Spring集成Mybatis配置与源码分析

1.配置

在spring配置文件中添加如下配置：
<!– SqlSessionFactory bean配置。
configuration与configLocation可以选择其中一个配置，若都配置了则使用configuration配置，若都不配置使用默认配置–>
<bean id=”sqlSessionFactory” class=”org.mybatis.spring.SqlSessionFactoryBean”>
<property name=”dataSource” ref=”dataSource”/>
<!–配置方式：setter注入–>
<property name=”configuration” ref=”configuration”/>
<!–配置方式：配置文件–>
<property name=”configLocation” value=”classpath:config/mybatis-config.xml”/>
<property name=”mapperLocations” value=”classpath:com/wxyh/study/dao/*/.xml”/>
<!–注入其他属性–>
</bean>
<!– spring与mybatis整合配置，扫描所有dao –>
<bean class=”org.mybatis.spring.mapper.MapperScannerConfigurer”>
<property name=”basePackage” value=”com.wxyh.study.dao.**.mapper”/>
<property name=”sqlSessionFactoryBeanName” value=”sqlSessionFactory”/>
</bean>
下面对主要源码进行分析讲解，源码版本mybatis-3.4.4，mybatis-spring-1.3.1。

2.SqlSessionFactoryBean源码分析

public class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>, InitializingBean, 
    ApplicationListener<ApplicationEvent> {

  // 核心字段，这些属性都提供了setter注入方法
  private Resource configLocation;
  private Configuration configuration;
  private Resource[] mapperLocations;
  private DataSource dataSource;
  private TransactionFactory transactionFactory;
  private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder();
  private SqlSessionFactory sqlSessionFactory;
  private String environment = SqlSessionFactoryBean.class.getSimpleName();
  private boolean failFast;
  private Interceptor[] plugins;
  private TypeHandler<?>[] typeHandlers;
  private String typeHandlersPackage;
  private Class<?>[] typeAliases;
  private String typeAliasesPackage;
  private Class<?> typeAliasesSuperType;
  private DatabaseIdProvider databaseIdProvider;
  private Class<? extends VFS> vfs;
  private Cache cache;
  private ObjectFactory objectFactory;
  private ObjectWrapperFactory objectWrapperFactory;

  @Override
  public void afterPropertiesSet() throws Exception {
    notNull(dataSource, "Property 'dataSource' is required");
    notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required");
    state((configuration == null && configLocation == null) || !(configuration != null && configLocation != null),
              "Property 'configuration' and 'configLocation' can not specified with together");

    this.sqlSessionFactory = buildSqlSessionFactory();
  }

   protected SqlSessionFactory buildSqlSessionFactory() throws IOException {

    Configuration configuration;
    XMLConfigBuilder xmlConfigBuilder = null;
    if (this.configuration != null) {
      // 注入了configuration bean，优先使用
      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) {
      // 有配置文件，后面会解析配置文件，把相关配置保存在configuration中
      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");
      }
      // 没有配置configuration与configLocation，使用默认配置
      configuration = new Configuration();
      if (this.configurationProperties != null) {
       configuration.setVariables(this.configurationProperties);
      }
    }

    // 略去设置或解析setter注入属性代码
    // ......
    if (xmlConfigBuilder != null) {
      try {
        // 解析配置文件mybatis-config.xml，详细源码解析见：http://blog.youkuaiyun.com/u011424653/article/details/78202010
        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));

    // 解析mapperLocations指定mapper配置文件
    if (!isEmpty(this.mapperLocations)) {
      for (Resource mapperLocation : this.mapperLocations) {
        if (mapperLocation == null) {
          continue;
        }

        try {
          // 逐个解析mapper配置文件，解析源码见：http://blog.youkuaiyun.com/u011424653/article/details/78202010#t3
          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");
      }
    }

    // 构建sqlSessionFactory对象
    return this.sqlSessionFactoryBuilder.build(configuration);
  }

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

SqlSessionFactoryBean是SqlSessionFactory的工厂bean。
启动项目时spring首先会创建SqlSessionFactoryBean对象，然后会把getObject()的返回值DefaultSqlSessionFactory对象作为bean注册到容器中。

3.MapperScannerConfigurer源码分析

public class MapperScannerConfigurer implements BeanDefinitionRegistryPostProcessor, 
    InitializingBean, ApplicationContextAware, BeanNameAware {

