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spring的啟動過程03.2-整合mybatis

概述:

講述bean工廠後置處理器之spring與mybatis的整合原理,首先我們來看下spring整合mybatis的方式

	<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
		<property name="basePackage" value="com.xx.pay.dao" />
	</bean>

定義MapperScannerConfigurer並指定dao包路徑

	<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"
		p:dataSource-ref="dataSource" p:configLocation="classpath:config/mybatis-config.xml"
		p:mapperLocations="classpath:mapper/*.xml" />
定義SqlSessionFactoryBean並指定mybatis的個性化配置檔案及mapper路徑

原理:

首先看下MapperScannerConfigurer類靜態結構圖

從介面的實現可以看出MapperScannerConfigurer類屬於bean工廠後置處理器,該類被觸發的時機請看《spring的啟動過程03-工廠後置處理器》。

直接跟蹤核心邏輯:

  @Override
  public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
    if (this.processPropertyPlaceHolders) {
      processPropertyPlaceHolders();
    }
	//建立Mapper掃描器
    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();
	//執行核心邏輯,掃描包路徑下的dao並生成對應的BeanDefinition註冊到bean工廠
    scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
  }	

手動建立ClassPathMapperScanner物件,由該物件執行主邏輯,該類靜態結構圖如下:


繼承了org.springframework.context.annotation.ClassPathBeanDefinitionScanner類,該類非常重要在spring解析context自定義名稱空間過程中也會用到此類。

後續會寫context名稱空間的原理,請後續關注。

首先分析scanner.registerFilters()方法:

  /**
   * Configures parent scanner to search for the right interfaces. It can search
   * for all interfaces or just for those that extends a markerInterface or/and
   * those annotated with the annotationClass
   * 增加掃描型別過濾
   */
  public void registerFilters() {
    boolean acceptAllInterfaces = true;

    // if specified, use the given annotation and / or marker interface
    if (this.annotationClass != null) {
      addIncludeFilter(new AnnotationTypeFilter(this.annotationClass));
      acceptAllInterfaces = false;
    }

    // override AssignableTypeFilter to ignore matches on the actual marker interface
    if (this.markerInterface != null) {
      addIncludeFilter(new AssignableTypeFilter(this.markerInterface) {
        @Override
        protected boolean matchClassName(String className) {
          return false;
        }
      });
      acceptAllInterfaces = false;
    }

    if (acceptAllInterfaces) {
      // 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");
      }
    });
  }
繼續檢視核心類org.springframework.context.annotation.ClassPathBeanDefinitionScanner
	/**
	 * Perform a scan within the specified base packages.
	 * @param basePackages the packages to check for annotated classes
	 * @return number of beans registered
	 */
	public int scan(String... basePackages) {
		int beanCountAtScanStart = this.registry.getBeanDefinitionCount();
		
		doScan(basePackages);

		// Register annotation config processors, if necessary.
		if (this.includeAnnotationConfig) {
			AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
		}

