MyBatis Plus插件机制与执行流程原理分析
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2020-09-10 02:03
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【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:
"sqlSessionFactoryBean" class="com.baomidou.mybatisplus.spring.MybatisSqlSessionFactoryBean"><property name="dataSource" ref="dataSource">property>
<property name="configLocation" value="classpath:mybatis-config.xml">property>
<property name="typeAliasesPackage" value="com.jane.mp.beans">property>
<property name="globalConfig" ref="globalConfiguration">property>
<property name="plugins">
<list>
<bean class="com.baomidou.mybatisplus.plugins.PaginationInterceptor">bean>
<bean class="com.baomidou.mybatisplus.plugins.SqlExplainInterceptor">
<property name="stopProceed" value="true">property>
bean>
<bean class="com.baomidou.mybatisplus.plugins.PerformanceInterceptor">
<property name="format" value="true">property>
bean>
<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:
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
*/
protected 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bean
BeanWrapper 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>() {
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>() {
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。
public 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
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
(); 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 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:
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本文链接:
https://janus.blog.csdn.net/article/details/108441600
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