SpringBoot和web开发

1 简介

• 使用SpringBoot步骤：

  • 1️⃣创建SpringBoot应用，选中我们需要的模块。
  • 2️⃣SpringBoot已经默认将这些场景配置好了，只需要在配置文件指定少量配置就可以运行起来。
  • 3️⃣自己编写业务逻辑代码。

• 自动配置原理：这个场景SpringBoot帮我们配置了什么？能不能修改？能修改哪些配置？能不能扩展？

xxxAutoConfiguration：帮我们在容器中自动配置组件。
xxxProperties：配置类封装配置文件的内容。

2 SpringBoot对静态资源的映射规则

• WebMvcAutoConfiguration的部分源码如下：

@Configuration
@ConditionalOnWebApplication
@ConditionalOnClass({ Servlet.class, DispatcherServlet.class,
		WebMvcConfigurerAdapter.class })
@ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
@AutoConfigureAfter({ DispatcherServletAutoConfiguration.class,
		ValidationAutoConfiguration.class })
public class WebMvcAutoConfiguration {
    
    @Configuration
	@Import(EnableWebMvcConfiguration.class)
	@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
	public static class WebMvcAutoConfigurationAdapter extends WebMvcConfigurerAdapter {
        //静态资源处理器
        @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));
            }
        }

        //欢迎页
        @Bean
        public WelcomePageHandlerMapping welcomePageHandlerMapping(
            ResourceProperties resourceProperties) {
            return new WelcomePageHandlerMapping(resourceProperties.getWelcomePage(),
                                                 this.mvcProperties.getStaticPathPattern());
        }
        
        //配置喜欢的图标
        @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);
                //所有**/favicon.ico
                mapping.setUrlMap(Collections.singletonMap("**/favicon.ico",
                                                           faviconRequestHandler()));
                return mapping;
            }

            @Bean
            public ResourceHttpRequestHandler faviconRequestHandler() {
                ResourceHttpRequestHandler requestHandler = new ResourceHttpRequestHandler();
                requestHandler
                    .setLocations(this.resourceProperties.getFaviconLocations());
                return requestHandler;
            }

        }
        
        
    }    

    
}    

• 1️⃣所有/webjars/**，都去classpath:/META-INF/resources/webjars/找静态资源。

  • webjars：以jar包的形式引入静态资源。
  • 官网。
  • 比如：浏览器发送http://localhost:8080/webjars/jquery/3.5.1/jquery.js请求，SpringBoot就会到classpath:/META-INF/resources/webjars/jquery/3.5.1/jquery.js这个路径查找jquery.js文件。

  <dependency>
      <groupId>org.webjars</groupId>
      <artifactId>jquery</artifactId>
      <version>3.5.1</version>
  </dependency>
  

  

• 2️⃣/**访问当前项目的任何资源(静态资源的文件夹)：

  "classpath:/META-INF/resources/"
  "classpath:/resources/"
  "classpath:/static/"
  "classpath:/public/"
  "/"
  

  • 比如：浏览器发送http://localhost:8080/asserts/css/bootstrap.min.css请求，SpringBoot就会到静态资源文件夹中寻找/asserts/css/bootstrap.min.css的路径去寻找bootstrap.min.css文件。

  

• 3️⃣欢迎页，静态资源文件夹下的index.html页面，被/**映射。

• 比如：浏览器发送http://localhost:8080请求，默认情况下，会去静态资源文件夹下找index.html页面。

• 4️⃣所有的**/favicon.ico都是在静态资源文件夹下寻找。

3 模板引擎

3.1 简介

• JSP、Velocity、Freemarker、Thymeleaf……都是模板引擎。
• 模板引擎的原理：

3.2 Thymeleaf

3.2.1 Thymeleaf概述

• SpringBoot推荐Thymeleaf。
• Thymeleaf语法更简单，功能更强大。

3.2.2 Thymeleaf准备

• 导入thymeleaf相关jar包的Maven坐标：

<properties>
    <thymeleaf.version>3.0.9.RELEASE</thymeleaf.version>
    <thymeleaf-layout-dialect.version>2.3.0</thymeleaf-layout-dialect.version>
</properties>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>

• ThymeleafProperties：

@ConfigurationProperties(prefix = "spring.thymeleaf")
public class ThymeleafProperties {

	private static final Charset DEFAULT_ENCODING = Charset.forName("UTF-8");

	private static final MimeType DEFAULT_CONTENT_TYPE = MimeType.valueOf("text/html");

	public static final String DEFAULT_PREFIX = "classpath:/templates/";

	public static final String DEFAULT_SUFFIX = ".html";
     
    //略
}    

• 从ThymeleafProperties的源码可知：我们只要将HTML页面放在classpath:/templates/，Thymeleaf就能自动渲染。

3.2.3 Thymeleaf使用

• 导入thymeleaf的名称空间：

<html lang="en" xmlns:th="http://www.thymeleaf.org">

• 使用thymeleaf语法：

<!DOCTYPE html>
<html lang="en" xmlns:th="http://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>
<body>

    <div th:text="helloworld">哇，好(*^▽^*)</div>

</body>
</html>

3.2.4 Thymeleaf语法规则

文本

• th:text：改变当前元素里面的文本内容。
• th:任意html属性：来替换原生属性的值。
• th:insert、th:replace：片段包含。
• th:each：遍历。
• th:if、th:unless、th:case：条件判断。
• th:object、th:with：声明变量。
• th:attr、th:attrprepend、th:attrappend：任意属性修改。
• th:value、th:href、th:src：修改指定属性默认值。
• th:fragment：声明片段。
• th"remove：移除。

表达式

Simple expressions:（表达式语法）
    Variable Expressions: ${...}：获取变量值；OGNL；
    		1）、获取对象的属性、调用方法
    		2）、使用内置的基本对象：
    			#ctx : the context object.
    			#vars: the context variables.
                #locale : the context locale.
                #request : (only in Web Contexts) the HttpServletRequest object.
                #response : (only in Web Contexts) the HttpServletResponse object.
                #session : (only in Web Contexts) the HttpSession object.
                #servletContext : (only in Web Contexts) the ServletContext object.
                
