spring-mybatis与原生mybatis使用对比

原生mybatis使用方法：

String resource = "mybatis-config.xml"; 
InputStream inputStream = Resources.getResourceAsStream(resource);
SqlSessionFactory sqlSessionFactory = new SqlSessionFactoryBuilder().build(inputStream); 
SqlSession session = sqlSessionFactory.openSession();    
try {      
           Employee employee = new Employee(null, "doubi", "1", "ddd@sys.com"); 
           EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);     
           mapper.addEmp(employee);               
           session.commit();    
} finally {
      session.close();    
}

spring使用方法，直接注入即可

@Autowired
EmployeeMapper employeeMapper

那么spring为我们做了什么？下面研究一下mybatis-spring.jar这个jar包

首先来看一下如何使用spring整合mybatis，下面是使用spring-mybatis的四种方法：

方法一：（使用MapperFactoryBean）

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <property name="dataSource" ref="dataSource"/>        
    <property name="configLocation" value="classpath:mybatis-config.xml"></property>        
    <!-- 自动扫描mapping.xml文件 -->        
    <property name="mapperLocations" value="classpath:mapper/*.xml"></property>    
</bean>
<!--上面生成sqlSessionFactory的几个方法基本相同-->

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

这样做的缺点是每一个mapper接口都要在xml里配置一下

方法二：采用接口org.apache.ibatis.session.SqlSession的实现类 org.mybatis.spring.SqlSessionTemplate

mybatis中, sessionFactory可由SqlSessionFactoryBuilder.来创建。MyBatis-Spring 中，使用了SqlSessionFactoryBean来替代。SqlSessionFactoryBean有一个必须属性dataSource，另外其还有一个通用属性configLocation（用来指定mybatis的xml配置文件路径）。

SqlSessionFactoryBean即相当于原生mybatis中的SqlSessionFactoryBuilder

<!-- spring和MyBatis完美整合，不需要mybatis的配置映射文件 -->    
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">        
    <property name="dataSource" ref="dataSource" />        
    <property name="configLocation"  value="classpath:sqlMapConfig.xml"/>        
    <!-- 自动扫描mapping.xml文件，**表示迭代查找,也可在sqlMapConfig.xml中单独指定xml文件-->        
    <property name="mapperLocations" value="classpath:com/hua/saf/**/*.xml" />    
</bean>        

<!-- mybatis spring sqlSessionTemplate,使用时直接让spring注入即可 -->    
<bean id="sqlSessionTemplate" class="org.mybatis.spring.SqlSessionTemplate">        
    <constructor-arg index="0" ref="sqlSessionFactory"></constructor-arg>    
</bean>

//使用方法：
@Repositorypublic class UserDao{    @Resource    private SqlSessionTemplate sqlSessionTemplate;        public User getUser(int id) {        return sqlSessionTemplate.selectOne(this.getClass().getName() + ".getUser", 1);    }   }

为什么可以这样写，来看一下SqlSessionTemplate

public class SqlSessionTemplate implements SqlSession {  private final SqlSessionFactory sqlSessionFactory;  private final ExecutorType executorType;  private final SqlSession sqlSessionProxy;  private final PersistenceExceptionTranslator exceptionTranslator;  /**   * Constructs a Spring managed SqlSession with the {@code SqlSessionFactory}   * provided as an argument.   *   * @param sqlSessionFactory   */  public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {    this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());  }

........省略......
   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());  }

}

如上面代码所示，SqlSessionTemplate类实现了原生Mybatis中的SqlSession接口，实际上它就是原生mybatis中的SqlSession

方法三：采用抽象类 org.mybatis.spring.support.SqlSessionDaoSupport 提供SqlSession

<!-- spring和MyBatis完美整合，不需要mybatis的配置映射文件 -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <property name="configLocation"  value="classpath:sqlMapConfig.xml"/>
        <!-- 自动扫描mapping.xml文件，**表示迭代查找,也可在sqlMapConfig.xml中单独指定xml文件-->
        <property name="mapperLocations" value="classpath:com/hua/saf/**/*.xml" />
    </bean>

