MyBatis Plus插件机制与执行流程原理分析

 

【1】MyBatis Plus插件

MyBatis Plus提供了分页插件PaginationInterceptor、执行分析插件SqlExplainInterceptor、性能分析插件PerformanceInterceptor以及乐观锁插件OptimisticLockerInterceptor。

Mybatis 通过插件 (Interceptor) 可以做到拦截四大对象相关方法的执行 ,根据需求完成相关数据的动态改变。

四大对象是：

• Executor
• StatementHandler
• ParameterHandler
• ResultSetHandler

四大对象的每个对象在创建时，都会执行interceptorChain.pluginAll()，会经过每个插件对象的 plugin()方法，目的是为当前的四大对象创建代理。代理对象就可以拦截到四大对象相关方法的执行，因为要执行四大对象的方法需要经过代理 。

① xml下插件的配置

如下所示：

<bean id="sqlSessionFactoryBean" class="com.baomidou.mybatisplus.spring.MybatisSqlSessionFactoryBean"><!-- 数据源 --><property name="dataSource" ref="dataSource"></property><property name="configLocation" value="classpath:mybatis-config.xml"></property><!-- 别名处理 --><property name="typeAliasesPackage" value="com.jane.mp.beans"></property><!-- 注入全局MP策略配置 --><property name="globalConfig" ref="globalConfiguration"></property><!-- 插件注册 --><property name="plugins"><list><!-- 注册分页插件 --><bean class="com.baomidou.mybatisplus.plugins.PaginationInterceptor"></bean><!-- 注册执行分析插件 --><bean class="com.baomidou.mybatisplus.plugins.SqlExplainInterceptor"><property name="stopProceed" value="true"></property></bean><!-- 注册性能分析插件 --><bean class="com.baomidou.mybatisplus.plugins.PerformanceInterceptor"><property name="format" value="true"></property><!-- <property name="maxTime" value="5"></property> --></bean><!-- 注册乐观锁插件 --><bean class="com.baomidou.mybatisplus.plugins.OptimisticLockerInterceptor"></bean></list></property></bean>

② springboot下注册插件

这里以分页插件为例：

@Bean public PaginationInterceptor paginationInterceptor() {     PaginationInterceptor paginationInterceptor = new PaginationInterceptor();     // 设置请求的页面大于最大页后操作， true调回到首页，false 继续请求  默认false     // paginationInterceptor.setOverflow(false);     // 设置最大单页限制数量，默认 500 条，-1 不受限制     // paginationInterceptor.setLimit(500);     // 开启 count 的 join 优化,只针对部分 left join     paginationInterceptor.setCountSqlParser(new JsqlParserCountOptimize(true));     return paginationInterceptor; }

③ SqlExplainInterceptor

SQL执行分析拦截器，全类名是com.baomidou.mybatisplus.plugins.SqlExplainInterceptor，只支持 MySQL5.6.3以上版本。

该插件的作用是分析 DELETE UPDATE语句 ,防止小白或者恶意进行DELETE UPDATE全表操作，不建议在生产环境中使用会造成性能下降，

在插件的底层通过SQL语句分析命令 Explain 分析当前的 SQL语句，根据结果集中的 Extra列来断定当前是否全表操作。

④ 性能分析插件

性能分析拦截器，全类名是com.baomidou.mybatisplus.plugins.PerformanceInterceptor，用于输出每条 SQL 语句及其执行时间。SQL性能执行分析 ,开发环境使用 超过指定时间，停止运行。

⑤ 乐观锁插件

全类名是com.baomidou.mybatisplus.plugins.OptimisticLockerInterceptor。如果想实现如下需求 : 当要更新一条记录的时候，希望这条记录没有被别人更新，就可以使用该插件进行判断。

乐观锁的实现原理(@Version 用于注解实体字段，必须要有) :

• 取出记录时，获取当前 version
• 更新时，带上这个version
• 执行更新时，set version = yourVersion+1 where version = yourVersion
• 如果 version不对，就更新失败

【2】获取sqlSessionFactoryBean

如下图所示，在系统启动时会初始化定义的bean。DefaultListableBeanFactory.preInstantiateSingletons方法中会从beanDefinitionNames中获取bean name然后依次创建。

