Spring-Mybatis源码分析

2023年10月23日 315次阅读 来源: Spring Boot

首先给出Spring-mybatis的配置文件

	<!-- 配置数据源 -->
	<bean id="dataSource" class="com.jolbox.bonecp.BoneCPDataSource"
		destroy-method="close">
		<property name="driverClass" value="${DriverClasses}" />
		<property name="jdbcUrl" value="${ecology.url}" />
		<property name="username" value="${ecology.user}" />
		<property name="password" value="${ecology.password}" />
		<property name="idleConnectionTestPeriod" value="60" />
		<property name="idleMaxAge" value="240" />
		<property name="maxConnectionsPerPartition" value="30" />
		<property name="minConnectionsPerPartition" value="10" />
		<property name="partitionCount" value="1" />
		<property name="acquireIncrement" value="5" />
		<property name="statementsCacheSize" value="100" />
		<property name="releaseHelperThreads" value="3" />
	</bean>
	<!-- 配置数据工厂 -->
	<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
		<!-- 自动扫描mapper.xml文件 -->
		<property name="configLocation" value="classpath:cn/resources/mybatis-cfg.xml" />
		<property name="mapperLocations" value="classpath:cn/resources/mapper/*Mapper.xml" />
		<property name="dataSource" ref="dataSource" />
	</bean>
	<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
		<property name="sqlSessionFactoryBeanName" value="sqlSessionFactory" />
		<property name="basePackage" value="cn.belle.mapper"></property>
	</bean>

mybatis-cfg.xml

<configuration>
	<settings>
		<!-- 启用自动将数据库字段和pojo中的字段做驼峰式的匹配 -->
        <setting name="mapUnderscoreToCamelCase" value="true"/>
		<!-- 懒加载模式 -->
		<setting name="lazyLoadingEnabled" value="false" />
		<!-- JdbcType enumeration. Most common are: NULL, VARCHAR and OTHER -->
		<setting name="jdbcTypeForNull" value="NULL" />
		<setting name="defaultStatementTimeout" value="30" />
	</settings>
</configuration>

核心类是MapperScannerConfigurer

public class MapperScannerConfigurer  implements BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware

这个类实现了BeanDefinitionRegistryPostProcessor这个抽象接口，让Spring容器在加载时执行postProcessBeanDefinitionRegistry方法

 1 public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException {
 2     if (this.processPropertyPlaceHolders) {
 3       processPropertyPlaceHolders();
 4     }
 5 
 6     ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
 7     scanner.setAddToConfig(this.addToConfig);
 8     scanner.setAnnotationClass(this.annotationClass);
 9     scanner.setMarkerInterface(this.markerInterface);
10     scanner.setSqlSessionFactory(this.sqlSessionFactory);
11     scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
12     scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
13     scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
14     scanner.setResourceLoader(this.applicationContext);
15     scanner.setBeanNameGenerator(this.nameGenerator);
16     scanner.registerFilters();
17     scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));
18   }

可以看到 scanner设置了大量属性，并且最后执行了scan方法

             public int scan(String[] basePackages)
/*     */   {
/* 224 */     int beanCountAtScanStart = this.registry.getBeanDefinitionCount();
/*     */     
/* 226 */     doScan(basePackages);
/*     */     
/*     */ 
/* 229 */     if (this.includeAnnotationConfig) {
/* 230 */       AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
/*     */     }
/*     */     
/* 233 */     return this.registry.getBeanDefinitionCount() - beanCountAtScanStart;
/*     */   }

doScan（注意这里不要搞错了，之前我就搞错了，这里的scan应该是子类的sacn）

   public Set<BeanDefinitionHolder> doScan(String[] basePackages)
/*     */   {
/* 164 */     Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
/*     */     
/* 166 */     if (beanDefinitions.isEmpty()) {
/* 167 */       this.logger.warn("No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.");
/*     */     } else {
/* 169 */       processBeanDefinitions(beanDefinitions);
/*     */     }
/*     */     
/* 172 */     return beanDefinitions;
/*     */   }

首先调用了父类的doScan

Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);