		return (this.registry.getBeanDefinitionCount() - beanCountAtScanStart);
	}
跟蹤 doScan(basePackages)
  /**
   * 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) {
    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;
  }
繼續看super.doScan(basePackages)。。。
	/**
	 * Perform a scan within the specified base packages,
	 * returning the registered bean definitions.
	 * <p>This method does <i>not</i> register an annotation config processor
	 * but rather leaves this up to the caller.
	 * @param basePackages the packages to check for annotated classes
	 * @return set of beans registered if any for tooling registration purposes (never {@code null})
	 */
	protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
		Assert.notEmpty(basePackages, "At least one base package must be specified");
		Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet<BeanDefinitionHolder>();
		for (String basePackage : basePackages) {
			Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
			for (BeanDefinition candidate : candidates) {
				ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
				candidate.setScope(scopeMetadata.getScopeName());
				String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
				if (candidate instanceof AbstractBeanDefinition) {
					postProcessBeanDefinition((AbstractBeanDefinition) candidate, beanName);
				}
				if (candidate instanceof AnnotatedBeanDefinition) {
					AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition) candidate);
				}
				if (checkCandidate(beanName, candidate)) {
					BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
					definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
					beanDefinitions.add(definitionHolder);
					registerBeanDefinition(definitionHolder, this.registry);
				}
			}
		}
		return beanDefinitions;
	}
繼續看findCandidateComponents方法
	/**
	 * Scan the class path for candidate components.
	 * @param basePackage the package to check for annotated classes
	 * @return a corresponding Set of autodetected bean definitions
	 */
	public Set<BeanDefinition> findCandidateComponents(String basePackage) {
		Set<BeanDefinition> candidates = new LinkedHashSet<BeanDefinition>();
		try {
			String packageSearchPath = ResourcePatternResolver.CLASSPATH_ALL_URL_PREFIX +
					resolveBasePackage(basePackage) + "/" + this.resourcePattern;
			//獲取包路徑下所有的class資源,這裡的包路徑可以直接配置到dao層,減少其它類的掃描頁可以重寫該類指定annotationClass
			//在dao類上加上該註解
			Resource[] resources = this.resourcePatternResolver.getResources(packageSearchPath);
			for (Resource resource : resources) {
				if (resource.isReadable()) {
					try {
						MetadataReader metadataReader = this.metadataReaderFactory.getMetadataReader(resource);
						//判斷是否符合要求
						if (isCandidateComponent(metadataReader)) {
							//定義BeanDefinition物件
							ScannedGenericBeanDefinition sbd = new ScannedGenericBeanDefinition(metadataReader);
							sbd.setResource(resource);
							sbd.setSource(resource);
							if (isCandidateComponent(sbd)) {
								candidates.add(sbd);
							}
						}
					}
					catch (Throwable ex) {
					}
				}
			}
		}
		catch (IOException ex) {
		}
		return candidates;
	}
繼續看如何判斷某個類符合要求
	/**
	 * Determine whether the given class does not match any exclude filter
	 * and does match at least one include filter.
	 * @param metadataReader the ASM ClassReader for the class
	 * @return whether the class qualifies as a candidate component
	 */
	protected boolean isCandidateComponent(MetadataReader metadataReader) throws IOException {
		for (TypeFilter tf : this.excludeFilters) {
			if (tf.match(metadataReader, this.metadataReaderFactory)) {
				return false;
			}
		}
		for (TypeFilter tf : this.includeFilters) {
			if (tf.match(metadataReader, this.metadataReaderFactory)) {
				return isConditionMatch(metadataReader);
			}
		}
		return false;
	}
跟蹤到這裡spring已經完成了對符合要求的class的載入轉換為BeanDefinition,完成了第一步,接著往下看如何對BeanDefinition的裝飾

檢視processBeanDefinitions(beanDefinitions)方法

  private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) {
    GenericBeanDefinition definition;
    for (BeanDefinitionHolder holder : beanDefinitions) {
      definition = (GenericBeanDefinition) holder.getBeanDefinition();
      // 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
	  //這個BeanDefinition實際上是個org.mybatis.spring.mapper.MapperFactoryBean工廠bean
      definition.setBeanClass(this.mapperFactoryBean.getClass());
      definition.getPropertyValues().add("addToConfig", this.addToConfig);
      boolean explicitFactoryUsed = false;
	  // 增加sqlSessionFactory屬性,這個可以手動指定,如果為空會自動採用配置的org.mybatis.spring.SqlSessionFactoryBean例項
      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)) {
        definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
        explicitFactoryUsed = true;
      } else if (this.sqlSessionTemplate != null) {
        definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
        explicitFactoryUsed = true;
      }
      if (!explicitFactoryUsed) {
        definition.setAutowireMode(AbstractBeanDefinition.AUTOWIRE_BY_TYPE);
      }
    }
  }
上面的方法說明了 DAO介面在spring容器中對應的BeanDefinition結構為beanName為dao的名稱,beanClass為org.mybatis.spring.mapper.MapperFactoryBean工廠Bean

在實際使用的server例子

public class BankPayServiceImpl implements IBankPayService {
	@Resource
	private IBankPayDao payDao;
}

spring在初始化BankPayServiceImpl例項過程中會注入IBankPayDao屬性,呼叫MapperFactoryBean的getObject()得到

org.apache.ibatis.binding.MapperProxy例項,這個過程涉及到spring初始化bean例項注入屬性的過程,該內容會在後續章節進行詳細講解。

總結:

從上面分析的情況可以看出,spring與mybatis的整合不復雜,大概過程分為兩步

第一步通過bean工廠後置處理器MapperScannerConfigurer掃描指定包路徑下符合要求的class並轉換成className為MapperFactoryBean的BeanDefinition例項;

第二步在例項化bean過程中,注入bean的屬性時會通過MapperFactoryBean的getObject方法獲取MapperProxy代理例項。

下個章節會講解Bean後置處理器,該處理器和bean工廠後置處理器是兩個不同的概念。