                ${session.foo}
            3）、内置的一些工具对象：
#execInfo : information about the template being processed.
#messages : methods for obtaining externalized messages inside variables expressions, in the same way as they would be obtained using #{…} syntax.
#uris : methods for escaping parts of URLs/URIs
#conversions : methods for executing the configured conversion service (if any).
#dates : methods for java.util.Date objects: formatting, component extraction, etc.
#calendars : analogous to #dates , but for java.util.Calendar objects.
#numbers : methods for formatting numeric objects.
#strings : methods for String objects: contains, startsWith, prepending/appending, etc.
#objects : methods for objects in general.
#bools : methods for boolean evaluation.
#arrays : methods for arrays.
#lists : methods for lists.
#sets : methods for sets.
#maps : methods for maps.
#aggregates : methods for creating aggregates on arrays or collections.
#ids : methods for dealing with id attributes that might be repeated (for example, as a result of an iteration).

    Selection Variable Expressions: *{...}：选择表达式：和${}在功能上是一样；
    	补充：配合 th:object="${session.user}：
   <div th:object="${session.user}">
    <p>Name: <span th:text="*{firstName}">Sebastian</span>.</p>
    <p>Surname: <span th:text="*{lastName}">Pepper</span>.</p>
    <p>Nationality: <span th:text="*{nationality}">Saturn</span>.</p>
    </div>
    
    Message Expressions: #{...}：获取国际化内容
    Link URL Expressions: @{...}：定义URL；
    		@{/order/process(execId=${execId},execType='FAST')}
    Fragment Expressions: ~{...}：片段引用表达式
    		<div th:insert="~{commons :: main}">...</div>
    		
Literals（字面量）
      Text literals: 'one text' , 'Another one!' ,…
      Number literals: 0 , 34 , 3.0 , 12.3 ,…
      Boolean literals: true , false
      Null literal: null
      Literal tokens: one , sometext , main ,…
Text operations:（文本操作）
    String concatenation: +
    Literal substitutions: |The name is ${name}|
Arithmetic operations:（数学运算）
    Binary operators: + , - , * , / , %
    Minus sign (unary operator): -
Boolean operations:（布尔运算）
    Binary operators: and , or
    Boolean negation (unary operator): ! , not
Comparisons and equality:（比较运算）
    Comparators: > , < , >= , <= ( gt , lt , ge , le )
    Equality operators: == , != ( eq , ne )
Conditional operators:条件运算（三元运算符）
    If-then: (if) ? (then)
    If-then-else: (if) ? (then) : (else)
    Default: (value) ?: (defaultvalue)
Special tokens:
    No-Operation: _ 

4 SpringMVC自动配置

4.1 SpringMVC自动配置

• SpringBoot自动配置好了SpringMVC，下面SpringBoot对SpringMVC的默认配置（WebMvcAutoConfiguration）：

  • 1️⃣Inclusion of ContentNegotiatingViewResolver and BeanNameViewResolver beans。

    • 自动配置了ViewResolver（视图解析器，根据方法的返回值得到视图对象（View），视图对象决定如何渲染（转发？重定向？））。
    • ContentNegotiatingViewResolver ：组合所有的视图解析器。
    • 如何定制？我们可以自己给容器中添加一个视图解析器，自动将其组合进来。

  • 2️⃣Support for serving static resources, including support for WebJars (see below)。

    • 支持静态资源文件夹路径和webjars。

  • 3️⃣Static index.html support.。

    • 首页访问。

  • 4️⃣Custom Favicon support (see below)。

    • favicon.ico。

  • 5️⃣自动注册了 of Converter, GenericConverter, Formatter beans。

    • Converter：转换器。
    • Formatter ：格式化器。

    @Bean
    @ConditionalOnProperty(prefix = "spring.mvc", name = "date-format") //在配置文件中配置日期格式化的规则
    public Formatter<Date> dateFormatter() {
        return new DateFormatter(this.mvcProperties.getDateFormat()); //日期格式化组件
    }
    

    • 我们自己添加的格式化器、转换器只需要放在容器中即可。

    @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);
        }
    }
    

  • 6️⃣Support for HttpMessageConverters (see below)。

    • HttpMessageConverter：SpringMVC用来转换Http的请求和响应的。比如JavaBean和JSON之间的转换。
    • HttpMessageConverters是从容器中获取的，并且获取所有的HttpMessageConverter。
    • 自己给容器中添加HttpMessageConverter，只需要自己将组件注册到容器中。

  • 7️⃣Automatic registration of MessageCodesResolver (see below)。

    • 定义错误代码生成规则。

  • 8️⃣Automatic use of a ConfigurableWebBindingInitializer bean (see below)。

    • 我们可以配置一个ConfigurableWebBindingInitializer来替换默认的。

  • ConfigurableWebBindingInitializer的作用就是初始化所有的WebDataBinder，而WebDataBinder的作用就是请求数据-->JavaBean。

• 9️⃣If you want to keep Spring Boot MVC features, and you just want to add additional MVC configuration (interceptors, formatters, view controllers etc.) you can add your own @Configuration class of type WebMvcConfigurerAdapter, but without @EnableWebMvc. If you wish to provide custom instances of RequestMappingHandlerMapping, RequestMappingHandlerAdapter or ExceptionHandlerExceptionResolver you can declare a WebMvcRegistrationsAdapter instance providing such components.

  If you want to take complete control of Spring MVC, you can add your own @Configuration annotated with @EnableWebMvc.

