MyBatis Plus插件機制與執行流程原理分析詳解
MyBatis Plus插件
MyBatis Plus提供了分頁插件PaginationInterceptor、執行分析插件SqlExplainInterceptor、性能分析插件PerformanceInterceptor以及樂觀鎖插件OptimisticLockerInterceptor。
Mybatis 通過插件 (Interceptor) 可以做到攔截四大對象相關方法的執行 ,根據需求完成相關數據的動態改變。
四大對象是：
Executor StatementHandler ParameterHandler ResultSetHandler四大對象的每個對象在創建時，都會執行interceptorChain.pluginAll()，會經過每個插件對象的 plugin()方法，目的是為當前的四大對象創建代理。代理對象就可以攔截到四大對象相關方法的執行，因為要執行四大對象的方法需要經過代理 。
① xml下插件的配置
如下所示：
<bean class='com.baomidou.mybatisplus.spring.MybatisSqlSessionFactoryBean'><!-- 數據源 --><property name='dataSource' ref='dataSource'></property><property name='configLocation' value='classpath:mybatis-config.xml'></property><!-- 別名處理 --><property name='typeAliasesPackage' value='com.jane.mp.beans'></property><!-- 注入全局MP策略配置 --><property name='globalConfig' ref='globalConfiguration'></property><!-- 插件注冊 --><property name='plugins'><list><!-- 注冊分頁插件 --><bean class='com.baomidou.mybatisplus.plugins.PaginationInterceptor'></bean><!-- 注冊執行分析插件 --><bean class='com.baomidou.mybatisplus.plugins.SqlExplainInterceptor'><property name='stopProceed' value='true'></property></bean><!-- 注冊性能分析插件 --><bean class='com.baomidou.mybatisplus.plugins.PerformanceInterceptor'><property name='format' value='true'></property><!-- <property name='maxTime' value='5'></property> --></bean><!-- 注冊樂觀鎖插件 --><bean class='com.baomidou.mybatisplus.plugins.OptimisticLockerInterceptor'></bean></list></property></bean>
② springboot下注冊插件
這里以分頁插件為例：
@Bean public PaginationInterceptor paginationInterceptor() { PaginationInterceptor paginationInterceptor = new PaginationInterceptor(); // 設置請求的頁面大于最大頁后操作， true調回到首頁，false 繼續請求 默認false // paginationInterceptor.setOverflow(false); // 設置最大單頁限制數量，默認 500 條，-1 不受限制 // paginationInterceptor.setLimit(500); // 開啟 count 的 join 優化,只針對部分 left join paginationInterceptor.setCountSqlParser(new JsqlParserCountOptimize(true)); return paginationInterceptor; }
③ SqlExplainInterceptor
SQL執行分析攔截器，全類名是com.baomidou.mybatisplus.plugins.SqlExplainInterceptor，只支持 MySQL5.6.3以上版本。
該插件的作用是分析 DELETE UPDATE語句 ,防止小白或者惡意進行DELETE UPDATE全表操作，不建議在生產環境中使用會造成性能下降，
在插件的底層通過SQL語句分析命令 Explain 分析當前的 SQL語句，根據結果集中的 Extra列來斷定當前是否全表操作。
④ 性能分析插件
性能分析攔截器，全類名是com.baomidou.mybatisplus.plugins.PerformanceInterceptor，用于輸出每條 SQL 語句及其執行時間。SQL性能執行分析 ,開發環境使用 超過指定時間，停止運行。
⑤ 樂觀鎖插件
全類名是com.baomidou.mybatisplus.plugins.OptimisticLockerInterceptor。如果想實現如下需求 : 當要更新一條記錄的時候，希望這條記錄沒有被別人更新，就可以使用該插件進行判斷。
樂觀鎖的實現原理(@Version 用于注解實體字段，必須要有) :
取出記錄時，獲取當前 version 更新時，帶上這個version 執行更新時，set version = yourVersion+1 where version = yourVersion 如果 version不對，就更新失敗【2】獲取sqlSessionFactoryBean
如下圖所示，在系統啟動時會初始化定義的bean。DefaultListableBeanFactory.preInstantiateSingletons方法中會從beanDefinitionNames中獲取bean name然后依次創建。
這里可以看到RootBeanDefinition是com.baomidou.mybatisplus.spring.MybatisSqlSessionFactoryBean。
① 獲取bean的過程中bean屬性
如下所示，在getBean過程中可以看到bean的屬性：
② createBean
第一次獲取bean的時候會走到AbstractAutowireCapableBeanFactory.createBean進行bean的創建。
/** 創建一個bean實例，為bean實例設置屬性值，調用post-processors-bean后置處理器 */@Overrideprotected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {//...暫時忽略其他代碼 try {// 這里會首先觸發BeanPostProcessors ，如果這里能獲取到bean則直接返回，不再走doCreateBean Object bean = resolveBeforeInstantiation(beanName, mbdToUse); if (bean != null) { return bean; } }//...暫時忽略其他代碼
在AbstractAutowireCapableBeanFactory.resolveBeforeInstantiation中就會分別執行bean后置處理器的前置和后置方法。
protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) { Object bean = null; if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)){ // Make sure bean class is actually resolved at this point. if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()){ Class<?> targetType = determineTargetType(beanName, mbd); if (targetType != null) { bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName); if (bean != null){ bean = applyBeanPostProcessorsAfterInitialization(bean, beanName); } } } mbd.beforeInstantiationResolved = (bean != null); } return bean;}
執行后置處理器的前置方法如下所示：
③ doCreateBean
AbstractAutowireCapableBeanFactory.doCreateBean是創建bean的核心方法，這會為bean屬性賦值并會觸發bean后置處理器、InitializingBean以及自定init方法等。
protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) throws BeanCreationException {// Instantiate the bean.--實例化beanBeanWrapper instanceWrapper = null;if (mbd.isSingleton()) { instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);}if (instanceWrapper == null) {//獲取bean的包裝對象-這里很重要 instanceWrapper = createBeanInstance(beanName, mbd, args);}final Object bean = (instanceWrapper != null ? instanceWrapper.getWrappedInstance() : null);Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);mbd.resolvedTargetType = beanType;// Allow post-processors to modify the merged bean definition.synchronized (mbd.postProcessingLock) { if (!mbd.postProcessed) { try {//調用MergedBeanDefinitionPostProcessors的postProcessMergedBeanDefinition方法 applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName); } catch (Throwable ex) { throw new BeanCreationException(mbd.getResourceDescription(), beanName, 'Post-processing of merged bean definition failed', ex); } mbd.postProcessed = true; }}//...//這里暫時忽略其他代碼// Initialize the bean instance.--初始化bean實例Object exposedObject = bean;try {//如下方法很重要 populateBean(beanName, mbd, instanceWrapper); if (exposedObject != null) { exposedObject = initializeBean(beanName, exposedObject, mbd); }}//...
④ populateBean
顧名思義，為bean實例屬性賦值。
AbstractAutowireCapableBeanFactory.populateBean
protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {//獲取屬性值列表PropertyValues pvs = mbd.getPropertyValues();//...該種符號表示暫時忽略其他代碼//在為bean屬性賦值前，給InstantiationAwareBeanPostProcessors 機會修改bean的狀態//應用場景如支持字段注入boolean continueWithPropertyPopulation = true;//循環調用InstantiationAwareBeanPostProcessors 的postProcessAfterInstantiation方法if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof InstantiationAwareBeanPostProcessor) { InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; if (!ibp.postProcessAfterInstantiation(bw.getWrappedInstance(), beanName)) { continueWithPropertyPopulation = false; break; } } }}if (!continueWithPropertyPopulation) { return;}//解析autowire注解字段，進行主動注入if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME || mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { MutablePropertyValues newPvs = new MutablePropertyValues(pvs); // Add property values based on autowire by name if applicable. if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_NAME) { autowireByName(beanName, mbd, bw, newPvs); } // Add property values based on autowire by type if applicable. if (mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_BY_TYPE) { autowireByType(beanName, mbd, bw, newPvs); } pvs = newPvs;}boolean hasInstAwareBpps = hasInstantiationAwareBeanPostProcessors();boolean needsDepCheck = (mbd.getDependencyCheck() != RootBeanDefinition.DEPENDENCY_CHECK_NONE);//循環調用InstantiationAwareBeanPostProcessors 的postProcessPropertyValues方法if (hasInstAwareBpps || needsDepCheck) { PropertyDescriptor[] filteredPds = filterPropertyDescriptorsForDependencyCheck(bw, mbd.allowCaching); if (hasInstAwareBpps) { for (BeanPostProcessor bp : getBeanPostProcessors()) { if (bp instanceof InstantiationAwareBeanPostProcessor) { InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp; pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName); if (pvs == null) { return; } } } } if (needsDepCheck) { checkDependencies(beanName, mbd, filteredPds, pvs); }}//在這里為屬性賦值，會進行類型轉換，這里注意關鍵詞deep copy//如果是引用類型且bean沒有存在，則會進行bean的創建過程applyPropertyValues(beanName, mbd, bw, pvs);}
