Mybatis 源码分析一、 SqlSessionFactory的创建过程
本次解析是基于Mybatis与Spring整合的方式，分析Mybatis的初始化过程。
一、配置文件解析过程
Spring与Mybatis整合配置过程
1.1 配置数据源
第三步：
我们很清楚的看到真正添加的是一个Mapper代理工厂对象。当需要使用Mapper的时候会调用getMapper()方法。
由于涉及到的参数有很多，我们主要介绍以上常见的几种，其他的解析源码，大家自行研究。
以上过程执行完成后，我们就获得了一个SqlSessionFactory对象。
xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:aop="http://www.springframework.org/schema/aop" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.1.xsd http://www.springframework.org/schema/aop http://www.springframework.org/schema/aop/spring-aop-4.1.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.1.xsd"> <bean name="tcoin-dataSource" class="com.alibaba.druid.pool.DruidDataSource" init-method="init" destroy-method="close"> <property name="url" value="${tcoin.jdbc.url}"/> <property name="username" value="${tcoin.jdbc.user}"/> <property name="password" value="${tcoin.jdbc.password}"/> <property name="initialSize" value="${tcoin.jdbc.initialSize}"/> <property name="maxActive" value="${tcoin.jdbc.maxActive}"/> <property name="minIdle" value="${tcoin.jdbc.minIdle}"/> <property name="maxWait" value="${jdbc.maxWait}"/> <property name="poolPreparedStatements" value="${jdbc.poolPreparedStatements}"/> <property name="maxPoolPreparedStatementPerConnectionSize" value="${jdbc.maxPoolPreparedStatementPerConnectionSize}"/> <property name="validationQuery" value="${jdbc.validationQuery}"/> <property name="testOnBorrow" value="${jdbc.testOnBorrow}"/> <property name="testOnReturn" value="${jdbc.testOnReturn}"/> <property name="testWhileIdle" value="${jdbc.testWhileIdle}"/> <property name="timeBetweenEvictionRunsMillis" value="${jdbc.timeBetweenEvictionRunsMillis}"/> <property name="minEvictableIdleTimeMillis" value="${jdbc.minEvictableIdleTimeMillis}"/> <property name="removeAbandoned" value="${jdbc.removeAbandoned}"/> <property name="removeAbandonedTimeout" value="${jdbc.removeAbandonedTimeout}"/> <property name="logAbandoned" value="${jdbc.logAbandoned}"/> <property name="filters" value="${jdbc.filters}"/> bean> <bean id="tcoin-sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="configLocation" value="classpath:config/framework-mybatis.xml" /> <property name="dataSource" ref="tcoin-dataSource" /> <property name="plugins"> <list> <ref bean="offsetLimitIntercepter" /> list> property> <property name="mapperLocations" value="classpath*:com/tairanchina/md/tcoin/rule/dal/dao/*Mapper*.xml" /> bean> <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer"> <property name="annotationClass" value="javax.annotation.Resource" /> <property name="basePackage" value="com.tairanchina.md.tcoin.rule.dal" /> <property name="sqlSessionFactoryBeanName" value="tcoin-sqlSessionFactory" /> bean>beans>
1.2 Mybaits配置文件
xml version="1.0" encoding="UTF-8" ?> DOCTYPE configuration[ELEMENT configuration (properties?, settings?, typeAliases?, typeHandlers?, objectFactory?, objectWrapperFactory?, plugins?, environments?, databaseIdProvider?, mappers?)>ELEMENT databaseIdProvider (property*)>ATTLIST databaseIdProvidertype CDATA #REQUIRED>ELEMENT properties (property*)>ATTLIST propertiesresource CDATA #IMPLIEDurl CDATA #IMPLIED>ELEMENT property EMPTY>ATTLIST propertyname CDATA #REQUIREDvalue CDATA #REQUIRED>ELEMENT settings (setting+)>ELEMENT setting EMPTY>ATTLIST settingname CDATA #REQUIREDvalue CDATA #REQUIRED>ELEMENT typeAliases (typeAlias*,package*)>ELEMENT typeAlias EMPTY>ATTLIST typeAliastype CDATA #REQUIREDalias CDATA #IMPLIED>ELEMENT typeHandlers (typeHandler*,package*)>ELEMENT typeHandler EMPTY>ATTLIST typeHandlerjavaType CDATA #IMPLIEDjdbcType CDATA #IMPLIEDhandler