1. 相关配置和代码

• maven配置

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.7.14</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.boge</groupId>
    <artifactId>mybatis-spring-boot</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>mybatis-spring-boot</name>
    <description>mybatis-spring-boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter</artifactId>
            <version>2.3.1</version>
        </dependency>

        <dependency>
            <groupId>com.alibaba</groupId>
            <artifactId>druid-spring-boot-starter</artifactId>
            <version>1.2.18</version>
        </dependency>

        <dependency>
            <groupId>com.mysql</groupId>
            <artifactId>mysql-connector-j</artifactId>
            <scope>runtime</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.mybatis.spring.boot</groupId>
            <artifactId>mybatis-spring-boot-starter-test</artifactId>
            <version>2.3.1</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

• application.yml

server:
  port: 8000
spring:
  main:
    allow-circular-references: true
    allow-bean-definition-overriding: true
  application:
    name: freedom-code
  datasource:
    type: com.alibaba.druid.pool.DruidDataSource
    # MYSQL 5 驱动：com.mysql.jdbc.Driver，MYSQL 6+ 驱动：com.mysql.cj.jdbc.Driver
    driver-class-name: com.mysql.jdbc.Driver
    url: jdbc:mysql://localhost:3306/mybatis-vip?characterEncoding=utf-8&serverTimezone=UTC
    username: root
    password: WSX2952fcx!
    druid:
      # 初始化大小，最小，最大
      initial-size: 5
      min-idle: 5
      max-active: 100
      # 配置获取连接等待超时的时间
      max-wait: 60000
      # 配置间隔多久才进行一次检测，检测需要关闭的空闲连接，单位毫秒
      time-between-eviction-runs-millis: 60000
      # 配置一个连接在池中最小生存时间
      min-evictable-idle-time-millis: 300000
      validation-query: select VERSION()
      test-while-idle: true
      test-on-borrow: false
      test-on-return: false

mybatis:
  # xml映射文件
  mapper-locations: "classpath:mapper/*.xml"
  type-aliases-package: "com.boge.pojo"
  configuration:
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
    map-underscore-to-camel-case: true

• 代码

@Mapper
public interface UserMapper {
    List<User> query();
}

@SpringBootApplication
public class MybatisSpringBootApplication {

    public static void main(String[] args) {
        SpringApplication.run(MybatisSpringBootApplication.class, args);
    }

}

测试代码

@SpringBootTest
class MybatisSpringBootApplicationTests {
    @Autowired
    private IUserService iUserService;

    @Test
    void contextLoads() {
        for (User user : iUserService.query()) {
            System.out.println(user);
        }
    }

}

2. 整合原理

关注三个对象的创建：

• SqlSessionFactory如何创建
• SqlSession如何创建
• Mapper接口的代理类如何创建（比如UserMapper）。

2.1 springboot自动配置

原理略。

2.2 MybatisAutoConfiguration

源码。

/*
 *    Copyright 2015-2022 the original author or authors.
 *
 *    Licensed under the Apache License, Version 2.0 (the "License");
 *    you may not use this file except in compliance with the License.
 *    You may obtain a copy of the License at
 *
 *       https://www.apache.org/licenses/LICENSE-2.0
 *
 *    Unless required by applicable law or agreed to in writing, software
 *    distributed under the License is distributed on an "AS IS" BASIS,
 *    WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 *    See the License for the specific language governing permissions and
 *    limitations under the License.
 */
package org.mybatis.spring.boot.autoconfigure;


