SprignMVC+myBatis整合+mybatis源码分析+动态代理实现流程+如何根据mapper接口生成其实现类

首先熟悉三个概念：
SqlSessionFactoryBean
–为整合应用提供SqlSession对象资源
MapperFactoryBean
–根据指定的Mapper接口生成Bean实例
MapperScannerConfigurer
–根据指定包批量扫描Mapper接口并生成实例

SqlSessionFactoryBean:
在单独使用MyBatis时，所有操作都是围绕SqlSession展开的，SqlSession是通过SqlSessionFactory获取的，SqlSessionFactory又是通过SqlSessionFactoryBuilder创建生成的。
在SpringMvc+MyBatis整合时，同样需要SqlSession。SqlSessionFactoryBean这个组件通过原来的SqlSessionFactoryBuilder生成SqlSessionFactory对象，为整合应用提供SqlSession对象。
Java代码

id="myDataSource" class="org.apache.commons.dbcp.BasicDataSource">  
    <property name="driverClassName" value="oracle.jdbc.OracleDriver" />  
    <property name="url" value="jdbc:oracle:thin:@localhost:1521:XE" />  
    <property name="username" value="jsd1403" />  
    <property name="password" value="root" />  
  

id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">  
    <property name="dataSource" ref="myDataSource" />  
    <property name="mapperLocations" value="classpath:com/lydia/entity/*.xml" />  
  

MapperFactoryBean：
其作用是根据Mapper接口获取我们想要的Mapper对象，它封装了原有的session.getMapper()功能的实现。
在定义MapperFactoryBean时，需要注入一下两个属性：
–SqlSessionFactoryBean对象，用于提供SqlSession
–要返回Mapper对象的Mapper接口
MapperFactoryBean配置如下：
Java代码

  
    <bean id="deptMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">  
        <property name="mapperInterface" value="com.lydia.entity.DeptMapper">property>  
          
        <property name="sqlSessionFactory" ref="sqlSessionFactory">property>  
    bean>  

MapperScannerConfigurer配置使用：
注意：使用MapperFactoryBean时，当有一个Mapper（可以理解为表对应的映射文件）就MapperFactoryBean，当mapper少数可以通过applicationContext配置文件，通过id获取。
如果大量的mapper，需要使用mybatis-spring.jar通过的MapperScannerConfigurer组件，通过这个组件可以自动扫描指定包下的各个Mapper接口，并注册对应的MapperFactoryBean对象。

把之前的MapperFactoryBean的配置注释掉，换成如下配置依然执行通过：
Java代码

  
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">  
      
    <property name="basePackage" value="com.lydia,com.tarena" />  
      
    <property name="sqlSessionFactory" ref="sqlSessionFactory">property>  
bean>  

注意：上面sqlSessionFactory属性也可以不用指定，默认会以Autowired方式注入。
如果指定的某个包下并不完全是我们定义的Mapper接口，我们也可以通过自定义注解的方式指定生成MapperFactoryBean对象。
配置如下：

  
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">  
        <property name="basePackage" value="com.lydia" />  
        <property name="annotationClass" value="com.lydia.annotation.MyBatisRepository" />  
    bean>  

自定义注解：MyBatisRepository.java
Java代码

public @interface MyBatisRepository {  
}  

在DeptMapper接口中使用：

//@Repository("deptMapper")  
@MyBatisRepository  
public interface DeptMapper {  
    void addDept(Dept dept);  
    void deleteDept(Dept dept);  
    void updateDept(Dept dept);  
    ......  
}  

测试：

public class TestCase {  
    @Test  
    public void testFindAll() throws Exception {  
        String conf = "applicationContext.xml";  
        ApplicationContext ac = new ClassPathXmlApplicationContext(conf);  
        //获取对应的mapper对象，并调用mapper接口中对应的方法  
        DeptMapper mapper = ac.getBean("deptMapper", DeptMapper.class);  
        List lists = mapper.findAllDept();  
        for (Dept dept : lists) {  
            System.out.println(dept);  
        }  
    }  
}  

