Mybatis-Spring原理-创新互联

一、@MapperScan(basePackages = { "com.uenpay.wfb.repository" })

MapperScan注解中有 @Import(MapperScannerRegistrar.class)，MapperScannerRegistrar实现了接口ImportBeanDefinitionRegistrar。

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通过MapperScannerRegistrar执行registerBeanDefinitions方法，扫描basePackages路径下的包，并把对应的mapper接口注入到spring的初始容器BeanDefinition，不过需要注意的是，这些接口的BeanDefinition的属性beanClass是 org.mybatis.spring.mapper.MapperFactoryBean

这一阶段就完成了mapper接口的初始注入

二、配置类 MybatisAutoConfiguration

mybatis-spring-boot-autoconfigure 包里有一个配置文件spring.factories里面包含配置类 MybatisAutoConfiguration

springboot由于自动装配原理，会自动加载mybatis的配置类 MybatisAutoConfiguration，配置类中会完成@Bean注解的实例化，并且创建了SqlSessionFactoryBean对象，SqlSessionFactoryBean是实现了FactoryBean接口的，下面执行了factory.getObject()方法

getObject()

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

    return this.sqlSessionFactory;
  }

afterPropertiesSet()方法中会执行buildSqlSessionFactory（）

protected SqlSessionFactory buildSqlSessionFactory() throws IOException {

    Configuration configuration;

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

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

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

    if (this.vfs != null) {
      configuration.setVfsImpl(this.vfs);
    }

    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 (ClasstypeAlias : 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 (TypeHandlertypeHandler : this.typeHandlers) {
        configuration.getTypeHandlerRegistry().register(typeHandler);
        if (LOGGER.isDebugEnabled()) {
          LOGGER.debug("Registered type handler: '" + typeHandler + "'");
        }
      }
    }

    if (this.databaseIdProvider != null) {//fix #64 set databaseId before parse mapper xmls
      try {
        configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource));
      } catch (SQLException e) {
        throw new NestedIOException("Failed getting a databaseId", e);
      }
    }

    if (this.cache != null) {
      configuration.addCache(this.cache);
    }

    if (xmlConfigBuilder != null) {
      try {
        // 解析mybatis-config.xml配置
        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 (!isEmpty(this.mapperLocations)) {
      for (Resource mapperLocation : this.mapperLocations) {
        if (mapperLocation == null) {
          continue;
        }

        try {
          // 解析 Mapper.xml文件，并封装成MappedStatement对象保存到Configuration
          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);
  }

三、SqlSessionFactory

SqlSessionFactory 初始化过程包括： SqlSessionFactoryBean 的加载及执行他的 getObject()方法，该方法的主要逻辑功能时加载 mybatis的配置类 mybatis-config.xml 和一些mapper.xml文件
加载 mapper.xml 解析一些标签和sql语句并封装成 MappedStatement 对象放到 Configuration的map集合中，其中key是mapper.xml文件中增删改查标签中的id

四、生成代理Bean

在生成mapper bean实例时，和其他Bean实例方式差不多，只不过应为mapper是接口，而他的beanClass属性是 org.mybatis.spring.mapper.MapperFactoryBean,所以对于其他常规bean还是有区别的，他会走FactoryBean的路线，通过factoryBean.getObject()返回代理对象，这里用到的是JDK动态代理，生成后填充到spring容器中。

代理几个关键的类

MapperFactoryBean

MapperProxyFactory

public class MapperProxyFactory{

  private final ClassmapperInterface;
  private final MapmethodCache = new ConcurrentHashMap();

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

  public ClassgetMapperInterface() {
    return mapperInterface;
  }

  public MapgetMethodCache() {
    return methodCache;
  }

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

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

}

MapperProxy

public class MapperProxyimplements InvocationHandler, Serializable {

  private static final long serialVersionUID = -6424540398559729838L;
  private final SqlSession sqlSession;
  private final ClassmapperInterface;
  private final MapmethodCache;

  public MapperProxy(SqlSession sqlSession, ClassmapperInterface, MapmethodCache) {
    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;
  }

}

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