  // 核心字段，这些属性都提供了setter注入方法
  private String basePackage;
  private boolean addToConfig = true;
  private SqlSessionFactory sqlSessionFactory;
  private SqlSessionTemplate sqlSessionTemplate;
  private String sqlSessionFactoryBeanName;
  private String sqlSessionTemplateBeanName;
  // mapper接口使用的注解类型
  private Class<? extends Annotation> annotationClass;
  // mapper接口的父接口类型
  private Class<?> markerInterface;
  private ApplicationContext applicationContext;
  private String beanName;
  private boolean processPropertyPlaceHolders;
  private BeanNameGenerator nameGenerator;

  @Override
  public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
    if (this.processPropertyPlaceHolders) {
      processPropertyPlaceHolders();
    }

    ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
    scanner.setAddToConfig(this.addToConfig);
    // 设置mapper接口使用的注解或父类型
    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);
    // 配置过滤basePackage包中mapper接口的规则，源码分析见4
    scanner.registerFilters();
    // 扫描basePackage包中mapper接口，将其封装为MapperFactoryBean<T>
    scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
  }

  ......

}

4.ClassPathMapperScanner源码分析

public class ClassPathMapperScanner extends ClassPathBeanDefinitionScanner {

  // 核心字段，这些属性都提供了setter注入方法
  private boolean addToConfig = true;
  private SqlSessionFactory sqlSessionFactory;
  private SqlSessionTemplate sqlSessionTemplate;
  private String sqlSessionTemplateBeanName;
  private String sqlSessionFactoryBeanName;
  private Class<? extends Annotation> annotationClass;
  private Class<?> markerInterface;
  private MapperFactoryBean<?> mapperFactoryBean = new MapperFactoryBean<Object>();

  /**
   * 配置扫描器以注册basePackage包中正确的接口为mapper
   */
  public void registerFilters() {
    boolean acceptAllInterfaces = true;

    // 把basePackage包中有annotationClass类型注解的所有接口注册为mapper
    if (this.annotationClass != null) {
      addIncludeFilter(new AnnotationTypeFilter(this.annotationClass));
      acceptAllInterfaces = false;
    }

    // 把basePackage包中派生自markerInterface类型接口的所有接口注册为mapper，
    // 重写matchClassName方法，以免注册markerInterface接口为mapper
    if (this.markerInterface != null) {
      addIncludeFilter(new AssignableTypeFilter(this.markerInterface) {
        @Override
        protected boolean matchClassName(String className) {
          return false;
        }
      });
      acceptAllInterfaces = false;
    }

    if (acceptAllInterfaces) {
      // 如果没有设置annotationClass和markerInterface，则注册basePackage包中所有类为mapper
      // default include filter that accepts all classes
      addIncludeFilter(new TypeFilter() {
        @Override
        public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
          return true;
        }
      });
    }

    // exclude package-info.java
    addExcludeFilter(new TypeFilter() {
      @Override
      public boolean match(MetadataReader metadataReader, MetadataReaderFactory metadataReaderFactory) throws IOException {
        String className = metadataReader.getClassMetadata().getClassName();
        return className.endsWith("package-info");
      }
    });
  }

  /**
   * Calls the parent search that will search and register all the candidates.
   * Then the registered objects are post processed to set them as
   * MapperFactoryBeans
   */
  @Override
  public Set<BeanDefinitionHolder> doScan(String... basePackages) {
    // 调用父类方法，扫描basePackages包中的mapper接口，返回BeanDefinitionHolder集合
    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 {
      processBeanDefinitions(beanDefinitions);
    }

    return beanDefinitions;
  }

  /**
   * 定义mapper的工厂bean MapperFactoryBean
   */
  private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
    GenericBeanDefinition definition;
    for (BeanDefinitionHolder holder : beanDefinitions) {
      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
      // 通过构造函数传参设置MapperFactoryBean所生产bean的类型
      definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
      definition.setBeanClass(this.mapperFactoryBean.getClass());

      definition.getPropertyValues().add("addToConfig", this.addToConfig);

      // 往MapperFactoryBean注入sqlSessionFactory
      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;
      }

      // 往MapperFactoryBean注入sqlSessionTemplate.
      // 如果已注入sqlSessionFactory则忽略该配置，使用sqlSessionTemplate，详见源码
      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);
      }
    }
  }

}

5.MapperFactoryBean源码分析

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

  // mapper bean的类型
  private Class<T> mapperInterface;
  // true，添加mapper到MapperRegistry
  private boolean addToConfig = true;

  public MapperFactoryBean() {
    //intentionally empty 
  }

  public MapperFactoryBean(Class<T> mapperInterface) {
    this.mapperInterface = mapperInterface;
  }