以上内容来源于http://lydia-fly.iteye.com/blog/2153076

---

MapperScannerConfigurer处理过程源码分析

本文将分析mybatis与spring整合的MapperScannerConfigurer的底层原理，之前已经分析过java中实现动态，可以使用jdk自带api和cglib第三方库生成动态代理。本文分析的mybatis版本3.2.7，mybatis-spring版本1.2.2。
MapperScannerConfigurer介绍
MapperScannerConfigurer是spring和mybatis整合的mybatis-spring jar包中提供的一个类。

想要了解该类的作用，就得先了解MapperFactoryBean。

MapperFactoryBean的出现为了代替手工使用SqlSessionDaoSupport或SqlSessionTemplate编写数据访问对象(DAO)的代码,使用动态代理实现。

比如下面这个官方文档中的配置：

id="userMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
  <property name="mapperInterface" value="org.mybatis.spring.sample.mapper.UserMapper" />
  <property name="sqlSessionFactory" ref="sqlSessionFactory" />

org.mybatis.spring.sample.mapper.UserMapper是一个接口，我们创建一个MapperFactoryBean实例，然后注入这个接口和sqlSessionFactory（mybatis中提供的SqlSessionFactory接口，MapperFactoryBean会使用SqlSessionFactory创建SqlSession）这两个属性。

之后想使用这个UserMapper接口的话，直接通过spring注入这个bean，然后就可以直接使用了，spring内部会创建一个这个接口的动态代理。

当发现要使用多个MapperFactoryBean的时候，一个一个定义肯定非常麻烦，于是mybatis-spring提供了MapperScannerConfigurer这个类，它将会查找类路径下的映射器并自动将它们创建成MapperFactoryBean。

<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
  <property name="basePackage" value="org.mybatis.spring.sample.mapper" />
bean>

这段配置会扫描org.mybatis.spring.sample.mapper下的所有接口，然后创建各自接口的动态代理类。
MapperScannerConfigurer底层代码分析
以以下代码为示例进行讲解(部分代码，其他代码及配置省略)：

package org.format.dynamicproxy.mybatis.dao;
public interface UserDao {
    public User getById(int id);
    public int add(User user);    
    public int update(User user);    
    public int delete(User user);    
    public List getAll();    
}

"org.mybatis.spring.mapper.MapperScannerConfigurer">
    "basePackage" value="org.format.dynamicproxy.mybatis.dao"/>
    "sqlSessionFactoryBeanName" value="sqlSessionFactory"/>

我们先通过测试用例debug查看userDao的实现类到底是什么。

我们可以看到，userDao是1个MapperProxy类的实例。
看下MapperProxy的源码，没错，实现了InvocationHandler，说明使用了jdk自带的动态代理。

public class MapperProxy<T> implements InvocationHandler, Serializable {
     

  private static final long serialVersionUID = -6424540398559729838L;
  private final SqlSession sqlSession;
  private final Class mapperInterface;
  private final Map methodCache;

  public MapperProxy(SqlSession sqlSession, Class mapperInterface, Map methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
  }

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (Object.class.equals(method.getDeclaringClass())) {
      try {
        return method.invoke(this, args);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }

}

下面开始分析MapperScannerConfigurer的源码
MapperScannerConfigurer实现了BeanDefinitionRegistryPostProcessor接口，BeanDefinitionRegistryPostProcessor接口是一个可以修改spring工长中已定义的bean的接口，该接口有个postProcessBeanDefinitionRegistry方法。

然后我们看下ClassPathMapperScanner中的关键是如何扫描对应package下的接口的。

其实MapperScannerConfigurer的作用也就是将对应的接口的类型改造为MapperFactoryBean，而这个MapperFactoryBean的属性mapperInterface是原类型。MapperFactoryBean本文开头已分析过。