父类的doScan

protected Set<BeanDefinitionHolder> doScan(String... basePackages)
/*     */   {
/* 245 */     Assert.notEmpty(basePackages, "At least one base package must be specified");
/* 246 */     Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet();
/* 247 */     for (String basePackage : basePackages) {
/* 248 */       Set<BeanDefinition> candidates = findCandidateComponents(basePackage);
/* 249 */       for (BeanDefinition candidate : candidates) {
/* 250 */         ScopeMetadata scopeMetadata = this.scopeMetadataResolver.resolveScopeMetadata(candidate);
/* 251 */         candidate.setScope(scopeMetadata.getScopeName());
/* 252 */         String beanName = this.beanNameGenerator.generateBeanName(candidate, this.registry);
/* 253 */         if ((candidate instanceof AbstractBeanDefinition)) {
/* 254 */           postProcessBeanDefinition((AbstractBeanDefinition)candidate, beanName);
/*     */         }
/* 256 */         if ((candidate instanceof AnnotatedBeanDefinition)) {
/* 257 */           AnnotationConfigUtils.processCommonDefinitionAnnotations((AnnotatedBeanDefinition)candidate);
/*     */         }
/* 259 */         if (checkCandidate(beanName, candidate)) {
/* 260 */           BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
/* 261 */           definitionHolder = AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
/* 262 */           beanDefinitions.add(definitionHolder);
/* 263 */           registerBeanDefinition(definitionHolder, this.registry);
/*     */         }
/*     */       }
/*     */     }
/* 267 */     return beanDefinitions;
/*     */   }

该方法主要做了以下操作： 1）扫描basePackage下面的java文件 2）解析扫描到的java文件 3）调用各个在上一步骤注册的过滤器，执行相应的方法。 4）为解析后的java注册bean，注册方式采用编码的动态注册实现。 5）构造MapperFactoryBean的属性，mapperInterface，sqlSessionFactory等等，填充到BeanDefinition里面去。 做完这些，MapperFactoryBean对象也就构造完成了，扫描方式添加dao的工作也完成了。

然后是processBeanDefinitions

  private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions)
/*     */   {
/* 177 */     for (BeanDefinitionHolder holder : beanDefinitions) {
/* 178 */       GenericBeanDefinition definition = (GenericBeanDefinition)holder.getBeanDefinition();
/*     */       
/* 180 */       if (this.logger.isDebugEnabled()) {
/* 181 */         this.logger.debug("Creating MapperFactoryBean with name '" + holder.getBeanName() + "' and '" + definition
/* 182 */           .getBeanClassName() + "' mapperInterface");
/*     */       }
/*     */       
/*     */ 
/*     */ 
/* 187 */       definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName());
/* 188 */       definition.setBeanClass(this.mapperFactoryBean.getClass());
/*     */       
/* 190 */       definition.getPropertyValues().add("addToConfig", Boolean.valueOf(this.addToConfig));
/*     */       
/* 192 */       boolean explicitFactoryUsed = false;
/* 193 */       if (StringUtils.hasText(this.sqlSessionFactoryBeanName)) {
/* 194 */         definition.getPropertyValues().add("sqlSessionFactory", new RuntimeBeanReference(this.sqlSessionFactoryBeanName));
/* 195 */         explicitFactoryUsed = true;
/* 196 */       } else if (this.sqlSessionFactory != null) {
/* 197 */         definition.getPropertyValues().add("sqlSessionFactory", this.sqlSessionFactory);
/* 198 */         explicitFactoryUsed = true;
/*     */       }
/*     */       
/* 201 */       if (StringUtils.hasText(this.sqlSessionTemplateBeanName)) {
/* 202 */         if (explicitFactoryUsed) {
/* 203 */           this.logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
/*     */         }
/* 205 */         definition.getPropertyValues().add("sqlSessionTemplate", new RuntimeBeanReference(this.sqlSessionTemplateBeanName));
/* 206 */         explicitFactoryUsed = true;
/* 207 */       } else if (this.sqlSessionTemplate != null) {
/* 208 */         if (explicitFactoryUsed) {
/* 209 */           this.logger.warn("Cannot use both: sqlSessionTemplate and sqlSessionFactory together. sqlSessionFactory is ignored.");
/*     */         }
/* 211 */         definition.getPropertyValues().add("sqlSessionTemplate", this.sqlSessionTemplate);
/* 212 */         explicitFactoryUsed = true;
/*     */       }
/*     */       
/* 215 */       if (!explicitFactoryUsed) {
/* 216 */         if (this.logger.isDebugEnabled()) {
/* 217 */           this.logger.debug("Enabling autowire by type for MapperFactoryBean with name '" + holder.getBeanName() + "'.");
/*     */         }
/* 219 */         definition.setAutowireMode(2);
/*     */       }
/*     */     }
/*     */   }