CDATA #REQUIRED>ELEMENT objectFactory (property*)>ATTLIST objectFactorytype CDATA #REQUIRED>ELEMENT objectWrapperFactory (property*)>ATTLIST objectWrapperFactorytype CDATA #REQUIRED>ELEMENT plugins (plugin+)>ELEMENT plugin (property*)>ATTLIST plugininterceptor CDATA #REQUIRED>ELEMENT environments (environment+)>ATTLIST environmentsdefault CDATA #REQUIRED>ELEMENT environment (transactionManager,dataSource)>ATTLIST environmentid CDATA #REQUIRED>ELEMENT transactionManager (property*)>ATTLIST transactionManagertype CDATA #REQUIRED>ELEMENT dataSource (property*)>ATTLIST dataSourcetype CDATA #REQUIRED>ELEMENT mappers (mapper*,package*)>ELEMENT mapper EMPTY>ATTLIST mapperresource CDATA #IMPLIEDurl CDATA #IMPLIEDclass CDATA #IMPLIED>ELEMENT package EMPTY>ATTLIST packagename CDATA #REQUIRED>]><configuration> <settings> <setting name="mapUnderscoreToCamelCase" value="true" /> <setting name="jdbcTypeForNull" value="NULL" /> <setting name="cacheEnabled" value="false" /> settings>configuration>
1.3 配置文件解析过程
本介绍略过Spring解析配置文件的过程，只分析Mybatis解析配置文件，初始化Myatis配置的过程。
1.3.1 SqlSessionFactoryBean创建过程
SqlSessionFactory是Mybatis的核心类之一，主要功能是提供创建Mybatis的核心接口SqlSession。
SqlSessionFactory的创建是使用构造者模式进行创建，SqlSessionFactoryBean源码位于org.mybaits.spring包下。源码如下：
- package org.mybatis.spring;
import static org.springframework.util.Assert.notNull;import static org.springframework.util.ObjectUtils.isEmpty;import static org.springframework.util.StringUtils.hasLength;import static org.springframework.util.StringUtils.tokenizeToStringArray;import java.io.IOException;import java.sql.SQLException;import java.util.Properties;import javax.sql.DataSource;import org.apache.ibatis.builder.xml.XMLConfigBuilder;import org.apache.ibatis.builder.xml.XMLMapperBuilder;import org.apache.ibatis.executor.ErrorContext;import org.apache.ibatis.logging.Log;import org.apache.ibatis.logging.LogFactory;import org.apache.ibatis.mapping.DatabaseIdProvider;import org.apache.ibatis.mapping.Environment;import org.apache.ibatis.plugin.Interceptor;import org.apache.ibatis.reflection.factory.ObjectFactory;import org.apache.ibatis.reflection.wrapper.ObjectWrapperFactory;import org.apache.ibatis.session.Configuration;import org.apache.ibatis.session.SqlSessionFactory;import org.apache.ibatis.session.SqlSessionFactoryBuilder;import org.apache.ibatis.transaction.TransactionFactory;import org.apache.ibatis.type.TypeHandler;import org.mybatis.spring.transaction.SpringManagedTransactionFactory;import org.springframework.beans.factory.FactoryBean;import org.springframework.beans.factory.InitializingBean;import org.springframework.context.ApplicationEvent;import org.springframework.context.ApplicationListener;import org.springframework.context.ConfigurableApplicationContext;import org.springframework.context.event.ContextRefreshedEvent;import org.springframework.core.NestedIOException;import org.springframework.core.io.Resource;import org.springframework.jdbc.datasource.TransactionAwareDataSourceProxy;-
public class SqlSessionFactoryBean implements FactoryBean<SqlSessionFactory>, InitializingBean, ApplicationListener<ApplicationEvent> { private static final Log logger = LogFactory.getLog(SqlSessionFactoryBean.class); private Resource configLocation; private Resource[] mapperLocations; private DataSource dataSource; private TransactionFactory transactionFactory; private Properties configurationProperties; private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder(); private SqlSessionFactory sqlSessionFactory; private String environment = SqlSessionFactoryBean.class.getSimpleName(); // EnvironmentAware