MyBatis插件之拦截器（Interceptor）

MyBatis插件之拦截器（Interceptor）⼀.背景在很多业务场景下我们需要去拦截sql，达到不⼊侵原有代码业务处理⼀些东西，⽐如：分页操作，数据权限过滤操作，SQL执⾏时间性能监控等等，这⾥我们就可以⽤到Mybatis的拦截器Interceptor⼆.Mybatis核⼼对象介绍从MyBatis代码实现的⾓度来看，MyBatis的主要的核⼼部件有以下⼏个：Configuration初始化基础配置，⽐如MyBatis的别名等，⼀些重要的类型对象，如，插件，映射器，ObjectFactory和typeHandler对象，MyBatis所有的配置信息都维持在Configuration对象之中SqlSessionFactorySqlSession⼯⼚SqlSession作为MyBatis⼯作的主要顶层API，表⽰和数据库交互的会话，完成必要数据库增删改查功能ExecutorMyBatis执⾏器，是MyBatis调度的核⼼，负责SQL语句的⽣成和查询缓存的维护StatementHandler封装了JDBCStatement操作，负责对JDBCstatement的操作，如设置参数、将Statement结果集转换成List集合。ParameterHandler负责对⽤户传递的参数转换成JDBCStatement所需要的参数，ResultSetHandlerTypeHandler负责将JDBC返回的ResultSet结果集对象转换成List类型的集合；负责java数据类型和jdbc数据类型之间的映射和转换MappedStatementMappedStatement维护了⼀条<select|update|delete|insert>节点的封装，SqlSource负责根据⽤户传递的parameterObject，动态地⽣成SQL语句，将信息封装到BoundSql对象中，并返回BoundSql表⽰动态⽣成的SQL语句以及相应的参数信息三.Mybatis执⾏概要图四.MyBatis拦截器原理实现1.Mybatis⽀持对Executor、StatementHandler、PameterHandler和ResultSetHandler接⼝进⾏拦截，也就是说会对这4种对象进⾏代理2.⾸先从配置⽂件解析开始通过SqlSessionFactoryBean去构建Configuration添加拦截器并构建获取SqlSessionFactory/***{@codeFactoryBean}thatcreatesanMyBatis{@codeSqlSessionFactory}.*ThisistheusualwaytosetupasharedMyBatis{@codeSqlSessionFactory}inaSpringapplicationcontext;*theSqlSessionFactorycanthenbepassedtoMyBatis-basedDAOsviadependencyinjection.**Either{@codeDataSourceTransactionManager}or{@codeJtaTransactionManager}canbeusedfortransaction*demarcationincombinationwitha{@codeSqlSessionFactory}.JTAshouldbeusedfortransactions*whichspanmultipledatabasesorwhencontainermanagedtransactions(CMT)arebeingused.**@authorPutthibongBoonbong*@authorHunterPresnall*@authorEduardoMacarron*@authorEddúMeléndez*@authorKazukiShimizu**@see#setConfigLocation*@see#setDataSource*/publicclassSqlSessionFactoryBeanimplementsFactoryBean<SqlSessionFactory>,InitializingBean,ApplicationListener<ApplicationEvent>{privatestaticfinalLogLOGGER=LogFactory.getLog(SqlSessionFactoryBean.class);privateResourceconfigLocation;privateConfigurationconfiguration;privateResource[]mapperLocations;privateDataSourcedataSource;privateTransactionFactorytransactionFactory;privatePropertiesconfigurationProperties;privateSqlSessionFactoryBuildersqlSessionFactoryBuilder=newSqlSessionFactoryBuilder();//...此处省略部分源码/***Builda{@codeSqlSessionFactory}instance.**ThedefaultimplementationusesthestandardMyBatis{@codeXMLConfigBuilder}APItobuilda*{@codeSqlSessionFactory}instancebasedonanReader.*Since1.3.0,itcanbespecifieda{@linkConfiguration}instancedirectly(withoutconfigfile).**@returnSqlSessionFactory*@throwsIOExceptionifloadingtheconfigfilefailed*/protectedSqlSessionFactorybuildSqlSessionFactory()throwsIOException{Configurationconfiguration;//根据配置信息构建Configuration实体类XMLConfigBuilderxmlConfigBuilder=null;if(this.configuration!