一、前言

​ SpringBoot中是没有MyBatis的，我们可以通过要用MyBatis的话，需要相比普通引用MyBatis需要多做哪些工作？来反推出整合自动配置的原理

二、对比SpringBoot中使用MyBatis区别

1.pom方面

相比平时不一样的是，引用的是starter：

<dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-starter</artifactId> <version>1.3.2</version> </dependency>

2.注解

在启动类打上了@MapperScan(“top.yejian123.springbootM.mapper”)

3.配置文件

application.properties

# Mybatis相关配置 mybatis: #核心配置文件路径 config-location: classpath:mybatis/mybatis-config.xml #映射配置文件路径 mapper-locations: classpath:mybatis/mapper/*.xml

三、逐个分析

3.1 跟进打开pom：

<dependencies> <!--SpringBoot--> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter</artifactId> </dependency> <!--jdbc--> <dependency> <groupId>org.springframework.boot</groupId> <artifactId>spring-boot-starter-jdbc</artifactId> </dependency> <!--autoconfigure--> <dependency> <groupId>org.mybatis.spring.boot</groupId> <artifactId>mybatis-spring-boot-autoconfigure</artifactId> </dependency> <!--mybatis--> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis</artifactId> </dependency> <!--mybatis-spring整合--> <dependency> <groupId>org.mybatis</groupId> <artifactId>mybatis-spring</artifactId> </dependency> </dependencies>

引入了一堆依赖，实际上看下来，相比以前新花样只有mybatis-spring-boot-autoconfigure

打开这个jar包看：

就四个文件，看到了MybatisProperties，源码：

@ConfigurationProperties(prefix = MybatisProperties.MYBATIS_PREFIX) public class MybatisProperties { public static final String MYBATIS_PREFIX = "mybatis"; //省略以下代码 }

看到了@ConfigurationProperties，这也理解 application.properties 里配置的东西了，在这处理的

3.2 @MapperScan(“com.**.mapper”)

打开源码：

@Retention(RetentionPolicy.RUNTIME) @Target(ElementType.TYPE) @Documented @Import(MapperScannerRegistrar.class) public @interface MapperScan { //... }

导入了MapperScannerRegistrar，是spring和mybatis整合的时候扫描注册用的，监听相关事件通知完成扫描Mapper注册

最终会发现主要是mybatis-spring-boot-autoconfigure，核心类是MybatisAutoConfiguration

四、MybatisAutoConfiguration

查看源码

package org.mybatis.spring.boot.autoconfigure; @org.springframework.context.annotation.Configuration @ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class }) @ConditionalOnBean(DataSource.class) @EnableConfigurationProperties(MybatisProperties.class) @AutoConfigureAfter(DataSourceAutoConfiguration.class) public class MybatisAutoConfiguration { private final MybatisProperties properties; private final Interceptor[] interceptors; private final ResourceLoader resourceLoader; private final DatabaseIdProvider databaseIdProvider; private final List<ConfigurationCustomizer> configurationCustomizers; public MybatisAutoConfiguration(MybatisProperties properties, ObjectProvider<Interceptor[]> interceptorsProvider, ResourceLoader resourceLoader, ObjectProvider<DatabaseIdProvider> databaseIdProvider, ObjectProvider<List<ConfigurationCustomizer>> configurationCustomizersProvider) { this.properties = properties; this.interceptors = interceptorsProvider.getIfAvailable(); this.resourceLoader = resourceLoader; this.databaseIdProvider = databaseIdProvider.getIfAvailable(); this.configurationCustomizers = configurationCustomizersProvider.getIfAvailable(); } @PostConstruct public void checkConfigFileExists() { if (this.properties.isCheckConfigLocation() && StringUtils.hasText(this.properties.getConfigLocation())) { Resource resource = this.resourceLoader.getResource(this.properties.getConfigLocation()); Assert.state(resource.exists(), "Cannot find config location: " + resource + " (please add config file or check your Mybatis configuration)"); } } @Bean @ConditionalOnMissingBean public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception { 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())); } Configuration configuration = this.properties.getConfiguration(); if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) { configuration = new Configuration(); } if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) { for (ConfigurationCustomizer customizer : this.configurationCustomizers) { customizer.customize(configuration); } } factory.setConfiguration(configuration); 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 (StringUtils.hasLength(this.properties.getTypeHandlersPackage())) { factory.setTypeHandlersPackage(this.properties.getTypeHandlersPackage()); } if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) { factory.setMapperLocations(this.properties.resolveMapperLocations()); } return factory.getObject(); } @Bean @ConditionalOnMissingBean public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) { ExecutorType executorType = this.properties.getExecutorType(); if (executorType != null) { return new SqlSessionTemplate(sqlSessionFactory, executorType); } else { return new SqlSessionTemplate(sqlSessionFactory); } } public static class AutoConfiguredMapperScannerRegistrar implements BeanFactoryAware, ImportBeanDefinitionRegistrar, ResourceLoaderAware { private BeanFactory beanFactory; private ResourceLoader resourceLoader; @Override public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { logger.debug("Searching for mappers annotated with @Mapper"); ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry); try { if (this.resourceLoader != null) { scanner.setResourceLoader(this.resourceLoader); } List<String> packages = AutoConfigurationPackages.get(this.beanFactory); if (logger.isDebugEnabled()) { for (String pkg : packages) { logger.debug("Using auto-configuration base package '{}'", pkg); } } scanner.setAnnotationClass(Mapper.class); scanner.registerFilters(); scanner.doScan(StringUtils.toStringArray(packages)); } catch (IllegalStateException ex) { logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.", ex); } } @Override public void setBeanFactory(BeanFactory beanFactory) throws BeansException { this.beanFactory = beanFactory; } @Override public void setResourceLoader(ResourceLoader resourceLoader) { this.resourceLoader = resourceLoader; } } @org.springframework.context.annotation.Configuration @Import({ AutoConfiguredMapperScannerRegistrar.class }) @ConditionalOnMissingBean(MapperFactoryBean.class) public static class MapperScannerRegistrarNotFoundConfiguration { @PostConstruct public void afterPropertiesSet() { logger.debug("No {} found.", MapperFactoryBean.class.getName()); } } }

会发现，

① : 导入了SqlSessionFactory ②：导入了sqlSessionTemplate ③：导入了mapperScanner

Spring Boot启动时，会去实例化jar包mybatis-spring-boot-autoconfigure-starter中MybatisAutoConfiguration中的配置bean，包括SqlSessionFactory、SqlSessionTemplate。流程图如下：