requires spring 3.1 private boolean failFast; private Interceptor[] plugins; private TypeHandler[] typeHandlers; private String typeHandlersPackage; private Class[] typeAliases; private String typeAliasesPackage; private Class typeAliasesSuperType; private DatabaseIdProvider databaseIdProvider; // issue #19. No default provider. private ObjectFactory objectFactory; private ObjectWrapperFactory objectWrapperFactory; public void setObjectFactory(ObjectFactory objectFactory) { this.objectFactory = objectFactory; }-
public void setObjectWrapperFactory(ObjectWrapperFactory objectWrapperFactory) { this.objectWrapperFactory = objectWrapperFactory; } public DatabaseIdProvider getDatabaseIdProvider() { return databaseIdProvider; }-
public void setDatabaseIdProvider(DatabaseIdProvider databaseIdProvider) { this.databaseIdProvider = databaseIdProvider; } public void setPlugins(Interceptor[] plugins) { this.plugins = plugins; } public void setTypeAliasesPackage(String typeAliasesPackage) { this.typeAliasesPackage = typeAliasesPackage; } public void setTypeAliasesSuperType(Class typeAliasesSuperType) { this.typeAliasesSuperType = typeAliasesSuperType; }-
public void setTypeHandlersPackage(String typeHandlersPackage) { this.typeHandlersPackage = typeHandlersPackage; }-
public void setTypeHandlers(TypeHandler[] typeHandlers) { this.typeHandlers = typeHandlers; }-
public void setTypeAliases(Class[] typeAliases) { this.typeAliases = typeAliases; } /**-
public void setFailFast(boolean failFast) { this.failFast = failFast; } public void setConfigLocation(Resource configLocation) { this.configLocation = configLocation; } public void setMapperLocations(Resource[] mapperLocations) { this.mapperLocations = mapperLocations; }-
public void setConfigurationProperties(Properties sqlSessionFactoryProperties) { this.configurationProperties = sqlSessionFactoryProperties; }-
public void setDataSource(DataSource dataSource) { if (dataSource instanceof TransactionAwareDataSourceProxy) { this.dataSource = ((TransactionAwareDataSourceProxy) dataSource).getTargetDataSource(); } else { this.dataSource = dataSource; } } public void setSqlSessionFactoryBuilder(SqlSessionFactoryBuilder sqlSessionFactoryBuilder) { this.sqlSessionFactoryBuilder = sqlSessionFactoryBuilder; } /** public void setTransactionFactory(TransactionFactory transactionFactory) { this.transactionFactory = transactionFactory; }-
public void setEnvironment(String environment) { this.environment = environment; } public void afterPropertiesSet() throws Exception { notNull(dataSource, "Property 'dataSource' is required"); notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required"); this.sqlSessionFactory = buildSqlSessionFactory(); }-
protected SqlSessionFactory buildSqlSessionFactory() throws IOException { Configuration configuration; XMLConfigBuilder xmlConfigBuilder = null; if (this.configLocation != null) { xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties); configuration = xmlConfigBuilder.getConfiguration(); } else { if (logger.isDebugEnabled()) { logger.debug("Property 'configLocation' not specified, using default MyBatis Configuration"); } configuration = new Configuration(); configuration.setVariables(this.configurationProperties); } if (this.objectFactory != null) { configuration.setObjectFactory(this.objectFactory); } if (this.objectWrapperFactory != null) { configuration.setObjectWrapperFactory(this.objectWrapperFactory); } if (hasLength(this.typeAliasesPackage)) { String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); for (String packageToScan : typeAliasPackageArray) { configuration.getTypeAliasRegistry().registerAliases(packageToScan, typeAliasesSuperType == null ? Object.class : typeAliasesSuperType); if (logger.isDebugEnabled()) { logger.debug("Scanned package: '" + packageToScan + "' for aliases"); } } } 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 (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(); } Environment environment = new Environment(this.environment, this.transactionFactory, this.dataSource); configuration.setEnvironment(environment); if (this.databaseIdProvider != null) { try { configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource)); } catch (SQLException e) { throw new NestedIOException("Failed getting a databaseId", e); } } if (!isEmpty(this.mapperLocations)) { for (Resource mapperLocation : this.mapperLocations) { if (mapperLocation == null) { continue; } try { 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 this.sqlSessionFactoryBuilder.build(configuration); } public SqlSessionFactory getObject() throws Exception { if (this.sqlSessionFactory == null) { afterPropertiesSet(); } return this.sqlSessionFactory; } public Class extends SqlSessionFactory> getObjectType() { return this.sqlSessionFactory == null ? SqlSessionFactory.class : this.sqlSessionFactory.getClass(); } public boolean isSingleton() { return true; } public void onApplicationEvent(ApplicationEvent event) { if (failFast && event instanceof ContextRefreshedEvent) { // fail-fast -> check all statements are completed this.sqlSessionFactory.getConfiguration().getMappedStatementNames(); } }}
我们将这段源码的解析分为两个部分，一部分是Spring对SqlSessionFactroyBean的初始化过程，另一过程是Mybaits的解析配置参数的过程。
首先SqlSessionFactoryBean 实现了了Spring 的FacatoryBean，顾名思义就是Spring的对象创建工厂，Spring在创建对象的时候会调用对象工厂的getObject()方法。
Spring首先会根据我们我们节点的配置，创建简单的SqlSessionFactoryBean，并对其参数进行初始化，初始化涉及到的参数主要有：
private Resource configLocation; private Resource[] mapperLocations; private DataSource dataSource; private TransactionFactory transactionFactory; private Properties configurationProperties; private SqlSessionFactoryBuilder sqlSessionFactoryBuilder = new SqlSessionFactoryBuilder(); private SqlSessionFactory sqlSessionFactory; private String environment = SqlSessionFactoryBean.class.getSimpleName(); // EnvironmentAware requires spring 3.1 private boolean failFast; private Interceptor[] plugins; private TypeHandler[] typeHandlers; private String typeHandlersPackage; private Class[] typeAliases; private String typeAliasesPackage; private Class typeAliasesSuperType; private DatabaseIdProvider databaseIdProvider; // issue #19. No default provider. private ObjectFactory objectFactory; private ObjectWrapperFactory objectWrapperFactory;
以上参数正对应我们在节点中通过配置的参数。在本例中对应的就是:
<bean id="tcoin-sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean"> <property name="configLocation" value="classpath:config/txframework-mybatis.xml" /> <property name="dataSource" ref="tcoin-dataSource" /> <property name="plugins"> <list> <ref bean="offsetLimitIntercepter" /> list> property> <property name="mapperLocations" value="classpath*:com/tairanchina/md/tcoin/rule/dal/dao/*Mapper*.xml" /> bean>
本例中Spring初始化创建SqlSessionFactoryBean就会根据我们的配置对其configaLocation、mapperLocations、dataSource、plugins进行初始化。之后会调用其中的getObject()方法。
public SqlSessionFactory getObject() throws Exception { if (this.sqlSessionFactory == null) { afterPropertiesSet(); } return this.sqlSessionFactory; }
对于getObject()方法，由于此时this.sqlSessionFactoty并没有赋值，故接着会执行
afterPropertiesSet()方法。
