spring boot中慎用@EnableWebMvc

末蓝、 2022-03-01 05:50 312阅读 0赞

什么情况？我为了自定义了一个HandlerInterceptor，非常普通的做法，先是继承了WebMvcConfigurerAdapter，再添加了@EnableWebMvc。注：本篇基于spring-webmvc 4.3.9版本。

@EnableWebMvc
    @Configuration
    public class XXXAutoConfiguration extends WebMvcConfigurerAdapter {
        @Override
        public void addInterceptors(InterceptorRegistry registry) {
            registry.addInterceptor(new XXXInterceptor());
        }
    }

运行起来之后：一会是ExceptionHandlerExceptionResolver失效，一会是HttpMessageConverters（由RequestMappingHandlerAdapter管理）报错，整个spring mvc环境都混乱了。

呵呵，恭喜你，真的摊上事了！

这就是spring-boot的奥秘，不知不觉中犯错，你以为是这样的，其实你根本就不了解源码（原理）！

不卖关子了！开始分析源码吧！

@EnableWebMvc开启后，意味着springmvc环境被你完全接管了（若不定义需要那些bean，确实啥都没有）。而WebMvcAutoConfiguration原本是自动装配的（注入一系列mvc的bean），影响它失效最重要的原因在于：@ConditionalOnMissingBean(WebMvcConfigurationSupport.class) ，是的，正是Condition发挥了的作用（Ioc容器中已经有了WebMvcConfigurationSupport，那WebMvcAutoConfiguration就不会再实例化注入）。

而WebMvcAutoConfiguration 原本是通过**spring-boot-autoconfigure-2.0.5.RELEASE.jar/META-INF/spring.factories**自动装配的。

@Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    @Documented
    @Import(DelegatingWebMvcConfiguration.class)
    public @interface EnableWebMvc {
    }
    @Configuration
    public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
    
    	private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();
    
    
    	@Autowired(required = false)
    	public void setConfigurers(List<WebMvcConfigurer> configurers) {
    		if (!CollectionUtils.isEmpty(configurers)) {
    			this.configurers.addWebMvcConfigurers(configurers);
    		}
    	}
    }
    public class WebMvcConfigurationSupport implements ApplicationContextAware, ServletContextAware {
    }
    @Configuration
    @ConditionalOnWebApplication
    @ConditionalOnClass({ Servlet.class, DispatcherServlet.class,
    		WebMvcConfigurerAdapter.class })
    @ConditionalOnMissingBean(WebMvcConfigurationSupport.class)//看这里吧
    @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
    @AutoConfigureAfter({ DispatcherServletAutoConfiguration.class,
    		ValidationAutoConfiguration.class })
    public class WebMvcAutoConfiguration {
    
    	public static final String DEFAULT_PREFIX = "";
    
    	public static final String DEFAULT_SUFFIX = "";
    
    	@Bean
    	@ConditionalOnMissingBean(HiddenHttpMethodFilter.class)
    	public OrderedHiddenHttpMethodFilter hiddenHttpMethodFilter() {
    		return new OrderedHiddenHttpMethodFilter();
    	}
    
    	@Bean
    	@ConditionalOnMissingBean(HttpPutFormContentFilter.class)
    	@ConditionalOnProperty(prefix = "spring.mvc.formcontent.putfilter", name = "enabled", matchIfMissing = true)
    	public OrderedHttpPutFormContentFilter httpPutFormContentFilter() {
    		return new OrderedHttpPutFormContentFilter();
    	}
    
    	// Defined as a nested config to ensure WebMvcConfigurerAdapter is not read when not
    	// on the classpath
    	@Configuration
    	@Import(EnableWebMvcConfiguration.class)
    	@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
    	public static class WebMvcAutoConfigurationAdapter extends WebMvcConfigurerAdapter {
    
    		private static final Log logger = LogFactory
    				.getLog(WebMvcConfigurerAdapter.class);
    
    		private final ResourceProperties resourceProperties;
    
    		private final WebMvcProperties mvcProperties;
    
    		private final ListableBeanFactory beanFactory;
    
    		private final HttpMessageConverters messageConverters;
    
    		final ResourceHandlerRegistrationCustomizer resourceHandlerRegistrationCustomizer;
    
    		public WebMvcAutoConfigurationAdapter(ResourceProperties resourceProperties,
    				WebMvcProperties mvcProperties, ListableBeanFactory beanFactory,
    				@Lazy HttpMessageConverters messageConverters,
    				ObjectProvider<ResourceHandlerRegistrationCustomizer> resourceHandlerRegistrationCustomizerProvider) {
    			this.resourceProperties = resourceProperties;
    			this.mvcProperties = mvcProperties;
    			this.beanFactory = beanFactory;
    			this.messageConverters = messageConverters;
    			this.resourceHandlerRegistrationCustomizer = resourceHandlerRegistrationCustomizerProvider
    					.getIfAvailable();
    		}
    