如下圖所示在創建sqlSessionFactoryBean過程中會創建其屬性globalConfiguration對象：
如下圖所示在創建sqlSessionFactoryBean過程中(從左側的方法順序就可以看出來)會創建其屬性PaginationInterceptor對象：
如下圖所示在創建sqlSessionFactoryBean過程中(從左側的方法順序就可以看出來)會創建其屬性SqlExplainInterceptor對象：
如下圖所示在創建sqlSessionFactoryBean過程中(從左側的方法順序就可以看出來)會創建其屬性PerformanceInterceptor對象：
如下圖所示在創建sqlSessionFactoryBean過程中(從左側的方法順序就可以看出來)會創建其屬性OptimisticLockerInterceptor對象：
⑤ initializeBean
AbstractAutowireCapableBeanFactory.initializeBean源碼如下：
protected Object initializeBean(final String beanName, final Object bean, RootBeanDefinition mbd){ if (System.getSecurityManager() != null) { AccessController.doPrivileged(new PrivilegedAction<Object>() { @Override public Object run() { invokeAwareMethods(beanName, bean); return null; } }, getAccessControlContext()); } else { //調用意識/通知方法 invokeAwareMethods(beanName, bean); } Object wrappedBean = bean; if (mbd == null || !mbd.isSynthetic()) { //調用bean后置處理器的前置方法 wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName); } //調用初始化方法 try { invokeInitMethods(beanName, wrappedBean, mbd); } catch (Throwable ex) { throw new BeanCreationException( (mbd != null ? mbd.getResourceDescription() : null), beanName, 'Invocation of init method failed', ex); }
AbstractAutowireCapableBeanFactory.invokeInitMethods方法源碼如下：
protected void invokeInitMethods(String beanName, final Object bean, RootBeanDefinition mbd) throws Throwable { boolean isInitializingBean = (bean instanceof InitializingBean); if (isInitializingBean && (mbd == null || !mbd.isExternallyManagedInitMethod('afterPropertiesSet'))) { if (logger.isDebugEnabled()) { logger.debug('Invoking afterPropertiesSet() on bean with name ’' + beanName + '’'); } //調用InitializingBean.afterPropertiesSet if (System.getSecurityManager() != null) { try { AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() { @Override public Object run() throws Exception { ((InitializingBean) bean).afterPropertiesSet(); return null; } }, getAccessControlContext()); } catch (PrivilegedActionException pae) { throw pae.getException(); } } else { ((InitializingBean) bean).afterPropertiesSet(); } }//調用自定義初始化方法 if (mbd != null) { String initMethodName = mbd.getInitMethodName(); if (initMethodName != null && !(isInitializingBean && 'afterPropertiesSet'.equals(initMethodName)) && !mbd.isExternallyManagedInitMethod(initMethodName)) { invokeCustomInitMethod(beanName, bean, mbd); } }}
如下圖所示，MybatisSqlSessionFactoryBean同樣實現了InitializingBean接口。那么我們就需要注意其afterPropertiesSet方法了。
⑥ MybatisSqlSessionFactoryBean.afterPropertiesSet
如下所示，代碼很簡短只是創建了sqlSessionFactory。
@Overridepublic void afterPropertiesSet() throws Exception{ notNull(dataSource, 'Property ’dataSource’ is required'); //sqlSessionFactoryBuilder在populateBean的applyPropertyValues過程中已經存在！ 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(); }
進入afterPropertiesSet()方法前MybatisSqlSessionFactoryBean如下所示：
我們看一下sqlSessionFactory，這是一段很長的過程：