所以最终我们还是要分析MapperFactoryBean的实现原理！

MapperFactoryBean继承了SqlSessionDaoSupport类，SqlSessionDaoSupport类继承DaoSupport抽象类，DaoSupport抽象类实现了InitializingBean接口，因此实例个MapperFactoryBean的时候，都会调用InitializingBean接口的afterPropertiesSet方法。

DaoSupport的afterPropertiesSet方法：

MapperFactoryBean重写了checkDaoConfig方法：

然后通过spring工厂拿对应的bean的时候：

这里的SqlSession是SqlSessionTemplate，SqlSessionTemplate的getMapper方法：

Configuration的getMapper方法，会使用MapperRegistry的getMapper方法：

MapperRegistry的getMapper方法：

MapperProxyFactory构造MapperProxy：

没错！ MapperProxyFactory就是使用了jdk组带的Proxy完成动态代理。
MapperProxy本来一开始已经提到。MapperProxy内部使用了MapperMethod类完成方法的调用：

下面，我们以UserDao的getById方法来debug看看MapperMethod的execute方法是如何走的。

@Test
public void testGet() {
    int id = 1;
    System.out.println(userDao.getById(id));
}
<select id="getById" parameterType="int" resultType="org.format.dynamicproxy.mybatis.bean.User">
    SELECT * FROM users WHERE id = #{id}
select>

以上转载于http://www.cnblogs.com/fangjian0423/p/spring-mybatis-MapperScannerConfigurer-analysis.html

---

java动态代理浅析

最近在公司看到了mybatis与spring整合中MapperScannerConfigurer的使用，该类通过反向代理自动生成基于接口的动态代理类。

于是想起了java的动态代理，然后就有了这篇文章。

本文使用动态代理模拟处理事务的拦截器。

接口：

public interface UserService {
    public void addUser();
    public void removeUser();
    public void searchUser();
}

实现类：

public class UserServiceImpl implements UserService {
     
    public void addUser() {
        System.out.println("add user");
    }
    public void removeUser() {
        System.out.println("remove user");
    }
    public void searchUser() {
        System.out.println("search user");
    }
}

java动态代理的实现有2种方式
1.jdk自带的动态代理
使用jdk自带的动态代理需要了解InvocationHandler接口和Proxy类，他们都是在java.lang.reflect包下。

InvocationHandler介绍：

InvocationHandler是代理实例的调用处理程序实现的接口。

每个代理实例都具有一个关联的InvocationHandler。对代理实例调用方法时，这个方法会调用InvocationHandler的invoke方法。

Proxy介绍：

Proxy 提供静态方法用于创建动态代理类和实例。

实例(模拟AOP处理事务)：

public class TransactionInterceptor implements InvocationHandler {
     

    private Object target;

    public void setTarget(Object target) {
        this.target = target;
    }

    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
        System.out.println("start Transaction");
        method.invoke(target, args);
        System.out.println("end Transaction");
        return null;
    }

}

测试代码：

public class TestDynamicProxy {

    @Test
    public void testJDK() {
        TransactionInterceptor transactionInterceptor = new TransactionInterceptor();
        UserService userService = new UserServiceImpl();
        transactionInterceptor.setTarget(userService);
        UserService userServiceProxy =
                (UserService) Proxy.newProxyInstance(
                        userService.getClass().getClassLoader(),
                        userService.getClass().getInterfaces(),
                        transactionInterceptor);
        userServiceProxy.addUser();
    }

}

测试结果：

start Transaction
add user
end Transaction

很明显，我们通过userServiceProxy这个代理类进行方法调用的时候，会在方法调用前后进行事务的开启和关闭。

2. 第三方库cglib

CGLIB是一个功能强大的，高性能、高质量的代码生成库，用于在运行期扩展Java类和实现Java接口。

它与JDK的动态代理的之间最大的区别就是：

JDK动态代理是针对接口的，而cglib是针对类来实现代理的，cglib的原理是对指定的目标类生成一个子类，并覆盖其中方法实现增强，但因为采用的是继承，所以不能对final修饰的类进行代理。