    		@Override
    		public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
    			converters.addAll(this.messageConverters.getConverters());
    		}
    
    		@Override
    		public void configureAsyncSupport(AsyncSupportConfigurer configurer) {
    			Long timeout = this.mvcProperties.getAsync().getRequestTimeout();
    			if (timeout != null) {
    				configurer.setDefaultTimeout(timeout);
    			}
    		}
    
    		@Override
    		public void configureContentNegotiation(ContentNegotiationConfigurer configurer) {
    			Map<String, MediaType> mediaTypes = this.mvcProperties.getMediaTypes();
    			for (Entry<String, MediaType> mediaType : mediaTypes.entrySet()) {
    				configurer.mediaType(mediaType.getKey(), mediaType.getValue());
    			}
    		}
    
    		@Bean
    		@ConditionalOnMissingBean
    		public InternalResourceViewResolver defaultViewResolver() {
    			InternalResourceViewResolver resolver = new InternalResourceViewResolver();
    			resolver.setPrefix(this.mvcProperties.getView().getPrefix());
    			resolver.setSuffix(this.mvcProperties.getView().getSuffix());
    			return resolver;
    		}
    
    		@Bean
    		@ConditionalOnBean(View.class)
    		@ConditionalOnMissingBean
    		public BeanNameViewResolver beanNameViewResolver() {
    			BeanNameViewResolver resolver = new BeanNameViewResolver();
    			resolver.setOrder(Ordered.LOWEST_PRECEDENCE - 10);
    			return resolver;
    		}
    
    		@Bean
    		@ConditionalOnBean(ViewResolver.class)
    		@ConditionalOnMissingBean(name = "viewResolver", value = ContentNegotiatingViewResolver.class)
    		public ContentNegotiatingViewResolver viewResolver(BeanFactory beanFactory) {
    			ContentNegotiatingViewResolver resolver = new ContentNegotiatingViewResolver();
    			resolver.setContentNegotiationManager(
    					beanFactory.getBean(ContentNegotiationManager.class));
    			// ContentNegotiatingViewResolver uses all the other view resolvers to locate
    			// a view so it should have a high precedence
    			resolver.setOrder(Ordered.HIGHEST_PRECEDENCE);
    			return resolver;
    		}
    
    		@Bean
    		@ConditionalOnMissingBean
    		@ConditionalOnProperty(prefix = "spring.mvc", name = "locale")
    		public LocaleResolver localeResolver() {
    			if (this.mvcProperties
    					.getLocaleResolver() == WebMvcProperties.LocaleResolver.FIXED) {
    				return new FixedLocaleResolver(this.mvcProperties.getLocale());
    			}
    			AcceptHeaderLocaleResolver localeResolver = new AcceptHeaderLocaleResolver();
    			localeResolver.setDefaultLocale(this.mvcProperties.getLocale());
    			return localeResolver;
    		}
    
    		@Bean
    		@ConditionalOnProperty(prefix = "spring.mvc", name = "date-format")
    		public Formatter<Date> dateFormatter() {
    			return new DateFormatter(this.mvcProperties.getDateFormat());
    		}
    
    		@Override
    		public MessageCodesResolver getMessageCodesResolver() {
    			if (this.mvcProperties.getMessageCodesResolverFormat() != null) {
    				DefaultMessageCodesResolver resolver = new DefaultMessageCodesResolver();
    				resolver.setMessageCodeFormatter(
    						this.mvcProperties.getMessageCodesResolverFormat());
    				return resolver;
    			}
    			return null;
    		}
    
    		@Override
    		public void addFormatters(FormatterRegistry registry) {
    			for (Converter<?, ?> converter : getBeansOfType(Converter.class)) {
    				registry.addConverter(converter);
    			}
    			for (GenericConverter converter : getBeansOfType(GenericConverter.class)) {
    				registry.addConverter(converter);
    			}
    			for (Formatter<?> formatter : getBeansOfType(Formatter.class)) {
    				registry.addFormatter(formatter);
    			}
    		}
    
    		private <T> Collection<T> getBeansOfType(Class<T> type) {
    			return this.beanFactory.getBeansOfType(type).values();
    		}
    