  @Override
  protected void checkDaoConfig() {
    super.checkDaoConfig();

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

    Configuration configuration = getSqlSession().getConfiguration();
    if (this.addToConfig && !configuration.hasMapper(this.mapperInterface)) {
      try {
        // 添加mapper到MapperRegistry，源码分析见xxxxxxxxxxx
        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();
      }
    }
  }

  @Override
  public T getObject() throws Exception {
    // getSqlSession()返回的是一个SqlSessionTemplate对象
    // getMapper方法从MapperRegistry中获取的是MapperProxyFactory对象
    return getSqlSession().getMapper(this.mapperInterface);
  }

}

public abstract class SqlSessionDaoSupport extends DaoSupport {

  // 通过sqlSessionFactory或sqlSessionTemplate，生成的sqlSession对象都是SqlSessionTemplate类型，
  // 实际上是SqlSession的代理对象
  private SqlSession sqlSession;
  private boolean externalSqlSession;

  public void setSqlSessionFactory(SqlSessionFactory sqlSessionFactory) {
    if (!this.externalSqlSession) {
      // 如果设置了sqlSessionTemplate，则不再使用sqlSessionFactory了
      this.sqlSession = new SqlSessionTemplate(sqlSessionFactory);
    }
  }

  public void setSqlSessionTemplate(SqlSessionTemplate sqlSessionTemplate) {
    this.sqlSession = sqlSessionTemplate;
    this.externalSqlSession = true;
  }

  /**
   * Users should use this method to get a SqlSession to call its statement methods
   * This is SqlSession is managed by spring. Users should not commit/rollback/close it
   * because it will be automatically done.
   *
   * @return Spring managed thread safe SqlSession
   */
  public SqlSession getSqlSession() {
    return this.sqlSession;
  }

  @Override
  protected void checkDaoConfig() {
    notNull(this.sqlSession, "Property 'sqlSessionFactory' or 'sqlSessionTemplate' are required");
  }

}

6.SqlSessionTemplate源码分析

public class SqlSessionTemplate implements SqlSession, DisposableBean {

  private final SqlSessionFactory sqlSessionFactory;
  private final ExecutorType executorType;
  // SqlSession的代理对象
  private final SqlSession sqlSessionProxy;
  private final PersistenceExceptionTranslator exceptionTranslator;

  public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
    this(sqlSessionFactory, sqlSessionFactory.getConfiguration().getDefaultExecutorType());
  }

  public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType) {
    this(sqlSessionFactory, executorType,
        new MyBatisExceptionTranslator(
            sqlSessionFactory.getConfiguration().getEnvironment().getDataSource(), true));
  }

  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;
    // 创建sqlSession的代理对象，调用sqlSession的所有方法，都被SqlSessionInterceptor的invoke方法拦截
    this.sqlSessionProxy = (SqlSession) newProxyInstance(
        SqlSessionFactory.class.getClassLoader(),
        new Class[] { SqlSession.class },
        new SqlSessionInterceptor());
  }

  /**
   * 内部类
   * jdk动态代理拦截器类
   */
  private class SqlSessionInterceptor implements InvocationHandler {
    @Override
    public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
      SqlSession sqlSession = getSqlSession(
          SqlSessionTemplate.this.sqlSessionFactory,
          SqlSessionTemplate.this.executorType,
          SqlSessionTemplate.this.exceptionTranslator);
      try {
        Object result = method.invoke(sqlSession, args);
        if (!isSqlSessionTransactional(sqlSession, SqlSessionTemplate.this.sqlSessionFactory)) {
          // force commit even on non-dirty sessions because some databases require
          // a commit/rollback before calling close()
          sqlSession.commit(true);
        }
        return result;
      } catch (Throwable t) {
        Throwable unwrapped = unwrapThrowable(t);
        if (SqlSessionTemplate.this.exceptionTranslator != null && unwrapped instanceof PersistenceException) {
          // release the connection to avoid a deadlock if the translator is no loaded. See issue #22
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
          sqlSession = null;
          Throwable translated = SqlSessionTemplate.this.exceptionTranslator.translateExceptionIfPossible((PersistenceException) unwrapped);
          if (translated != null) {
            unwrapped = translated;
          }
        }
        throw unwrapped;
      } finally {
        if (sqlSession != null) {
          closeSqlSession(sqlSession, SqlSessionTemplate.this.sqlSessionFactory);
        }
      }
    }
  }

}