实例：

public class UserServiceCallBack implements MethodInterceptor {
     

    @Override
    public Object intercept(Object o, Method method, Object[] args, MethodProxy methodProxy) throws Throwable {
        System.out.println("start Transaction by cglib");
        methodProxy.invokeSuper(o, args);
        System.out.println("end Transaction by cglib");
        return null;
    }

}

测试代码：

public class TestDynamicProxy {

    @Test
    public void testCGLIB() {
        Enhancer enhancer = new Enhancer();
        enhancer.setSuperclass(UserServiceImpl.class);
        enhancer.setCallback(new UserServiceCallBack());
        UserServiceImpl proxy = (UserServiceImpl)enhancer.create();
        proxy.addUser();
    }

}

测试结果：

start Transaction by cglib
add user
end Transaction by cglib

以上转载于http://www.cnblogs.com/fangjian0423/p/java-dynamic-proxy.html

---

mybatis如何根据mapper接口生成其实现类

mybatis里头给sqlSession指定执行哪条sql的时候，有两种方式，一种是写mapper的xml的namespace+statementId，如下：

public Student findStudentById(Integer studId) {
logger.debug(“Select Student By ID :{}”, studId);
SqlSession sqlSession = MyBatisSqlSessionFactory.getSqlSession();
try {
return sqlSession.selectOne(“com.mybatis3.StudentMapper.findStudentById”, studId);
} finally {
sqlSession.close();
}
}
另外一种方法是指定mapper的接口：

public Student findStudentById(Integer studId) {
logger.debug(“Select Student By ID :{}”, studId);
SqlSession sqlSession = MyBatisSqlSessionFactory.getSqlSession();
try {
StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
return studentMapper.findStudentById(studId);
} finally {
sqlSession.close();
}
}
一般的话，比较推荐第二种方法，因为手工写namespace和statementId极大增加了犯错误的概率，而且也降低了开发的效率。

问题
mapper的实现类如何生成

如果使用mapper接口的方式，问题来了，这个是个接口，通过sqlSession对象get出来的一定是个实现类，问题是，我们并没有手工去写 实现类，那么谁去干了这件事情呢？答案是mybatis通过JDK的动态代理方式，在启动加载配置文件时，根据配置mapper的xml去生成。

mybatis-spring帮忙做了什么

自动open和close session

一、mapper代理类是如何生成的
启动时加载解析mapper的xml

如果不是集成spring的，会去读取节点，去加载mapper的xml配置

<configuration>
    <settings>
        <setting name="cacheEnabled" value="true"/>
        <setting name="lazyLoadingEnabled" value="true"/>
        <setting name="multipleResultSetsEnabled" value="true"/>
        <setting name="useColumnLabel" value="true"/>
        <setting name="useGeneratedKeys" value="false"/>
        <setting name="defaultExecutorType" value="SIMPLE"/>
        <setting name="defaultStatementTimeout" value="2"/>
    settings>
    <typeAliases>
        <typeAlias alias="CommentInfo" type="com.xixicat.domain.CommentInfo"/>
    typeAliases>
    <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/demo"/>
                <property name="username" value="root"/>
                <property name="password" value=""/>
            dataSource>
        environment>
    environments>
    <mappers>
        <mapper resource="com/xixicat/dao/CommentMapper.xml"/>
    mappers>
configuration>

如果是集成spring的，会去读spring的sqlSessionFactory的xml配置中的mapperLocations，然后去解析mapper的xml

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
        
        <property name="configLocation" value="classpath:mybatis-config.xml"/>
        <property name="typeAliasesPackage" value="com.xixicat.domain"/>
        
        <property name="mapperLocations" value="classpath:com/xixicat/dao/*.xml"/>
    bean>

然后绑定namespace(XMLMapperBuilder)

private void bindMapperForNamespace() {
    String namespace = builderAssistant.getCurrentNamespace();
    if (namespace != null) {
      Class boundType = null;
      try {
        boundType = Resources.classForName(namespace);
      } catch (ClassNotFoundException e) {
        //ignore, bound type is not required
      }
      if (boundType != null) {
        if (!configuration.hasMapper(boundType)) {
          // Spring may not know the real resource name so we set a flag
          // to prevent loading again this resource from the mapper interface
          // look at MapperAnnotationBuilder#loadXmlResource
          configuration.addLoadedResource("namespace:" + namespace);
          configuration.addMapper(boundType);
        }
      }
    }
  }

