Mybatisi和Spring整合源码分析

语言: CN / TW / HK

一、MybatisSpring的使用

1.创建 Maven 工程。

2.添加依赖,代码如下

<dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis</artifactId>
      <version>3.5.7-ybe</version>
    </dependency>
    <dependency>
      <groupId>org.mybatis</groupId>
      <artifactId>mybatis-spring</artifactId>
      <version>2.0.6-ybe</version>
    </dependency>
    <dependency>
      <groupId>mysql</groupId>
      <artifactId>mysql-connector-java</artifactId>
      <version>8.0.20</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-context</artifactId>
      <version>5.3.16</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-tx</artifactId>
      <version>5.3.16</version>
    </dependency>
    <dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>druid</artifactId>
      <version>1.2.8</version>
    </dependency>
    <dependency>
      <groupId>org.springframework</groupId>
      <artifactId>spring-jdbc</artifactId>
      <version>5.2.20.RELEASE</version>
    </dependency>

3.添加实体如下,

package com.ybe.entity;

import java.io.Serializable;

public class Book implements Serializable {
    int id;
    double price;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

4.添加 Mapper接口以及BookMapper.xml文件,

public interface BookMapper {

     Book getBook(@Param("id") int id);
}

<?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.ybe.mapper.BookMapper">
    <cache></cache>
    <select id="getBook" resultType="com.ybe.entity.Book">
        select * from book where id = #{id}
    </select>
</mapper>

5.添加 BookService 和 BookServiceImpl代码如下,

package com.ybe.service;

import com.ybe.entity.Book;

public interface BookSerivce {
    Book getBook(int id);
}

package com.ybe.service.impl;

import com.ybe.entity.Book;
import com.ybe.mapper.BookMapper;
import com.ybe.service.BookSerivce;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;

@Component
public class BookServiceImpl implements BookSerivce {
    @Autowired
    BookMapper bookMapper;
    public Book getBook(int id) {
        return bookMapper.getBook(id);
    }
}

6.添加配置类,代码如下

package com.ybe.config;

@Configuration
@MapperScan(basePackages = {"com.ybe.mapper"})
@ComponentScan(basePackages = {"com.ybe"})
public class MyBatisConfig {

    @Bean
    public SqlSessionFactoryBean sqlSessionFactory(DataSource dataSource) throws IOException {
        SqlSessionFactoryBean factoryBean = new SqlSessionFactoryBean();
        factoryBean.setDataSource(dataSource);
        factoryBean.setConfigLocation(new ClassPathResource("mybatis.xml"));
        factoryBean.setMapperLocations(new PathMatchingResourcePatternResolver()
        .getResources("classpath:com/ybe/mapper/*.xml"));
        factoryBean.setTypeAliases(Book.class);
        return factoryBean;
    }

    @Bean
    public DataSource dataSource(){
        DruidDataSource dataSource = new DruidDataSource();
        dataSource.setUsername("xxx");
        dataSource.setPassword("xxx");
        dataSource.setDriverClassName("com.mysql.cj.jdbc.Driver");
        dataSource.setUrl("jdbc:mysql://localhost:3306/aopTest?useUnicode=true&characterEncoding=UTF-8&serverTimezone=GMT%2B8");
        return dataSource;
    }

    @Bean
    public DataSourceTransactionManager transactionManager(DataSource dataSource) {
        return new DataSourceTransactionManager(dataSource);
    }

}

7.添加主类代码,代码如下

AnnotationConfigApplicationContext configApplicationContext = new AnnotationConfigApplicationContext(MyBatisConfig.class);
BookSerivce bookSerivce = configApplicationContext.getBean(BookSerivce.class);
Book book = bookSerivce.getBook(1);
System.out.println(book.getId());

二、Mybatis和Spring的整合

​ 因为Mybatis中使用的是Mapper.class 接口来找到数据库sql语句,并且是通过SqlSessionFactory的SqlSession来连接数据库和执行Sql语句的。所以Mybatis和Spring的整合,其实就是把Mybatis的SqlSessionFactory类和Mapper.Class接口注入到SpringIOC中。并且SqlSessionFactory类中的事务管理对象(SpringManagedTransactionFactory )会集成Spring的事务。

