1、概述
原生Mybatis源码简析(上)
原生Mybatis源码简析(下)
在介绍原生Mybatis源码简析文章中，我们知道，Mapper接口的生命周期是在方法级别，方法执行结束，Mapper接口的动态代理实现类的生命就终结了。在下一次执行时，会再次重新生成新的代理类。但是当mybatis与spring结合使用时，mapper接口的代理实现类的生命周期是全局的，这是如何实现的呢？首先在spring中引入mybatis时，是需要加入mybatis-spring包的引用的。在spring的xml配置中需要加入如下配置：
那mapper接口的代理实现类的单例实现机制，定是与这两个bean有关了。
2、SqlSessionFactoryBean
SqlSessionFactoryBean，从名字就可看出他是一个FactoryBean，如此就直接看起getObject方法
public SqlSessionFactory getObject() throws Exception {
if (this.sqlSessionFactory == null) {
afterPropertiesSet();
}
return this.sqlSessionFactory;
}
public void afterPropertiesSet() throws Exception {
notNull(dataSource, "Property 'dataSource' is required");
notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
"Property 'configuration' and 'configLocation' can not specified with together");
this.sqlSessionFactory = buildSqlSessionFactory();
}
在getObject方法中调用了afterPropertiesSet方法，内部又调用了buildSqlSessionFactory方法，该方法内容很长，不再贴代码了，但方法实现比较简单，就是根据SqlSessionFactoryBean的众多配置属性来构建出Configuration对象，进而实例化SqlSessionFactory对象。与原厂mybatis的实现大同小异。
3、MapperScannerConfigurer
MapperScannerConfigurer类实现了BeanDefinitionRegistryPostProcessor接口，则重点看下postProcessBeanDefinitionRegistry方法的实现
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);
scanner.setSqlSessionFactory(this.sqlSessionFactory);
scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
scanner.setResourceLoader(this.applicationContext);
scanner.setBeanNameGenerator(this.nameGenerator);
scanner.setMapperFactoryBeanClass(this.mapperFactoryBeanClass);
scanner.registerFilters();
scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
ClassPathMapperScanner类是mybatis-spring框架提供的类，实现了spring框架的ClassPathBeanDefinitionScanner类。
protected Set doScan(String... basePackages) {
Assert.notEmpty(basePackages, "At least one base package must be specified");
Set beanDefinitions = new LinkedHashSet();
for (String basePackage : basePackages) {
Set candidates = findCandidateComponents(basePackage);
for (BeanDefinition candidate : candidates) {
ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
candidate.setScope(scopeMetadata.getScopeName());
String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
if (candidate instanceof AbstractBeanDefinition) {
postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
}
if (candidate instanceof AnnotatedBeanDefinition) {
AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
}
if (checkCandidate(beanName, candidate)) {
BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder =
AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
registerBeanDefinition(definitionHolder, this.registry);
}
}
}
return beanDefinitions;
}
ClassPathBeanDefinitionScanner类的doScan方法会根据传入的basePackage，扫描包下的所有.class文件，并根据该类文件生成相应的BeanDefinition对象。针对mybatis的mapper接口，这里生成的BeanDefinition对象其实是半成品的对象，他的beanClass属性是接口的全限定类名。然后将半成品的BeanDefinition对象集合返回，在ClassPathMapperScanner类的processBeanDefinitions方法中，对这些半成品的BeanDefinition进行二次加工。
private void processBeanDefinitions(Set beanDefinitions) {
GenericBeanDefinition definition;
for (BeanDefinitionHolder holder : beanDefinitions) {
definition = (GenericBeanDefinition) holder.getBeanDefinition();
String beanClassName = definition.getBeanClassName();
LOGGER.debug(() -> "Creating MapperFactoryBean with name '" + holder.getBeanName()
+ "' and '" + beanClassName + "' mapperInterface");
// the mapper interface is the original class of the bean
// but, the actual class of the bean is MapperFactoryBean
definition.getConstructorArgumentValues().addGenericArgumentValue(beanClassName); // issue #59
definition.setBeanClass(this.mapperFactoryBeanClass);
definition.getPropertyValues().add("addToConfig", this.addToConfig);
boolean explicitFactoryUsed = false;
if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
explicitFactoryUsed = true;
} else if (this.sqlSessionFactory != null) {
definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
explicitFactoryUsed = true;
}
if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
if (explicitFactoryUsed) {
LOGGER.warn(() -> "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
explicitFactoryUsed = true;
} else if (this.sqlSessionTemplate != null) {
if (explicitFactoryUsed) {
LOGGER.warn(() -> "Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
}
definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
explicitFactoryUsed = true;
}
if (!explicitFactoryUsed) {
LOGGER.debug(() -> "Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
}
}
}
重点是definition.setBeanClass(this.mapperFactoryBeanClass);这段方法。
private Class mapperFactoryBeanClass = MapperFactoryBean.class;
MapperFactoryBean类也是一个FactoryBean，重置了beanClass属性之后，此时的BeanDefinition就是一个成品的了，之后实例化的时候，mapper接口对应的对象就是MapperFactoryBean的实例。如此便实现了mapper接口的全局单例话。
有空得再看看源码分析下，spring的事务是如何与mybatis的事务整合在一起的？