SpringBoot对于SpringMVC的支持

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版本说明这里使用的 SpringBoot 2.0.0.Release

SpringBoot对于SpringMVC的支持

在之前的开发中很多场景下使用的是基于xml配置文件或者是Java配置类的方式来进行SpringMVC的配置。一般来讲，初始的步骤如下所示

• 1、初始化SpringMVC的DispatcherServlet
• 2、搭建转码过滤器，保证客户端请求进行正确的转码
• 3、搭建视图解析器(View Resolver),告诉Spring从什么地方查找视图，以及这些视图使用什么语言编写等
• 4、配置静态资源的位置
• 5、配置所支持的地域以及资源bundle
• 6、配置multipart解析器，保证文件上传能够正常工作
• 7、将Tomcat或者Jetty包含能够在Web服务器上运行应用
• 8、建立错误页面

当然不止是上面这些工作。如下图所示，为SpringMVC核心的处理流程。

核心处理流

功能流图

1.1 分发器和multipart配置

首先在默认的配置文件中加入如下的一行代码,表示已debug模式运行SpringBoot的应用。

debug=true

配置完成之后会看到控制台会打印出debug信息。

DispatcherServletAutoConfiguration matched:
      - @ConditionalOnClass found required class 'org.springframework.web.servlet.DispatcherServlet' (OnClassCondition)
      - found 'session' scope (OnWebApplicationCondition)

   DispatcherServletAutoConfiguration.DispatcherServletConfiguration matched:
      - @ConditionalOnClass found required class 'javax.servlet.ServletRegistration' (OnClassCondition)
      - Default DispatcherServlet did not find dispatcher servlet beans (DispatcherServletAutoConfiguration.DefaultDispatcherServletCondition)

   DispatcherServletAutoConfiguration.DispatcherServletRegistrationConfiguration matched:
      - @ConditionalOnClass found required class 'javax.servlet.ServletRegistration' (OnClassCondition)
      - DispatcherServlet Registration did not find servlet registration bean (DispatcherServletAutoConfiguration.DispatcherServletRegistrationCondition)

   DispatcherServletAutoConfiguration.DispatcherServletRegistrationConfiguration#dispatcherServletRegistration matched:
      - @ConditionalOnBean (names: dispatcherServlet; types: org.springframework.web.servlet.DispatcherServlet; SearchStrategy: all) found bean 'dispatcherServlet' (OnBeanCondition)

   EmbeddedWebServerFactoryCustomizerAutoConfiguration matched:
      - @ConditionalOnWebApplication (required) found 'session' scope (OnWebApplicationCondition)

   EmbeddedWebServerFactoryCustomizerAutoConfiguration.TomcatWebServerFactoryCustomizerConfiguration matched:
      - @ConditionalOnClass found required classes 'org.apache.catalina.startup.Tomcat', 'org.apache.coyote.UpgradeProtocol' (OnClassCondition)

   ErrorMvcAutoConfiguration matched:
      - @ConditionalOnClass found required classes 'javax.servlet.Servlet', 'org.springframework.web.servlet.DispatcherServlet' (OnClassCondition)
      - found 'session' scope (OnWebApplicationCondition)

   ErrorMvcAutoConfiguration#basicErrorController matched:
      - @ConditionalOnMissingBean (types: org.springframework.boot.web.servlet.error.ErrorController; SearchStrategy: current) did not find any beans (OnBeanCondition)

   ErrorMvcAutoConfiguration#errorAttributes matched:
      - @ConditionalOnMissingBean (types: org.springframework.boot.web.servlet.error.ErrorAttributes; SearchStrategy: current) did not find any beans (OnBeanCondition)

   ErrorMvcAutoConfiguration.DefaultErrorViewResolverConfiguration#conventionErrorViewResolver matched:
      - @ConditionalOnBean (types: org.springframework.web.servlet.DispatcherServlet; SearchStrategy: all) found bean 'dispatcherServlet'; @ConditionalOnMissingBean (types: org.springframework.boot.autoconfigure.web.servlet.error.DefaultErrorViewResolver; SearchStrategy: all) did not find any beans (OnBeanCondition)

   ErrorMvcAutoConfiguration.WhitelabelErrorViewConfiguration matched:
      - @ConditionalOnProperty (server.error.whitelabel.enabled) matched (OnPropertyCondition)
      - ErrorTemplate Missing did not find error template view (ErrorMvcAutoConfiguration.ErrorTemplateMissingCondition)

