细呀，IDEA还可以这样搭建半自动映射框架Mybatis

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篇首语：本文由小常识网(cha138.com)小编为大家整理，主要介绍了细呀，IDEA还可以这样搭建半自动映射框架Mybatis相关的知识，希望对你有一定的参考价值。

  • 首先我们建立一个SpringBoot工程，然后导入mybatis-spring-boot-starter依赖
<dependency>
    <groupId>org.mybatis.spring.boot</groupId>
    <artifactId>mybatis-spring-boot-starter</artifactId>
    <version>2.1.4</version>
</dependency>
  • 导入后发现这个依赖其实就是帮助我们导入了mybatis需要的依赖，其中和自动配置相关最重要的一个就是mybatis-spring-boot-autoconfigure
<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>
  • MyBatis自动配置中是如何工作的
  • 如上面分析自动配置的关键类我们就从mybatis-spring-boot-autoconfigure开始着手分析。

  • spring.factories
# Auto Configure
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\\
org.mybatis.spring.boot.autoconfigure.MybatisLanguageDriverAutoConfiguration,\\
org.mybatis.spring.boot.autoconfigure.MybatisAutoConfiguration

  • 从spring.factories文件看到这里通过SPI机制加载了两个类

  • MybatisAutoConfiguration

  • MybatisLanguateDriverAutoConfiguration.

  • MybatisAutoConfiguration

//表示这是一个Spring配置类
@Configuration 
//这个类需要在classpath中存在SqlSessionFactory和SqlSessionFactoryBean时才生效
@ConditionalOnClass({SqlSessionFactory.class, SqlSessionFactoryBean.class}) --
//这个类需要有一个DataSource的Canidate注册到Spring容器中 
@ConditionalOnSingleCandidate(DataSource.class)
//使MybatisProperties注解类生效
@EnableConfigurationProperties({MybatisProperties.class})
//需要在DataSourceAutoConfiguration和MybatisLanguageDriverAutoConfiguration自动配置之后执行
@AutoConfigureAfter({DataSourceAutoConfiguration.class, MybatisLanguageDriverAutoConfiguration.class})
public class MybatisAutoConfiguration implements InitializingBean {
   
}
  • MybatisAutoConfiguration#sqlSessionFactory
@Bean
@ConditionalOnMissingBean
public SqlSessionFactory sqlSessionFactory(DataSource dataSource) throws Exception {
	//创建一个SqlSessionFactoryBean, 在mybatis-spring项目下
    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()));
	}
    
    //应用Configuration对象
	this.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());
	}

	Set<String> factoryPropertyNames = (Set)Stream.of((new BeanWrapperImpl(SqlSessionFactoryBean.class)).getPropertyDescriptors()).map(FeatureDescriptor::getName).collect(Collectors.toSet());
	Class<? extends LanguageDriver> defaultLanguageDriver = this.properties.getDefaultScriptingLanguageDriver();
	if (factoryPropertyNames.contains("scriptingLanguageDrivers") && !ObjectUtils.isEmpty(this.languageDrivers)) {
		factory.setScriptingLanguageDrivers(this.languageDrivers);
		if (defaultLanguageDriver == null && this.languageDrivers.length == 1) {
			defaultLanguageDriver = this.languageDrivers[0].getClass();
		}
	}

    //设置默认的语言驱动类
	if (factoryPropertyNames.contains("defaultScriptingLanguageDriver")) {
		factory.setDefaultScriptingLanguageDriver(defaultLanguageDriver);
	}
  
    //这里默认会返回一个DefaultSqlSessionFactory对象
	return factory.getObject();
}
  • MybatisAutoConfiguration#sqlSessionTemplate
@Bean
@ConditionalOnMissingBean
public SqlSessionTemplate sqlSessionTemplate(SqlSessionFactory sqlSessionFactory) {
	ExecutorType executorType = this.properties.getExecutorType();
	return executorType != null ? new SqlSessionTemplate(sqlSessionFactory, executorType) : new SqlSessionTemplate(sqlSessionFactory);
}

  • 这里也就知道了MyBatis自动配置其实就是替我们完成了SqlSessionFactory和SqlSessionTempate的创建, 省去了自己导入相关依赖和配置相关Bean的麻烦.

