SpringMVC之全局异常拦截器

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 {
   
	
	@Bean
	public 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 ExceptionHandlerExceptionResolver
		ExceptionHandlerExceptionResolver exceptionHandlerResolver = createExceptionHandlerExceptionResolver();
		...
		exceptionHandlerResolver.afterPropertiesSet();
		exceptionResolvers.add(exceptionHandlerResolver);
		ResponseStatusExceptionResolver responseStatusResolver = new ResponseStatusExceptionResolver();
		responseStatusResolver.setMessageSource(this.applicationContext);
		exceptionResolvers.add(responseStatusResolver);
		exceptionResolvers.add(new DefaultHandlerExceptionResolver());
	}
}
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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 AbstractHandlerMethodExceptionResolver
		implements 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
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