4.2 扩展SpringMVC

• 以前的springmvc.xml中配置拦截器等：

<mvc:view-controller path="/hello" view-name="success"/>
<mvc:interceptors>
    <mvc:interceptor>
        <mvc:mapping path="/hello"/>
        <bean></bean>
    </mvc:interceptor>
</mvc:interceptors>

• 现在在SpringBoot中，编写一个配置类（用@Configuration注解标注的类），并且继承WebMvcConfigurerAdapter，但是不要标注@EnableWebMvc注解。这样既可以保留自动配置功能，又能使用我们自己扩展的配置。

package com.sunxiaping.springboot.config;

import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@Configuration
public class SpringMvcConfig extends WebMvcConfigurerAdapter {
    
    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        registry.addViewController("/index").setViewName("index");
        registry.addViewController("/").setViewName("index");
        registry.addViewController("/index.html").setViewName("index");
        registry.addViewController("/index.htm").setViewName("index");
    }
}

• 原理：

  • 1️⃣WebMvcAutoConfiguration是SpringMVC的自动配置类。
  • 2️⃣在做其他自动配置的时候，会导入@Import(EnableWebMvcConfiguration.class)。

  @Configuration
  @ConditionalOnWebApplication
  @ConditionalOnClass({ Servlet.class, DispatcherServlet.class,
  		WebMvcConfigurerAdapter.class })
  @ConditionalOnMissingBean(WebMvcConfigurationSupport.class)
  @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
  @AutoConfigureAfter({ DispatcherServletAutoConfiguration.class,
  		ValidationAutoConfiguration.class })
  public class WebMvcAutoConfiguration {
      
      @Configuration
  	@Import(EnableWebMvcConfiguration.class)
  	@EnableConfigurationProperties({ WebMvcProperties.class, ResourceProperties.class })
  	public static class WebMvcAutoConfigurationAdapter extends WebMvcConfigurerAdapter {
         //其他略
      }
      
      @Configuration
  	public static class EnableWebMvcConfiguration extends DelegatingWebMvcConfiguration {
          
      }    
      
      //其他略
  }          
  

  • 3️⃣DelegatingWebMvcConfiguration的部分源码如下：

  @Configuration
  public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
  
  	private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();
  
  	//会将所有的WebMvcConfigurer都导入到容器中
  	@Autowired(required = false)
  	public void setConfigurers(List<WebMvcConfigurer> configurers) {
  		if (!CollectionUtils.isEmpty(configurers)) {
  			this.configurers.addWebMvcConfigurers(configurers);
  		}
  	}
      
      //循环遍历所有的WebMvcConfigurer，并将每个WebMvcConfigurer配置的ViewController加入到容器中
      //这样就可以将所有的WebMvcConfigurer的相关配置一起作用
      @Override
  	protected void addViewControllers(ViewControllerRegistry registry) {
  		this.configurers.addViewControllers(registry);
  	}
      
      //其他略
  	
  }
  

  • 4️⃣容器中的所有WebMvcConfigurer都会一起起作用。
  • 5️⃣我们自己配置类也会被调用。

  4.3 全面接管SpringMVC

  • SpringBoot对SpringMVC的自动配置不需要了，所有的都需要我们配置。
  • 只需要在配置类中加@EnableWebMvc注解即可。

  package com.sunxiaping.springboot.config;
  
  import org.springframework.context.annotation.Configuration;
  import org.springframework.web.servlet.config.annotation.EnableWebMvc;
  import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
  import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;
  
  @Configuration
  @EnableWebMvc
  public class SpringMvcConfig extends WebMvcConfigurerAdapter {
  
      @Override
      public void addViewControllers(ViewControllerRegistry registry) {
          registry.addViewController("/index").setViewName("index");
          registry.addViewController("/").setViewName("index");
          registry.addViewController("/index.html").setViewName("index");
          registry.addViewController("/index.htm").setViewName("index");
      }
  }
  

  • 原理如下：

    • @EnableWebMvc注解源码如下：

    @Retention(RetentionPolicy.RUNTIME)
    @Target(ElementType.TYPE)
    @Documented
    @Import(DelegatingWebMvcConfiguration.class) //会向容器中导入DelegatingWebMvcConfiguration组件
    public @interface EnableWebMvc {
    }
    

    • DelegatingWebMvcConfiguration的部分源码如下：

    @Configuration
    public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
    	//其他略
    }    
    

    • WebMvcAutoConfiguration的部分源码如下：

    @Configuration
    @ConditionalOnWebApplication
    @ConditionalOnClass({ Servlet.class, DispatcherServlet.class,
    		WebMvcConfigurerAdapter.class })
    @ConditionalOnMissingBean(WebMvcConfigurationSupport.class) //只有在容器中没有WebMvcConfigurationSupport组件的时候，WebMvcAutoConfiguration才会起效,而@EnableWebMvc会将WebMvcConfigurationSupport组件导入到容器中
    @AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE + 10)
    @AutoConfigureAfter({ DispatcherServletAutoConfiguration.class,
    		ValidationAutoConfiguration.class })
    public class WebMvcAutoConfiguration {
        //其他略   
    }    
    

5 如何修改SpringBoot的默认配置

• 1️⃣SpringBoot在自动配置很多组件的时候，先看容器中有没有用户自己配置（@Bean、@Component），如果有，就使用用户自己配置的；如果没有，才自动配置；如果有些组件可以有多个（比如ViewResolver），就将用户配置的和自己默认的组合起来。
• 2️⃣在SpringBoot中会有非常多的xxxConfigurer帮助我们进行扩展配置。
• 3️⃣在SpringBoot中会有非常多的xxxCustomizer帮助我们进行定制配置。

6 错误处理机制

6.1 SpringBoot错误的默认效果

• 如果是浏览器：返回一个默认的错误页面：

• 如果是其他客户端：返回一个默认的JSON数据。

• 原理：可以参照ErrorMvcAutoConfiguration（错误处理的自动配置）。

  • ErrorMvcAutoConfiguration的部分源码如下：

  @Configuration
  @ConditionalOnWebApplication
  @ConditionalOnClass({ Servlet.class, DispatcherServlet.class })
  // Load before the main WebMvcAutoConfiguration so that the error View is available
  @AutoConfigureBefore(WebMvcAutoConfiguration.class)
  @EnableConfigurationProperties(ResourceProperties.class)
  public class ErrorMvcAutoConfiguration {
      //给容器中添加DefaultErrorAttributes组件
      @Bean
  	@ConditionalOnMissingBean(value = ErrorAttributes.class, search = SearchStrategy.CURRENT)
  	public DefaultErrorAttributes errorAttributes() {
  		return new DefaultErrorAttributes();
  	}
      //给容器中添加BasicErrorController组件
  	@Bean
  	@ConditionalOnMissingBean(value = ErrorController.class, search = SearchStrategy.CURRENT)
  	public BasicErrorController basicErrorController(ErrorAttributes errorAttributes) {
  		return new BasicErrorController(errorAttributes, this.serverProperties.getError(),
  				this.errorViewResolvers);
  	}
      //给容器中添加ErrorPageCustomizer组件
  	@Bean
  	public ErrorPageCustomizer errorPageCustomizer() {
  		return new ErrorPageCustomizer(this.serverProperties);
  	}
      