这里可以看到RootBeanDefinition是com.baomidou.mybatisplus.spring.MybatisSqlSessionFactoryBean。

① 获取bean的过程中bean属性

如下所示，在getBean过程中可以看到bean的属性：

② createBean

第一次获取bean的时候会走到AbstractAutowireCapableBeanFactory.createBean进行bean的创建。

 /** 创建一个bean实例，为bean实例设置属性值，调用post-processors-bean后置处理器 */@Overrideprotected Object createBean(String beanName, RootBeanDefinition mbd, Object[] args) throws BeanCreationException {//...暂时忽略其他代码  try {// 这里会首先触发BeanPostProcessors ，如果这里能获取到bean则直接返回，不再走doCreateBean    Object bean = resolveBeforeInstantiation(beanName, mbdToUse);    if (bean != null) {      return bean;    }  }//...暂时忽略其他代码
//如果上面没有获取到bean，则会走doCreateBean--这也是创建bean的核心过程  Object beanInstance = doCreateBean(beanName, mbdToUse, args);//...暂时忽略其他代码  return beanInstance;}

在AbstractAutowireCapableBeanFactory.resolveBeforeInstantiation中就会分别执行bean后置处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;}

执行后置处理器的前置方法如下所示：

③ doCreateBean

AbstractAutowireCapableBeanFactory.doCreateBean是创建bean的核心方法，这会为bean属性赋值并会触发bean后置处理器、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.--实例化beanBeanWrapper instanceWrapper = null;if (mbd.isSingleton()) {  instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);}if (instanceWrapper == null) {//获取bean的包装对象-这里很重要  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 {//调用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;  }}//...//这里暂时忽略其他代码
// Initialize the bean instance.--初始化bean实例Object exposedObject = bean;try {//如下方法很重要  populateBean(beanName, mbd, instanceWrapper);  if (exposedObject != null) {    exposedObject = initializeBean(beanName, exposedObject, mbd);  }}//...
// Register bean as disposable.try {  registerDisposableBeanIfNecessary(beanName, bean, mbd);}//...return exposedObject;}

④ populateBean

顾名思义，为bean实例属性赋值。

AbstractAutowireCapableBeanFactory.populateBean

protected void populateBean(String beanName, RootBeanDefinition mbd, BeanWrapper bw) {//获取属性值列表PropertyValues pvs = mbd.getPropertyValues();
//...该种符号表示暂时忽略其他代码
//在为bean属性赋值前，给InstantiationAwareBeanPostProcessors 机会修改bean的状态//应用场景如支持字段注入boolean continueWithPropertyPopulation = true;
//循环调用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，进行主动注入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);//循环调用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);  }}//在这里为属性赋值，会进行类型转换，这里注意关键词deep copy//如果是引用类型且bean没有存在，则会进行bean的创建过程applyPropertyValues(beanName, mbd, bw, pvs);}

如下图所示在创建sqlSessionFactoryBean过程中会创建其属性globalConfiguration对象：

如下图所示在创建sqlSessionFactoryBean过程中(从左侧的方法顺序就可以看出来)会创建其属性PaginationInterceptor对象：

如下图所示在创建sqlSessionFactoryBean过程中(从左侧的方法顺序就可以看出来)会创建其属性SqlExplainInterceptor对象：

如下图所示在创建sqlSessionFactoryBean过程中(从左侧的方法顺序就可以看出来)会创建其属性PerformanceInterceptor对象：

如下图所示在创建sqlSessionFactoryBean过程中(从左侧的方法顺序就可以看出来)会创建其属性OptimisticLockerInterceptor对象：

