在SpringMVC自动装配核心类之WebMvcAutoConfiguration内部实例化EnableWebMvcConfiguration过程中会触发其父类WebMvcConfigurationSupport内部初始化HandlerExceptionResolver。

1.WebMvcConfigurationSupport

public class WebMvcConfigurationSupport implements ApplicationContextAware, ServletContextAware {@Beanpublic HandlerExceptionResolver handlerExceptionResolver(@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager) {List<HandlerExceptionResolver> exceptionResolvers = new ArrayList<>();configureHandlerExceptionResolvers(exceptionResolvers);if (exceptionResolvers.isEmpty()) {addDefaultHandlerExceptionResolvers(exceptionResolvers, contentNegotiationManager);}extendHandlerExceptionResolvers(exceptionResolvers);HandlerExceptionResolverComposite composite = new HandlerExceptionResolverComposite();composite.setOrder(0);composite.setExceptionResolvers(exceptionResolvers);return composite;}protected final void addDefaultHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers,ContentNegotiationManager manager) {//得到 ExceptionHandlerExceptionResolverExceptionHandlerExceptionResolver exceptionHandlerResolver = createExceptionHandlerExceptionResolver();...exceptionHandlerResolver.afterPropertiesSet();exceptionResolvers.add(exceptionHandlerResolver);ResponseStatusExceptionResolver responseStatusResolver = new ResponseStatusExceptionResolver();responseStatusResolver.setMessageSource(this.applicationContext);exceptionResolvers.add(responseStatusResolver);exceptionResolvers.add(new DefaultHandlerExceptionResolver());}
}

最终返回HandlerExceptionResolver类型为HandlerExceptionResolverComposite。并且其resolvers属性包含了三种元素分别为ExceptionHandlerExceptionResolver、ResponseStatusExceptionResolver、DefaultHandlerExceptionResolver。

不管应用中是否显式指定全局异常拦截注解@ControllerAdvice。SpringMVC都会执行初始化异常处理解析器【HandlerExceptionResolver】的逻辑，唯一的区别就是ExceptionHandlerExceptionResolver内部其属性exceptionHandlerAdviceCache是否存在元素，元素存在与否表明了应用中是否显式指定全局异常拦截注解@ControllerAdvice。

1.2.ExceptionHandlerExceptionResolver

ControllerAdviceBean是对全局异常Handler的抽象，ExceptionHandlerMethodResolver是对Handler核心方法的抽象。

最终目的是建立并在属性exceptionHandlerAdviceCache缓存 ControllerAdviceBean & ExceptionHandlerMethodResolver 的对应关系，方便后续直接使用。

public class ExceptionHandlerExceptionResolver extends AbstractHandlerMethodExceptionResolverimplements ApplicationContextAware, InitializingBean {Map<ControllerAdviceBean, ExceptionHandlerMethodResolver> exceptionHandlerAdviceCache = new LinkedHashMap<>();public void afterPropertiesSet() {initExceptionHandlerAdviceCache();...}private void initExceptionHandlerAdviceCache() {// 返回 @ControllerAdvice 注解的类List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());for (ControllerAdviceBean adviceBean : adviceBeans) {// 全局异常拦截handler：其实就是指@ControllerAdvice注解的类Class<?> beanType = adviceBean.getBeanType();// 封装全局异常拦截handler相关属性：核心是拦截handler中的方法ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType);if (resolver