SpringBoot 源码解析 （九）----- Spring Boot的核心能力

本篇我们在SpringBoot中整合Mybatis这个orm框架，毕竟分析一下其自动配置的源码，我们先来回顾一下以前Spring中是如何整合Mybatis的，大家可以看看我这篇文章Mybaits 源码解析 （十）----- Spring-Mybatis框架使用与源码解析 

Spring-Mybatis使用

添加maven依赖

<dependency>
    <groupId>org.springframework</groupId>
    <artifactId>spring-jdbc</artifactId>
    <version>4.3.8.RELEASE</version>
</dependency>

<!-- https://mvnrepository.com/artifact/org.mybatis/mybatis-spring -->
<dependency>
    <groupId>org.mybatis</groupId>
    <artifactId>mybatis-spring</artifactId>
    <version>1.3.2</version>
</dependency>

在src/main/resources下添加mybatis-config.xml文件

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration
        PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
        "http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <typeAliases>
        <typeAlias alias="User" type="com.chenhao.bean.User" />
    </typeAliases>
    <plugins>
        <plugin interceptor="com.github.pagehelper.PageInterceptor">
            <property name="helperDialect" value="mysql"/>
        </plugin>
    </plugins>

</configuration>

在src/main/resources/mapper路径下添加User.xml

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" 
"http://mybatis.org/dtd/mybatis-3-mapper.dtd">
    
<mapper namespace="com.chenhao.mapper.UserMapper">
    <select id="getUser" parameterType="int"
        resultType="com.chenhao.bean.User">
        SELECT *
        FROM USER
        WHERE id = #{id}
    </select>
</mapper>

在src/main/resources/路径下添加beans.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans.xsd">
 
    <bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
        <property name="driverClassName" value="com.mysql.jdbc.Driver"></property>
        <property name="url" value="jdbc:mysql://127.0.0.1:3306/test"></property>
        <property name="username" value="root"></property>
        <property name="password" value="root"></property>
    </bean>
 
    <bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="configLocation" value="classpath:mybatis-config.xml"></property>
        <property name="dataSource" ref="dataSource" />
        <property name="mapperLocations" value="classpath:mapper/*.xml" />
    </bean>
    
    <bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
        <property name="basePackage" value="com.chenhao.mapper" />
    </bean>
 
</beans>

注解的方式

• 以上分析都是在spring的XML配置文件applicationContext.xml进行配置的，mybatis-spring也提供了基于注解的方式来配置sqlSessionFactory和Mapper接口。
• sqlSessionFactory主要是在@Configuration注解的配置类中使用@Bean注解的名为sqlSessionFactory的方法来配置；
• Mapper接口主要是通过在@Configuration注解的配置类中结合@MapperScan注解来指定需要扫描获取mapper接口的包。

@Configuration
@MapperScan("com.chenhao.mapper")
public class AppConfig {

  @Bean
  public DataSource dataSource() {
     return new EmbeddedDatabaseBuilder()
            .addScript("schema.sql")
            .build();
  }
 
  @Bean
  public DataSourceTransactionManager transactionManager() {
    return new DataSourceTransactionManager(dataSource());
  }
 
  @Bean
  public SqlSessionFactory sqlSessionFactory() throws Exception {
    //创建SqlSessionFactoryBean对象
    SqlSessionFactoryBean sessionFactory = new SqlSessionFactoryBean();
    //设置数据源
    sessionFactory.setDataSource(dataSource());
    //设置Mapper.xml路径
    sessionFactory.setMapperLocations(new PathMatchingResourcePatternResolver().getResources("classpath:mapper/*.xml"));
    // 设置MyBatis分页插件
    PageInterceptor pageInterceptor = new PageInterceptor();
    Properties properties = new Properties();
    properties.setProperty("helperDialect", "mysql");
    pageInterceptor.setProperties(properties);
    sessionFactory.setPlugins(new Interceptor[]{pageInterceptor});
    return sessionFactory.getObject();
  }
}