​ 整个整合的过程分为两部分,第一部分 Mapper接口注入;第二部分 SqlSessionFactoryBean 注入。

2.1 Mapper 接口注入

​ 试想一下我们在写Mapper接口的时候并没有写实现类,只是写了Mapper.xml文件。那在注入到Spring容器中,具体的实现类是啥?我这里直接给答案,Mapper接口在Spring容器中对应的实现类是一个MapperFactoryBean 的类,最终存在beanFactory.singletonObjects中。MapperFactoryBean实现了FactoryBean接口,在获取Mapper接口的时候,默认返回的是MapperFactoryBean的getObject()方法,其中具体返回xxxMapper接口的动态代理类(JDK代理方式)。动态代理类会进行缓存。

原理

​ 通过配置@MapperScan(basePackages = {"com.ybe.mapper"}) 注解,向 BeanDefinitionRegistry 中添加类型为 MapperScannerConfigurer 的BeanDefinition对象并且初始化对象相关属性,在org.springframework.context.support.AbstractApplicationContext#invokeBeanFactoryPostProcessors 中会进行调用MapperScannerConfigurer 的postProcessBeanDefinitionRegistry 方法,该方法会扫描配置的包路径下的Mapper接口class文件,生成BeanClass为MapperFactoryBean的ScannedGenericBeanDefinition,注册到 BeanDefinitionRegistry 中。

源码解析

  1. @MapperScan注解源码如下
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@Documented
@Import(MapperScannerRegistrar.class)
@Repeatable(MapperScans.class)
  1. 在 org.springframework.context.support.AbstractApplicationContext#invokeBeanFactoryPostProcessors 方法中,会先执行 org.springframework.context.annotation.ConfigurationClassPostProcessor#processConfigBeanDefinitions的方法,其中会执行MapperScannerRegistrar类的registerBeanDefinitions方法,向 BeanDefinitionRegistry 注册了一个类型为 MapperScannerConfigurer的BeanDefinition对象。代码如下,
BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
registry.registerBeanDefinition(beanName, builder.getBeanDefinition());
  1. MapperScannerConfigurer实现了BeanDefinitionRegistryPostProcessor接口。MapperScannerConfigurer主要用来扫描具体的 Mapper接口class文件,生成BeanClass类型为MapperFactoryBean的ScannedGenericBeanDefinition对象后注入 BeanDefinitionRegistry 中。具体类图如下

  2. 在org.springframework.context.support.AbstractApplicationContext#invokeBeanFactoryPostProcessors中会接着执行,MapperScannerConfigurer的postProcessBeanDefinitionRegistry 方法。postProcessBeanDefinitionRegistry中大概逻辑为

搜索指定包下面的Mapper接口,

// 开始搜索 basePackage
scanner.scan(
    StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS));

生成ScannedGenericBeanDefinition,并以Mapper接口名称为BeanName注入到BeanDefinitionRegistry对象中。

BeanDefinitionHolder definitionHolder = new BeanDefinitionHolder(candidate, beanName);
definitionHolder =
    AnnotationConfigUtils.applyScopedProxyMode(scopeMetadata, definitionHolder, this.registry);
beanDefinitions.add(definitionHolder);
registerBeanDefinition(definitionHolder, this.registry);

然后再设置ScannedGenericBeanDefinition的BeanClass类型为MapperFactoryBean类。 关键代码代码如下

// 设置 definition 的  构造函数的参数值类型为 beanClassName,
// 在创建 MapperFactoryBean 时,会根据beanClassName创建类,然后把类作为参数调用MapperFactoryBean带参数的构造方法
definition.getConstructorArgumentValues().addGenericArgumentValue(beanClassName); // issue #59
// 设置 definition 的  Bean 类型为 MapperFactoryBean.class
definition.setBeanClass(this.mapperFactoryBeanClass);
  1. 每个Mapper接口文件对应的BeanDefinition为 ScannedGenericBeanDefinition,BeanDefinition的BeanClass实现类为 MapperFactoryBean 类。此时查看beanFactory的 beanDefinitionMap 中的值,如下图

