mybatis與spring整合源碼分析

1.配置applicationContext.xml

	<bean id="dataSource" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close">
		<property name="driverClassName" value="com.mysql.jdbc.Driver" />
		<property name="url" value="jdbc:mysql://122.152.131.141:3306/school" />
		<property name="username" value="zw121" />
		<property name="password" value="122334" />
	</bean>

	<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
		<property name="dataSource" ref="dataSource" />
		<property name="configLocation" value="classpath:mybatis.xml" />
		<property name="mapperLocations">
			<array>
				<!-- 配置單個映射文件 -->
				<!-- <value>classpath:mappers/UserMapper.xml</value> -->
				<!-- 配置多個映射文件使用 * 通配符 -->
				<value>classpath:mappers/*Mapper.xml</value>
			</array>
		</property>
		<!-- 配置別名，使用包掃描 -->
		<property name="typeAliasesPackage" value="com.qhf.pojo"></property>
	</bean>
	
	<!-- 掃描接口文件，其2選1 -->
	<!-- 1.掃描接口文件，只能單個文件 -->
	<!-- 
	<bean id="userMapper" class="org.mybatis.spring.mapper.MapperFactoryBean">
		<property name="mapperInterface" value="com.qhf.dao.UserMapper"></property>
		<property name="sqlSessionFactory" ref="sqlSessionFactory"></property>
	</bean>
	 -->
	<!-- 2.掃描包下的接口文件，此方法簡便 -->
	<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
		<property name="basePackage" value="com.qhf.dao"></property>
	</bean>

主要就是配置 SqlSessionFactoryBean 的初始化 bean 對象
還有 MapperFactoryBean 的初始化 bean 對象，此 bean 針對一個 mapper 接口
MapperScannerConfigurer 的初始化 bean 對象，掃描包下的全部接口文件

2.SqlSessionFactoryBean

實現接口 FactoryBean 接口，getBean() 方法返回 sqlSessionFactory 工廠類對象。
實現 InitializingBean 接口，則 bean 初始化時會調用此類的 afterPropertiesSet() 方法。

public class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>, InitializingBean, ApplicationListener<ApplicationEvent> { 
  //...
  @Override
  public void afterPropertiesSet() throws Exception {
    notNull(dataSource, "Property 'dataSource' is required");
    notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");

    this.sqlSessionFactory = buildSqlSessionFactory();
  }

  @Override
  public SqlSessionFactory getObject() throws Exception {
    if (this.sqlSessionFactory == null) {
      afterPropertiesSet();
    }

    return this.sqlSessionFactory;
  }
}

sqlSessionFactory 的初始化實際上就是調用 buildSqlSessionFactory() 方法時初始化的。

protected SqlSessionFactory buildSqlSessionFactory() throws IOException {

    Configuration configuration;

    XMLConfigBuilder xmlConfigBuilder = null;
    if (this.configLocation != null) {
      xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
      configuration = xmlConfigBuilder.getConfiguration();
    } else {
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Property 'configLocation' not specified, using default MyBatis Configuration");
      }
      configuration = new Configuration();
      configuration.setVariables(this.configurationProperties);
    }

    if (this.objectFactory != null) {
      configuration.setObjectFactory(this.objectFactory);
    }

    if (this.objectWrapperFactory != null) {
      configuration.setObjectWrapperFactory(this.objectWrapperFactory);
    }

    if (hasLength(this.typeAliasesPackage)) {
      String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage,
          ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
      for (String packageToScan : typeAliasPackageArray) {
        configuration.getTypeAliasRegistry().registerAliases(packageToScan,
                typeAliasesSuperType == null ? Object.class : typeAliasesSuperType);
        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Scanned package: '" + packageToScan + "' for aliases");
        }
      }
    }

    if (!isEmpty(this.typeAliases)) {
      for (Class<?> typeAlias : this.typeAliases) {
        configuration.getTypeAliasRegistry().registerAlias(typeAlias);
        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Registered type alias: '" + typeAlias + "'");
        }
      }
    }

    if (!isEmpty(this.plugins)) {
      for (Interceptor plugin : this.plugins) {
        configuration.addInterceptor(plugin);
        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Registered plugin: '" + plugin + "'");
        }
      }
    }

    if (hasLength(this.typeHandlersPackage)) {
      String[] typeHandlersPackageArray = tokenizeToStringArray(this.typeHandlersPackage,
          ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);
      for (String packageToScan : typeHandlersPackageArray) {
        configuration.getTypeHandlerRegistry().register(packageToScan);
        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Scanned package: '" + packageToScan + "' for type handlers");
        }
      }
    }

    if (!isEmpty(this.typeHandlers)) {
      for (TypeHandler<?> typeHandler : this.typeHandlers) {
        configuration.getTypeHandlerRegistry().register(typeHandler);
        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Registered type handler: '" + typeHandler + "'");
        }
      }
    }

    if (xmlConfigBuilder != null) {
      try {
        xmlConfigBuilder.parse();

        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Parsed configuration file: '" + this.configLocation + "'");
        }
      } catch (Exception ex) {
        throw new NestedIOException("Failed to parse config resource: " + this.configLocation, ex);
      } finally {
        ErrorContext.instance().reset();
      }
    }

    if (this.transactionFactory == null) {
      this.transactionFactory = new SpringManagedTransactionFactory();
    }

    configuration.setEnvironment(new Environment(this.environment, this.transactionFactory, this.dataSource));

    if (this.databaseIdProvider != null) {
      try {
        configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
      } catch (SQLException e) {
        throw new NestedIOException("Failed getting a databaseId", e);
      }
    }

    if (!isEmpty(this.mapperLocations)) {
      for (Resource mapperLocation : this.mapperLocations) {
        if (mapperLocation == null) {
          continue;
        }

        try {
          XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
              configuration, mapperLocation.toString(), configuration.getSqlFragments());
          xmlMapperBuilder.parse();
        } catch (Exception e) {
          throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
        } finally {
          ErrorContext.instance().reset();
        }