    		@Override
    		public void addResourceHandlers(ResourceHandlerRegistry registry) {
    			if (!this.resourceProperties.isAddMappings()) {
    				logger.debug("Default resource handling disabled");
    				return;
    			}
    			Integer cachePeriod = this.resourceProperties.getCachePeriod();
    			if (!registry.hasMappingForPattern("/webjars/**")) {
    				customizeResourceHandlerRegistration(
    						registry.addResourceHandler("/webjars/**")
    								.addResourceLocations(
    										"classpath:/META-INF/resources/webjars/")
    						.setCachePeriod(cachePeriod));
    			}
    			String staticPathPattern = this.mvcProperties.getStaticPathPattern();
    			if (!registry.hasMappingForPattern(staticPathPattern)) {
    				customizeResourceHandlerRegistration(
    						registry.addResourceHandler(staticPathPattern)
    								.addResourceLocations(
    										this.resourceProperties.getStaticLocations())
    						.setCachePeriod(cachePeriod));
    			}
    		}
    
    		@Bean
    		public WelcomePageHandlerMapping welcomePageHandlerMapping(
    				ResourceProperties resourceProperties) {
    			return new WelcomePageHandlerMapping(resourceProperties.getWelcomePage(),
    					this.mvcProperties.getStaticPathPattern());
    		}
    
    		private void customizeResourceHandlerRegistration(
    				ResourceHandlerRegistration registration) {
    			if (this.resourceHandlerRegistrationCustomizer != null) {
    				this.resourceHandlerRegistrationCustomizer.customize(registration);
    			}
    
    		}
    
    		@Bean
    		@ConditionalOnMissingBean({ RequestContextListener.class,
    				RequestContextFilter.class })
    		public static RequestContextFilter requestContextFilter() {
    			return new OrderedRequestContextFilter();
    		}
    
    		@Configuration
    		@ConditionalOnProperty(value = "spring.mvc.favicon.enabled", matchIfMissing = true)
    		public static class FaviconConfiguration {
    
    			private final ResourceProperties resourceProperties;
    
    			public FaviconConfiguration(ResourceProperties resourceProperties) {
    				this.resourceProperties = resourceProperties;
    			}
    
    			@Bean
    			public SimpleUrlHandlerMapping faviconHandlerMapping() {
    				SimpleUrlHandlerMapping mapping = new SimpleUrlHandlerMapping();
    				mapping.setOrder(Ordered.HIGHEST_PRECEDENCE + 1);
    				mapping.setUrlMap(Collections.singletonMap("**/favicon.ico",
    						faviconRequestHandler()));
    				return mapping;
    			}
    
    			@Bean
    			public ResourceHttpRequestHandler faviconRequestHandler() {
    				ResourceHttpRequestHandler requestHandler = new ResourceHttpRequestHandler();
    				requestHandler
    						.setLocations(this.resourceProperties.getFaviconLocations());
    				return requestHandler;
    			}
    
    		}
    
    	}
    	/**
    	 * Configuration equivalent to {@code @EnableWebMvc}.
    	 */
    	@Configuration
    	public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration {
    		@Bean
    		@Override
    		public RequestMappingHandlerAdapter requestMappingHandlerAdapter() {
    			RequestMappingHandlerAdapter adapter = super.requestMappingHandlerAdapter();
    			adapter.setIgnoreDefaultModelOnRedirect(this.mvcProperties == null ? true
    					: this.mvcProperties.isIgnoreDefaultModelOnRedirect());
    			return adapter;
    		}
    
    		@Override
    		protected RequestMappingHandlerAdapter createRequestMappingHandlerAdapter() {
    			if (this.mvcRegistrations != null
    					&& this.mvcRegistrations.getRequestMappingHandlerAdapter() != null) {
    				return this.mvcRegistrations.getRequestMappingHandlerAdapter();
    			}
    			return super.createRequestMappingHandlerAdapter();
    		}
    
    		@Bean
    		@Primary
    		@Override
    		public RequestMappingHandlerMapping requestMappingHandlerMapping() {
    			// Must be @Primary for MvcUriComponentsBuilder to work
    			return super.requestMappingHandlerMapping();
    		}
    
    		@Bean
    		@Override
    		public Validator mvcValidator() {
    			if (!ClassUtils.isPresent("javax.validation.Validator",
    					getClass().getClassLoader())) {
    				return super.mvcValidator();
    			}
    			return WebMvcValidator.get(getApplicationContext(), getValidator());
    		}
        }
    }

那如果我真的要使用@EnableWebMvc的话，这推荐：

*  @EnableWebMvc+extends WebMvcConfigurerAdapter，在扩展的类中重写父类的方法即可（想想xml的时代缺啥加啥）