最核心的有两点：

• 创建一个SqlSessionFactoryBean，并设置数据源和Mapper.xml路径，其中会解析Mapper.xml文件，最后通过getObject()返回一个SqlSessionFactory 注入Spring容器中
• 通过@MapperScan扫描所有Mapper接口，扫描过程会将Mapper接口生成MapperFactoryBean这个特殊的Bean，并且在其getObject()通过SqlSession().getMapper(this.mapperInterface)生成每个mapper接口真实的代理类

MapperFactoryBean

//最终注入Spring容器的就是这里的返回对象
public T getObject() throws Exception {
    //获取父类setSqlSessionFactory方法中创建的SqlSessionTemplate
    //通过SqlSessionTemplate获取mapperInterface的代理类
    //我们例子中就是通过SqlSessionTemplate获取com.chenhao.mapper.UserMapper的代理类
    //获取到Mapper接口的代理类后，就把这个Mapper的代理类对象注入Spring容器
    return this.getSqlSession().getMapper(this.mapperInterface);
}

接下来我们看看SpringBoot是如何引入Mybatis的

SpringBoot引入Mybatis

添加mybatis依赖

<dependency>
    <groupId>com.alibaba</groupId>
    <artifactId>druid</artifactId>
    <version>1.1.9</version>
</dependency>
<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>1.3.2</version>
</dependency>

全局配置文件中配置数据源和mybatis属性

spring:
  datasource:
    url: jdbc:mysql:///springboot
    username: root
    password: admin
    type: com.alibaba.druid.pool.DruidDataSource
    initialSize: 5
    minIdle: 5
    maxActive: 20
mybatis:
  config-location: classpath:mybatis/mybatis-config.xml
  mapper-locations: classpath:mybatis/mapper/*.xml
  type-aliases-package: org.com.cay.spring.boot.entity

加入Mapper扫描注解@MapperScan

@SpringBootApplication
@EnableScheduling
@ServletComponentScan
@MapperScan("com.supplychain.app.mapper")
public class Application {

    public static void main(String[] args) {
        TimeZone.setDefault(TimeZone.getTimeZone("GMT+8"));
        System.setProperty("user.timezone", "GMT+8");
        SpringApplication.run(Application.class, args);
    }
}

源码解析

mybatis-spring-boot-starter

我们看到mybatis-spring-boot-starter实际上引入了jdbc的场景启动器，这一块我们上一篇文章已经分析过了，还引入了mybatis-spring的依赖，最终还引入了mybatis-spring-boot-autoconfigure这个依赖，其实mybatis-spring-boot-starter只是引入各种需要的依赖，最核心的代码是在引入的mybatis-spring-boot-autoconfigure这个项目当中，我们来看看这个项目

我们看到mybatis-spring-boot-autoconfigure也像spring-boot-autoconfigure一样配置了spring.factories这个配置文件，并且在配置文件中配置了MybatisAutoConfiguration这个自动配置类，我们知道SpringBoot启动时会获取所有spring.factories配置文件中的自动配置类并且进行解析其中的Bean，那么我们就来看看MybatisAutoConfiguration这个自动配置类做了啥？

MybatisAutoConfiguration

@org.springframework.context.annotation.Configuration
@ConditionalOnClass({ SqlSessionFactory.class, SqlSessionFactoryBean.class })
@ConditionalOnBean(DataSource.class)
//引入MybatisProperties配置类
@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();
    }

    @Bean
    @ConditionalOnMissingBean
    //往Spring容器中注入SqlSessionFactory对象
    //并且设置数据源、MapperLocations(Mapper.xml路径)等
    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());
        }
        //获取SqlSessionFactoryBean的getObject()中的对象注入Spring容器，也就是SqlSessionFactory对象
        return factory.getObject();
    }

