Mybatis源码:@MapperScan解析过程

目录

0.说明

1.@MapperScan

2. MapperScannerRegister

3.ClassPathMapperScanner

4. MapperFactoryBean


0.说明


mybatis构建过程主要包括:

  1. 解析mybatis配置文件,构造Configuration配置类对象和SqlSessionFactory;
  2. 利用@MapperScan注册BeanDefinition到BeanFactory工厂中;

其中第一步中创建了Mapper接口代理类,并存储到Configuration中;

下面主要介绍第二步,利用@MapperScan注册BeanDefinition的过程;

1.@MapperScan

/**
 * Use this annotation to register MyBatis mapper interfaces when using Java
 * Config. It performs when same work as {@link MapperScannerConfigurer} via
 * {@link MapperScannerRegistrar}.
 */
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperScannerRegistrar.class)
public @interface MapperScan {

  /**
   * Alias for the {@link #basePackages()} attribute. Allows for more concise
   * annotation declarations e.g.:
   * {@code @EnableMyBatisMapperScanner("org.my.pkg")} instead of {@code
   * @EnableMyBatisMapperScanner(basePackages= "org.my.pkg"})}.
   */
  String[] value() default {};

  /**
   * Base packages to scan for MyBatis interfaces. Note that only interfaces
   * with at least one method will be registered; concrete classes will be
   * ignored.
   */
  String[] basePackages() default {};

  /**
   * Type-safe alternative to {@link #basePackages()} for specifying the packages
   * to scan for annotated components. The package of each class specified will be scanned.
   * 

Consider creating a special no-op marker class or interface in each package * that serves no purpose other than being referenced by this attribute. */ Class[] basePackageClasses() default {}; /** * The {@link BeanNameGenerator} class to be used for naming detected components * within the Spring container. */ Class nameGenerator() default BeanNameGenerator.class; /** * This property specifies the annotation that the scanner will search for. *

* The scanner will register all interfaces in the base package that also have * the specified annotation. *

* Note this can be combined with markerInterface. */ Class annotationClass() default Annotation.class; /** * This property specifies the parent that the scanner will search for. *

* The scanner will register all interfaces in the base package that also have * the specified interface class as a parent. *

* Note this can be combined with annotationClass. */ Class markerInterface() default Class.class; /** * Specifies which {@code SqlSessionTemplate} to use in the case that there is * more than one in the spring context. Usually this is only needed when you * have more than one datasource. */ String sqlSessionTemplateRef() default ""; /** * Specifies which {@code SqlSessionFactory} to use in the case that there is * more than one in the spring context. Usually this is only needed when you * have more than one datasource. */ String sqlSessionFactoryRef() default ""; /** * Specifies a custom MapperFactoryBean to return a mybatis proxy as spring bean. * */ Class factoryBean() default MapperFactoryBean.class; }

MapperScan注解属性如下:

  1. value、basePackages、basePackageClasses都是用于提供扫描接口类的包名;
  2. BeanNameGenerator作为Bean名称生成器,支持自定义;
  3. annotationClass、markerInterface作为marker标记,限定需要扫描的接口需要满足的条件(包含特定注解或实现某个接口);
  4. sqlSessionTemplateRef、sqlSessionFactoryRef在有多个数据源的情况下指定使用哪一个数据源;
  5. factoryBean,指定FactoryBean实现类,用于生成接口代理类,默认为MapperFactoryBean.class, 支持自定义;

另外MapperScan通过import注解导入了MapperScannerRegistrar类,该接口实现了ImportBeanDefinitionRegistrar接口,用于注册BeanDefinition;

2. MapperScannerRegistrar

MapperScannerRegistrar类结构如下:

ImportBeanDefinitionRegistrar:是spring开放出来的用于注册其他BeanDefinition的接口,供子类具体实现;

MapperScannerRegistrar:实现ImportBeanDefinitionRegistrar接口,同时依赖ClassPathMapperScanner获取候选bean定义, 并对bean定义进行后处理;

