Mybatis动态代理实现全过程？回答正确率不到1%

@SpringBootApplication @MapperScan(basePackages = "com.example.springdatasourcedruid.dal") public class SpringDatasourceDruidApplication { public static void main(String[] args) { SpringApplication.run(SpringDatasourceDruidApplication.class, args); } } 

/**
*指定mapper接口所在的包，然后包下面的所有接口在编译之后都会生成相应的实现类
*这个注解引入了MapperScannerRegistrar类
*/ @Retention(RetentionPolicy.RUNTIME) @Target(ElementType.TYPE) @Documented @Import(MapperScannerRegistrar.class) @Repeatable(MapperScans.class) public @interface MapperScan { //扫描的包路径列表 String[] basePackages() default {}; //代理工厂类类型 Class<? extends MapperFactoryBean> factoryBean() default MapperFactoryBean.class; //作用范围，这里默认是单例 String defaultScope() default AbstractBeanDefinition.SCOPE_DEFAULT; } 

public class MapperScannerRegistrar implements ImportBeanDefinitionRegistrar, ResourceLoaderAware { //Spring 会回调该方法 @Override public void registerBeanDefinitions(AnnotationMetadata importingClassMetadata, BeanDefinitionRegistry registry) { //获取MapperScan注解设置的全部属性信息 AnnotationAttributes mapperScanAttrs = AnnotationAttributes .fromMap(importingClassMetadata.getAnnotationAttributes(MapperScan.class.getName())); if (mapperScanAttrs != null) { //调用具体的实现  registerBeanDefinitions(importingClassMetadata, mapperScanAttrs, registry, generateBaseBeanName(importingClassMetadata, 0)); } } //注册一个 BeanDefinition  ，这里会构建并且向容器中注册一个bd 也就是一个自定义的扫描器 MapperScannerConfigurer //mapperFactoryBeanClass的类型MapperFactoryBean void registerBeanDefinitions(AnnotationMetadata annoMeta, AnnotationAttributes annoAttrs, BeanDefinitionRegistry registry, String beanName) { //构建一个 BeanDefinition 他的实例对象是 MapperScannerConfigurer BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition(MapperScannerConfigurer.class); builder.addPropertyValue("processPropertyPlaceHolders", true); Class<? extends MapperFactoryBean> mapperFactoryBeanClass = annoAttrs.getClass("factoryBean"); if (!MapperFactoryBean.class.equals(mapperFactoryBeanClass)) { builder.addPropertyValue("mapperFactoryBeanClass", mapperFactoryBeanClass); } registry.registerBeanDefinition(beanName, builder.getBeanDefinition()); } } 

public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) { if (this.processPropertyPlaceHolders) { processPropertyPlaceHolders(); } //初始化扫描器，可以扫描项目下的class文件转换成BeanDefinition  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(lazyInitialization)) { scanner.setLazyInitialization(Boolean.valueOf(lazyInitialization)); } if (StringUtils.hasText(defaultScope)) { scanner.setDefaultScope(defaultScope); } //这一步是很重要的，他是注册了一系列的过滤器，使得Spring在扫描到Mapper接口的时候不被过滤掉  scanner.registerFilters(); //执行扫描  scanner.scan( StringUtils.tokenizeToStringArray(this.basePackage, ConfigurableApplicationContext.CONFIG_LOCATION_DELIMITERS)); } 

private void processBeanDefinitions(Set<BeanDefinitionHolder> beanDefinitions) { AbstractBeanDefinition definition; BeanDefinitionRegistry registry = getRegistry(); for (BeanDefinitionHolder holder : beanDefinitions) { definition = (AbstractBeanDefinition) holder.getBeanDefinition(); String beanClassName = definition.getBeanClassName(); definition.getConstructorArgumentValues().addGenericArgumentValue(beanClassName); // issue #59 //将对应的Mapper接口，设置为MapperFactoryBean definition.setBeanClass(this.mapperFactoryBeanClass); definition.getPropertyValues().add("addToConfig", this.addToConfig); //-------忽略了非关键代码-------------------------------- //将Mapper接口注册到BeanDefinition，这时候实际的实现类已经被指定为MapperFactoryBean registry.registerBeanDefinition(proxyHolder.getBeanName(), proxyHolder.getBeanDefinition()); } } 

public <T> T getBean(String name, Class<T> requiredType) throws BeansException { return this.doGetBean(name, requiredType, (Object[])null, false); } 

public class MapperFactoryBean<T> extends SqlSessionDaoSupport implements FactoryBean<T> { @Override public T getObject() throws Exception { return getSqlSession().getMapper(this.mapperInterface); } } 