=null){configuration=this.configuration;configuration=this.configuration;if(configuration.getVariables()==null){configuration.setVariables(this.configurationProperties);}elseif(this.configurationProperties!=null){configuration.getVariables().putAll(this.configurationProperties);}}elseif(this.configLocation!=null){xmlConfigBuilder=newXMLConfigBuilder(this.configLocation.getInputStream(),null,this.configurationProperties);configuration=xmlConfigBuilder.getConfiguration();}else{if(LOGGER.isDebugEnabled()){LOGGER.debug("Property'configuration'or'configLocation'notspecified,usingdefaultMyBatisConfiguration");}configuration=newConfiguration();if(this.configurationProperties!=null){configuration.setVariables(this.configurationProperties);}}//...此处省略部分源码if(hasLength(this.typeAliasesPackage)){String[]typeAliasPackageArray=tokenizeToStringArray(this.typeAliasesPackage,ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS);for(StringpackageToScan:typeAliasPackageArray){configuration.getTypeAliasRegistry().registerAliases(packageToScan,typeAliasesSuperType==null?Object.class:typeAliasesSuperType);if(LOGGER.isDebugEnabled()){LOGGER.debug("Scannedpackage:'"+packageToScan+"'foraliases");}}}if(!isEmpty(this.typeAliases)){for(Class<?>typeAlias:this.typeAliases){configuration.getTypeAliasRegistry().registerAlias(typeAlias);if(LOGGER.isDebugEnabled()){LOGGER.debug("Registeredtypealias:'"+typeAlias+"'");}}}//查看是否注⼊拦截器，有的话添加到Interceptor集合⾥⾯if(!isEmpty(this.plugins)){for(Interceptorplugin:this.plugins){configuration.addInterceptor(plugin);if(LOGGER.isDebugEnabled()){LOGGER.debug("Registeredplugin:'"+plugin+"'");}}}//...此处省略部分源码returnthis.sqlSessionFactoryBuilder.build(configuration);}//...此处省略部分源码}通过原始的XMLConfigBuilder构建configuration添加拦截器publicclassXMLConfigBuilderextendsBaseBuilder{//解析配置privatevoidparseConfiguration(XNoderoot){try{//省略部分代码pluginElement(root.evalNode("plugins"));}catch(Exceptione){thrownewBuilderException("ErrorparsingSQLMapperConfiguration.Cause:"+e,e);}}privatevoidpluginElement(XNodeparent)throwsException{if(parent!=null){for(XNodechild:parent.getChildren()){Stringinterceptor=child.getStringAttribute("interceptor");Propertiesproperties=child.getChildrenAsProperties();InterceptorinterceptorInstance=(Interceptor)resolveClass(interceptor).newInstance();interceptorInstance.setProperties(properties);//调⽤InterceptorChain.addInterceptorconfiguration.addInterceptor(interceptorInstance);}}}}上⾯是两种不同的形式构建configuration并添加拦截器interceptor，上⾯第⼆种⼀般是以前XML配置的情况，这⾥主要是解析配置⽂件的plugin节点，根据配置的interceptor属性实例化Interceptor对象，然后添加到Configuration对象中的InterceptorChain属性中3.定义了拦截器链，初始化配置⽂件的时候就把所有的拦截器添加到拦截器链中org.apache.ibatis.plugin.InterceptorChain源代码如下：publicclassInterceptorChain{privatefinalList<Interceptor>interceptors=newArrayList<Interceptor>();publicObjectpluginAll(Objecttarget){//循环调⽤每个Interceptor.plugin⽅法for(Interceptorinterceptor:interceptors){target=interceptor.plugin(target);}returntarget;}//添加拦截器publicvoidaddInterceptor(Interceptorinterceptor){interceptors.add(interceptor);}publicList<Interceptor>getInterceptors(){returnCollections.unmodifiableList(interceptors);}}4.