SpringBoot源码分析（三）整合MyBatis

梦里梦外; 2023-02-22 13:41 12阅读 0赞

# 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>
        
        <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>

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：

![mybatis-spring-boot-autoconfigure][]

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：

![img][]

[mybatis-spring-boot-autoconfigure]: https://img-blog.csdnimg.cn/20200703235503968.png?x-oss-process=image/watermark,type_ZmFuZ3poZW5naGVpdGk,shadow_10,text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L1EzODM4NDE4,size_16,color_FFFFFF,t_70
[img]: https://imgconvert.csdnimg.cn/aHR0cHM6Ly9vc2NpbWcub3NjaGluYS5uZXQvb3NjbmV0LzcxOTZmNGI2YzdkMzg2ZDQxNjI1YjAxZjIwNjY2MjhjYmU5LmpwZw?x-oss-process=image/format,png