/**
 * {@link EnableAutoConfiguration Auto-Configuration} for Mybatis. Contributes a {@link SqlSessionFactory} and a
 * {@link SqlSessionTemplate}. If {@link org.mybatis.spring.annotation.MapperScan} is used, or a configuration file is
 * specified as a property, those will be considered, otherwise this auto-configuration will attempt to register mappers
 * based on the interface definitions in or under the root auto-configuration package.
 *
 * @author Eddú Meléndez
 * @author Josh Long
 * @author Kazuki Shimizu
 * @author Eduardo Macarrón
 */
@org.springframework.context.annotation.Configuration
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
@ConditionalOnSingleCandidate(DataSource.class)
@EnableConfigurationProperties(MybatisProperties.class)
@AutoConfigureAfter({ DataSourceAutoConfiguration.class, MybatisLanguageDriverAutoConfiguration.class })
public class MybatisAutoConfiguration implements InitializingBean {

  private static final Logger logger = LoggerFactory.getLogger(MybatisAutoConfiguration.class);

  private final MybatisProperties properties;

  private final Interceptor[] interceptors;

  private final TypeHandler[] typeHandlers;

  private final LanguageDriver[] languageDrivers;

  private final ResourceLoader resourceLoader;

  private final DatabaseIdProvider databaseIdProvider;

  private final List<ConfigurationCustomizer> configurationCustomizers;

  private final List<SqlSessionFactoryBeanCustomizer> sqlSessionFactoryBeanCustomizers;

  public MybatisAutoConfiguration(MybatisProperties properties, ObjectProvider<Interceptor[]> interceptorsProvider,
      ObjectProvider<TypeHandler[]> typeHandlersProvider, ObjectProvider<LanguageDriver[]> languageDriversProvider,
      ResourceLoader resourceLoader, ObjectProvider<DatabaseIdProvider> databaseIdProvider,
      ObjectProvider<List<ConfigurationCustomizer>> configurationCustomizersProvider,
      ObjectProvider<List<SqlSessionFactoryBeanCustomizer>> sqlSessionFactoryBeanCustomizers) {
    this.properties = properties;
    this.interceptors = interceptorsProvider.getIfAvailable();
    this.typeHandlers = typeHandlersProvider.getIfAvailable();
    this.languageDrivers = languageDriversProvider.getIfAvailable();
    this.resourceLoader = resourceLoader;
    this.databaseIdProvider = databaseIdProvider.getIfAvailable();
    this.configurationCustomizers = configurationCustomizersProvider.getIfAvailable();
    this.sqlSessionFactoryBeanCustomizers = sqlSessionFactoryBeanCustomizers.getIfAvailable();
  }

  @Override
  public void afterPropertiesSet() {
    checkConfigFileExists();
  }

  private 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()));
    }
    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);
    }
    Resource[] mapperLocations = this.properties.resolveMapperLocations();
    if (!ObjectUtils.isEmpty(mapperLocations)) {
      factory.setMapperLocations(mapperLocations);
    }
    Set<String> factoryPropertyNames = Stream
        .of(new BeanWrapperImpl(SqlSessionFactoryBean.class).getPropertyDescriptors()).map(PropertyDescriptor::getName)
        .collect(Collectors.toSet());
    Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();
    if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) {
      // Need to mybatis-spring 2.0.2+
      factory.setScriptingLanguageDrivers(this.languageDrivers);
      if (defaultLanguageDriver == null && this.languageDrivers.length == 1) {
        defaultLanguageDriver = this.languageDrivers[0].getClass();
      }
    }
    if (factoryPropertyNames.contains("defaultScriptingLanguageDriver")) {
      // Need to mybatis-spring 2.0.2+
      factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver);
    }
    applySqlSessionFactoryBeanCustomizers(factory);
    return factory.getObject();
  }

  private void applyConfiguration(SqlSessionFactoryBean factory) {
    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);
  }

  private void applySqlSessionFactoryBeanCustomizers(SqlSessionFactoryBean factory) {
    if (!CollectionUtils.isEmpty(this.sqlSessionFactoryBeanCustomizers)) {
      for (SqlSessionFactoryBeanCustomizer customizer : this.sqlSessionFactoryBeanCustomizers) {
        customizer.customize(factory);
      }
    }
  }

