通过实例结合源码的方式解读，其中涉及到的文件来自于笔者的Github毕设项目，引用的jar包为
mybatis-spring-1.3.0.jar
Mybatis
Mybatis是基于ORM(Object relation mapping)思想而开发的框架插件，本质原理用一句笔者的话便是使用了JAVA连接数据库的方式来执行相应的SQL(PreparedStatement)，并在此基础上提供了丰富的动态SQL配置以及缓存等概念。(后续文章会提及)
其基本上是企业与传统数据库(Oracle/Mysql等)交互常用的数据库持久层框架，以JAVA语言来说，其与Spring的搭配使用也是广为流传。
本文将从源码的角度浅析Mybatis与Spring的亲密搭配
范例
笔者本文只关注SqlSessionFactoryBean的配置，样例如下
<!--数据源，引用common-pool包的数据源类-->
<bean id="dataSource-mysql" class="org.apache.commons.dbcp.BasicDataSource">
<property name="driverClassName" value="${jdbc.driverClassName}" />
<property name="url" value="${jdbc.url}" />
<property name="username" value="${jdbc.username}" />
<property name="password" value="${jdbc.password}" />
<property name="initialSize" value="1" />
<property name="maxActive" value="20" />
</bean>
<!--sqlSessionFactoryBean创建-->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource-mysql" />
<property name="typeAliasesPackage" value="com.du.wx.model" />
<property name="mapperLocations" value="classpath:com/du/wx/resources/mapper/*.xml"/>
</bean>
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<!-- joggle代表接口 -->
<property name="basePackage" value="com.du.wx.mapper.joggle" />
</bean>
由上述的配置可知，在配置SqlSessionFactory数据库会话工厂Bean对象时必须依赖相应的数据源属性dataSource
SqlSessionFactoryBean
笔者分层次来解析此类
基础内部属性
优先观察SqlSessionFactoryBean的内部属性，代码片段如下
private static final Log LOGGER = LogFactory.getLog(SqlSessionFactoryBean.class);
private Resource configLocation;
private Configuration configuration;
private Resource[] mapperLocations;
private DataSource dataSource;
private TransactionFactory transactionFactory;
private Properties configurationProperties;
private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
private SqlSessionFactory sqlSessionFactory;
//EnvironmentAware requires spring 3.1
private String environment = SqlSessionFactoryBean.class.getSimpleName();
private boolean failFast;
private Interceptor[] plugins;
private TypeHandler<?>[] typeHandlers;
private String typeHandlersPackage;
private Class<?>[] typeAliases;
private String typeAliasesPackage;
private Class<?> typeAliasesSuperType;
//issue #19. No default provider.
private DatabaseIdProvider databaseIdProvider;
private Class<? extends VFS> vfs;
private Cache cache;
private ObjectFactory objectFactory;
private ObjectWrapperFactory objectWrapperFactory;
常用的属性如下：
configLocation mybatis主配置文件路径，支持classpath语法
mapperLocations 指定mybatis的mapper配置文件，支持classpath语法
dataSource 数据源
typeAliasesPackage 指定model层类名的别名扫描包，这与mapper配置中的parameterType和resultType搭配使用
InitializingBean复写方法
紧接着看下其复写的afterPropertiesSet()方法，代码如下
@Override
public void afterPropertiesSet() throws Exception {
//datasource not allowed to be null.
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();
}
与前文提及的对应，必须确保dataSource属性已经得到配置。
实例化步骤
最后查看关键实例方法buildSqlSessionFactory()方法，由于片段过长，笔者截取几段来进行讲解
Mybatis主文件加载
Configuration configuration;
XMLConfigBuilder xmlConfigBuilder = null;
if (this.configuration != null) {
configuration = this.configuration;
if (configuration.getVariables() == null) {
configuration.setVariables(this.configurationProperties);
} else if (this.configurationProperties != null) {
configuration.getVariables().putAll(this.configurationProperties);
}
} else if (this.configLocation != null) {
//如果spring配置中configLocation属性不为空，则加载指定的Mybatis配置
xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
configuration = xmlConfigBuilder.getConfiguration();
} else {
//否则则采用默认的Mybatis配置，@see Configuration
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Property `configuration` or 'configLocation' not specified, using default MyBatis Configuration");
}
configuration = new Configuration();
configuration.setVariables(this.configurationProperties);
}
通过上述配置表明，内部属性configLocation是非必须配置项
model别名映射扫描
if (hasLength(this.typeAliasesPackage)) {
//截取typeAliasesPackage属性的包，支持,或;
String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
for (String packageToScan : typeAliasPackageArray) {
//对应方法的目的是通过扫描包得到其包以及子包目录下的所有Class，然后为每个class注册别名
configuration.getTypeAliasRegistry().registerAliases(packageToScan,
typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");
}
}
}
即对内部属性typeAliasesPackage支持,;作为分隔符以加载多个目录，主要是为了方便编程人员使用parameterType/resultType等属性
mapper配置文件加载
if (!isEmpty(this.mapperLocations)) {
//mapperLocations
for (Resource mapperLocation : this.mapperLocations) {
if (mapperLocation == null) {
continue;
}
try {
//对扫描的每个配置文件进行解析，并保存其中的必要参数，后续会分析
XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
configuration, mapperLocation.toString(), configuration.getSqlFragments());
xmlMapperBuilder.parse();
} catch (Exception e) {
throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
} finally {
ErrorContext.instance().reset();
}
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");
}
}
} else {
if (LOGGER.isDebugEnabled()) {
LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");
}
}
关键处理XML配置的mapper文件，用到了mybatis包中的org.apache.ibatis.builder.xml.XMLMapperBuilder类进行解析。这个后续分析
Configuration-所有关于Mybatis的信息均存储在Mybatis包中的org.apache.ibatis.session.Configuration类上
return this.sqlSessionFactoryBuilder.build(configuration);
Spring呢，就通过SqlSessionFactoryBuilder类来创建相应的SqlSessionFactory对象。具体的由于篇幅过长，就放在后文分析。
总结
从上文便可以看出来Spring框架是如何整合Mybatis的，就是这个Mybatis的关键类Configuration。而相应的开关数据库等一系列的功能都是通过Spring的SqlSessionFactory对象来操控的。这也是两者结合最核心的地方