    @Bean
    @ConditionalOnMissingBean
    //往Spring容器中注入SqlSessionTemplate对象
    public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
        ExecutorType executorType = this.properties.getExecutorType();
        if (executorType != null) {
            return new SqlSessionTemplate(sqlSessionFactory, executorType);
        } else {
            return new SqlSessionTemplate(sqlSessionFactory);
        }
    }
    
    //other code...
}

在自动配置的时候会导入一个Properties配置类MybatisProperties，咱们来看一下

@ConfigurationProperties(prefix = MybatisProperties.MYBATIS_PREFIX)
public class MybatisProperties {

    public static final String MYBATIS_PREFIX = "mybatis";

    /**
     * Location of MyBatis xml config file.
     */
    private String configLocation;

    /**
     * Locations of MyBatis mapper files.
     */
    private String[] mapperLocations;

    /**
     * Packages to search type aliases. (Package delimiters are ",; 	
")
     */
    private String typeAliasesPackage;

    /**
     * Packages to search for type handlers. (Package delimiters are ",; 	
")
     */
    private String typeHandlersPackage;

    /**
     * Indicates whether perform presence check of the MyBatis xml config file.
     */
    private boolean checkConfigLocation = false;

    /**
     * Execution mode for {@link org.mybatis.spring.SqlSessionTemplate}.
     */
    private ExecutorType executorType;

    /**
     * Externalized properties for MyBatis configuration.
     */
    private Properties configurationProperties;

    /**
     * A Configuration object for customize default settings. If {@link #configLocation}
     * is specified, this property is not used.
     */
    @NestedConfigurationProperty
    private Configuration configuration;

    //other code...
}

​该Properties配置类作用主要用于与yml/properties中以mybatis开头的属性进行一一对应，如下

mybatis:
  config-location: classpath:mybatis/mybatis-config.xml
  mapper-locations: classpath:mybatis/mapper/*.xml
  type-aliases-package: org.com.cay.spring.boot.entity

​在MybatisAutoConfiguration自动配置类中，SpringBoot默认自动配置了两个Bean，分别是SqlSessionFactory和SqlSessionTemplate。我们看到上面代码中第71行，其实是返回的factory.getObject();，也就是注入Spring容器中的是SqlSessionFactory对象，SqlSessionFactory主要是将Properties配置类中的属性赋值到SqlSessionFactoryBean中，类似以前xml中配置的SqlSessionFactory

<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
        <property name="dataSource" ref="dataSource"></property>
        <!-- 自动扫描mapping.xml文件 -->
        <property name="mapperLocations" value="classpath:com/cn/mapper/*.xml"></property>
        ...
</bean>

另外一个Bean为SqlSessionTemplate，通过SqlSessionFactory来生成SqlSession代理类：

public class SqlSessionTemplate implements SqlSession, DisposableBean {

    private final SqlSessionFactory sqlSessionFactory;

    private final ExecutorType executorType;

    private final SqlSession sqlSessionProxy;

    private final PersistenceExceptionTranslator exceptionTranslator;

    //other code...
    
    public SqlSessionTemplate(SqlSessionFactory sqlSessionFactory, ExecutorType executorType,
          PersistenceExceptionTranslator exceptionTranslator) {

        notNull(sqlSessionFactory, "Property 'sqlSessionFactory' is required");
        notNull(executorType, "Property 'executorType' is required");

        this.sqlSessionFactory = sqlSessionFactory;
        this.executorType = executorType;
        this.exceptionTranslator = exceptionTranslator;
        
        //生成SqlSessioin代理类
        this.sqlSessionProxy = (SqlSession) newProxyInstance(
            SqlSessionFactory.class.getClassLoader(),
            new Class[] { SqlSession.class },
            new SqlSessionInterceptor());
    }
}

而@MapperScan注解是和Spring整合Mybatis的使用是一样的，都是在配置类上指定Mapper接口的路径，大家可以看一下我以前的一篇文章Mybaits 源码解析 （十一）----- @MapperScan将Mapper接口生成代理注入到Spring-静态代理和动态代理结合使用