从以下代码可以看出mybatis在实例化Executor、ParameterHandler、ResultSetHandler、StatementHandler四⼤接⼝对象的时候调⽤interceptorChain.pluginAll()⽅法插⼊进去的。其实就是循环执⾏拦截器链所有的拦截器的plugin()⽅法，mybatis官⽅推荐的plugin⽅法是Plugin.wrap()⽅法,这个类就是我们上⾯的TargetProxy类org.apache.ibatis.session.Configuration类，其代码如下：publicclassConfiguration{protectedfinalInterceptorChaininterceptorChain=newInterceptorChain();//创建参数处理器publicParameterHandlernewParameterHandler(MappedStatementmappedStatement,ObjectparameterObject,BoundSqlboundSql){//创建ParameterHandlerParameterHandlerparameterHandler=mappedStatement.getLang().createParameterHandler(mappedStatement,parameterObject,boundSql);//插件在这⾥插⼊parameterHandler=(ParameterHandler)interceptorChain.pluginAll(parameterHandler);returnparameterHandler;}//创建结果集处理器publicResultSetHandlernewResultSetHandler(Executorexecutor,MappedStatementmappedStatement,RowBoundsrowBounds,ParameterHandlerparameResultHandlerresultHandler,BoundSqlboundSql){//创建DefaultResultSetHandlerResultSetHandlerresultSetHandler=newDefaultResultSetHandler(executor,mappedStatement,parameterHandler,resultHandler,boundSql,rowBounds)//插件在这⾥插⼊resultSetHandler=(ResultSetHandler)interceptorChain.pluginAll(resultSetHandler);returnresultSetHandler;}//创建语句处理器publicStatementHandlernewStatementHandler(Executorexecutor,MappedStatementmappedStatement,ObjectparameterObject,RowBoundsrowBounds,//创建路由选择语句处理器StatementHandlerstatementHandler=newRoutingStatementHandler(executor,mappedStatement,parameterObject,rowBounds,resultHandler,boundSq//插件在这⾥插⼊statementHandler=(StatementHandler)interceptorChain.pluginAll(statementHandler);returnstatementHandler;}publicExecutornewExecutor(Transactiontransaction){returnnewExecutor(transaction,defaultExecutorType);}//产⽣执⾏器publicExecutornewExecutor(Transactiontransaction,ExecutorTypeexecutorType){executorType=executorType==null?defaultExecutorType:executorType;//这句再做⼀下保护,囧,防⽌粗⼼⼤意的⼈将defaultExecutorType设成null?executorType=executorType==null?ExecutorType.SIMPLE:executorType;Executorexecutor;//然后就是简单的3个分⽀，产⽣3种执⾏器BatchExecutor/ReuseExecutor/SimpleExecutorif(ExecutorType.BATCH==executorType){executor=newBatchExecutor(this,transaction);}elseif(ExecutorType.REUSE==executorType){executor=newReuseExecutor(this,transaction);}else{executor=newSimpleExecutor(this,transaction);}//如果要求缓存，⽣成另⼀种CachingExecutor(默认就是有缓存),装饰者模式,所以默认都是返回CachingExecutorif(cacheEnabled){executor=newCachingExecutor(executor);}//此处调⽤插件,通过插件可以改变Executor⾏为executor=(Executor)interceptorChain.pluginAll(executor);returnexecutor;}}5.Mybatis的Plugin动态代理org.apache.ibatis.plugin.Plugin源代码如下publicclassPluginimplementsInvocationHandler{publicstaticObjectwrap(Objecttarget,Interceptorinterceptor){//从拦截器的注解中获取拦截的类名和⽅法信息Map<Class<?