  @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);
    }
  }

  /**
   * This will just scan the same base package as Spring Boot does. If you want more power, you can explicitly use
   * {@link org.mybatis.spring.annotation.MapperScan} but this will get typed mappers working correctly, out-of-the-box,
   * similar to using Spring Data JPA repositories.
   */
  public static class AutoConfiguredMapperScannerRegistrar
      implements BeanFactoryAware, EnvironmentAware, ImportBeanDefinitionRegistrar {

    private BeanFactory beanFactory;
    private Environment environment;

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {

      if (!AutoConfigurationPackages.has(this.beanFactory)) {
        logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.");
        return;
      }

      logger.debug("Searching for mappers annotated with @Mapper");

      List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
      if (logger.isDebugEnabled()) {
        packages.forEach(pkg -> logger.debug("Using auto-configuration base package '{}'", pkg));
      }

      BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
      builder.addPropertyValue("processPropertyPlaceHolders", true);
      builder.addPropertyValue("annotationClass", Mapper.class);
      builder.addPropertyValue("basePackage", StringUtils.collectionToCommaDelimitedString(packages));
      BeanWrapper beanWrapper = new BeanWrapperImpl(MapperScannerConfigurer.class);
      Set<String> propertyNames = Stream.of(beanWrapper.getPropertyDescriptors()).map(PropertyDescriptor::getName)
          .collect(Collectors.toSet());
      if (propertyNames.contains("lazyInitialization")) {
        // Need to mybatis-spring 2.0.2+
        builder.addPropertyValue("lazyInitialization", "${mybatis.lazy-initialization:false}");
      }
      if (propertyNames.contains("defaultScope")) {
        // Need to mybatis-spring 2.0.6+
        builder.addPropertyValue("defaultScope", "${mybatis.mapper-default-scope:}");
      }

      // for spring-native
      boolean injectSqlSession = environment.getProperty("mybatis.inject-sql-session-on-mapper-scan", Boolean.class,
          Boolean.TRUE);
      if (injectSqlSession && this.beanFactory instanceof ListableBeanFactory) {
        ListableBeanFactory listableBeanFactory = (ListableBeanFactory) this.beanFactory;
        Optional<String> sqlSessionTemplateBeanName = Optional
            .ofNullable(getBeanNameForType(SqlSessionTemplate.class, listableBeanFactory));
        Optional<String> sqlSessionFactoryBeanName = Optional
            .ofNullable(getBeanNameForType(SqlSessionFactory.class, listableBeanFactory));
        if (sqlSessionTemplateBeanName.isPresent() || !sqlSessionFactoryBeanName.isPresent()) {
          builder.addPropertyValue("sqlSessionTemplateBeanName",
              sqlSessionTemplateBeanName.orElse("sqlSessionTemplate"));
        } else {
          builder.addPropertyValue("sqlSessionFactoryBeanName", sqlSessionFactoryBeanName.get());
        }
      }
      builder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);

      registry.registerBeanDefinition(MapperScannerConfigurer.class.getName(), builder.getBeanDefinition());
    }

    @Override
    public void setBeanFactory(BeanFactory beanFactory) {
      this.beanFactory = beanFactory;
    }

    @Override
    public void setEnvironment(Environment environment) {
      this.environment = environment;
    }

    private String getBeanNameForType(Class<?> type, ListableBeanFactory factory) {
      String[] beanNames = factory.getBeanNamesForType(type);
      return beanNames.length > 0 ? beanNames[0] : null;
    }

  }

  /**
   * If mapper registering configuration or mapper scanning configuration not present, this configuration allow to scan
   * mappers based on the same component-scanning path as Spring Boot itself.
   */
  @org.springframework.context.annotation.Configuration
  @Import(AutoConfiguredMapperScannerRegistrar.class)
  @ConditionalOnMissingBean({ MapperFactoryBean.class, MapperScannerConfigurer.class })
  public static class MapperScannerRegistrarNotFoundConfiguration implements InitializingBean {