---

⑤ initializeBean

AbstractAutowireCapableBeanFactory.initializeBean源码如下：

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 {  //调用意识/通知方法    invokeAwareMethods(beanName, bean);  }
  Object wrappedBean = bean;  if (mbd == null || !mbd.isSynthetic()) {  //调用bean后置处理器的前置方法    wrappedBean = applyBeanPostProcessorsBeforeInitialization(wrappedBean, beanName);  }  //调用初始化方法  try {    invokeInitMethods(beanName, wrappedBean, mbd);  }  catch (Throwable ex) {    throw new BeanCreationException(        (mbd != null ? mbd.getResourceDescription() : null),        beanName, "Invocation of init method failed", ex);  }
  if (mbd == null || !mbd.isSynthetic()) {  //  //调用bean后置处理器的后置方法    wrappedBean = applyBeanPostProcessorsAfterInitialization(wrappedBean, beanName);  }  return wrappedBean;}

AbstractAutowireCapableBeanFactory.invokeInitMethods方法源码如下：

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 + "'");    }    //调用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();    }  }//调用自定义初始化方法  if (mbd != null) {    String initMethodName = mbd.getInitMethodName();    if (initMethodName != null && !(isInitializingBean && "afterPropertiesSet".equals(initMethodName)) &&        !mbd.isExternallyManagedInitMethod(initMethodName)) {      invokeCustomInitMethod(beanName, bean, mbd);    }  }}

如下图所示，MybatisSqlSessionFactoryBean同样实现了InitializingBean接口。那么我们就需要注意其afterPropertiesSet方法了。

⑥ MybatisSqlSessionFactoryBean.afterPropertiesSet

如下所示，代码很简短只是创建了sqlSessionFactory。

@Overridepublic void afterPropertiesSet() throws Exception {    notNull(dataSource, "Property 'dataSource' is required"); //sqlSessionFactoryBuilder在populateBean的applyPropertyValues过程中已经存在！    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();}

进入afterPropertiesSet()方法前MybatisSqlSessionFactoryBean如下所示：

我们看一下sqlSessionFactory，这是一段很长的过程：

protected SqlSessionFactory buildSqlSessionFactory() throws Exception {    Configuration configuration;    // TODO 加载自定义 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会从这里创建MybatisXMLConfigBuilder， //其构造方法又创建了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 使用自定义配置        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 支持自定义通配符        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 自定义枚举类扫描处理    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));            }        }        // 取得类型转换注册器        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));    // 设置元数据相关    GlobalConfigUtils.setMetaData(dataSource, globalConfig);    SqlSessionFactory sqlSessionFactory = this.sqlSessionFactoryBuilder.build(configuration);    // TODO SqlRunner    SqlRunner.FACTORY = sqlSessionFactory;    // TODO 缓存 sqlSessionFactory    globalConfig.setSqlSessionFactory(sqlSessionFactory);    // TODO 设置全局参数属性    globalConfig.signGlobalConfig(sqlSessionFactory);    if (!isEmpty(this.mapperLocations)) {        if (globalConfig.isRefresh()) {            //TODO 设置自动刷新配置 减少配置            new MybatisMapperRefresh(this.mapperLocations, sqlSessionFactory, 2,                2, true);        }        for (Resource mapperLocation : this.mapperLocations) {            if (mapperLocation == null) {                continue;            }
            try {                // TODO  这里也换了噢噢噢噢                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;}

上面代码主要做了如下事情：

• 获取MybatisXMLConfigBuilder对象
• 获取Configuration对象-MybatisConfiguration
• 配置对象Configuration添加插件configuration.addInterceptor(plugin);
• xmlConfigBuilder.parse()对configuration做进一步处理
• 获取SpringManagedTransactionFactory用来创建SpringManagedTransaction
• 获取一个DefaultSqlSessionFactory实例对象
• globalConfig.setSqlSessionFactory(sqlSessionFactory)中会创建MybatisSqlSessionTemplate
• 解析mapperLocation对应的一个个mapper配置文件，使用助手builderAssistant的addMappedStatement方法将一个个结点添加配置对象中
• 其他属性设置等等

也就是说，在MybatisSqlSessionFactoryBean.afterPropertiesSet方法执行结束后，SqlSessionFactory、SqlSessionTemplate、Configuration等都已存在！

【3】查询执行流程分析

示例代码如下：

•  

List<Employee > emps = employeeMapper.selectPage(page, null);

如下图所示，此时我们获取到的employeeMapper其实是个代理对象：