  	@Configuration
  	static class DefaultErrorViewResolverConfiguration {
  
  		private final ApplicationContext applicationContext;
  
  		private final ResourceProperties resourceProperties;
  
  		DefaultErrorViewResolverConfiguration(ApplicationContext applicationContext,
  				ResourceProperties resourceProperties) {
  			this.applicationContext = applicationContext;
  			this.resourceProperties = resourceProperties;
  		}
           //给容器中添加DefaultErrorViewResolver组件
  		@Bean
  		@ConditionalOnBean(DispatcherServlet.class)
  		@ConditionalOnMissingBean
  		public DefaultErrorViewResolver conventionErrorViewResolver() {
  			return new DefaultErrorViewResolver(this.applicationContext,
  					this.resourceProperties);
  		}
  	}
      //其他略
      
  }    
  

  • ErrorPageCustomizer：

  @Configuration
  @ConditionalOnWebApplication
  @ConditionalOnClass({ Servlet.class, DispatcherServlet.class })
  // Load before the main WebMvcAutoConfiguration so that the error View is available
  @AutoConfigureBefore(WebMvcAutoConfiguration.class)
  @EnableConfigurationProperties(ResourceProperties.class)
  public class ErrorMvcAutoConfiguration {
      /**
  	 * {@link EmbeddedServletContainerCustomizer} that configures the container's error
  	 * pages.
  	 */
  	private static class ErrorPageCustomizer implements ErrorPageRegistrar, Ordered {
  
  		private final ServerProperties properties;
  
  		protected ErrorPageCustomizer(ServerProperties properties) {
  			this.properties = properties;
  		}
       
           //            @Value("${error.path:/error}")  
           //getPath() = private String path = "/error";
           //系统出现错误以后会来到error请求进行处理。就如同在web.xml中配置错误页面规则
  		@Override
  		public void registerErrorPages(ErrorPageRegistry errorPageRegistry) {
  			ErrorPage errorPage = new ErrorPage(this.properties.getServletPrefix()
  					+ this.properties.getError().getPath());
  			errorPageRegistry.addErrorPages(errorPage);
  		}
  
  		@Override
  		public int getOrder() {
  			return 0;
  		}
  
  	}
      //其他略
  }    
  

  • BasicErrorController：处理默认的/error请求。

  @Controller
  @RequestMapping("${server.error.path:${error.path:/error}}")
  public class BasicErrorController extends AbstractErrorController {
      //产生HTML类型的数据，浏览器发送的请求来到这个方法处理
      @RequestMapping(produces = "text/html")
  	public ModelAndView errorHtml(HttpServletRequest request,
  			HttpServletResponse response) {
  		HttpStatus status = getStatus(request);
           //getErrorAttributes其实就是调用的DefaultErrorAttributes的getErrorAttributes方法，而DefaultErrorAttributes是从容器中获取的。
  		Map<String, Object> model = Collections.unmodifiableMap(getErrorAttributes(
  				request, isIncludeStackTrace(request, MediaType.TEXT_HTML)));
  		response.setStatus(status.value());
  		ModelAndView modelAndView = resolveErrorView(request, response, status, model);
  		return (modelAndView == null ? new ModelAndView("error", model) : modelAndView);
  	}
      
      //产生JSON数据，其他客户端来到这个方法处理
  	@RequestMapping
  	@ResponseBody
  	public ResponseEntity<Map<String, Object>> error(HttpServletRequest request) {
  		Map<String, Object> body = getErrorAttributes(request,
  				isIncludeStackTrace(request, MediaType.ALL));
  		HttpStatus status = getStatus(request);
  		return new ResponseEntity<Map<String, Object>>(body, status);
  	}
  
  	//略   
  }    
  

  • DefaultErrorViewResolver：

  public class DefaultErrorViewResolver implements ErrorViewResolver, Ordered {
  	private static final Map<Series, String> SERIES_VIEWS;
  
  	static {
  		Map<Series, String> views = new HashMap<Series, String>();
  		views.put(Series.CLIENT_ERROR, "4xx");
  		views.put(Series.SERVER_ERROR, "5xx");
  		SERIES_VIEWS = Collections.unmodifiableMap(views);
  	}
      @Override
  	public ModelAndView resolveErrorView(HttpServletRequest request, HttpStatus status,
  			Map<String, Object> model) {
  		ModelAndView modelAndView = resolve(String.valueOf(status), model);
  		if (modelAndView == null && SERIES_VIEWS.containsKey(status.series())) {
  			modelAndView = resolve(SERIES_VIEWS.get(status.series()), model);
  		}
  		return modelAndView;
  	}
  
  	private ModelAndView resolve(String viewName, Map<String, Object> model) {
          //默认SpringBoot可以去找到一个页面 比如：/error/404
  		String errorViewName = "error/" + viewName;
          //模板引擎可以解析这个页面地址就用模板引擎解析
  		TemplateAvailabilityProvider provider = this.templateAvailabilityProviders
  				.getProvider(errorViewName, this.applicationContext);
  		if (provider != null) {
               //模板引擎可用的情况下返回errorViewName指定的视图地址
  			return new ModelAndView(errorViewName, model);
  		}
          //模板引擎不可用，就在静态资源文件夹下找errorViewName对象的页面
  		return resolveResource(errorViewName, model);
  	}
  
  	private ModelAndView resolveResource(String viewName, Map<String, Object> model) {
  		for (String location : this.resourceProperties.getStaticLocations()) {
  			try {
  				Resource resource = this.applicationContext.getResource(location);
  				resource = resource.createRelative(viewName + ".html");
  				if (resource.exists()) {
  					return new ModelAndView(new HtmlResourceView(resource), model);
  				}
  			}
  			catch (Exception ex) {
  			}
  		}
  		return null;
  	}    
      //其他略
      
