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MyBatis Plus插件机制与执行流程原理分析详解

程序员文章站 2022-05-09 09:40:24
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performance...

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。

MyBatis Plus插件机制与执行流程原理分析详解

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:

MyBatis Plus插件机制与执行流程原理分析详解

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

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:

MyBatis Plus插件机制与执行流程原理分析详解

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); 
}}//...

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:

MyBatis Plus插件机制与执行流程原理分析详解


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:

MyBatis Plus插件机制与执行流程原理分析详解


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:

MyBatis Plus插件机制与执行流程原理分析详解


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:

MyBatis Plus插件机制与执行流程原理分析详解


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:

MyBatis Plus插件机制与执行流程原理分析详解


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); 
 }

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。

MyBatis Plus插件机制与执行流程原理分析详解

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:

MyBatis Plus插件机制与执行流程原理分析详解

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:

MyBatis Plus插件机制与执行流程原理分析详解

MyBatis Plus插件机制与执行流程原理分析详解

总结

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