  2. MapperFactoryBean是一个泛型类,泛型用来表示不同接口类型。继承了SqlSessionDaoSupport类,该类中存储了Maybatis的SqlSession工厂类。MapperFactoryBean也是一个实现了FactoryBean 的类,用来返回具体的类型以及根据类型来生成具体的Mapper接口代理类。

@Override
public T getObject() throws Exception {
    // 返回根据接口类型返回 SqlSession中的Mapper代理对象
    return getSqlSession().getMapper(this.mapperInterface);
}

/**
   * {@inheritDoc}
   */
@Override
public Class<T> getObjectType() {
    return this.mapperInterface;
}
  1. 在beanFactory.preInstantiateSingletons()方法中会把BeanDefinition生成具体的Bean对象,在创建 MapperFactoryBean 对象的时候会调用带参数的构造方法(上面有具体说明)。因为在配置类中我们注入了SqlSessionFactoryBean对象(具体解析过程在下面章节讲解),SqlSessionFactoryBean对象实现了FactoryBean 接口,在Srping容器中会返回SqlSessionFactory类型对象。在给MapperFactoryBean属性赋值的时候会把SqlSessionFactoryBean的实际SqlSessionFactory对象赋值给sqlSessionTemplate属性。最终会在beanFactory.singletonObjects对象中添加以Mapper接口名称为key,以 MapperFactoryBean 类型为value的 记录。

  2. 在获取Mapper接口的Bean对象的时候,会调用getObject()方法,其中会调SqlSessionTemplate的getMapper(),代码如下

@Override
public <T> T getMapper(Class<T> type) {
  return getConfiguration().getMapper(type, this);
}
  1. 以上调用Configuration的getMapper()方法,configuration就是Mybatis的类了。代码如下,
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
    // 根据Mapper接口类型获取已经注册的对象
    return mapperRegistry.getMapper(type, sqlSession);
}
  1. 返回创建的动态代理对象,这里返回的动态代理对象之后不会更新beanFactory.singletonObjects的对象,并且会进行缓存处理。关键代码如下
@SuppressWarnings("unchecked")
public <T> T getMapper(Class<T> type, SqlSession sqlSession) {
  // 根据 Mapper 接口类型获取已经注册的对象
  final MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory<T>) knownMappers.get(type);
  if (mapperProxyFactory == null) {
    throw new BindingException("Type " + type + " is not known to the MapperRegistry.");
  }
  try {
    // 创建动态代理对象
    return mapperProxyFactory.newInstance(sqlSession);
  } catch (Exception e) {
    throw new BindingException("Error getting mapper instance. Cause: " + e, e);
  }
}
  1. 总结一下,beanFactory.singletonObjects关于Mapper接口存储的Bean对象是泛型的MapperFactoryBean对象。但是根据Mapper接口获取Bean对象会返回上面的动态代理对象,并且动态代理对象会缓存在beanFactory.factoryBeanObjectCache中,这是因为MapperFactoryBean实现的FactoryBean 接口。

2.1 SqlSessionFactoryBean 注入

SqlSessionFactoryBean介绍

通过@Bean方式可以将SqlSessionFactoryBean对象注入到Spring容器,SqlSessionFactoryBean对象在MapperFactoryBean对象中会用到。注入代码如下,

@Bean
public SqlSessionFactoryBean sqlSessionFactory(DataSource dataSource) throws IOException {
    // 创建 SqlSessionFactoryBean 的类
    SqlSessionFactoryBean factoryBean = new SqlSessionFactoryBean();
    // 设置数据源
    factoryBean.setDataSource(dataSource);
    // 设置配置文件路径
    factoryBean.setConfigLocation(new ClassPathResource("mybatis.xml"));
    // 设置 mybaits.xml 文件
    factoryBean.setMapperLocations(new PathMatchingResourcePatternResolver()
                                   .getResources("classpath:com/ybe/mapper/*.xml"));
    // 设置别名
    factoryBean.setTypeAliases(Book.class);
    return factoryBean;
}