  }    
  

  • DefaultErrorAttributes：

  @Order(Ordered.HIGHEST_PRECEDENCE)
  public class DefaultErrorAttributes{
      //帮助我们在页面中共享信息
      @Override
  	public Map<String, Object> getErrorAttributes(RequestAttributes requestAttributes,
  			boolean includeStackTrace) {
  		Map<String, Object> errorAttributes = new LinkedHashMap<String, Object>();
  		errorAttributes.put("timestamp", new Date());
  		addStatus(errorAttributes, requestAttributes);
  		addErrorDetails(errorAttributes, requestAttributes, includeStackTrace);
  		addPath(errorAttributes, requestAttributes);
  		return errorAttributes;
  	}
  }
  

  • 步骤：

    • 一旦系统出现4xx或者5xx之类的错误，ErrorPageCustomizer就会生效（定制错误的响应规则），就会来到/error请求，就会被BasicErrorController处理。
    • 响应页面：去哪个页面是由DefaultErrorViewResolver解析得到的。

    public abstract class AbstractErrorController implements ErrorController {
         /**
    	 * Resolve any specific error views. By default this method delegates to
    	 * {@link ErrorViewResolver ErrorViewResolvers}.
    	 * @param request the request
    	 * @param response the response
    	 * @param status the HTTP status
    	 * @param model the suggested model
    	 * @return a specific {@link ModelAndView} or {@code null} if the default should be
    	 * used
    	 * @since 1.4.0
    	 */
    	protected ModelAndView resolveErrorView(HttpServletRequest request,
    			HttpServletResponse response, HttpStatus status, Map<String, Object> model) {
    		for (ErrorViewResolver resolver : this.errorViewResolvers) {
    			ModelAndView modelAndView = resolver.resolveErrorView(request, status, model);
    			if (modelAndView != null) {
    				return modelAndView;
    			}
    		}
    		return null;
    	}
        //其他略
    }    
    

6.2 如果定制错误响应

6.2.1 如何定制错误页面

• 1️⃣如果有模板引擎的情况下，默认请求error/状态码，并且返回error/状态码的视图地址，那么我们只需要将错误页面命名为错误状态码.html并放在模板引擎文件夹（默认是classpath:/template）里面的error文件夹下。
  • 我们可以使用4xx和5xx作为错误页面的文件名来匹配这种类型的所有错误，精确优先（比如同时存在404.html和4xx.html，那么当发生404的错误的时候，会优先寻找404.html，一旦匹配到了，就响应404.html）。
  • 页面能获取的信息：
    • timestamp：时间戳。
    • status：状态码。
    • error：错误提示。
    • exception：异常对象。
    • errors：JSR303错误校验的信息。
    • path：错误路径。
• 2️⃣如果没有模板引擎（模板引擎找不多对应的错误页面），就去静态资源文件夹下寻找。
• 3️⃣以上都没有错误页面，就来到SpringBoot默认的错误提示页面。

6.2.2 如何定制错误的JSON数据

• 1️⃣自定义异常处理&返回定义JSON数据：

package com.sunxiaping.springboot.config;

import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;
import org.springframework.web.bind.annotation.ResponseBody;

import java.util.HashMap;
import java.util.Map;

/**
 * @ControllerAdvice标注的类：就是对控制器进行增强，在这个类中，可以使用@InitBinder、@InitBinder和@ModelAttribute，这些功能都可以被所有的控制器共享
 */
@ControllerAdvice
public class SelfExceptionHandler {
    //浏览器客户端返回的都是JSON
    @ExceptionHandler(value = SelfException.class)
    @ResponseBody
    public Map<String,Object> handleException(SelfException e){
        Map<String,Object> map = new HashMap<>();
        map.put("code",1);
        map.put("msg",e.getMessage());
        return map;
    }   
}

• 2️⃣转发到/error进行自适应响应效果处理：

package com.sunxiaping.springboot.config;

import org.springframework.web.bind.annotation.ControllerAdvice;
import org.springframework.web.bind.annotation.ExceptionHandler;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.util.HashMap;
import java.util.Map;

/**
 * @ControllerAdvice标注的类：就是对控制器进行增强，在这个类中，可以使用@InitBinder、@InitBinder和@ModelAttribute，这些功能都可以被所有的控制器共享
 */
@ControllerAdvice
public class SelfExceptionHandler {

    @ExceptionHandler(value = SelfException.class)
    public String handleException(HttpServletRequest request, HttpServletResponse response, SelfException e) {
        Map<String, Object> map = new HashMap<>();
        //传入我们自己的错误状态码，否则就不会进入定制的错误页面的解析流程
        request.setAttribute("javax.servlet.error.status_code", 500);
        map.put("code", 1);
        map.put("msg", e.getMessage());
        return "forward:/error";
    }

}

• 3️⃣将我们的定制数据携带出去：

  • 出现错误以后，会来到/error请求，会被BasicErrorController处理，响应出去可以获取的数据是由getErrorAttributes得到的（是AbstractErrorController中规定的方法），所以我们可以编写一个ErrorController的实现类或AbstractErrorController的子类，放在容器中。
  • 页面上能用的数据或者是JSON返回能用的数据都是通过errorAttributes.getErrorAttributes()方法得到的，容器中的DefaultErrorAttributes.getErrorAttributes()方法是默认进行数据处理的。

  package com.sunxiaping.springboot.config;
  
  import org.springframework.web.bind.annotation.ControllerAdvice;
  import org.springframework.web.bind.annotation.ExceptionHandler;
  
  import javax.servlet.http.HttpServletRequest;
  import javax.servlet.http.HttpServletResponse;
  import java.util.HashMap;
  import java.util.Map;
  
  /**
   * @ControllerAdvice标注的类：就是对控制器进行增强，在这个类中，可以使用@InitBinder、@InitBinder和@ModelAttribute，这些功能都可以被所有的控制器共享
   */
  @ControllerAdvice
  public class SelfExceptionHandler {
  
