1. 相关配置和代码

• maven

<?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>mybatisplus-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>com.baomidou</groupId>
            <artifactId>mybatis-plus-boot-starter</artifactId>
            <version>3.5.3.1</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>
        <!-- https://mvnrepository.com/artifact/org.projectlombok/lombok -->
        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>1.18.28</version>
            <scope>provided</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: sdfsaxs!
    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

# mybatisplus的配置
mybatis-plus:
  configuration:
    # 是否开启自动驼峰命名规则
    map-underscore-to-camel-case: true
    # 对所有的 resultMap 都进行自动映射
    auto-mapping-behavior: full
    # #控制台打印完整带参数SQL语句
    log-impl: org.apache.ibatis.logging.stdout.StdOutImpl
  mapper-locations: classpath:mapper/**/*.xml
  type-aliases-package: "com.boge.pojo"

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

@Data
@TableName("t_user")
public class UserDO implements Serializable {
    @TableId(type = IdType.ASSIGN_ID)
    private Integer id;

    private String userName;

    private String password;

    private String realName;

    private Integer age;

    private Integer dId;

}

@MapperScan("com.boge.mapper")
@SpringBootApplication
public class MybatisSpringBootApplication {

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

}

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 spring boot自动配置

2.2 MybatisPlusAutoConfiguration

源码

/**
 * {@link EnableAutoConfiguration Auto-Configuration} for Mybatis. Contributes a
 * {@link SqlSessionFactory} and a {@link SqlSessionTemplate}.
 * <p>
 * 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.
 * </p>
 * <p> copy from {@link org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration}</p>
 *
 * @author Eddú Meléndez
 * @author Josh Long
 * @author Kazuki Shimizu
 * @author Eduardo Macarrón
 */
@Configuration(proxyBeanMethods = false)
@ConditionalOnClass({SqlSessionFactory.class, SqlSessionFactoryBean.class})
@ConditionalOnSingleCandidate(DataSource.class)
@EnableConfigurationProperties(MybatisPlusProperties.class)
@AutoConfigureAfter({DataSourceAutoConfiguration.class, MybatisPlusLanguageDriverAutoConfiguration.class})
public class MybatisPlusAutoConfiguration implements InitializingBean {

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

    private final MybatisPlusProperties 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;

    private final List<MybatisPlusPropertiesCustomizer> mybatisPlusPropertiesCustomizers;

    private final ApplicationContext applicationContext;

    public MybatisPlusAutoConfiguration(MybatisPlusProperties properties,
                                        ObjectProvider<Interceptor[]> interceptorsProvider,
                                        ObjectProvider<TypeHandler[]> typeHandlersProvider,
                                        ObjectProvider<LanguageDriver[]> languageDriversProvider,
                                        ResourceLoader resourceLoader,
                                        ObjectProvider<DatabaseIdProvider> databaseIdProvider,
                                        ObjectProvider<List<ConfigurationCustomizer>> configurationCustomizersProvider,
                                        ObjectProvider<List<SqlSessionFactoryBeanCustomizer>> sqlSessionFactoryBeanCustomizers,
                                        ObjectProvider<List<MybatisPlusPropertiesCustomizer>> mybatisPlusPropertiesCustomizerProvider,
                                        ApplicationContext applicationContext) {
        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();
        this.mybatisPlusPropertiesCustomizers = mybatisPlusPropertiesCustomizerProvider.getIfAvailable();
        this.applicationContext = applicationContext;
    }

    @Override
    public void afterPropertiesSet() {
        if (!CollectionUtils.isEmpty(mybatisPlusPropertiesCustomizers)) {
            mybatisPlusPropertiesCustomizers.forEach(i -> i.customize(properties));
        }
        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 {
        // TODO 使用 MybatisSqlSessionFactoryBean 而不是 SqlSessionFactoryBean
        MybatisSqlSessionFactoryBean factory = new MybatisSqlSessionFactoryBean();
        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);
        }
        if (!ObjectUtils.isEmpty(this.properties.resolveMapperLocations())) {
            factory.setMapperLocations(this.properties.resolveMapperLocations());
        }
        // TODO 修改源码支持定义 TransactionFactory
        this.getBeanThen(TransactionFactory.class, factory::setTransactionFactory);

        // TODO 对源码做了一定的修改(因为源码适配了老旧的mybatis版本,但我们不需要适配)
        Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();
        if (!ObjectUtils.isEmpty(this.languageDrivers)) {
            factory.setScriptingLanguageDrivers(this.languageDrivers);
        }
        Optional.ofNullable(defaultLanguageDriver).ifPresent(factory::setDefaultScriptingLanguageDriver);

        applySqlSessionFactoryBeanCustomizers(factory);