这里先去判断该namespace能不能找到对应的class，若可以则调用

configuration.addMapper(boundType);
configuration委托给MapperRegistry:

public  void addMapper(Class type) {
     
    mapperRegistry.addMapper(type);
  }

生成该mapper的代理工厂(MapperRegistry)

public  void addMapper(Class type) {
     
    if (type.isInterface()) {
      if (hasMapper(type)) {
     
        throw new BindingException("Type " + type + " is already known to the MapperRegistry.");
      }
      boolean loadCompleted = false;
      try {
        knownMappers.put(type, new MapperProxyFactory<T>(type));
        // It's important that the type is added before the parser is run
        // otherwise the binding may automatically be attempted by the
        // mapper parser. If the type is already known, it won't try.
        MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type);
        parser.parse();
        loadCompleted = true;
      } finally {
        if (!loadCompleted) {
          knownMappers.remove(type);
        }
      }
    }
  }

这里的重点就是MapperProxyFactory类：

public class MapperProxyFactory {

  private final Class mapperInterface;
  private final Map methodCache = new ConcurrentHashMap();

  public MapperProxyFactory(Class mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  public Class getMapperInterface() {
    return mapperInterface;
  }

  public Map getMethodCache() {
    return methodCache;
  }

  @SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }

  public T newInstance(SqlSession sqlSession) {
    final MapperProxy mapperProxy = new MapperProxy(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }

}

getMapper的时候生成mapper代理类

@SuppressWarnings("unchecked")
  public  T getMapper(Class type, SqlSession sqlSession) {
    final MapperProxyFactory mapperProxyFactory = (MapperProxyFactory) knownMappers.get(type);
    if (mapperProxyFactory == null) {
      throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
    }
    try {
      return mapperProxyFactory.newInstance(sqlSession);
    } catch (Exception e) {
      throw new BindingException("Error getting mapper instance. Cause: " + e, e);
    }
  }

new出来MapperProxy

public T newInstance(SqlSession sqlSession) {
    final MapperProxy mapperProxy = new MapperProxy(sqlSession, mapperInterface, methodCache);
    return newInstance(mapperProxy);
  }
@SuppressWarnings("unchecked")
  protected T newInstance(MapperProxy mapperProxy) {
    return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy);
  }
这里给代理类注入了sqlSession

MapperProxy实现InvocationHandler接口进行拦截代理

public class MapperProxy<T> implements InvocationHandler, Serializable {
     

  private static final long serialVersionUID = -6424540398559729838L;
  private final SqlSession sqlSession;
  private final Class mapperInterface;
  private final Map methodCache;

  public MapperProxy(SqlSession sqlSession, Class mapperInterface, Map methodCache) {
    this.sqlSession = sqlSession;
    this.mapperInterface = mapperInterface;
    this.methodCache = methodCache;
  }

  @Override
  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
    if (Object.class.equals(method.getDeclaringClass())) {
      try {
        return method.invoke(this, args);
      } catch (Throwable t) {
        throw ExceptionUtil.unwrapThrowable(t);
      }
    }
    final MapperMethod mapperMethod = cachedMapperMethod(method);
    return mapperMethod.execute(sqlSession, args);
  }

  private MapperMethod cachedMapperMethod(Method method) {
    MapperMethod mapperMethod = methodCache.get(method);
    if (mapperMethod == null) {
      mapperMethod = new MapperMethod(mapperInterface, method, sqlSession.getConfiguration());
      methodCache.put(method, mapperMethod);
    }
    return mapperMethod;
  }
}