  • MybatisLanguageDriverAutoConfiguration

  • 这个类的配置是对各个语言的支持，比如Thymeleaf， Velocity，LegacyVelociy， FreeMarker等视图组件的支持。

@Configuration
@ConditionalOnClass({LanguageDriver.class})
public class MybatisLanguageDriverAutoConfiguration {
    private static final String CONFIGURATION_PROPERTY_PREFIX = "mybatis.scripting-language-driver";

    public MybatisLanguageDriverAutoConfiguration() {
    }

    @Configuration
    @ConditionalOnClass({ThymeleafLanguageDriver.class})
    public static class ThymeleafConfiguration {
        public ThymeleafConfiguration() {
        }
    }

    @Configuration
    @ConditionalOnClass({VelocityLanguageDriver.class, VelocityLanguageDriverConfig.class})
    public static class VelocityConfiguration {
        public VelocityConfiguration() {
        }
    }

    @Configuration
    @ConditionalOnClass({Driver.class})
         @ConditionalOnMissingClass({"org.mybatis.scripting.velocity.VelocityLanguageDriverConfig"})
    public static class LegacyVelocityConfiguration {
        public LegacyVelocityConfiguration() {
        }
    }

    @Configuration
    @ConditionalOnClass({FreeMarkerLanguageDriver.class, FreeMarkerLanguageDriverConfig.class})
    public static class FreeMarkerConfiguration {
        public FreeMarkerConfiguration() {
        }
    }

    @Configuration
    @ConditionalOnClass({FreeMarkerLanguageDriver.class})
    @ConditionalOnMissingClass({"org.mybatis.scripting.freemarker.FreeMarkerLanguageDriverConfig"})
    public static class LegacyFreeMarkerConfiguration {
        public LegacyFreeMarkerConfiguration() {
        }
    }
}

  • MybatisLanguageDriverAutoConfiguration类在org.mybatis.spring.boot.autoconfigure包下，我删掉了内部静态类下的代码，为了保持这个类看起来更直观

  • 自定义Mapper是如何被扫描的

  • 业务开发中，我们是声明接口（Mapper），那么我们自定义的Mapper是如何被扫描的呢, 我们继续顺着MybatisAutoConfiguration代码分析,其内部包含了一个AutoConfiguredMapperScannerRegistrar的内部静态类.

  • AutoConfiguredMapperScannerRegistrar

  • registerBeanDefinitions


public static class AutoConfiguredMapperScannerRegistrar 
    implements BeanFactoryAware, ImportBeanDefinitionRegistrar {
	private BeanFactory beanFactory;

	public AutoConfiguredMapperScannerRegistrar() {
	}

	public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) {
		if (!AutoConfigurationPackages.has(this.beanFactory)) {
			
		} else {
	        //1.获取到SpringBoot的基础包路径
			List<String> packages = AutoConfigurationPackages.get(this.beanFactory);
			
            //2.生成一个BeanDefinition的构造器，用于构建MapperScannerConfigurer的                         //BeanDefinition
			BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class);
			builder.addPropertyValue("processPropertyPlaceHolders", true);
            //3.设置@Mapper注解的接口才会被当成Mapper接口
			builder.addPropertyValue("annotationClass", Mapper.class);
            
			builder.addPropertyValue("basePackage", StringUtils.collectionToCommaDelimitedString(packages));
			BeanWrapper beanWrapper = new BeanWrapperImpl(MapperScannerConfigurer.class);
			//4.获取MapperScannerConfigurer的属性名称
            Set<String> propertyNames = (Set)Stream.of(beanWrapper.getPropertyDescriptors()).map(FeatureDescriptor::getName).collect(Collectors.toSet());
			if (propertyNames.contains("lazyInitialization")) {
				builder.addPropertyValue("lazyInitialization", "${mybatis.lazy-initialization:false}");
			}

			if (propertyNames.contains("defaultScope")) {
				builder.addPropertyValue("defaultScope", "${mybatis.mapper-default-scope:}");
			}
            //5.这里添加一个MapperScannerConfigurer的BeanDefinition对象，也就是注入一个
            //MapperScannerConfigurer对象
			registry.registerBeanDefinition(MapperScannerConfigurer.class.getName(), builder.getBeanDefinition());
		}
	}