        // TODO 此处必为非 NULL
        GlobalConfig globalConfig = this.properties.getGlobalConfig();
        // TODO 注入填充器
        this.getBeanThen(MetaObjectHandler.class, globalConfig::setMetaObjectHandler);
        // TODO 注入参与器
        this.getBeanThen(PostInitTableInfoHandler.class, globalConfig::setPostInitTableInfoHandler);
        // TODO 注入主键生成器
        this.getBeansThen(IKeyGenerator.class, i -> globalConfig.getDbConfig().setKeyGenerators(i));
        // TODO 注入sql注入器
        this.getBeanThen(ISqlInjector.class, globalConfig::setSqlInjector);
        // TODO 注入ID生成器
        this.getBeanThen(IdentifierGenerator.class, globalConfig::setIdentifierGenerator);
        // TODO 设置 GlobalConfig 到 MybatisSqlSessionFactoryBean
        factory.setGlobalConfig(globalConfig);
        return factory.getObject();
    }

    /**
     * 检查spring容器里是否有对应的bean,有则进行消费
     *
     * @param clazz    class
     * @param consumer 消费
     * @param <T>      泛型
     */
    private <T> void getBeanThen(Class<T> clazz, Consumer<T> consumer) {
        if (this.applicationContext.getBeanNamesForType(clazz, false, false).length > 0) {
            consumer.accept(this.applicationContext.getBean(clazz));
        }
    }

    /**
     * 检查spring容器里是否有对应的bean,有则进行消费
     *
     * @param clazz    class
     * @param consumer 消费
     * @param <T>      泛型
     */
    private <T> void getBeansThen(Class<T> clazz, Consumer<List<T>> consumer) {
        if (this.applicationContext.getBeanNamesForType(clazz, false, false).length > 0) {
            final Map<String, T> beansOfType = this.applicationContext.getBeansOfType(clazz);
            List<T> clazzList = new ArrayList<>();
            beansOfType.forEach((k, v) -> clazzList.add(v));
            consumer.accept(clazzList);
        }
    }

    // TODO 入参使用 MybatisSqlSessionFactoryBean
    private void applyConfiguration(MybatisSqlSessionFactoryBean factory) {
        // TODO 使用 MybatisConfiguration
        MybatisConfiguration configuration = this.properties.getConfiguration();
        if (configuration == null && !StringUtils.hasText(this.properties.getConfigLocation())) {
            configuration = new MybatisConfiguration();
        }
        if (configuration != null && !CollectionUtils.isEmpty(this.configurationCustomizers)) {
            for (ConfigurationCustomizer customizer : this.configurationCustomizers) {
                customizer.customize(configuration);
            }
        }
        factory.setConfiguration(configuration);
    }

    private void applySqlSessionFactoryBeanCustomizers(MybatisSqlSessionFactoryBean 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+
                // TODO 兼容了mybatis.lazy-initialization配置
                builder.addPropertyValue("lazyInitialization", "${mybatis-plus.lazy-initialization:${mybatis.lazy-initialization:false}}");
            }
            if (propertyNames.contains("defaultScope")) {
                // Need to mybatis-spring 2.0.6+
                builder.addPropertyValue("defaultScope", "${mybatis-plus.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.");
        }
    }

    @Order
    @Bean
    @ConditionalOnMissingBean
    public DdlApplicationRunner ddlApplicationRunner(@Autowired(required = false) List<IDdl> ddlList) {
        if (ObjectUtils.isEmpty(ddlList)) {
            return null;
        }
        return new DdlApplicationRunner(ddlList);
    }
}

2.3 debug流程

2.3.1 MapperScannerRegistrar

主要为MapperScannerConfigurer定制beanDefinition

2.3.2MapperScannerConfigurer

MapperScannerConfigurer实现了BeanDefinitionRegistryPostProcessor。

方法postProcessBeanDefinitionRegistry可以修改beanDefinition信息。为mapper接口定制beanDefinition。

2.3.3 创建MybatisPlusAutoConfiguration

2.3.4 创建sqlSessionFactory

这里用MybatisSqlSessionFactoryBean来创建sqlSessionFactory。



重点看buildSqlSessionFactory方法

2.3.5 创建SqlSessionTemplate

2.3.6 mapper接口代理对象创建

打断点到MybatisMapperRegistry