      @ExceptionHandler(value = SelfException.class)
      public String handleException(HttpServletRequest request, HttpServletResponse response, SelfException e) {
          Map<String, Object> map = new HashMap<>();
          //传入我们自己的错误状态码
          request.setAttribute("javax.servlet.error.status_code", 500);
          map.put("code", 1);
          map.put("msg", e.getMessage());
  
          request.setAttribute("ext", map);
          return "forward:/error";
      }
  
  }
  

  package com.sunxiaping.springboot.config;
  
  import org.springframework.boot.autoconfigure.web.DefaultErrorAttributes;
  import org.springframework.stereotype.Component;
  import org.springframework.web.context.request.RequestAttributes;
  
  import java.util.Map;
  
  @Component
  public class SelfErrorAttributes extends DefaultErrorAttributes {
      @Override
      public Map<String, Object> getErrorAttributes(RequestAttributes requestAttributes, boolean includeStackTrace) {
          Map<String, Object> map = super.getErrorAttributes(requestAttributes, includeStackTrace);
          Object ext = requestAttributes.getAttribute("ext", RequestAttributes.SCOPE_REQUEST);
          map.put("ext", ext);
          return map;
      }
  }
  

7 配置嵌入式Servlet容器

7.1 如何定制和修改Servlet容器的相关配置

7.1.1 修改和server有关的配置(ServerProperties)

server:
  port: 8081
  context-path: /spring
  tomcat:
    uri-encoding: utf-8

# 通用的servlet容器配置
server:
	xxx: 
# Tomcat的设置
server:
	tomcat: 
		xxx: 	

7.1.2 编写一个EmbeddedServletContainerCustomizer(嵌入式的Servlet容器的定制器)来修改Servlet有关配置

package com.sunxiaping.springboot.config;

import org.springframework.boot.context.embedded.ConfigurableEmbeddedServletContainer;
import org.springframework.boot.context.embedded.EmbeddedServletContainerCustomizer;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.web.servlet.config.annotation.ViewControllerRegistry;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurerAdapter;

@Configuration
public class SpringMvcConfig extends WebMvcConfigurerAdapter {

    @Override
    public void addViewControllers(ViewControllerRegistry registry) {
        registry.addViewController("/index").setViewName("index");
        registry.addViewController("/").setViewName("index");
        registry.addViewController("/index.html").setViewName("index");
        registry.addViewController("/index.htm").setViewName("index");
    }

    @Bean
    public EmbeddedServletContainerCustomizer embeddedServletContainerCustomizer() {
        return new EmbeddedServletContainerCustomizer() {
            /**定制嵌入式的Servlet容器的相关规则
             * @param container
             */
            @Override
            public void customize(ConfigurableEmbeddedServletContainer container) {
                container.setPort(8081);
            }
        };
    }   
}

7.1.3 注册Servlet三大组件

package com.sunxiaping.springboot.servet;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class SelfServlet extends HttpServlet {

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        resp.getWriter().println("hello servlet");
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doGet(req, resp);
    }
}

package com.sunxiaping.springboot.config;

import com.sunxiaping.springboot.servet.SelfServlet;
import org.springframework.boot.web.servlet.ServletRegistrationBean;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;

@Configuration
public class ServletConfig {

    /**
     * 注册Servlet,向容器中添加ServletRegistrationBean组件
     * 注册Filter，向容器中添加FilterRegistrationBean组件
     * 注册Listener，向容器中添加ServletListenerRegistrationBean组件
     *
     * @return
     */
    @Bean
    public ServletRegistrationBean servletRegistrationBean() {
        return new ServletRegistrationBean(new SelfServlet(), "/hello");
    }
}

7.2 SpringBoot支持其他的Servlet容器

• SpringBoot默认支持Tomcat、Jetty、Undertow。

• Tomcat(默认支持)：

<dependency>
    <!-- 引入web模块，默认支持Tomcat -->
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
</dependency>

• Jetty：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <groupId>org.springframework.boot</groupId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-jetty</artifactId>
</dependency>

• Undertow：

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-web</artifactId>
    <exclusions>
        <exclusion>
            <artifactId>spring-boot-starter-tomcat</artifactId>
            <groupId>org.springframework.boot</groupId>
        </exclusion>
    </exclusions>
</dependency>
<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-undertow</artifactId>
</dependency>

7.3 嵌入式Servlet容器自动配置原理

• EmbeddedServletContainerAutoConfiguration：嵌入式的Servlet容器自动配置

@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
@Configuration
@ConditionalOnWebApplication
@Import(BeanPostProcessorsRegistrar.class) 
//BeanPostProcessorsRegistrar：给容器中导入一些组件。
//导入了EmbeddedServletContainerCustomizerBeanPostProcessor
//后置处理器：Bean初始化前后（创建完对象，还没赋值）执行初始化工作。
public class EmbeddedServletContainerAutoConfiguration {
    
	@Configuration
	@ConditionalOnClass({ Servlet.class, Tomcat.class }) //判断当前是否引入了Tomcat的依赖
	@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)//判断当前容器没有用户自己定义的EmbeddedServletContainerFactory：嵌入式的Servlet容器工厂；作用是创建嵌入式的Servlet容器
	public static class EmbeddedTomcat {

		@Bean
		public TomcatEmbeddedServletContainerFactory tomcatEmbeddedServletContainerFactory() {
			return new TomcatEmbeddedServletContainerFactory();
		}

	}
    
    /**
	 * Nested configuration if Jetty is being used.
	 */
	@Configuration
	@ConditionalOnClass({ Servlet.class, Server.class, Loader.class,
			WebAppContext.class })
	@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
	public static class EmbeddedJetty {

		@Bean
		public JettyEmbeddedServletContainerFactory jettyEmbeddedServletContainerFactory() {
			return new JettyEmbeddedServletContainerFactory();
		}

	}

	/**
	 * Nested configuration if Undertow is being used.
	 */
	@Configuration
	@ConditionalOnClass({ Servlet.class, Undertow.class, SslClientAuthMode.class })
	@ConditionalOnMissingBean(value = EmbeddedServletContainerFactory.class, search = SearchStrategy.CURRENT)
	public static class EmbeddedUndertow {

		@Bean
		public UndertowEmbeddedServletContainerFactory undertowEmbeddedServletContainerFactory() {
			return new UndertowEmbeddedServletContainerFactory();
		}