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

  • AutoConfiguredMapperScannerRegistrar类是MybatisAutoConfiguration的内部静态类，位于包org.mybatis.spring.boot.autoconfigure下。

  • 可以看到这个类实现了ImportBeanDefinitionRegistrar接口，ImportBeanDefinitionRegistrar接口是Spring用来动态注册Bean的，也就是会向Spring容器中注入一个BeanDefinition， 这个BeanDefinition就是MapperScannerConfigurer。
    ImportBeanDefinitionRegistrar实现类只能通过其他类@Import的方式来加载，通常是配置类或者启动类，所以MybatisAutoConfiguration类下还有一个内部类MapperScannerRegistrarNotFoundConfiguration如下。


@Configuration
@Import({MybatisAutoConfiguration.AutoConfiguredMapperScannerRegistrar.class})
@ConditionalOnMissingBean({MapperFactoryBean.class, MapperScannerConfigurer.class})
public static class MapperScannerRegistrarNotFoundConfiguration implements InitializingBean {
        
}
  • 这个方法里最后会调用接口BeanDefinitionRegistry.registerBeanDefinition， beanName是"org.mybatis.spring.mapper.MapperScannerConfigurer", registerBeanDefinition方法实际会调用DefaultListableBeanFactory.registerBeanDefinition。DefaultListableBeanFactory是BeanDefinitionRegistry接口的实现类。


public class DefaultListableBeanFactory extends AbstractAutowireCapableBeanFactory 
    implements ConfigurableListableBeanFactory, 
               BeanDefinitionRegistry, 
               Serializable {

}

  • AutoConfiguredMapperScannerRegistrar类和MapperScanner注解的作用是一样的，如果你没有通过以下三种配置方式扫描Mapper接口的包路径

  • 配置MapperScannerConfigurer扫描器类型的Spring Bean

  • @Mapper注解

  • <mybatis: scan/>标签

  • 那么这里就会通过AutoConfiguredMapperScannerRegistrar类添加一个MapperScannerConfigurer扫描器对象，去扫描SpringBoot包设置的基础包路径，也就是启动类的同级目录。 如果设置了@Mapper注解，则会当成Mapper接口解析，那么这里自动配置则不生效。

  • MapperScannerConfigurer

  • MapperScannerConfigurer
  • MapperScannerConfigurer实现了BeanDefinitionRegistryPostProcessor接口，BeanDefinitionRegistryPostProcessor 接口又继承了BeanFactoryPostProcessor接口， 也就是说在MapperScannerConfigurer类里需要实现这两个接口的方法。
public interface BeanDefinitionRegistryPostProcessor extends BeanFactoryPostProcessor {
    void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry var1) throws BeansException;
}

@FunctionalInterface
public interface BeanFactoryPostProcessor {
    void postProcessBeanFactory(ConfigurableListableBeanFactory var1) throws BeansException;
}
  • 在MapperScannerConfigurer类里可以看到这里只实现了postProcessBeanDefinitionRegistry。

  • BeanDefinitionRegistryPostProcessor

  • Spring里有两个用来动态注册Bean到容器中（BeanDefinitionRegistryPostProcessor和ImportBeanDefinitionRegistrar）。ImportBeanDefinitionRegistrar上文中有提到。
    BeanDefinitionRegistryPostProcessor接口实现了BeanFactoryPostProcessor接口，是Spring框架的BeanDefinitionRegistry的后置处理器，用来注册额外的BeanDefinition，postProcessBeanDefinitionRegistry方法会在所有的beanDefinition被加载了，但是所有的Bean还没创建前调用。BeanDefinitionRegistryPostProcessor经常被用来注册BeanFactoryPostProcessor的BeanDefinition。

  • postProcessBeanDefinitionRegistry

public class MapperScannerConfigurer implements BeanDefinitionRegistryPostProcessor, InitializingBean, ApplicationContextAware, BeanNameAware {
    
    public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) {
        if (this.processPropertyPlaceHolders) {
            this.processPropertyPlaceHolders();
        }