protected SqlSessionFactory buildSqlSessionFactory() throws Exception{ Configuration configuration; // TODO 加載自定義 MybatisXmlConfigBuilder MybatisXMLConfigBuilder 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) { //通常如果配置了configLocation會從這里創建MybatisXMLConfigBuilder， //其構造方法又創建了MybatisConfiguration xmlConfigBuilder = new MybatisXMLConfigBuilder(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'); } // TODO 使用自定義配置 configuration = new MybatisConfiguration(); 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)) { // TODO 支持自定義通配符 String[] typeAliasPackageArray; if (typeAliasesPackage.contains('*') && !typeAliasesPackage.contains(',') && !typeAliasesPackage.contains(';')) { typeAliasPackageArray = PackageHelper.convertTypeAliasesPackage(typeAliasesPackage); } else { typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); } if (typeAliasPackageArray == null) { throw new MybatisPlusException('not find typeAliasesPackage:' + typeAliasesPackage); } for (String packageToScan : typeAliasPackageArray) { configuration.getTypeAliasRegistry().registerAliases(packageToScan, typeAliasesSuperType == null ? Object.class : typeAliasesSuperType); if (LOGGER.isDebugEnabled()) { LOGGER.debug('Scanned package: ’' + packageToScan + '’ for aliases'); } } } // TODO 自定義枚舉類掃描處理 if (hasLength(this.typeEnumsPackage)) { Set<Class> classes = null; if (typeEnumsPackage.contains('*') && !typeEnumsPackage.contains(',') && !typeEnumsPackage.contains(';')) { classes = PackageHelper.scanTypePackage(typeEnumsPackage); } else { String[] typeEnumsPackageArray = tokenizeToStringArray(this.typeEnumsPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); if (typeEnumsPackageArray == null) { throw new MybatisPlusException('not find typeEnumsPackage:' + typeEnumsPackage); } classes = new HashSet<Class>(); for (String typePackage : typeEnumsPackageArray) { classes.addAll(PackageHelper.scanTypePackage(typePackage)); } } // 取得類型轉換注冊器 TypeHandlerRegistry typeHandlerRegistry = configuration.getTypeHandlerRegistry(); for (Class cls : classes) { if (cls.isEnum()) { if (IEnum.class.isAssignableFrom(cls)) { typeHandlerRegistry.register(cls.getName(), com.baomidou.mybatisplus.handlers.EnumTypeHandler.class.getCanonicalName()); } else { // 使用原生 EnumOrdinalTypeHandler typeHandlerRegistry.register(cls.getName(), org.apache.ibatis.type.EnumOrdinalTypeHandler.class.getCanonicalName()); } } } } if (!isEmpty(this.typeAliases)) { for (Class<?> typeAlias : 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 (TypeHandler<?> typeHandler : 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 { 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)); // 設置元數據相關 GlobalConfigUtils.setMetaData(dataSource, globalConfig); SqlSessionFactory sqlSessionFactory = this.sqlSessionFactoryBuilder.build(configuration); // TODO SqlRunner SqlRunner.FACTORY = sqlSessionFactory; // TODO 緩存 sqlSessionFactory globalConfig.setSqlSessionFactory(sqlSessionFactory); // TODO 設置全局參數屬性 globalConfig.signGlobalConfig(sqlSessionFactory); if (!isEmpty(this.mapperLocations)) { if (globalConfig.isRefresh()) { //TODO 設置自動刷新配置 減少配置 new MybatisMapperRefresh(this.mapperLocations, sqlSessionFactory, 2, 2, true); } for (Resource mapperLocation : this.mapperLocations) { if (mapperLocation == null) { continue; } try { // TODO 這里也換了噢噢噢噢 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 sqlSessionFactory; }
上面代碼主要做了如下事情：
獲取MybatisXMLConfigBuilder對象 獲取Configuration對象-MybatisConfiguration 配置對象Configuration添加插件configuration.addInterceptor(plugin); xmlConfigBuilder.parse()對configuration做進一步處理 獲取SpringManagedTransactionFactory用來創建SpringManagedTransaction 獲取一個DefaultSqlSessionFactory實例對象 globalConfig.setSqlSessionFactory(sqlSessionFactory)中會創建MybatisSqlSessionTemplate 解析mapperLocation對應的一個個mapper配置文件，使用助手builderAssistant的addMappedStatement方法將一個個結點添加配置對象中 其他屬性設置等等也就是說，在MybatisSqlSessionFactoryBean.afterPropertiesSet方法執行結束后，SqlSessionFactory、SqlSessionTemplate、Configuration等都已存在！
【3】查詢執行流程分析
示例代碼如下：
List<Employee > emps = employeeMapper.selectPage(page, null);
如下圖所示，此時我們獲取到的employeeMapper其實是個代理對象：
總結
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