这里的代理拦截，主要是寻找到MapperMethod，通过它去执行SQL。
MapperMethod委托给SqlSession去执行sql

public Object execute(SqlSession sqlSession, Object[] args) {
    Object result;
    if (SqlCommandType.INSERT == command.getType()) {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.insert(command.getName(), param));
    } else if (SqlCommandType.UPDATE == command.getType()) {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.update(command.getName(), param));
    } else if (SqlCommandType.DELETE == command.getType()) {
      Object param = method.convertArgsToSqlCommandParam(args);
      result = rowCountResult(sqlSession.delete(command.getName(), param));
    } else if (SqlCommandType.SELECT == command.getType()) {
      if (method.returnsVoid() && method.hasResultHandler()) {
        executeWithResultHandler(sqlSession, args);
        result = null;
      } else if (method.returnsMany()) {
        result = executeForMany(sqlSession, args);
      } else if (method.returnsMap()) {
        result = executeForMap(sqlSession, args);
      } else {
        Object param = method.convertArgsToSqlCommandParam(args);
        result = sqlSession.selectOne(command.getName(), param);
      }
    } else if (SqlCommandType.FLUSH == command.getType()) {
        result = sqlSession.flushStatements();
    } else {
      throw new BindingException("Unknown execution method for: " + command.getName());
    }
    if (result == null && method.getReturnType().isPrimitive() && !method.returnsVoid()) {
      throw new BindingException("Mapper method '" + command.getName() 
          + " attempted to return null from a method with a primitive return type (" + method.getReturnType() + ").");
    }
    return result;
  }

其实这里就回到了第一种模式，该模式是直接指定了statement的Id（这里是command.getName()），而通过mapper的接口方式，则多了这么步骤，最后通过MapperMethod，给sqlSession传入statement的id。

sqlSession其实自己也不执行sql，它只是mybatis对外公布的一个api入口，具体它委托给了executor去执行sql。

什么时候去getMapper

• 手工get，比如

  public void createStudent(Student student) {
  SqlSession sqlSession = MyBatisSqlSessionFactory.getSqlSession();
  try {
  StudentMapper studentMapper = sqlSession.getMapper(StudentMapper.class);
  studentMapper.insertStudent(student);
  sqlSession.commit();
  } finally {
  sqlSession.close();
  }
  }

• 集成spring的话
  在spring容器给指定的bean注入mapper的时候get出来(见MapperFactoryBean的getObject方法)
  二、mybatis-spring帮忙做了什么
  通过MapperScannerConfigurer将mapper适配成spring bean

    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
        <property name="basePackage" value="com.xixicat.dao"/>
    bean>

这里使用 MapperFactoryBean将Mapper接口配置成 Spring bean 实体同时注入sqlSessionFactory。
MapperScannerConfigurer给每个mapper生成对应的MapperFactoryBean

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));
  }

委托给ClassPathMapperScanner去scan

public Set doScan(String... basePackages) {
    Set beanDefinitions = super.doScan(basePackages);

    if (beanDefinitions.isEmpty()) {
      logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
    } else {
      for (BeanDefinitionHolder holder : beanDefinitions) {
        GenericBeanDefinition definition = (GenericBeanDefinition) holder.getBeanDefinition();

        if (logger.isDebugEnabled()) {
          logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName() 
              + "' and '" + definition.getBeanClassName() + "' mapperInterface");
        }

        // the mapper interface is the original class of the bean
        // but, the actual class of the bean is MapperFactoryBean
        definition.getPropertyValues().add("mapperInterface", definition.getBeanClassName());
        definition.setBeanClass(MapperFactoryBean.class);

        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) {
          if (logger.isDebugEnabled()) {
            logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
          }
          definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
        }
      }
    }

    return beanDefinitions;
  }

这里出现了MapperFactoryBean的身影，然后判断配置文件是指定注入sqlSessionFactory，还是 sqlTemplate(二者不能同时指定，这里是指定了sqlSessionFactory)。这里通过 sqlSessionFactoryBeanName暂时先注入引用，因为此时还在给spring托管的bean进行create，不确定 sqlSessionFactory是否已经被创建。
关于MapperFactoryBean

public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> {
     

  private Class mapperInterface;

  private boolean addToConfig = true;