最关键的两行

definition.getConstructorArgumentValues().addGenericArgumentValue(definition.getBeanClassName());
definition.setBeanClass(this.mapperFactoryBean.getClass());

到这里动态注册的过程已经实现，dao层的接口已经全部被改造成MapperFactoryBean

所以最终我们还是要分析MapperFactoryBean的实现原理！

MapperFactoryBean继承了SqlSessionDaoSupport类，SqlSessionDaoSupport类继承DaoSupport抽象类，DaoSupport抽象类实现了InitializingBean接口，因此实例个MapperFactoryBean的时候，都会调用InitializingBean接口的afterPropertiesSet方法。

           public final void afterPropertiesSet() throws IllegalArgumentException, BeanInitializationException
/*    */   {
/* 44 */     checkDaoConfig();
/*    */     
/*    */     try
/*    */     {
/* 48 */       initDao();
/*    */     }
/*    */     catch (Exception ex) {
/* 51 */       throw new BeanInitializationException("Initialization of DAO failed", ex);
/*    */     }
/*    */   }

MapperFactoryBean重写了checkDaoConfig方法

protected void checkDaoConfig()
/*     */   {
/*  74 */     super.checkDaoConfig();
/*     */     
/*  76 */     Assert.notNull(this.mapperInterface, "Property 'mapperInterface' is required");
/*     */     
/*  78 */     Configuration configuration = getSqlSession().getConfiguration();
/*  79 */     if ((this.addToConfig) && (!configuration.hasMapper(this.mapperInterface))) {
/*     */       try {
/*  81 */         configuration.addMapper(this.mapperInterface);
/*     */       } catch (Exception e) {
/*  83 */         this.logger.error("Error while adding the mapper '" + this.mapperInterface + "' to configuration.", e);
/*  84 */         throw new IllegalArgumentException(e);
/*     */       } finally {
/*  86 */         ErrorContext.instance().reset();
/*     */       }
/*     */     }
/*     */   }

然后通过spring工厂拿对应的bean的时候：

 public T getObject()
/*     */     throws Exception
/*     */   {
/*  96 */     return getSqlSession().getMapper(this.mapperInterface);
/*     */   }

这里的SqlSession是SqlSessionTemplate，SqlSessionTemplate的getMapper方法：

public <T> T getMapper(Class<T> type)
/*     */   {
/* 319 */     return getConfiguration().getMapper(type, this);
/*     */   }

Configuration的getMapper方法，会使用MapperRegistry的getMapper方法：

 public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
/* 717 */     return this.mapperRegistry.getMapper(type, sqlSession);
/*     */   }

getMapper

    */   public <T> T getMapper(Class<T> type, SqlSession sqlSession)
/*     */   {
/*  45 */     MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type);
/*  46 */     if (mapperProxyFactory == null) {
/*  47 */       throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
/*     */     }
/*     */     try {
/*  50 */       return mapperProxyFactory.newInstance(sqlSession);
/*     */     } catch (Exception e) {
/*  52 */       throw new BindingException("Error getting mapper instance. Cause: " + e, e);
/*     */     }
/*     */   }

newInstance

protected T newInstance(MapperProxy<T> mapperProxy)
/*    */   {
/* 47 */     return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[] { this.mapperInterface }, mapperProxy);
/*    */   }
/*    */

这里就出现了动态代理

mapperProxy的源码

public class MapperProxy<T>
/*    */   implements InvocationHandler, Serializable

它的invoke

  public Object invoke(Object proxy, Method method, Object[] args) throws Throwable
/*    */   {
/* 45 */     if (Object.class.equals(method.getDeclaringClass())) {
/*    */       try {
/* 47 */         return method.invoke(this, args);
/*    */       } catch (Throwable t) {
/* 49 */         throw ExceptionUtil.unwrapThrowable(t);
/*    */       }
/*    */     }
/* 52 */     MapperMethod mapperMethod = cachedMapperMethod(method);
/* 53 */     return mapperMethod.execute(this.sqlSession, args);
/*    */   }

这两行相信大家已经很熟悉了

  MapperMethod mapperMethod = cachedMapperMethod(method);
/* 53 */     return mapperMethod.execute(this.sqlSession, args);
    原文作者：Spring Boot
    原文地址: https://blog.csdn.net/qq_28007533/article/details/74977170
    本文转自网络文章，转载此文章仅为分享知识，如有侵权，请联系博主进行删除。
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