MyBaits自动配置原理

首先我们建立一个SpringBoot工程，导入mybatis-spring-boot-starter依赖。

<dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-starter</artifactId> <version>2.1.4</version> </dependency>

导入后发现这个依赖其实就是帮助我们导入了mybatis需要的依赖，其中和自动配置相关最重要的一个就是mybatis-spring-boot-autoconfigure

<dependencies> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> </dependency> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-jdbc</artifactId> </dependency> <dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-autoconfigure</artifactId> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> </dependency> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis-spring</artifactId> </dependency> </dependencies> MyBatis自动配置中是如何工作的

如上面分析自动配置的关键类我们就从mybatis-spring-boot-autoconfigure开始着手分析。

spring.factories # Auto Configure org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ org.mybatis.spring.boot.autoconfigure.MybatisLanguageDriverAutoConfiguration,\ org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration

从spring.factories文件看到这里通过SPI机制加载了两个类

MybatisAutoConfiguration

MybatisLanguateDriverAutoConfiguration.

MybatisAutoConfiguration

//表示这是一个Spring配置类 @Configuration //这个类需要在classpath中存在SqlSessionFactory和SqlSessionFactoryBean时才生效 @ConditionalOnClass({SqlSessionFactory.class, SqlSessionFactoryBean.class}) -- //这个类需要有一个DataSource的Canidate注册到Spring容器中 @ConditionalOnSingleCandidate(DataSource.class) //使MybatisProperties注解类生效 @EnableConfigurationProperties({MybatisProperties.class}) //需要在DataSourceAutoConfiguration和MybatisLanguageDriverAutoConfiguration自动配置之后执行 @AutoConfigureAfter({DataSourceAutoConfiguration.class, MybatisLanguageDriverAutoConfiguration.class}) public class MybatisAutoConfiguration implements InitializingBean { }

MybatisAutoConfiguration#sqlSessionFactory

@Bean @ConditionalOnMissingBean public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception { //创建一个SqlSessionFactoryBean, 在mybatis-spring项目下 SqlSessionFactoryBean factory = new SqlSessionFactoryBean(); factory.setDataSource(dataSource); factory.setVfs(SpringBootVFS.class); if (StringUtils.hasText(this.properties.getConfigLocation())) { factory.setConfigLocation(this.resourceLoader.getResource(this.properties.getConfigLocation())); } //应用Configuration对象 this.applyConfiguration(factory); if (this.properties.getConfigurationProperties() != null) { factory.setConfigurationProperties(this.properties.getConfigurationProperties()); } if (!ObjectUtils.isEmpty(this.interceptors)) { factory.setPlugins(this.interceptors); } if (this.databaseIdProvider != null) { factory.setDatabaseIdProvider(this.databaseIdProvider); } if (StringUtils.hasLength(this.properties.getTypeAliasesPackage())) { factory.setTypeAliasesPackage(this.properties.getTypeAliasesPackage()); } if (this.properties.getTypeAliasesSuperType() != null) { factory.setTypeAliasesSuperType(this.properties.getTypeAliasesSuperType()); } if (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) { factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage()); } if (!ObjectUtils.isEmpty(this.typeHandlers)) { factory.setTypeHandlers(this.typeHandlers); } if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) { factory.setMapperLocations(this.properties.resolveMapperLocations()); } Set<String> factoryPropertyNames = (Set)Stream.of((new BeanWrapperImpl(SqlSessionFactoryBean.class)).getPropertyDescriptors()).map(FeatureDescriptor::getName).collect(Collectors.toSet()); Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver(); if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) { factory.setScriptingLanguageDrivers(this.languageDrivers); if (defaultLanguageDriver == null && this.languageDrivers.length == 1) { defaultLanguageDriver = this.languageDrivers[0].getClass(); } } //设置默认的语言驱动类 if (factoryPropertyNames.contains("defaultScriptingLanguageDriver")) { factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver); } //这里默认会返回一个DefaultSqlSessionFactory对象 return factory.getObject(); }