  /**
   * Sets the mapper interface of the MyBatis mapper
   *
   * @param mapperInterface class of the interface
   */
  public void setMapperInterface(Class mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  /**
   * If addToConfig is false the mapper will not be added to MyBatis. This means
   * it must have been included in mybatis-config.xml.
   * 

   * If it is true, the mapper will be added to MyBatis in the case it is not already
   * registered.
   * 

   * By default addToCofig is true.
   *
   * @param addToConfig
   */
  public void setAddToConfig(boolean addToConfig) {
    this.addToConfig = addToConfig;
  }

  /**
   * {
     @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);
  }

  /**
   * {
     @inheritDoc}
   */
  public Class getObjectType() {
    return this.mapperInterface;
  }

  /**
   * {
     @inheritDoc}
   */
  public boolean isSingleton() {
    return true;
  }

}

注意这里继承了SqlSessionDaoSupport，在spring把sqlSessionFactory创建出来后，会去把之前注入的引用改为真的实例，调用SqlSessionDaoSupport的setSqlSessionFactory方法。

public abstract class SqlSessionDaoSupport extends DaoSupport {
     

  private SqlSession sqlSession;

  private boolean externalSqlSession;

  public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
    if (!this.externalSqlSession) {
      this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
    }
  }

  public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {
    this.sqlSession = sqlSessionTemplate;
    this.externalSqlSession = true;
  }

  /**
   * Users should use this method to get a SqlSession to call its statement methods
   * This is SqlSession is managed by spring. Users should not commit/rollback/close it
   * because it will be automatically done.
   *
   * @return Spring managed thread safe SqlSession
   */
  public SqlSession getSqlSession() {
    return this.sqlSession;
  }

  /**
   * {@inheritDoc}
   */
  protected void checkDaoConfig() {
    notNull(this.sqlSession, "Property 'sqlSessionFactory' or 'sqlSessionTemplate' are required");
  }

}

这里值得注意的是setSqlSessionFactory方法new了一个SqlSessionTemplate。
SqlSessionTemplate
它的一个重要的构造器为

public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
      PersistenceExceptionTranslator exceptionTranslator) {

    notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
    notNull(executorType, "Property 'executorType' is required");

    this.sqlSessionFactory = sqlSessionFactory;
    this.executorType = executorType;
    this.exceptionTranslator = exceptionTranslator;
    this.sqlSessionProxy = (SqlSession) newProxyInstance(
        SqlSessionFactory.class.getClassLoader(),
        new Class[] { SqlSession.class },
        new SqlSessionInterceptor());
  }

mybatis-srping比传统mybatis方法多做的事情就在于此，生成了一个sqlSessionProxy。这里static import了java.lang.reflect.Proxy.newProxyInstance;也就是使用使用jdk代理进行了 SqlSessionInterceptor拦截。
SqlSessionInterceptor

private class SqlSessionInterceptor implements InvocationHandler {
     
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      SqlSession sqlSession = getSqlSession(
          SqlSessionTemplate.this.sqlSessionFactory,
          SqlSessionTemplate.this.executorType,
          SqlSessionTemplate.this.exceptionTranslator);
      try {
        Object result = method.invoke(sqlSession, args);
        if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
          // force commit even on non-dirty sessions because some databases require
          // a commit/rollback before calling close()
          sqlSession.commit(true);
        }
        return result;
      } catch (Throwable t) {
        Throwable unwrapped = unwrapThrowable(t);
        if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
          // release the connection to avoid a deadlock if the translator is no loaded. See issue #22
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
          sqlSession = null;
          Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
          if (translated != null) {
            unwrapped = translated;
          }
        }
        throw unwrapped;
      } finally {
        if (sqlSession != null) {
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
        }
      }
    }
  }

到了这里就明白了mybatis-spring帮忙做了session的open和close。
以上转载于http://www.cnblogs.com/ChenLLang/p/5307590.html

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