        ClassPathMapperScanner scanner = new ClassPathMapperScanner(registry);
        scanner.setAddToConfig(this.addToConfig);
        scanner.setAnnotationClass(this.annotationClass);
        scanner.setMarkerInterface(this.markerInterface);
        scanner.setSqlSessionFactory(this.sqlSessionFactory);
        scanner.setSqlSessionTemplate(this.sqlSessionTemplate);
        scanner.setSqlSessionFactoryBeanName(this.sqlSessionFactoryBeanName);
        scanner.setSqlSessionTemplateBeanName(this.sqlSessionTemplateBeanName);
        scanner.setResourceLoader(this.applicationContext);
        scanner.setBeanNameGenerator(this.nameGenerator);
        scanner.setMapperFactoryBeanClass(this.mapperFactoryBeanClass);
        if (StringUtils.hasText(this.lazyInitialization)) {
            scanner.setLazyInitialization(Boolean.valueOf(this.lazyInitialization));
        }

        if (StringUtils.hasText(this.defaultScope)) {
            scanner.setDefaultScope(this.defaultScope);
        }

        scanner.registerFilters();
        scanner.scan(StringUtils.tokenizeToStringArray(this.basePackage, ",; \\t\\n"));
    }
}

  • MapperScannerConfigurer在包org.mybatis.spring.mapper下.

  • 这里会调用ClassPathMapperScanner.scan()，而ClassPathMapperScanner又继承了ClassPathBeanDefinitionScanner，所以这里scan()会调用ClassPathBeanDefinitionScanner.scan()， 而ClassPathBeanDefinitionScanner.scan() 第二句代码又调用了this.doScan(basePackages)， this.doScan()又调用了ClassPathMapperScanner.doScan(), 而这个方法第一句代码又调用了super.doScan(basePackages)，父子类来回互相调用，有点晕头转向的。

  • org.mybatis.spring.mapper.ClassPathMapperScanner
    org.springframework.context.annotation.ClassPathBeanDefinitionScanner这个类在spring-context.jar

  • ClassPathMapperScanner

  • ClassPathBeanDefinitionScanner#scan

public int scan(String... basePackages) {
    int beanCountAtScanStart = this.registry.getBeanDefinitionCount();
    this.doScan(basePackages);
    if (this.includeAnnotationConfig) {
        AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
    }

    return this.registry.getBeanDefinitionCount() - beanCountAtScanStart;
}
  • ClassPathMapperScanner#doScan()
    这个方法里在mybatis自动配置算比较重要的一个方法，也就是帮助我们自动配置MapperFactoryBean， 会把根据basePackage注册进Spring容器的BeanDefinition的beanClass设置成MapperFactoryBean。
public Set<BeanDefinitionHolder> doScan(String... basePackages) {
    Set<BeanDefinitionHolder> beanDefinitions = super.doScan(basePackages);
    if (beanDefinitions.isEmpty()) {
        LOGGER.warn(() -> {
            return "No MyBatis mapper was found in '" + Arrays.toString(basePackages) + "' package. Please check your configuration.";
        });
    } else {
        //这是一个关键方法，会处理已经注册进Spring容器的beanDefinition，也就是会把
        //已经注册进Spring容器的beanDefinitiond的beanClass为MapperFactoryBean
        this.processBeanDefinitions(beanDefinitions);
    }

    return beanDefinitions;
}
  • ClassPathBeanDefinitionScanner#doScan()
protected Set<BeanDefinitionHolder> doScan(String... basePackages) {
    Assert.notEmpty(basePackages, "At least one base package must be specified");
    Set<BeanDefinitionHolder> beanDefinitions = new LinkedHashSet();
    String[] var3 = basePackages;
    int var4 = basePackages.length;
    
    for(int var5 = 0; var5 < var4; ++var5) {
        String basePackage = var3[var5];
        //这个方法会扫描指定basePackage下被@Mapper注解标注的接口
        Set<BeanDefinition> candidates = this.findCandidateComponents(basePackage);
        Iterator var8 = candidates.iterator();

        while(var8.hasNext()) {
            BeanDefinition candidate = (BeanDefinition)var8.next细呀，IDEA还可以这样搭建半自动映射框架Mybatis


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