Spring MVC : WebMvcConfigurationSupport 中定义的 HandlerExceptionResolver 组件

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本文深入解析SpringMVC框架中异常处理的核心组件HandlerExceptionResolver，包括其默认配置的三种实现：ExceptionHandlerExceptionResolver、ResponseStatusExceptionResolver和DefaultHandlerExceptionResolver，阐述它们如何协同工作以处理控制器抛出的异常。

概述

Spring MVC的缺省配置类WebMvcConfigurationSupport定义了一组HandlerExceptionResolver组件到容器，供Spring MVC运行时使用，具体来讲，是被DispatcherServlet使用。本文介绍WebMvcConfigurationSupport定义了哪些HandlerExceptionResolver组件，都是什么类型，以及它们的应用目的。

`HandlerExceptionResolver`组件定义

WebMvcConfigurationSupport的bean定义方法HandlerExceptionResolver handlerExceptionResolver() 用于定义DispatcherServlet最终使用的一组HandlerExceptionResolver。该bean实际类型是HandlerExceptionResolverComposite，表示多个HandlerExceptionResolver的组合:

	/**
	 * Returns a {@link HandlerExceptionResolverComposite} containing a list of exception
	 * resolvers obtained either through {@link #configureHandlerExceptionResolvers} or
	 * through {@link #addDefaultHandlerExceptionResolvers}.
	 * <p><strong>Note:</strong> This method cannot be made final due to CGLIB constraints.
	 * Rather than overriding it, consider overriding {@link #configureHandlerExceptionResolvers}
	 * which allows for providing a list of resolvers.
	 */
	@Bean
	public HandlerExceptionResolver handlerExceptionResolver() {
		List<HandlerExceptionResolver> exceptionResolvers = new ArrayList<>();
		configureHandlerExceptionResolvers(exceptionResolvers);
		if (exceptionResolvers.isEmpty()) {
			addDefaultHandlerExceptionResolvers(exceptionResolvers);
		}
		extendHandlerExceptionResolvers(exceptionResolvers);
		HandlerExceptionResolverComposite composite = new HandlerExceptionResolverComposite();
		composite.setOrder(0);
		composite.setExceptionResolvers(exceptionResolvers);
		return composite;
	}

bean定义方法HandlerExceptionResolver handlerExceptionResolver() 的工作流程基本如下：

创建空的List<HandlerExceptionResolver> exceptionResolvers;
让实现子类指定自己的HandlerExceptionResolver到exceptionResolvers;

void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers)

如果实现子类没指定自己的HandlerExceptionResolver,则添加缺省的HandlerExceptionResolver到exceptionResolvers;

final void addDefaultHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers)

让实现子类增加更多自定义的HandlerExceptionResolver到exceptionResolvers，或者修改exceptionResolvers内容;

void extendHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers)

将所有List<HandlerExceptionResolver> exceptionResolvers包装成一个HandlerExceptionResolverComposite。

缺省情况下，开发人员并不定制和修改exceptionResolvers,换句话讲，此时exceptionResolvers中只有以上第三步WebMvcConfigurationSupport缺省定义的HandlerExceptionResolver被放到exceptionResolvers中。

下面我们重点分析一下这个方法。

final void addDefaultHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers)

1. `addDefaultHandlerExceptionResolvers`

	protected final void addDefaultHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
        // 定义一个 ExceptionHandlerExceptionResolver
		ExceptionHandlerExceptionResolver exceptionHandlerResolver = createExceptionHandlerExceptionResolver();
		exceptionHandlerResolver.setContentNegotiationManager(mvcContentNegotiationManager());
		exceptionHandlerResolver.setMessageConverters(getMessageConverters());
		exceptionHandlerResolver.setCustomArgumentResolvers(getArgumentResolvers());
		exceptionHandlerResolver.setCustomReturnValueHandlers(getReturnValueHandlers());
		if (jackson2Present) {
			exceptionHandlerResolver.setResponseBodyAdvice(
					Collections.singletonList(new JsonViewResponseBodyAdvice()));
		}
		if (this.applicationContext != null) {
			exceptionHandlerResolver.setApplicationContext(this.applicationContext);
		}
		exceptionHandlerResolver.afterPropertiesSet();
		exceptionResolvers.add(exceptionHandlerResolver);

       // 定义一个 ResponseStatusExceptionResolver
		ResponseStatusExceptionResolver responseStatusResolver = new ResponseStatusExceptionResolver();
		responseStatusResolver.setMessageSource(this.applicationContext);
		exceptionResolvers.add(responseStatusResolver);

       // 定义一个  DefaultHandlerExceptionResolver
		exceptionResolvers.add(new DefaultHandlerExceptionResolver());
	}