=123456

applicationContext.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:p="http://www.springframework.org/schema/p" xmlns:context="http://www.springframework.org/schema/context" xmlns:tx="http://www.springframework.org/schema/tx" xsi:schemaLocation="
		http://www.springframework.org/schema/beans
		http://www.springframework.org/schema/beans/spring-beans-4.0.xsd
		http://www.springframework.org/schema/context
		http://www.springframework.org/schema/context/spring-context-4.0.xsd
		http://www.springframework.org/schema/tx
		http://www.springframework.org/schema/tx/spring-tx-4.0.xsd">

	<bean class="tk.mybatis.spring.mapper.MapperScannerConfigurer">
		<property name="basePackage" value="com.isea533.mybatis.mapper" />
		<property name="properties">
			<value>
				mappers=tk.mybatis.mapper.common.Mapper
			</value>
		</property>
	</bean>
	<bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
		<property name="ignoreResourceNotFound" value="true" />
		<property name="locations">
			<list>
				<value>classpath:config/db.properties</value>
			</list>
		</property>
	</bean>
	<!-- 1. 数据源 : DriverManagerDataSource -->
	<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
		<property name="driverClassName" value="${driver}" />
		<property name="url" value="${url}" />
		<property name="username" value="${username}" />
		<property name="password" value="${password}" />
	</bean>

	<!-- 2. mybatis的SqlSession的工厂: SqlSessionFactoryBean dataSource:引用数据源 MyBatis定义数据源,同意加载配置 -->
	<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
		<property name="dataSource" ref="dataSource"></property>
		<property name="configLocation" value="classpath:config/mybatis-config.xml" />
	</bean>

	<!-- 3. mybatis自动扫描加载Sql映射文件/接口 : MapperScannerConfigurer sqlSessionFactory basePackage:指定sql映射文件/接口所在的包（自动扫描） -->
	<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
		<property name="basePackage" value="com.ihefe.mapper"></property>
		<property name="sqlSessionFactory" ref="sqlSessionFactory"></property>
	</bean>

	<!-- 4. 事务管理 : DataSourceTransactionManager dataSource:引用上面定义的数据源 -->
	<bean id="txManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
		<property name="dataSource" ref="dataSource"></property>
	</bean>

	<!-- 5. 使用声明式事务 transaction-manager：引用上面定义的事务管理器 -->
	<tx:annotation-driven transaction-manager="txManager" />

	<!-- 注解扫描包 -->
	<context:component-scan base-package="com.ihefe" />
</beans>

解决：

applicationContext.xml中：
<property name="sqlSessionFactory" ref="sqlSessionFactory"></property>
改成即可
<property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"></property>

原因：

在注入SqlSessionFactory时，可有两种方式，一种直接以对象的方式注入，此种方式会直接实例化dataSource，但是此时properties还没有进行解析，因此会出现上述的异常。另一种方式以属性名称注入成员变量，此方式注入时properties已经被解析替换，因此项目可以正常运行