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MyBatis相信很多人都会使用，但是当MyBatis整合到了Spring中，我们发现在Spring中使用更加方便了。例如获取Dao的实例，在Spring的我们只需要使用注入的方式就可以了使用Dao了，完全不需要调用SqlSession的getMapper方法去获取Dao的实例，更不需要我们去管理SqlSessionFactory，也不需要去创建SqlSession之类的了，对于插入操作也不需要我们commit。
既然那么方便，Spring到底为我们做了哪些工作呢，它如何将MyBatis整合到Spring中的呢，Spring在整合MyBatis时候做了哪些封装，以及做了哪些拓展，又是怎么实现这些封装以及拓展的，让我们来打开这一部分的源代码，一探究竟。
首先我们来先回顾下MyBatis的用法，以及Spring中MyBatis的使用方法。
po用于对于数据库中数据的映射，使得开发者更加专注于Java类的使用，而不是对数据库的操作
/**
* @author： Fighter168
*/
public class Person {
private String id;
private String name;
//set get 方法、、、
}
mapper是数据库操作的映射文件，也就是我们常说的dao文件
/**
* @author： Fighter168
*/
public interface PersonDao {
public List<Person> query();
public void save(Person p);
public void delete(String id);
}
配置文件主要用于程序中可变性高的设置，Mybatis的配置文件主要存在于configuration.xml中，当然configuration.xml中省略了其他mybatis的配置，例如settings里面的配置等等，如果没有玩过MyBatis的同学可以去参考网上MyBatis的教程自己去了解了解。
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!-- 对事务的管理和连接池的配置 -->
<environments default="development">
<environment id="development">
<transactionManager type="JDBC" />
<dataSource type="POOLED">
<property name="driver" value="com.mysql.jdbc.Driver" />
<property name="url" value="jdbc:mysql://localhost:3306/test" />
<property name="username" value="root" />
<property name="password" value="root" />
</dataSource>
</environment>
</environments>
<!-- mapping 文件路径配置 -->
<mappers>
<mapper resource="resource/PersonMapper.xml" />
</mappers>
</configuration>映射文件对应于Mybatis全局配置中的mappers配置属性，主要用于建立对应数据库操作接口的SQL映射。
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://www.mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="net.itaem.dao.PersonDao" >
<resultMap id="resultMap" type="net.itaem.po.Person" >
<result column="id" property="id" jdbcType="CHAR" />
<result column="name" property="name" jdbcType="CHAR" />
</resultMap>
<!--添加-->
<insert id="save" parameterType="net.itaem.po.Person">
insert into person(id,name) value(#{id,jdbcType=CHAR},#{name,jdbcType=CHAR})
</insert>
<!--查询-->
<select id="query" resultMap="resultMap">
select * from person
</select>
<!--删除-->
<delete id="delete" parameterType="java.lang.String">
delete from person where id=#{id,jdbcType=CHAR}
</delete>
</mapper>/**
* @author： Fighter168
*/
public class Test {
public static void main(String[] args) throws Exception {
Reader reader=Resources.getResourceAsReader("resource/configuration.xml");
SqlSessionFactory sessionFactory=new SqlSessionFactoryBuilder().build(reader);
SqlSession session=sessionFactory.openSession();
PersonDao personDao=session.getMapper(PersonDao.class);
Person person=new Person("11","Fighter168");
personDao.save(person);
//这里一定要提交，不然数据无法插入
session.commit();
session.close();
}
}
<?xml version="1.0" encoding="UTF-8"?> <beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-3.0.xsd"> <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close"> <property name="driverClassName" value="com.mysql.jdbc.Driver"/> <property name="url" value="jdbc:mysql://localhost:3306/test"/> <property name="username" value="root"/> <property name="password" value="123abc"/> <!-- 连接池启动时候的初始连接数 --> <property name="initialSize" value="10"/> <!-- 最小空闲值 --> <property name="minIdle" value="5"/> <!-- 最大空闲值 --> <property name="maxIdle" value="20"/> <property name="maxWait" value="2000"/> <!-- 连接池最大值 --> <property name="maxActive" value="50"/> <property name="logAbandoned" value="true"/> <property name="removeAbandoned" value="true"/> <property name="removeAbandonedTimeout" value="180"/> </bean> <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="configLocation" value="classpath:/resource/cfg.xml"/> <property name="dataSource" ref="dataSource"/> </bean> <bean id="personDao" class="org.mybatis.spring.mapper.MapperFactoryBean"> <property name="mapperInterface" value="net.itaem.dao.PersonDao"/> <property name="sqlSessionFactory" ref="sqlSessionFactory"/> </bean> </beans>