    @Override
    public void afterPropertiesSet() {
      logger.debug(
          "Not found configuration for registering mapper bean using @MapperScan, MapperFactoryBean and MapperScannerConfigurer.");
    }

  }

}

2.3 debug过程

按照代码的执行顺序。

2.3.1 AutoConfiguredMapperScannerRegistrar

主要是为MapperScannerConfigurer定制bean信息。

    @Override
    public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {

      if (!AutoConfigurationPackages.has(this.beanFactory)) {
        logger.debug("Could not determine auto-configuration package, automatic mapper scanning disabled.");
        return;
      }

      logger.debug("Searching for mappers annotated with @Mapper");
	// 获得基本的包
      List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
      if (logger.isDebugEnabled()) {
        packages.forEach(pkg -> logger.debug("Using auto-configuration base package '{}'", pkg));
      }
		// 定制属性值
      BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
      builder.addPropertyValue("processPropertyPlaceHolders", true);
      builder.addPropertyValue("annotationClass", Mapper.class);
      builder.addPropertyValue("basePackage", StringUtils.collectionToCommaDelimitedString(packages));
      BeanWrapper beanWrapper = new BeanWrapperImpl(MapperScannerConfigurer.class);
      Set<String> propertyNames = Stream.of(beanWrapper.getPropertyDescriptors()).map(PropertyDescriptor::getName)
          .collect(Collectors.toSet());
      if (propertyNames.contains("lazyInitialization")) {
        // Need to mybatis-spring 2.0.2+
        builder.addPropertyValue("lazyInitialization", "${mybatis.lazy-initialization:false}");
      }
      if (propertyNames.contains("defaultScope")) {
        // Need to mybatis-spring 2.0.6+
        builder.addPropertyValue("defaultScope", "${mybatis.mapper-default-scope:}");
      }

      // for spring-native
      boolean injectSqlSession = environment.getProperty("mybatis.inject-sql-session-on-mapper-scan", Boolean.class,
          Boolean.TRUE);
      if (injectSqlSession && this.beanFactory instanceof ListableBeanFactory) {
        ListableBeanFactory listableBeanFactory = (ListableBeanFactory) this.beanFactory;
        Optional<String> sqlSessionTemplateBeanName = Optional
            .ofNullable(getBeanNameForType(SqlSessionTemplate.class, listableBeanFactory));
        Optional<String> sqlSessionFactoryBeanName = Optional
            .ofNullable(getBeanNameForType(SqlSessionFactory.class, listableBeanFactory));
        if (sqlSessionTemplateBeanName.isPresent() || !sqlSessionFactoryBeanName.isPresent()) {
          builder.addPropertyValue("sqlSessionTemplateBeanName",
              sqlSessionTemplateBeanName.orElse("sqlSessionTemplate"));
        } else {
          builder.addPropertyValue("sqlSessionFactoryBeanName", sqlSessionFactoryBeanName.get());
        }
      }
      builder.setRole(BeanDefinition.ROLE_INFRASTRUCTURE);
	// 放入BeanDefiniotn注册中心
      registry.registerBeanDefinition(MapperScannerConfigurer.class.getName(), builder.getBeanDefinition());
    }

2.3.2 MapperScannerConfigurer

MapperScannerConfigurer实现了BeanDefinitionRegistryPostProcessor。
方法postProcessBeanDefinitionRegistry可以修改beanDefinition信息。为mapper接口定制beanDefinition。

进入processBeanDefinitions方法

2.3.4 创建MapperFactoryBean

2.3.5 创建MybatisAutoConfiguration

2.3.6 创建sqlSessionFactory

这里还是利用SqlSessionFactoryBean来创建sqlSessionFactory的bean对象。

2.3.7 创建SqlSessionTemplate

2.3.8 mapper接口代理对象创建