   ErrorMvcAutoConfiguration.WhitelabelErrorViewConfiguration#beanNameViewResolver matched:
      - @ConditionalOnMissingBean (types: org.springframework.web.servlet.view.BeanNameViewResolver; SearchStrategy: all) did not find any beans (OnBeanCondition)

   ErrorMvcAutoConfiguration.WhitelabelErrorViewConfiguration#defaultErrorView matched:
      - @ConditionalOnMissingBean (names: error; SearchStrategy: all) did not find any beans (OnBeanCondition)

   GenericCacheConfiguration matched:
      - Cache org.springframework.boot.autoconfigure.cache.GenericCacheConfiguration automatic cache type (CacheCondition)

   HttpEncodingAutoConfiguration matched:
      - @ConditionalOnClass found required class 'org.springframework.web.filter.CharacterEncodingFilter' (OnClassCondition)
      - found 'session' scope (OnWebApplicationCondition)
      - @ConditionalOnProperty (spring.http.encoding.enabled) matched (OnPropertyCondition)

   HttpEncodingAutoConfiguration#characterEncodingFilter matched:
      - @ConditionalOnMissingBean (types: org.springframework.web.filter.CharacterEncodingFilter; SearchStrategy: all) did not find any beans (OnBeanCondition)

   HttpMessageConvertersAutoConfiguration matched:
      - @ConditionalOnClass found required class 'org.springframework.http.converter.HttpMessageConverter' (OnClassCondition)

   HttpMessageConvertersAutoConfiguration#messageConverters matched:
      - @ConditionalOnMissingBean (types: org.springframework.boot.autoconfigure.http.HttpMessageConverters; SearchStrategy: all) did not find any beans (OnBeanCondition)

   HttpMessageConvertersAutoConfiguration.StringHttpMessageConverterConfiguration matched:
      - @ConditionalOnClass found required class 'org.springframework.http.converter.StringHttpMessageConverter' (OnClassCondition)
      
  MultipartAutoConfiguration matched:
      - @ConditionalOnClass found required classes 'javax.servlet.Servlet', 'org.springframework.web.multipart.support.StandardServletMultipartResolver', 'javax.servlet.MultipartConfigElement' (OnClassCondition)
      - found 'session' scope (OnWebApplicationCondition)
      - @ConditionalOnProperty (spring.servlet.multipart.enabled) matched (OnPropertyCondition)

   MultipartAutoConfiguration#multipartConfigElement matched:
      - @ConditionalOnMissingBean (types: javax.servlet.MultipartConfigElement,org.springframework.web.multipart.commons.CommonsMultipartResolver; SearchStrategy: all) did not find any beans (OnBeanCondition)

   MultipartAutoConfiguration#multipartResolver matched:
      - @ConditionalOnMissingBean (types: org.springframework.web.multipart.MultipartResolver; SearchStrategy: all) did not find any beans (OnBeanCondition)

下面就来分析一下DispatcherServletAutoConfiguration配置类

DispatcherServletAutoConfiguration

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication(type = Type.SERVLET)
@ConditionalOnClass(DispatcherServlet.class)
@AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class)
@EnableConfigurationProperties(ServerProperties.class)
public class DispatcherServletAutoConfiguration {

首先会发现它是一个 @Configuration 注解标注的类，说明这是一个典型的Spring配置类。在这个配置类上标注了一个注解 @EnableConfigurationProperties(ServerProperties.class) ,这个注解表示使用了SpringBoot自动配置原理，对于配置文件与配置类进行了映射，在这里看到向这个配置中注入的自动配置类的 ServerProperties 这里就是在配置文件中以server开头的所有配置。例如在配置文件可以进行端口的设置，访问路径配置

server.port=8080
server.servlet.context-path=/hello

在它的内部有一个静态内部类DispatcherServletConfiguration ，这个内部类也是作为一个配置类存在，这里需要注意一个注解 @Conditional 这个注解表示满足条件之后才会向容器中注入对应的组件。这里会看到如果容器中有 DefaultDispatcherServletCondition 这个类才会进行处理。也就是说在这里需要一个默认的DispatcherServlet才会生效

@Configuration
@Conditional(DefaultDispatcherServletCondition.class)
@ConditionalOnClass(ServletRegistration.class)
@EnableConfigurationProperties(WebMvcProperties.class)
protected static class DispatcherServletConfiguration {

	private final WebMvcProperties webMvcProperties;

	public DispatcherServletConfiguration(WebMvcProperties webMvcProperties) {
		this.webMvcProperties = webMvcProperties;
	}