>,Set<Method>>signatureMap=getSignatureMap(interceptor);//取得要改变⾏为的类(ParameterHandler|ResultSetHandler|StatementHandler|Executor)Class<?>type=target.getClass();//取得接⼝Class<?>[]interfaces=getAllInterfaces(type,signatureMap);//产⽣代理，是Interceptor注解的接⼝的实现类才会产⽣代理if(interfaces.length>0){returnProxy.newProxyInstance(type.getClassLoader(),interfaces,newPlugin(target,interceptor,signatureMap));}returntarget;}@OverridepublicObjectinvoke(Objectproxy,Methodmethod,Object[]args)throwsThrowable{try{//获取需要拦截的⽅法Set<Method>methods=signatureMap.get(method.getDeclaringClass());//是Interceptor实现类注解的⽅法才会拦截处理if(methods!=null&&methods.contains(method)){//******调⽤Iercept，也即插⼊了我们⾃⼰的逻辑********returnercept(newInvocation(target,method,args));}//最后还是执⾏原来逻辑returnmethod.invoke(target,args);}catch(Exceptione){throwExceptionUtil.unwrapThrowable(e);}}//取得签名Map,就是获取Interceptor实现类上⾯的注解，要拦截的是那个类（Executor//,ParameterHandler，ResultSetHandler，StatementHandler）的那个⽅法privatestaticMap<Class<?>,Set<Method>>getSignatureMap(Interceptorinterceptor){//取Intercepts注解，例⼦可参见ExamplePlugin.javaInterceptsinterceptsAnnotation=interceptor.getClass().getAnnotation(Intercepts.class);//issue#251//必须得有Intercepts注解，没有报错if(interceptsAnnotation==null){thrownewPluginException("No@Interceptsannotationwasfoundininterceptor"+interceptor.getClass().getName());}//value是数组型，Signature的数组Signature[]sigs=interceptsAnnotation.value();//每个class⾥有多个Method需要被拦截,所以这么定义Map<Class<?>,Set<Method>>signatureMap=newHashMap<Class<?>,Set<Method>>();for(Signaturesig:sigs){Set<Method>methods=signatureMap.get(sig.type());if(methods==null){methods=newHashSet<Method>();signatureMap.put(sig.type(),methods);}try{Methodmethod=sig.type().getMethod(sig.method(),sig.args());methods.add(method);}catch(NoSuchMethodExceptione){thrownewPluginException("Couldnotfindmethodon"+sig.type()+"named"+sig.method()+".Cause:"+e,e);}}returnsignatureMap;}//取得接⼝privatestaticClass<?>[]getAllInterfaces(Class<?>type,Map<Class<?>,Set<Method>>signatureMap){privatestaticClass<?>[]getAllInterfaces(Class<?>type,Map<Class<?>,Set<Method>>signatureMap){Set<Class<?>>interfaces=newHashSet<Class<?>>();while(type!=null){for(Class<?>c:type.getInterfaces()){//拦截其他的⽆效if(signatureMap.containsKey(c)){interfaces.add(c);}}type=type.getSuperclass();}returninterfaces.toArray(newClass<?>[interfaces.size()]);}}6.我们⾃⼰实现的拦截器@Slf4j@Component@Intercepts({@Signature(method="prepare",type=StatementHandler.class,args={Connection.class,Integer.class}),@Signature(method="query",type=Executor.class,args={MappedStatement.class,Object.class,RowBounds.class,ResultHandler.class,CacheKey.c@SuppressWarnings("unchecked")publicclassSqliteDataSourceInterceptorimplementsInterceptor{@OverridepublicObjectplugin(Objecttarget){//调⽤插件returnPlugin.wrap(target,this);}@OverridepublicvoidsetProperties(Propertiespr