	}
    //略
    
}    

• EmbeddedServletContainerFactory：嵌入式的Servlet容器工厂

public interface EmbeddedServletContainerFactory {

	/**
	 * 获取的嵌入式的Servlet容器
	 */
	EmbeddedServletContainer getEmbeddedServletContainer(
			ServletContextInitializer... initializers);

}

• EmbeddedServletContainer：嵌入式的Servlet容器。

public interface EmbeddedServletContainer {

	/**
	 * Starts the embedded servlet container. Calling this method on an already started
	 * container has no effect.
	 * @throws EmbeddedServletContainerException if the container cannot be started
	 */
	void start() throws EmbeddedServletContainerException;

	/**
	 * Stops the embedded servlet container. Calling this method on an already stopped
	 * container has no effect.
	 * @throws EmbeddedServletContainerException if the container cannot be stopped
	 */
	void stop() throws EmbeddedServletContainerException;

	/**
	 * Return the port this server is listening on.
	 * @return the port (or -1 if none)
	 */
	int getPort();

}

• 以TomcatEmbeddedServletContainerFactory为例：

public class TomcatEmbeddedServletContainerFactory
		extends AbstractEmbeddedServletContainerFactory implements ResourceLoaderAware {
   	@Override
	public EmbeddedServletContainer getEmbeddedServletContainer(
			ServletContextInitializer... initializers) {
         //创建一个Tomcat
		Tomcat tomcat = new Tomcat();
         //配置TOmcat的基本环境
		File baseDir = (this.baseDirectory != null ? this.baseDirectory
				: createTempDir("tomcat"));
		tomcat.setBaseDir(baseDir.getAbsolutePath());
		Connector connector = new Connector(this.protocol);
		tomcat.getService().addConnector(connector);
		customizeConnector(connector);
		tomcat.setConnector(connector);
		tomcat.getHost().setAutoDeploy(false);
		configureEngine(tomcat.getEngine());
		for (Connector additionalConnector : this.additionalTomcatConnectors) {
			tomcat.getService().addConnector(additionalConnector);
		}
		prepareContext(tomcat.getHost(), initializers);
         //将配置好的Tomcat传入进去，返回一个嵌入式的Servlet容器，并且启动Tomcat服务器
		return getTomcatEmbeddedServletContainer(tomcat);
	}
    
    protected TomcatEmbeddedServletContainer getTomcatEmbeddedServletContainer(
			Tomcat tomcat) {
		return new TomcatEmbeddedServletContainer(tomcat, getPort() >= 0);
	}
    
    public TomcatEmbeddedServletContainer(Tomcat tomcat, boolean autoStart) {
		Assert.notNull(tomcat, "Tomcat Server must not be null");
		this.tomcat = tomcat;
		this.autoStart = autoStart;
		initialize();
	}
    private void initialize() throws EmbeddedServletContainerException {
		TomcatEmbeddedServletContainer.logger
				.info("Tomcat initialized with port(s): " + getPortsDescription(false));
		synchronized (this.monitor) {
			try {
				addInstanceIdToEngineName();
				try {
					// Remove service connectors to that protocol binding doesn't happen
					// yet
					removeServiceConnectors();

					// 启动Tomcat
					this.tomcat.start();

					// We can re-throw failure exception directly in the main thread
					rethrowDeferredStartupExceptions();

					Context context = findContext();
					try {
						ContextBindings.bindClassLoader(context, getNamingToken(context),
								getClass().getClassLoader());
					}
					catch (NamingException ex) {
						// Naming is not enabled. Continue
					}

					// Unlike Jetty, all Tomcat threads are daemon threads. We create a
					// blocking non-daemon to stop immediate shutdown
					startDaemonAwaitThread();
				}
				catch (Exception ex) {
					containerCounter.decrementAndGet();
					throw ex;
				}
			}
			catch (Exception ex) {
				throw new EmbeddedServletContainerException(
						"Unable to start embedded Tomcat", ex);
			}
		}
	}
    //略
}    

• 我们对嵌入式容器的配置修改是怎么修改的？

  • 1️⃣ServerProperties。ServerProperties其实是EmbeddedServletContainerCustomizer的子类。
  • 2️⃣EmbeddedServletContainerCustomizer：定制器帮我们修改了Servlet容器的配置。

• 容器中导入了EmbeddedServletContainerCustomizerBeanPostProcessor：

public class EmbeddedServletContainerCustomizerBeanPostProcessor
		implements BeanPostProcessor, BeanFactoryAware {
    //在初始化之前
 	@Override
	public Object postProcessBeforeInitialization(Object bean, String beanName)
			throws BeansException {
         //如果当前初始化的是一个ConfigurableEmbeddedServletContainer类型的组件
		if (bean instanceof ConfigurableEmbeddedServletContainer) {
             //EmbeddedServletContainerCustomizer定制器，调用每个定制器的customize方法，来给Servlet容器进行属性赋值
			postProcessBeforeInitialization((ConfigurableEmbeddedServletContainer) bean);
		}
		return bean;
	}
    @Override
	public Object postProcessAfterInitialization(Object bean, String beanName)
			throws BeansException {
		return bean;
	}

	private void postProcessBeforeInitialization(
			ConfigurableEmbeddedServletContainer bean) {
		for (EmbeddedServletContainerCustomizer customizer : getCustomizers()) {
			customizer.customize(bean);
		}
	}
    private Collection<EmbeddedServletContainerCustomizer> getCustomizers() {
		if (this.customizers == null) {
			// Look up does not include the parent context
			this.customizers = new ArrayList<EmbeddedServletContainerCustomizer>(
					this.beanFactory
                               //从容器中获取所有EmbeddedServletContainerCustomizer类型的组件
                               //所以定制容器，可以给容器中配置EmbeddedServletContainerCustomizer类型的组件
							.getBeansOfType(EmbeddedServletContainerCustomizer.class,
									false, false)
							.values());
			Collections.sort(this.customizers, AnnotationAwareOrderComparator.INSTANCE);
			this.customizers = Collections.unmodifiableList(this.customizers);
		}
		return this.customizers;
	}
    //其他略
    