SqlSessionFactoryBean的类继承关系图如下,

SqlSessionFactoryBean实现了InitializingBean接口 ,会在初始化后会执行afterPropertiesSet方法,其中会调用buildSqlSessionFactory()方法进行SqlSessionFactory的创建。SqlSessionFactoryBean也实现了FactoryBean 接口,在容器中如果获取SqlSessionFactoryBean对象会返回SqlSessionFactory对象,并且也会在beanFactory.factoryBeanObjectCache进行缓存。getObject源码如下,

@Override
public SqlSessionFactory getObject() throws Exception {
  if (this.sqlSessionFactory == null) {
    afterPropertiesSet();
  }

  return this.sqlSessionFactory;
}

buildSqlSessionFactory()具体逻辑

​ 1. 根据 configLocation 创建 XMLConfigBuilder 以及 Configuration对象

xmlConfigBuilder = new XMLConfigBuilder(this.configLocation.getInputStream(), null, this.configurationProperties);
targetConfiguration = xmlConfigBuilder.getConfiguration();

​ 2. 读取SqlSessionFactoryBean的属性对象给 targetConfiguration 赋值

Optional.ofNullable(this.objectFactory).ifPresent(targetConfiguration::setObjectFactory);
Optional.ofNullable(this.objectWrapperFactory).ifPresent(targetConfiguration::setObjectWrapperFactory);
Optional.ofNullable(this.vfs).ifPresent(targetConfiguration::setVfsImpl);

if (hasLength(this.typeAliasesPackage)) {
    scanClasses(this.typeAliasesPackage, this.typeAliasesSuperType).stream()
        .filter(clazz -> !clazz.isAnonymousClass()).filter(clazz -> !clazz.isInterface())
        .filter(clazz -> !clazz.isMemberClass()).forEach(targetConfiguration.getTypeAliasRegistry()::registerAlias);
}
......

​ 3. 解析主配置文件

xmlConfigBuilder.parse();

​ 4. targetConfiguration设置环境变量,如果配置的transactionFactory 事务工厂类为 null,则创建 SpringManagedTransactionFactory 事务工厂类,该事务工厂会直接调用org.springframework.jdbc.datasource.DataSourceUtils去获取数据库连接对象,所以和Spring的事务进行了集成。代码如下,

// 设置环境变量,如果事务工程类为 null,则创建 SpringManagedTransactionFactory 事务工厂类
targetConfiguration.setEnvironment(new Environment(this.environment,
this.transactionFactory == null ? new SpringManagedTransactionFactory() : this.transactionFactory,
this.dataSource));

​ 5. 如果 mapperLocations 不为null ,则循环遍历 xxxMapper.xml 文件流,解析之后给 targetConfiguration 的相关对象赋值。代码如下,

for (Resource mapperLocation : this.mapperLocations) {
    if (mapperLocation == null) {
        continue;
    }
    try {
        // 构建 XMLMapperBuilder 对象,进行mapper.xml 文件资源解析
        XMLMapperBuilder xmlMapperBuilder = new XMLMapperBuilder(mapperLocation.getInputStream(),
                                                                 targetConfiguration, mapperLocation.toString(), targetConfiguration.getSqlFragments());
        xmlMapperBuilder.parse();
    } catch (Exception e) {
        throw new NestedIOException("Failed to parse mapping resource: '" + mapperLocation + "'", e);
    } finally {
        ErrorContext.instance().reset();
    }
    LOGGER.debug(() -> "Parsed mapper file: '" + mapperLocation + "'");
}
  1. 总结一下,整个过程比较简单,其主要就是Mybaits初始化的过程,更详细Mybatis初始化过程请参考上一篇文章。