@Override public <T> T getMapper(Class<T> type) { return getConfiguration().getMapper(type, this); } 

public <T> T getMapper(Class<T> type, SqlSession sqlSession) { return this.mapperRegistry.getMapper(type, sqlSession); } 

public <T> T getMapper(Class<T> type, SqlSession sqlSession) { MapperProxyFactory<T> mapperProxyFactory = (MapperProxyFactory)this.knownMappers.get(type); if (mapperProxyFactory == null) { throw new BindingException("Type " + type + " is not known to the MapperRegistry."); } else { try { return mapperProxyFactory.newInstance(sqlSession); } catch (Exception var5) { throw new BindingException("Error getting mapper instance. Cause: " + var5, var5); } } } 

protected T newInstance(MapperProxy<T> mapperProxy) { return Proxy.newProxyInstance(this.mapperInterface.getClassLoader(), new Class[]{this.mapperInterface}, mapperProxy); } public T newInstance(SqlSession sqlSession) { MapperProxy<T> mapperProxy = new MapperProxy(sqlSession, this.mapperInterface, this.methodCache); return this.newInstance(mapperProxy); } 

public Object invoke(Object proxy, Method method, Object[] args) throws Throwable { try { return Object.class.equals(method.getDeclaringClass()) ? method.invoke(this, args) : this.cachedInvoker(method).invoke(proxy, method, args, this.sqlSession); } catch (Throwable var5) { throw ExceptionUtil.unwrapThrowable(var5); } } 

private MapperProxy.MapperMethodInvoker cachedInvoker(Method method) throws Throwable { try { return (MapperProxy.MapperMethodInvoker)MapUtil.computeIfAbsent(this.methodCache, method, (m) -> { if (m.isDefault()) { try { return privateLookupInMethod == null ? new MapperProxy.DefaultMethodInvoker(this.getMethodHandleJava8(method)) : new MapperProxy.DefaultMethodInvoker(this.getMethodHandleJava9(method)); } catch (InstantiationException | InvocationTargetException | NoSuchMethodException | IllegalAccessException var4) { throw new RuntimeException(var4); } } else { //如果不是默认方法，执行该段逻辑 return new MapperProxy.PlainMethodInvoker(new MapperMethod(this.mapperInterface, method, this.sqlSession.getConfiguration())); } }); } catch (RuntimeException var4) { Throwable cause = var4.getCause(); throw (Throwable)(cause == null ? var4 : cause); } } 

public Object invoke(Object proxy, Method method, Object[] args, SqlSession sqlSession) throws Throwable { return this.mapperMethod.execute(sqlSession, args); } 

public Object execute(SqlSession sqlSession, Object[] args) { Object result; Object param; switch(this.command.getType()) { case INSERT: param = this.method.convertArgsToSqlCommandParam(args); result = this.rowCountResult(sqlSession.insert(this.command.getName(), param)); break; case UPDATE: param = this.method.convertArgsToSqlCommandParam(args); result = this.rowCountResult(sqlSession.update(this.command.getName(), param)); break; case DELETE: param = this.method.convertArgsToSqlCommandParam(args); result = this.rowCountResult(sqlSession.delete(this.command.getName(), param)); break; case SELECT: if (this.method.returnsVoid() && this.method.hasResultHandler()) { this.executeWithResultHandler(sqlSession, args); result = null; } else if (this.method.returnsMany()) { result = this.executeForMany(sqlSession, args); } else if (this.method.returnsMap()) { result = this.executeForMap(sqlSession, args); } else if (this.method.returnsCursor()) { result = this.executeForCursor(sqlSession, args); } else { param = this.method.convertArgsToSqlCommandParam(args); result = sqlSession.selectOne(this.command.getName(), param); if (this.method.returnsOptional() && (result == null || !this.method.getReturnType().equals(result.getClass()))) { result = Optional.ofNullable(result); } } break; case FLUSH: result = sqlSession.flushStatements(); break; default: throw new BindingException("Unknown execution method for: " + this.command.getName()); } if (result == null && this.method.getReturnType().isPrimitive() && !this.method.returnsVoid()) { throw new BindingException("Mapper method '" + this.command.getName() + " attempted to return null from a method with a primitive return type (" + this.method.getReturnType() + ")."); } else { return result; } }