        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Parsed mapper file: '" + mapperLocation + "'");
        }
      }
    } else {
      if (LOGGER.isDebugEnabled()) {
        LOGGER.debug("Property 'mapperLocations' was not specified or no matching resources found");
      }
    }

    return this.sqlSessionFactoryBuilder.build(configuration);
  }

總體來說：
- 生成一個 Configuration 對象，此對象是 mybatis 的核心。
- 把配置的 configLocation（mybatis原始配置文件，整合之後基本不用配置），objectFactory，objectWrapperFactory，typeAliasesPackage（別名，省了configLocation 裏別名的配置），typeAliases，plugins，typeHandlersPackage，typeHandlers，transactionFactory，databaseIdProvider，mapperLocations（掃描 xml 映射文件）初始化和解析。
- 最後通過 sqlSessionFactoryBuilder.build(configuration) 方法把此 configuration 對象傳給了 DefaultSqlSessionFactory 實例對象，其中 DefaultSqlSessionFactory 實現了 SqlSessionFactory 接口，是生產 SqlSession 的工廠。

public class SqlSessionFactoryBuilder {
  //...
  public SqlSessionFactory build(Configuration config) {
    return new DefaultSqlSessionFactory(config);
  }
}


public class DefaultSqlSessionFactory implements SqlSessionFactory {

  private final Configuration configuration;

  public DefaultSqlSessionFactory(Configuration configuration) {
    this.configuration = configuration;
  }
  //...
}

當單獨使用 mybatis 時通過 sqlSessionFactory.openSession() 來獲取 sqlSession，才能操作數據庫。

SqlSession sqlSession = sqlSessionFactory.openSession();
UserMapper userMapper = sqlSession.getMapper(UserMapper.class);
//...

當交給 Spring 管理，可以通過下面方式獲取 userMapper 對象

UserMapper userMapper = (UserMapper)context.getBean("userMapper");

或

@Autowired

UserMapper userMapper;

先看此配置，是對單個 mapper 接口的 bean 對象的創建。

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

3.MapperFactoryBean

配置 MapperFactoryBean 的 bean 時的屬性是 mapperInterface，sqlSessionFactory

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

<property name="sqlSessionFactory" ref="sqlSessionFactory"/>屬性初始化時會調用 MapperFactoryBean 從父類 SqlSessionDaoSupport 中繼承下來的 setSqlSessionFactory() 方法，並使用 SqlSessionTemplate 對 sqlSessionFactory 進行加工生產 sqlSession（通過動態代理）

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

MapperFactoryBean 實現了 InitializingBean 接口，則 bean 初始化時會調用此類的 afterPropertiesSet() 方法，此方法在其父類中。

public abstract class DaoSupport implements InitializingBean {
    @Override
	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);
		}
	}
}

checkDaoConfig() 方法在 DaoSupport 的子類 MapperFactoryBean 中實現。

public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> {
  @Override
  protected void checkDaoConfig() {
    super.checkDaoConfig(); // notNull(this.sqlSession, "Property 'sqlSessionFactory' or 'sqlSessionTemplate' are required");

    notNull(this.mapperInterface, "Property 'mapperInterface' is required");

    Configuration configuration = getSqlSession().getConfiguration();
    if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
      try {
        configuration.addMapper(this.mapperInterface);
      } catch (Exception e) {
        logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", e);
        throw new IllegalArgumentException(e);
      } finally {
        ErrorContext.instance().reset();
      }
    }
  }
}

getSession() 方法返回 this.sqlSession，getConfiguration() 返回 Configuration 對象
再檢查 Configuration 對象中是否已配置了 <property name="mapperInterface" value="com.qhf.dao.UserMapper"/> 此mapper 接口（因爲手動配置，所以還是要檢查。重點是 mybatis 中讀取映射文件時解析到<mapper namespace="xxx.UserMapper">時會自動進行類型的註冊）
如果沒有的話便會通過 configuration.addMapper(this.mapperInterface) 方法進行 mapper 接口的註冊
回到1中最後的問題：UserMapper userMapper = (UserMapper)context.getBean("userMapper"); 爲什麼能自動返回了 userMapper 對象？MapperFactoryBean 實現 FactoryBean 接口，重寫了其接口方法來獲取 mapper 對象。

public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> {  
  @Override
  public T getObject() throws Exception {
    return getSqlSession().getMapper(this.mapperInterface);
  }
}

4.MapperScannerConfigurer

同樣是繼承 InitializingBean，但是此方法沒作用；重點在父接口 BeanDefinitionRegistryPostProcessor，BeanDefinitionRegistryPostProcessor實現了BeanFactoryPostProcessor接口，是Spring框架的BeanDefinitionRegistry的後處理器，用來註冊額外的BeanDefinition。postProcessBeanDefinitionRegistry方法會在所有的BeanDefinition已經被加載了，但所有Bean還沒有被創建前調用。BeanDefinitionRegistryPostProcessor經常被用來註冊BeanFactoryPostProcessor的BeanDefinition。MapperScannerConfigurer 重寫了其 postProcessBeanDefinitionRegistry() 方法。

public class MapperScannerConfigurer implements BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware {
  @Override
  public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
    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));
  }
}

後續加上

mybatis與spring整合源碼分析

1.配置applicationContext.xml

2.SqlSessionFactoryBean

3.MapperFactoryBean

4.MapperScannerConfigurer

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