问题描述
在web项目中同时集成了spring mvc和mybatis。
将jdbc配置参数独立在外部配置文件中，然后通过<context:property-placeholder>引入。
此时在Spring中注入org.mybatis.spring.mapper.MapperScannerConfigurer，如下所示：
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="org.chench.test.springmvc.dao" />
<property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>如果直接配置属性sqlSessionFactory，并设置为指定的sqlSessionFactory对象，那么在启动spring时会报错：
代码语言：javascript复制Caused by: java.lang.NumberFormatException: For input string: "${master.acquireIncrement}"数据源配置中无法正确引用外部文件中配置的jdbc参数。
必须修改为配置属性sqlSessionFactoryBeanName，才能正确引用到对应的jdbc配置参数。
代码语言：javascript复制<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<property name="basePackage" value="org.chench.test.springmvc.dao" />
<property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" />
</bean>这是什么原因呢？
原因分析及解决方案
实际上，这是MyBatis早期版本的一个BUG，详见：https://github.com/mybatis/old-google-code-issues/issues/414 。 而且，在最新版本的MyBatis中，同样不再推荐使用设置Bean属性的方式，而是通过设置Value属性。
代码语言：javascript复制 /**
* Specifies which {@code SqlSessionFactory} to use in the case that there is
* more than one in the spring context. Usually this is only needed when you
* have more than one datasource.
* <p>
* @deprecated Use {@link #setSqlSessionFactoryBeanName(String)} instead.
*
* @param sqlSessionFactory
*/
// 这是一个声明为废弃的方法，不推荐使用
@Deprecated
public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
this.sqlSessionFactory = sqlSessionFactory;
}
/**
* Specifies which {@code SqlSessionFactory} to use in the case that there is
* more than one in the spring context. Usually this is only needed when you
* have more than one datasource.
* <p>
* Note bean names are used, not bean references. This is because the scanner
* loads early during the start process and it is too early to build mybatis
* object instances.
*
* @since 1.1.0
*
* @param sqlSessionFactoryName Bean name of the {@code SqlSessionFactory}
*/
// 解释了为什么应该使用设置Value的方式而不是引用Bean的原因
public void setSqlSessionFactoryBeanName(String sqlSessionFactoryName) {
this.sqlSessionFactoryBeanName = sqlSessionFactoryName;
}实际上，通常情况下无需手动为MapperScannerConfigurer注册SqlSessionFactory，这个工作由Spring框架完成，因为MapperScannerConfigurer已经实现了接口BeanDefinitionRegistryPostProcessor。
代码语言：javascript复制public class MapperScannerConfigurer implements BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware {
@Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
if (this.processPropertyPlaceHolders) {
processPropertyPlaceHolders();
}
ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
scanner.setAddToConfig(this.addToConfig);
scanner.setAnnotationClass(this.annotationClass);
scanner.setMarkerInterface(this.markerInterface);
// 由Spring框架自动注入SqlSessionFactory
scanner.setSqlSessionFactory(this.sqlSessionFactory);
scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
// 由Spring框架自注入sqlSessionFactoryBeanName
scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
scanner.setResourceLoader(this.applicationContext);
scanner.setBeanNameGenerator(this.nameGenerator);
scanner.registerFilters();
scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
}