	@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
	public DispatcherServlet dispatcherServlet() {
		DispatcherServlet dispatcherServlet = new DispatcherServlet();
		dispatcherServlet.setDispatchOptionsRequest(
			this.webMvcProperties.isDispatchOptionsRequest());
			dispatcherServlet.setDispatchTraceRequest(
			this.webMvcProperties.isDispatchTraceRequest());
			dispatcherServlet.setThrowExceptionIfNoHandlerFound(
		    this.webMvcProperties.isThrowExceptionIfNoHandlerFound());
		return dispatcherServlet;
	}

	@Bean
	@ConditionalOnBean(MultipartResolver.class)
	@ConditionalOnMissingBean(name = DispatcherServlet.MULTIPART_RESOLVER_BEAN_NAME)
	public MultipartResolver multipartResolver(MultipartResolver resolver) {
		// Detect if the user has created a MultipartResolver but named it incorrectly
		return resolver;
	}

}

第一步首先来看看对于 DefaultDispatcherServletCondition 进行分析

@Order(Ordered.LOWEST_PRECEDENCE - 10)
private static class DefaultDispatcherServletCondition extends SpringBootCondition {

        //继承父类实现获取匹配结果方法
        /**
        * 两个参数
        * 第一个参数ConditionContext 进行操作的上下文
        * 第二个参数AnnotatedTypeMetadata 注解类型的元数据
        */
        
	@Override
	public ConditionOutcome getMatchOutcome(ConditionContext context,
			AnnotatedTypeMetadata metadata) {
		//定义默认的DispatcherServlet信息	
		ConditionMessage.Builder message = ConditionMessage
				.forCondition("Default DispatcherServlet");
		//从配合beanFactory中进行遍历		
		ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
		
		List<String> dispatchServletBeans = Arrays.asList(beanFactory
			.getBeanNamesForType(DispatcherServlet.class, false, false));
		//找到dispatcherServlet
		if (dispatchServletBeans.contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
			return ConditionOutcome.noMatch(message.found("dispatcher servlet bean")
				 .items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
		}
		if (beanFactory.containsBean(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
			return ConditionOutcome
				 .noMatch(message.found("non dispatcher servlet bean")
				     .items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
		}
		if (dispatchServletBeans.isEmpty()) {
			return ConditionOutcome
				 .match(message.didNotFind("dispatcher servlet beans").atAll());
		}
		return ConditionOutcome.match(message
				.found("dispatcher servlet bean", "dispatcher servlet beans")
				.items(Style.QUOTE, dispatchServletBeans)
				.append("and none is named " + DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
	}

}

我们知道在使用@Bean注解的时候如果没有指定name属性默认会以方法名为容器中Bean的ID，在上面这类中对容器中的DispatchServlet进行匹配的时候需要满足下面这个Bean的条件。而这个bean的配置正是可以在webMvcProperteis中进行配置的。

@Bean(name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
public DispatcherServlet dispatcherServlet() {
	DispatcherServlet dispatcherServlet = new DispatcherServlet();
	dispatcherServlet.setDispatchOptionsRequest(
			this.webMvcProperties.isDispatchOptionsRequest());
			dispatcherServlet.setDispatchTraceRequest(
			this.webMvcProperties.isDispatchTraceRequest());
			dispatcherServlet.setThrowExceptionIfNoHandlerFound(
			this.webMvcProperties.isThrowExceptionIfNoHandlerFound());
	return dispatcherServlet;
}

在其内部还有另外一个内部类DispatcherServletRegistrationConfiguration

@Configuration
@Conditional(DispatcherServletRegistrationCondition.class)
@ConditionalOnClass(ServletRegistration.class)
@EnableConfigurationProperties(WebMvcProperties.class)
@Import(DispatcherServletConfiguration.class)
protected static class DispatcherServletRegistrationConfiguration {

	private final WebMvcProperties webMvcProperties;

	private final MultipartConfigElement multipartConfig;

	public DispatcherServletRegistrationConfiguration(WebMvcProperties webMvcProperties,
		ObjectProvider<MultipartConfigElement> multipartConfigProvider) {
		this.webMvcProperties = webMvcProperties;
		this.multipartConfig = multipartConfigProvider.getIfAvailable();
	}