public void afterPropertiesSet() throws Exception { notNull(dataSource, "Property 'dataSource' is required"); notNull(sqlSessionFactoryBuilder, "Property 'sqlSessionFactoryBuilder' is required"); this.sqlSessionFactory = buildSqlSessionFactory(); }
这时通过两个断言，判断dataSource以及sqlSessionFactoryBuilder（SqlSessionFactory 创建者模式的具体创建SqlSessionFactory创建对象）不能为null。
接着就会执行创建SqlSessionFactory的具体方法。
protected SqlSessionFactory buildSqlSessionFactory() throws IOException { Configuration configuration; XMLConfigBuilder xmlConfigBuilder = null; if (this.configLocation != null) { xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties); configuration = xmlConfigBuilder.getConfiguration(); } else { if (logger.isDebugEnabled()) { logger.debug("Property 'configLocation' not specified, using default MyBatis Configuration"); } configuration = new Configuration(); configuration.setVariables(this.configurationProperties); } if (this.objectFactory != null) { configuration.setObjectFactory(this.objectFactory); } if (this.objectWrapperFactory != null) { configuration.setObjectWrapperFactory(this.objectWrapperFactory); } if (hasLength(this.typeAliasesPackage)) { String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); for (String packageToScan : typeAliasPackageArray) { configuration.getTypeAliasRegistry().registerAliases(packageToScan, typeAliasesSuperType == null ? Object.class : typeAliasesSuperType); if (logger.isDebugEnabled()) { logger.debug("Scanned package: '" + packageToScan + "' for aliases"); } } } 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 (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(); } Environment environment = new Environment(this.environment, this.transactionFactory, this.dataSource); configuration.setEnvironment(environment); if (this.databaseIdProvider != null) { try { configuration.setDatabaseId(this.databaseIdProvider.getDatabaseId(this.dataSource)); } catch (SQLException e) { throw new NestedIOException("Failed getting a databaseId", e); } } if (!isEmpty(this.mapperLocations)) { for (Resource mapperLocation : this.mapperLocations) { if (mapperLocation == null) { continue; } try { 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 this.sqlSessionFactoryBuilder.build(configuration); }
上述方法简单来说主要完成的工作是根据我们的配置文件构建Conffiguration对象，再由这个对象根据创建者模式的方式创建SqlSessionFactory对象。下面我们一步步解析整个方法的执行过程。
XMLConfigBuilder 是用于解析配置的XML文件，读取配置参数，并将读取的数据存入Configuration的了类中，几乎我们使用到的Mybatis的所有配置都在这里。
第一步：
xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties); configuration = xmlConfigBuilder.getConfiguration();
根据我们配置的configuration参数，读取Mybatis的主配置文件，生成Configuration对象，注意此时并没有去真正解析该配置文件。
同样我们可以看到，我们可以不配置configuration属性，这时Mybatis会给我们执行一个默认的属性。
第二步：
根据我们在SqlSessionFactoryBean节点中配置的属性，对Configuration中对应的属性进行赋值，具体每个属性的处理方式，我们会在Configuration解析Mybatis配置文件时，再进一步研究。
if (this.objectFactory != null) { configuration.setObjectFactory(this.objectFactory); } if (this.objectWrapperFactory != null) { configuration.setObjectWrapperFactory(this.objectWrapperFactory); } if (hasLength(this.typeAliasesPackage)) { String[] typeAliasPackageArray = tokenizeToStringArray(this.typeAliasesPackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS); for (String packageToScan : typeAliasPackageArray) { configuration.getTypeAliasRegistry().registerAliases(packageToScan, typeAliasesSuperType == null ? Object.class : typeAliasesSuperType); if (logger.isDebugEnabled()) { logger.debug("Scanned package: '" + packageToScan + "' for aliases"); } } } 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 + "'"); } } }
以上两步操作，完成了我们在Spring bean节点里面配置的参数的解析，下面我们研究Mybatis配置文件的解析过程。