ClassPathMapperScanner:继承ClassPathBeanDefinitionScanner,完成指定包下bean定义的注册;

(传送门 Spring源码:ClassPathBeanDefinitionScanner源码分析)

覆盖的ImportBeanDefinitionRegistrar接口中的registerBeanDefinitions方法具体如下,主要完成了ClassPathMapperScanner的构造,并执行doScan方法进行扫描;

MapperScannerRegistrar.registerBeanDefinitions:

@Override
  public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {

    AnnotationAttributes annoAttrs = AnnotationAttributes.fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName()));
    ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);

    // this check is needed in Spring 3.1
    if (resourceLoader != null) {
      scanner.setResourceLoader(resourceLoader);
    }

    Class annotationClass = annoAttrs.getClass("annotationClass");
    if (!Annotation.class.equals(annotationClass)) {
      scanner.setAnnotationClass(annotationClass);
    }

    Class markerInterface = annoAttrs.getClass("markerInterface");
    if (!Class.class.equals(markerInterface)) {
      scanner.setMarkerInterface(markerInterface);
    }

    Class generatorClass = annoAttrs.getClass("nameGenerator");
    if (!BeanNameGenerator.class.equals(generatorClass)) {
      scanner.setBeanNameGenerator(BeanUtils.instantiateClass(generatorClass));
    }

    Class mapperFactoryBeanClass = annoAttrs.getClass("factoryBean");
    if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) {
      scanner.setMapperFactoryBean(BeanUtils.instantiateClass(mapperFactoryBeanClass));
    }

    scanner.setSqlSessionTemplateBeanName(annoAttrs.getString("sqlSessionTemplateRef"));
    scanner.setSqlSessionFactoryBeanName(annoAttrs.getString("sqlSessionFactoryRef"));

    List basePackages = new ArrayList();
    for (String pkg : annoAttrs.getStringArray("value")) {
      if (StringUtils.hasText(pkg)) {
        basePackages.add(pkg);
      }
    }
    for (String pkg : annoAttrs.getStringArray("basePackages")) {
      if (StringUtils.hasText(pkg)) {
        basePackages.add(pkg);
      }
    }
    for (Class clazz : annoAttrs.getClassArray("basePackageClasses")) {
      basePackages.add(ClassUtils.getPackageName(clazz));
    }
    scanner.registerFilters();
    scanner.doScan(StringUtils.toStringArray(basePackages));
  }

 

3.ClassPathMapperScanner

ClassPathMapperScanner主要用于注册指定包名下的bean定义,并对注册的bean定义进行后处理,这里主要是设置beanClass为MapperFactoryBean、设置构造函数参数对象、设置autoWireMode=byType(MapperScan注解属性没有指定时,默认将容器中的DefalultSqlSectionFactory绑定到set方法的入参对象中,构造PropertyValue值),其doScan方法如下:

/**
   * 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 doScan(String... basePackages) {
    Set 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;
  }

  private void processBeanDefinitions(Set 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
      definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName()); // issue #59
      definition.setBeanClass(this.mapperFactoryBean.getClass());

      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);
      }
    }
  }

4. MapperFactoryBean

MapperFactoryBean实现FactoryBean接口,继承SqlSessionDaoSupport,其中SqlSessionDaoSupport有成员变量sqlSession,初始化是在setSqlSessionFactory方法中完成的(setSqlSessionFactory是根据autoWire=byType属性注入进来的)

SqlSessionDaoSupport.setSqlSessionFactory:

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

因为MapperFactoryBean是FactoryBean的子类,所以bean实例化时会调用MapperFactoryBean的getObject方法:

@Override
  public T getObject() throws Exception {
    return getSqlSession().getMapper(this.mapperInterface);
 }

进而调用sqlSession的getMapper接口,即是sqlSessionTemplete的getMapper方法:

@Override
  public  T getMapper(Class type) {
    return getConfiguration().getMapper(type, this);
  }

这样最终就从Configuration中获取mapper接口的代理对象;而Configuration中的mapper接口代理对象是在mybatis配置解析时构造完成的;

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