spring-mybatis與原生mybatis使用對比

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為我們做了什么？下面研究一下mybatis-spring.jar這個jar包
首先來看一下如何使用spring整合mybatis，下面是使用spring-mybatis的四種方法：
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>        
    <!-- 自動掃描mapping.xml文件 -->        
    <property name="mapperLocations" value="classpath:mapper/*.xml"></property>    
</bean>
<!--上面生成sqlSessionFactory的幾個方法基本相同-->

<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>

這樣做的缺點是每一個mapper接口都要在xml里配置一下

方法二：采用接口org.apache.ibatis.session.SqlSession的實現類
org.mybatis.spring.SqlSessionTemplate

mybatis中, sessionFactory可由SqlSessionFactoryBuilder.來創建。MyBatis-Spring
中，使用了SqlSessionFactoryBean來替代。SqlSessionFactoryBean有一個必須屬性dataSource，另外其還有一個通用屬性configLocation（用來指定mybatis的xml配置文件路徑）。

SqlSessionFactoryBean即相當于原生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"/>        
    <!-- 自動掃描mapping.xml文件，**表示迭代查找,也可在sqlMapConfig.xml中單獨指定xml文件-->        
    <property name="mapperLocations" value="classpath:com/hua/saf/**/*.xml" />    
</bean>        

<!-- mybatis spring sqlSessionTemplate,使用時直接讓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);    }   }

為什么可以這樣寫，來看一下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());  }

}

如上面代碼所示，SqlSessionTemplate類實現了原生Mybatis中的SqlSession接口，實際上它就是原生mybatis中的SqlSession

方法三：采用抽象類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"/>
        <!-- 自動掃描mapping.xml文件，**表示迭代查找,也可在sqlMapConfig.xml中單獨指定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);    }    /**   * 執行insert操作   * @param statement   * @return   */  public int insert(String statement) {    return getSqlSession().insert(statement);  }  /**   * 執行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);  }    /**   * 獲取一個list集合   * @param statement   * @return   */  public List<?> selectList(String statement) {    return getSqlSession().selectList(statement);  }    /**   * 根據參數 獲取一個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);  }    /**   * 獲取Object對象   * @param statement   * @return   */  public Object selectOne(String statement) {    return getSqlSession().selectOne(statement);  }    /**   * 獲取connection, 以便執行較為復雜的用法   * @return   */  public Connection getConnection() {    return getSqlSession().getConnection();  }  }

    如上代碼，一個Dao類繼承了SqlSessionDaoSupport類后，就可以在類中注入SessionFactory，進而通過getSqlSession()獲取當前SqlSession

    下面是SqlSessionDaoSupport的源碼，它是一個抽象類，并擁有sqlSession屬性，在setSqlSessionFactory方法中實例化了該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：（也是最常見的使用方法，使用MapperScannerConfigurer，它將會查找類路徑下的映射器并自動將它們創建成MapperFactoryBean）

    由于直接使用MapperFactoryBean會在配置文件中配置大量mapper，因此這里使用包掃描的方式通過注解獲取該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" />
        <!-- 自動掃描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會自動查找其下的類 ,包下的類需要使用@MapperScan注解,否則容器注入會失敗 -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.hua.saf.*" />
        <property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" />
</bean>

//使用如下代碼，即可完成注入@Resource
br/>@Resource

下面看一下MapperScannerConfigurer這個類：

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; }

總結：spring-mybatis與原生Mybatis相比，如下概念：

1）SqlSessionFactory類在兩者中都存在

2）前者用SqlSessionFactoryBean生成SqlSessionFactory，后者則使用SqlSessionFactoryBuilder;

3）前者使用SqlSessionTemplate，后者使用SqlSession，實際上前者實現了后者

4）MapperFactoryBean中實現了原生mybatis中下面的步驟，因此通過該類可以直接獲取到一個mapper接口的實現對象

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

以上是個人總結，如有錯誤，歡迎指正

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