public  class BaseDao extends SqlSessionDaoSupport{  //使用sqlSessionFactory  @Autowired   private  SqlSessionFactory sqlSessionFactory;      @Autowired   public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory)    {        super.setSqlSessionFactory(sqlSessionFactory);    }    /**   * 执行insert操作   * @param statement   * @return   */  public int insert(String statement) {    return getSqlSession().insert(statement);  }  /**   * 执行insert操作   * @param statement   * @param parameter   * @return   */  public int insert(String statement, Object parameter) {    return getSqlSession().insert(statement, parameter);  }    public int update(String statement) {    return getSqlSession().update(statement);  }  public int update(String statement, Object parameter) {    return getSqlSession().update(statement, parameter);  }    public int delete(String statement) {    return getSqlSession().delete(statement);  }    public int delete(String statement, Object parameter) {    return getSqlSession().delete(statement, parameter);  }    /**   * 获取一个list集合   * @param statement   * @return   */  public List<?> selectList(String statement) {    return getSqlSession().selectList(statement);  }    /**   * 根据参数 获取一个list集合   * @param statement   * @param parameter   * @return   */  public List<?> selectList(String statement, Object parameter) {    return getSqlSession().selectList(statement, parameter);  }    public Map<?, ?> selectMap(String statement, String mapKey) {    return getSqlSession().selectMap(statement, mapKey);  }  public Map<?, ?> selectMap(String statement, Object parameter, String mapKey) {    return getSqlSession().selectMap(statement, parameter, mapKey);  }    /**   * 获取Object对象   * @param statement   * @return   */  public Object selectOne(String statement) {    return getSqlSession().selectOne(statement);  }    /**   * 获取connection, 以便执行较为复杂的用法   * @return   */  public Connection getConnection() {    return getSqlSession().getConnection();  }  }

如上代码，一个Dao类继承了SqlSessionDaoSupport类后，就可以在类中注入SessionFactory，进而通过getSqlSession()获取当前SqlSession

下面是 SqlSessionDaoSupport的源码 ，它是一个抽象类，并拥有sqlSession属性，在setSqlSessionFactory方法中实例化了该sqlSession：

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;  }  public SqlSession getSqlSession() {    return this.sqlSession;  }  protected void checkDaoConfig() {    notNull(this.sqlSession, "Property 'sqlSessionFactory' or 'sqlSessionTemplate' are required");  }}

方法四：（也是 最常见的使用方法 ，使用MapperScannerConfigurer，它将会查找类路径下的映射器并自动将它们创建成MapperFactoryBean）

由于直接使用MapperFactoryBean会在配置文件中配置大量mapper，因此这里使用包扫描的方式通过注解获取该bean

<!-- spring和MyBatis完美整合，不需要mybatis的配置映射文件 -->
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource" />
        <!-- 自动扫描mapping.xml文件，**表示迭代查找 -->
        <property name="mapperLocations" value="classpath:com/hua/saf/**/*.xml" />
    </bean>

    <!-- DAO接口所在包名，Spring会自动查找其下的类 ,包下的类需要使用@MapperScan注解,否则容器注入会失败 -->
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.hua.saf.*" />
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" />
    </bean>




//使用如下代码，即可完成注入
@Resource
private UserDao userDao;

下面看一下MapperScannerConfigurer这个类：

public class MapperScannerConfigurer implements BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware {  private String basePackage;  private boolean addToConfig = true;  private SqlSessionFactory sqlSessionFactory;  private SqlSessionTemplate sqlSessionTemplate;  private String sqlSessionFactoryBeanName;  private String sqlSessionTemplateBeanName;  private Class<? extends Annotation> annotationClass;  private Class<?> markerInterface;  private ApplicationContext applicationContext;  private String beanName;  private boolean processPropertyPlaceHolders;  private BeanNameGenerator nameGenerator;




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));  }

ClassPathMapperScanner ：

public Set<BeanDefinitionHolder> doScan(String... basePackages) {    Set<BeanDefinitionHolder> 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;  }

总结：spring-mybatis与原生Mybatis相比，如下概念：

1）SqlSessionFactory类在两者中都存在

2）前者用SqlSessionFactoryBean生成SqlSessionFactory，后者则使用SqlSessionFactoryBuilder;

3）前者使用SqlSessionTemplate，后者使用SqlSession，实际上前者实现了后者

4）MapperFactoryBean中实现了原生mybatis中下面的步骤，因此通过该类可以直接获取到一个mapper接口的实现对象

EmployeeMapper mapper = session.getMapper(EmployeeMapper.class);

以上是个人总结，如有错误，欢迎指正