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(); } }
以上代码关键在于xmlConfigBuilder.parse()，也即具体解析Mybatis的配置文件的过程。对应的是XMLConfiguBuilder中的parse()方法。
public Configuration parse() { if (parsed) { throw new BuilderException("Each XMLConfigBuilder can only be used once."); } parsed = true; parseConfiguration(parser.evalNode("/configuration")); return configuration; }
上述方法也很巧妙的用了一个标识来确保配置文件只解析一次，这点技巧也值得我们在开发中学习。通过上述方法我们跟踪到parseConfiguration()方法中；以下内容会涉及到XML文件的解析方式，也即java的基础知识，这里不做过多探讨，有疑问的小伙伴可以自行查找相关资料。
private void parseConfiguration(XNode root) { try { propertiesElement(root.evalNode("properties")); //issue #117 read properties first typeAliasesElement(root.evalNode("typeAliases")); pluginElement(root.evalNode("plugins")); objectFactoryElement(root.evalNode("objectFactory")); objectWrapperFactoryElement(root.evalNode("objectWrapperFactory")); settingsElement(root.evalNode("settings")); environmentsElement(root.evalNode("environments")); // read it after objectFactory and objectWrapperFactory issue #631 databaseIdProviderElement(root.evalNode("databaseIdProvider")); typeHandlerElement(root.evalNode("typeHandlers")); mapperElement(root.evalNode("mappers")); } catch (Exception e) { throw new BuilderException("Error parsing SQL Mapper Configuration. Cause: " + e, e); } }
上述方法中根据Mybatis中的可配参数，逐步进行解析，分别对应的是以下几种：
- properties 全局参数
- setting 设置
- typeAliases 别名。
- typeHandler 类处理器
- ObjectFactory 对象
- plugin 插件
- environment环境
- DatabaseIdProvider 数据库标识
- Mapper映射器
1、properties
- 用于配置全局参数，之后就可以使用${参数名}进行引用。
-
private void propertiesElement(XNode context) throws Exception {if (context != null) {Properties defaults = context.getChildrenAsProperties();String resource = context.getStringAttribute("resource");String url = context.getStringAttribute("url");if (resource != null && url != null) {throw new BuilderException("The properties element cannot specify both a URL and a resource based property file reference. Please specify one or the other.");}if (resource != null) {defaults.putAll(Resources.getResourceAsProperties(resource));} else if (url != null) {defaults.putAll(Resources.getUrlAsProperties(url));}Properties vars = configuration.getVariables();if (vars != null) {defaults.putAll(vars);}parser.setVariables(defaults);configuration.setVariables(defaults);}}
Properties defaults = context . getChildrenAsProperties ();
这行代码就已经将我们配置的全局参数读到Configuration中了，但又对"url"以及"resource"两个参数进行了特殊处理，因为resource参数对应的是类路径的属性文件，url对应的是指定路径下的属性文件，两个属性文件不能共存，并且这两个属性文件中的属性会覆盖我们在propertis中配置的同名属性。
2、setting
-
private void settingsElement(XNode context) throws Exception {if (context != null) {Properties props = context.getChildrenAsProperties();// Check that all settings are known to the configuration classMetaClass metaConfig = MetaClass.forClass(Configuration.class);for (Object key : props.keySet()) {if (!metaConfig.hasSetter(String.valueOf(key))) {throw new BuilderException("The setting " + key + " is not known. Make sure you spelled it correctly (case sensitive).");}}configuration.setAutoMappingBehavior(AutoMappingBehavior.valueOf(props.getProperty("autoMappingBehavior", "PARTIAL")));configuration.setCacheEnabled(booleanValueOf(props.getProperty("cacheEnabled"), true));configuration.setProxyFactory((ProxyFactory) createInstance(props.getProperty("proxyFactory")));configuration.setLazyLoadingEnabled(booleanValueOf(props.getProperty("lazyLoadingEnabled"), false));configuration.setAggressiveLazyLoading(booleanValueOf(props.getProperty("aggressiveLazyLoading"), true));configuration.setMultipleResultSetsEnabled(booleanValueOf(props.getProperty("multipleResultSetsEnabled"), true));configuration.setUseColumnLabel(booleanValueOf(props.getProperty("useColumnLabel"), true));configuration.setUseGeneratedKeys(booleanValueOf(props.getProperty("useGeneratedKeys"), false));configuration.setDefaultExecutorType(ExecutorType.valueOf(props.getProperty("defaultExecutorType", "SIMPLE")));configuration.setDefaultStatementTimeout(integerValueOf(props.getProperty("defaultStatementTimeout"), null));configuration.setMapUnderscoreToCamelCase(booleanValueOf(props.getProperty("mapUnderscoreToCamelCase"), false));configuration.setSafeRowBoundsEnabled(booleanValueOf(props.getProperty("safeRowBoundsEnabled"), false));configuration.setLocalCacheScope(LocalCacheScope.valueOf(props.getProperty("localCacheScope", "SESSION")));configuration.setJdbcTypeForNull(JdbcType.valueOf(props.getProperty("jdbcTypeForNull", "OTHER")));configuration.setLazyLoadTriggerMethods(stringSetValueOf(props.getProperty("lazyLoadTriggerMethods"), "equals,clone,hashCode,toString"));configuration.setSafeResultHandlerEnabled(booleanValueOf(props.getProperty("safeResultHandlerEnabled"), true));configuration.setDefaultScriptingLanguage(resolveClass(props.getProperty("defaultScriptingLanguage")));configuration.setCallSettersOnNulls(booleanValueOf(props.getProperty("callSettersOnNulls"), false));configuration.setLogPrefix(props.getProperty("logPrefix"));configuration.setLogImpl(resolveClass(props.getProperty("logImpl")));configuration.setConfigurationFactory(resolveClass(props.getProperty("configurationFactory")));}}
setting中可设置的参数较多，我们不过多研究。
别名的设置有两种方式，一种是包扫描的方式批量设置别名，一种是我们针对每个类自定义别名。
private void typeAliasesElement(XNode parent) { if (parent != null) { for (XNode child : parent.getChildren()) { if ("package".equals(child.getName())) { String typeAliasPackage = child.getStringAttribute("name"); configuration.getTypeAliasRegistry().registerAliases(typeAliasPackage); } else { String alias = child.getStringAttribute("alias"); String type = child.getStringAttribute("type"); try { Class clazz = Resources.classForName(type); if (alias == null) { typeAliasRegistry.registerAlias(clazz); } else { typeAliasRegistry.registerAlias(alias, clazz); } } catch (ClassNotFoundException e) { throw new BuilderException("Error registering typeAlias for '" + alias + "'. Cause: " + e, e); } } } } }
public void registerAlias(Class type) { String alias = type.getSimpleName(); Alias aliasAnnotation = type.getAnnotation(Alias.class); if (aliasAnnotation != null) { alias = aliasAnnotation.value(); } registerAlias(alias, type); }
上面的代码我们可以看到如果我们设置了别名，会使用的别名。如果我们没有设置别名，就会用类的名称，第一个字母小写的方式设置别名。
4、
plugin
private void pluginElement(XNode parent) throws Exception { if (parent != null) { for (XNode child : parent.getChildren()) { String interceptor = child.getStringAttribute("interceptor"); Properties properties = child.getChildrenAsProperties(); Interceptor interceptorInstance = (Interceptor) resolveClass(interceptor).newInstance(); interceptorInstance.setProperties(properties); configuration.addInterceptor(interceptorInstance); } } }
上述代码可以看到所有配置的插件之后，将其添加到configuration
public void addInterceptor(Interceptor interceptor) { interceptorChain.addInterceptor(interceptor); }
public class InterceptorChain { private final List<Interceptor> interceptors = new ArrayList<Interceptor>(); public Object pluginAll(Object target) { for (Interceptor interceptor : interceptors) { target = interceptor.plugin(target); } return target; } public void addInterceptor(Interceptor interceptor) { interceptors.add(interceptor); } public List<Interceptor> getInterceptors() { return Collections.unmodifiableList(interceptors); }}
