实践MyBatis-Spring

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MyBatis-Spring

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<dependency>
	<groupId>org.mybatis</groupId>
	<artifactId>mybatis-spring</artifactId>
	<version>1.3.1</version>
</dependency>

SqlSessionFactoryBean

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<bean id = "sqlSessionFactory" class = "org.mybatis.spring.SqlSessionFactoryBean">
	<property name="dataSource" ref="dataSource" />
</bean>

img

mapperLocations：支持通配符，比如：classpath*:sqlmap/*-mapper.xml"

一般情况下，mybatis的配置文件可以不需要（mybatis-config.xml），如下情况可能需要（configLocation）：

  1. 需要定制<settings>，其实configurationProperties属性可以支持
  2. 需要定制<typeAliases>，其实typeHandlersPackage属性可以支持
  3. mapper xml和mapper class不在相同的classpath下，其实mapperLocation属性可以支持

mybatis配置文件中会被忽略。

SqlSessionTemplate

SqlSession的一种实现，使用了代理模式，线程安全，由于每次都获取新的SQLSession，因而不支持一级缓存

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public class UserDaoImpl implements UserDao {
   private SqlSession sqlSession;
   public void setSqlSession(SqlSession sqlSession) {
     	this.sqlSession = sqlSession;
   }
   public User getUser(String userId) {
     	return (User) sqlSession.selectOne("org.mybatis.spring.sample.mapper.UserMapper.getUser", userId);
   }
}

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<bean id = "sqlSession" class = "org.mybatis.spring.SqlSessionTemplate">
  <constructor-arg index="0" ref="sqlSessionFactory" />
</bean>

<bean id = "userDao" class = "org.mybatis.spring.sample.dao.UserDaoImpl">
  <property name="sqlSession" ref="sqlSession" />
</bean>

SqlSessionDaoSupport

基于SqlSessionTemplate的一种扩展

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public class UserDaoImpl extends SqlSessionDaoSupport implements UserDao {
	public User getUser (String userId) {
		return (User) getSqlSession().selectOne("org.mybatis.spring.sample.mapper.UserMapper.getUser",userId);
    }
}

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<bean id="userMapper" class="org.mybatis.spring.sample.mapper.UserDaoImpl">
  <property name="sqlSessionFactory" ref="sqlSessionFactory" />
</bean>

MapperFactoryBean

Spring中定义Mapper，线程安全，每次都获取新的SQLSession

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<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>

MapperFactoryBean默认添加了依赖注入注解@Autowired

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

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public abstract class SqlSessionDaoSupport extends DaoSupport {

  private SqlSession sqlSession;

  private boolean externalSqlSession;

  @Autowired(required = false)
  public final void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
    if (!this.externalSqlSession) {
      this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
    }
  }

  @Autowired(required = false)
  public final void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {
    this.sqlSession = sqlSessionTemplate;
    this.externalSqlSession = true;
  }
  ...
}

Mapper Scan

基于扫描自动生产Mapper

base-package：扫描Mapper的基础包，支持Ant匹配

factory-ref or template-ref：

annotation：被此注解的mapper接口，比如@Mapper

marker-interface：实现此接口的mapper接口，比如MyMapper

NOTE：<context:component-scan/> won’t be able to scan and register mappers. Mappers are interfaces and, in order to register them to Spring, the scanner must know how to create a MapperFactoryBean for each interface it finds.

<mybatis:scan/>

类似<context:component-scan/>

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<mybatis:scan base-package="org.mybatis.spring.sample.mapper" />

@MapperScan

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@Configuration
@MapperScan("org.mybatis.spring.sample.mapper")
public class AppConfig {

  @Bean
  public DataSource dataSource() {
    return new EmbeddedDatabaseBuilder().addScript("schema.sql").build()
  }

  @Bean
  public SqlSessionFactory sqlSessionFactory() throws Exception {
    SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
    sessionFactory.setDataSource(dataSource());
    return sessionFactory.getObject();
  }
}

MapperScannerConfigurer

推荐使用sqlSessionFactoryBean和sqlSessionTemplateBean，如果没有显示注入，由于开启了按类型自动注入，则会自动注入，参见如下源代码：

org.mybatis.spring.mapper.ClassPathMapperScanner.processBeanDefinitions(Set<BeanDefinitionHolder>)

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