	@Bean(name = DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)
	@ConditionalOnBean(value = DispatcherServlet.class, name = DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)
	public DispatcherServletRegistrationBean dispatcherServletRegistration(DispatcherServlet dispatcherServlet) {
		DispatcherServletRegistrationBean registration = new DispatcherServletRegistrationBean(dispatcherServlet,
					this.webMvcProperties.getServlet().getPath());
		registration.setName(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			registration.setLoadOnStartup(this.webMvcProperties.getServlet().getLoadOnStartup());
		if (this.multipartConfig != null) {
			registration.setMultipartConfig(this.multipartConfig);
		}
		return registration;
	}

}

	@Order(Ordered.LOWEST_PRECEDENCE - 10)
	private static class DefaultDispatcherServletCondition extends SpringBootCondition {

		@Override
		public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
			ConditionMessage.Builder message = ConditionMessage.forCondition("Default DispatcherServlet");
			ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
			List<String> dispatchServletBeans = Arrays
					.asList(beanFactory.getBeanNamesForType(DispatcherServlet.class, false, false));
			if (dispatchServletBeans.contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
				return ConditionOutcome
						.noMatch(message.found("dispatcher servlet bean").items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
			}
			if (beanFactory.containsBean(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
				return ConditionOutcome.noMatch(
						message.found("non dispatcher servlet bean").items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
			}
			if (dispatchServletBeans.isEmpty()) {
				return ConditionOutcome.match(message.didNotFind("dispatcher servlet beans").atAll());
			}
			return ConditionOutcome.match(message.found("dispatcher servlet bean", "dispatcher servlet beans")
					.items(Style.QUOTE, dispatchServletBeans)
					.append("and none is named " + DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
		}

	}

	@Order(Ordered.LOWEST_PRECEDENCE - 10)
	private static class DispatcherServletRegistrationCondition extends SpringBootCondition {

		@Override
		public ConditionOutcome getMatchOutcome(ConditionContext context, AnnotatedTypeMetadata metadata) {
			ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
			ConditionOutcome outcome = checkDefaultDispatcherName(beanFactory);
			if (!outcome.isMatch()) {
				return outcome;
			}
			return checkServletRegistration(beanFactory);
		}

		private ConditionOutcome checkDefaultDispatcherName(ConfigurableListableBeanFactory beanFactory) {
			List<String> servlets = Arrays
					.asList(beanFactory.getBeanNamesForType(DispatcherServlet.class, false, false));
			boolean containsDispatcherBean = beanFactory.containsBean(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME);
			if (containsDispatcherBean && !servlets.contains(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME)) {
				return ConditionOutcome.noMatch(
						startMessage().found("non dispatcher servlet").items(DEFAULT_DISPATCHER_SERVLET_BEAN_NAME));
			}
			return ConditionOutcome.match();
		}

		private ConditionOutcome checkServletRegistration(ConfigurableListableBeanFactory beanFactory) {
			ConditionMessage.Builder message = startMessage();
			List<String> registrations = Arrays
					.asList(beanFactory.getBeanNamesForType(ServletRegistrationBean.class, false, false));
			boolean containsDispatcherRegistrationBean = beanFactory
					.containsBean(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME);
			if (registrations.isEmpty()) {
				if (containsDispatcherRegistrationBean) {
					return ConditionOutcome.noMatch(message.found("non servlet registration bean")
							.items(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
				}
				return ConditionOutcome.match(message.didNotFind("servlet registration bean").atAll());
			}
			if (registrations.contains(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME)) {
				return ConditionOutcome.noMatch(message.found("servlet registration bean")
						.items(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
			}
			if (containsDispatcherRegistrationBean) {
				return ConditionOutcome.noMatch(message.found("non servlet registration bean")
						.items(DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
			}
			return ConditionOutcome.match(message.found("servlet registration beans").items(Style.QUOTE, registrations)
					.append("and none is named " + DEFAULT_DISPATCHER_SERVLET_REGISTRATION_BEAN_NAME));
		}

		private ConditionMessage.Builder startMessage() {
			return ConditionMessage.forCondition("DispatcherServlet Registration");
		}

	}

在Spring中往往会通过 @Order 注解来声明优先级，可以看到上面的内容对于两个静态内部类都做了是优先级的配置。在其中还有一个比较重要的注解值得关注 @AutoConfigureAfter(ServletWebServerFactoryAutoConfiguration.class) 对于这些注解来说都是为了进一步的优化配置顺序细节处理。