插件相当于拦截器，采用责任链模式设计，具体我们在自定义插件实现的时候进行研究。
5、Mapper
private void mapperElement(XNode parent) throws Exception { if (parent != null) { for (XNode child : parent.getChildren()) { if ("package".equals(child.getName())) { String mapperPackage = child.getStringAttribute("name"); configuration.addMappers(mapperPackage); } else { String resource = child.getStringAttribute("resource"); String url = child.getStringAttribute("url"); String mapperClass = child.getStringAttribute("class"); if (resource != null && url == null && mapperClass == null) { ErrorContext.instance().resource(resource); InputStream inputStream = Resources.getResourceAsStream(resource); XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, resource, configuration.getSqlFragments()); mapperParser.parse(); } else if (resource == null && url != null && mapperClass == null) { ErrorContext.instance().resource(url); InputStream inputStream = Resources.getUrlAsStream(url); XMLMapperBuilder mapperParser = new XMLMapperBuilder(inputStream, configuration, url, configuration.getSqlFragments()); mapperParser.parse(); } else if (resource == null && url == null && mapperClass != null) { Class mapperInterface = Resources.classForName(mapperClass); configuration.addMapper(mapperInterface); } else { throw new BuilderException("A mapper element may only specify a url, resource or class, but not more than one."); } } } }
上述代码我们可以看到添加映射器Mapper的方法有四种设置方式，根据包名package设置，根据url设置、根据resource设置、根据class设置，最后添加Mapper的方法是
configuration
.
addMappers
(
mapperPackage
);
我们看一下真正添加映射器的方法
MapperRegistry注册器中的添加方法。
public <T> void addMapper(Class<T> type) { if (type.isInterface()) { if (hasMapper(type)) { throw new BindingException("Type " + type + " is already known to the MapperRegistry."); } boolean loadCompleted = false; try { knownMappers.put(type, new MapperProxyFactory<T>(type)); // It's important that the type is added before the parser is run // otherwise the binding may automatically be attempted by the // mapper parser. If the type is already known, it won't try. MapperAnnotationBuilder parser = new MapperAnnotationBuilder(config, type); parser.parse(); loadCompleted = true; } finally { if (!loadCompleted) { knownMappers.remove(type); } } } }
public <T> T getMapper(Class<T> type, SqlSession sqlSession) { final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type); if (mapperProxyFactory == null) throw new BindingException("Type " + type + " is not known to the MapperRegistry."); try { return mapperProxyFactory.newInstance(sqlSession); } catch (Exception e) { throw new BindingException("Error getting mapper instance. Cause: " + e, e); } }
return
mapperProxyFactory.
newInstance
(sqlSession)
; 这行代码是真正返回Mapper代理对象的方法。
protected T newInstance(MapperProxy<T> mapperProxy) { return (T) Proxy.newProxyInstance(mapperInterface.getClassLoader(), new Class[] { mapperInterface }, mapperProxy); } public T newInstance(SqlSession sqlSession) { final MapperProxy<T> mapperProxy = new MapperProxy<T>(sqlSession, mapperInterface, methodCache); return newInstance(mapperProxy); }
从上面代码我们可以很清晰的看到我们真正操作的是由Mybatis通过JDK动态代理的方式生成的对象，这也解释了为什么我们需要有Mapper接口，具体Mapper的执行过程，我们会在后面的博文中学习。
二、使用技术分析
1、与Spring结合过程
我们通过上面的代码分析可以了解到如果我们需要通过Spring工厂帮我们创建对象，需要实现FactoryBean接口，重现其中的getObject()方法。
2、XML文件解析
对于配置文件的解析，最基础的技术就是XML解析，所以对于尝试开发自己框架的小伙伴，XML文件解析技术需要熟练掌握
3、基本Java技术
代码中充斥着大量的反射技术，反射技术的存在也是XML配置文件解析使用的基础。
动态代理技术，常见的动态代理技术有JDK动态代理，前提是需要有接口，以及CGLIB框架，不需要有接口。
4、使用的设计模式
基本可以看到的有创建SqlSessionFactory对象时使用的Builder模式
插件使用的责任链模式。
当然源码中也使用了不少设计模式，目前我了解的设计模式知识不多，先探讨到这里。