}    

总结：

• 1️⃣SpringBoot根据导入的依赖情况，给容器中添加相应的EmbeddedServletContainerFactory（以TomcatEmbeddedServletContainerFactory为例）。
• 2️⃣容器中某个组件要创建对象就会惊动后置处理器（EmbeddedServletContainerCustomizerBeanPostProcessor），是因为EmbeddedServletContainerAutoConfiguration中使用@Import注解，导入了BeanPostProcessorsRegistrar，而BeanPostProcessorsRegistrar是一个ImportBeanDefinitionRegistrar，向容器中导入了EmbeddedServletContainerCustomizerBeanPostProcessor，简而言之，只要是嵌入式的Servlet容器工厂，后置处理器就工作。
• 3️⃣后置处理器，从容器中获取所有的EmbeddedServletContainerCustomizer，调用定制器的customize（ServerProperties其实就是EmbeddedServletContainerCustomizer）。

7.4 嵌入式Servlet容器启动原理

• 1️⃣SpringBoot应用启动运行run方法。
• 2️⃣refreshContext(context)；SpringBoot刷新IOC容器（创建IOC容器，并初始化容器，创建容器中的每一个组件）；如果是Web应用，创建的是AnnotationConfigEmbeddedWebApplicationContext；如果不是web应用，创建的是ConfigurableWebApplicationContext。
• 3️⃣refresh(context);刷新刚才创建好的web容器。

@Override
public void refresh() throws BeansException, IllegalStateException {
    synchronized (this.startupShutdownMonitor) {
        // Prepare this context for refreshing.
        prepareRefresh();

        // Tell the subclass to refresh the internal bean factory.
        ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

        // Prepare the bean factory for use in this context.
        prepareBeanFactory(beanFactory);

        try {
            // Allows post-processing of the bean factory in context subclasses.
            postProcessBeanFactory(beanFactory);

            // Invoke factory processors registered as beans in the context.
            invokeBeanFactoryPostProcessors(beanFactory);

            // Register bean processors that intercept bean creation.
            registerBeanPostProcessors(beanFactory);

            // Initialize message source for this context.
            initMessageSource();

            // Initialize event multicaster for this context.
            initApplicationEventMulticaster();

            // 刷新容器
            onRefresh();

            // Check for listener beans and register them.
            registerListeners();

            // Instantiate all remaining (non-lazy-init) singletons.
            finishBeanFactoryInitialization(beanFactory);

            // Last step: publish corresponding event.
            finishRefresh();
        }

        catch (BeansException ex) {
            if (logger.isWarnEnabled()) {
                logger.warn("Exception encountered during context initialization - " +
                            "cancelling refresh attempt: " + ex);
            }

            // Destroy already created singletons to avoid dangling resources.
            destroyBeans();

            // Reset 'active' flag.
            cancelRefresh(ex);

            // Propagate exception to caller.
            throw ex;
        }

        finally {
            // Reset common introspection caches in Spring's core, since we
            // might not ever need metadata for singleton beans anymore...
            resetCommonCaches();
        }
    }
}

• 4️⃣onRefresh();web的IOC容器重写了onRefresh方法。
• 5️⃣web的IOC容器会创建嵌入式的Servlet容器。

public class EmbeddedWebApplicationContext extends GenericWebApplicationContext {
    
    @Override
	protected void onRefresh() {
		super.onRefresh();
		try {
            //创建嵌入式的Servlet容器
			createEmbeddedServletContainer();
		}
		catch (Throwable ex) {
			throw new ApplicationContextException("Unable to start embedded container",
					ex);
		}
	}
    
    private void createEmbeddedServletContainer() {
		EmbeddedServletContainer localContainer = this.embeddedServletContainer;
		ServletContext localServletContext = getServletContext();
		if (localContainer == null && localServletContext == null) {
            //获取嵌入式的Servlet容器工厂
             //从IOC容器中获取EmbeddedServletContainerFactory组件。TomcatEmbeddedServletContainerFactory创建对象，后置处理器一看是这个对象，就获取所有的定制器来先定制Servlet容器的相关配置
			EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
			this.embeddedServletContainer = containerFactory
					.getEmbeddedServletContainer(getSelfInitializer());
		}
		else if (localServletContext != null) {
			try {
				getSelfInitializer().onStartup(localServletContext);
			}
			catch (ServletException ex) {
				throw new ApplicationContextException("Cannot initialize servlet context",
						ex);
			}
		}
		initPropertySources();
	}
    //其他略
    
}    

• 6️⃣获取嵌入式的Servlet容器工厂：

public class EmbeddedWebApplicationContext extends GenericWebApplicationContext {
    
    @Override
	protected void onRefresh() {
		super.onRefresh();
		try {
            //创建嵌入式的Servlet容器
			createEmbeddedServletContainer();
		}
		catch (Throwable ex) {
			throw new ApplicationContextException("Unable to start embedded container",
					ex);
		}
	}
    
    private void createEmbeddedServletContainer() {
		EmbeddedServletContainer localContainer = this.embeddedServletContainer;
		ServletContext localServletContext = getServletContext();
		if (localContainer == null && localServletContext == null) {
            //获取嵌入式的Servlet容器工厂
             //从IOC容器中获取EmbeddedServletContainerFactory组件。TomcatEmbeddedServletContainerFactory创建对象，后置处理器一看是这个对象，就获取所有的定制器来先定制Servlet容器的相关配置
			EmbeddedServletContainerFactory containerFactory = getEmbeddedServletContainerFactory();
			this.embeddedServletContainer = containerFactory
					.getEmbeddedServletContainer(getSelfInitializer());
		}
		else if (localServletContext != null) {
			try {
				getSelfInitializer().onStartup(localServletContext);
			}
			catch (ServletException ex) {
				throw new ApplicationContextException("Cannot initialize servlet context",
						ex);
			}
		}
		initPropertySources();
	}
    //其他略
    
}    

• 7️⃣使用容器工厂获取嵌入式的Servlet容器：this.embeddedServletContainer = containerFactory.getEmbeddedServletContainer(getSelfInitializer());
• 8️⃣嵌入式的Servlet容器创建对象并启动Servlet容器。