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!-- mapping 文件路径配置 -->
<mappers>
<mapper resource="resource/PersonMapper.xml" />
</mappers>
</configuration><?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://www.mybatis.org/dtd/mybatis-3-mapper.dtd" >
<mapper namespace="net.itaem.dao.PersonDao" >
<resultMap id="resultMap" type="net.itaem.po.Person" >
<result column="id" property="id" jdbcType="CHAR" />
<result column="name" property="name" jdbcType="CHAR" />
</resultMap>
<!--添加-->
<insert id="save" parameterType="net.itaem.po.Person">
insert into person(id,name) value(#{id,jdbcType=CHAR},#{name,jdbcType=CHAR})
</insert>
<!--查询-->
<select id="query" resultMap="resultMap">
select * from person
</select>
<!--删除-->
<delete id="delete" parameterType="java.lang.String">
delete from person where id=#{id,jdbcType=CHAR}
</delete>
</mapper>/**
* @author： Fighter168
*/
public class SpringTest {
public static void main(String[] args) {
ApplicationContext context=new ClassPathXmlApplicationContext("resource/ApplicationContext.xml");
PersonDao personDao=(PersonDao) context.getBean("personDao");
Person person=new Person("12","Fighter168");
personDao.save(person);
}
} /**
* {@inheritDoc}
*/
public void afterPropertiesSet() throws Exception {
notNull(dataSource, "Property 'dataSource' is required");
notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
this.sqlSessionFactory = buildSqlSessionFactory();
}
/**
* {@inheritDoc}
*/
public SqlSessionFactory getObject() throws Exception {
if (this.sqlSessionFactory == null) {
afterPropertiesSet();
}
return this.sqlSessionFactory;
} 所以我们在给dao注入sqlSessionFactory的时候，依赖填写SqlSessionFactoryBean 的实例就可以了。SqlSession session=sessionFactory.openSession(); PersonDao personDao=session.getMapper(PersonDao.class);但在我们在spring的测试用例中使用mybatis的时候是这样使用的：
PersonDao personDao=(PersonDao) context.getBean("personDao"); 为什么spring可以这样做呢，答案就在MapperFactoryBean这里
public final void afterPropertiesSet() throws IllegalArgumentException, BeanInitializationException {
// Let abstract subclasses check their configuration.
checkDaoConfig();
// Let concrete implementations initialize themselves.
try {
initDao();
}
catch (Exception ex) {
throw new BeanInitializationException("Initialization of DAO failed", ex);
}
}
/**
* {@inheritDoc}
*/
@Override
protected void checkDaoConfig() {
super.checkDaoConfig();
notNull(this.mapperInterface, "Property 'mapperInterface' is required");
Configuration configuration = getSqlSession().getConfiguration();
if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
try {
configuration.addMapper(this.mapperInterface);
} catch (Throwable t) {
logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", t);
throw new IllegalArgumentException(t);
} finally {
ErrorContext.instance().reset();
}
}
} /**
* {@inheritDoc}
*/
public T getObject() throws Exception {
return getSqlSession().getMapper(this.mapperInterface);
} <!-- 去掉该配置 <bean id="personDao" class="org.mybatis.spring.mapper.MapperFactoryBean"> <property name="mapperInterface" value="net.itaem.dao.PersonDao"/> <property name="sqlSessionFactory" ref="sqlSessionFactory"/> </bean> --> <!-- 如果 net.itaem.dao 包下面有很多dao需要注册，那么可以使用这种扫描的方式添加dao--> <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"> <property name="basePackage" value="net.itaem.dao"/> </bean>
/**
* {@inheritDoc}
*
* @since 1.0.2
*/
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
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.registerFilters();
scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
}
spring源码剖析（八）spring整合mybatis原理
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原文地址：http://blog.csdn.net/fighterandknight/article/details/51448161
