SpringMVC源码解析(一)：web容器启动流程

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 
         	http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.xc.mvc</groupId>
    <artifactId>springmvc</artifactId>
    <version>1.0-SNAPSHOT</version>

    <packaging>war</packaging>

    <dependencies>
        <!-- SpringMVC -->
        <dependency>
            <groupId>org.springframework</groupId>
            <artifactId>spring-webmvc</artifactId>
            <version>5.3.27</version>
        </dependency>

        <!-- ServletAPI -->
        <dependency>
            <groupId>javax.servlet</groupId>
            <artifactId>javax.servlet-api</artifactId>
            <version>3.1.0</version>
            <scope>provided</scope>
        </dependency>

        <!-- Jackson -->
        <dependency>
            <groupId>com.fasterxml.jackson.core</groupId>
            <artifactId>jackson-databind</artifactId>
            <version>2.12.1</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <configuration>
                    <!--配置Maven中Java的编译版本 -->
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

/**
 * web工程的初始化类，用来代替web.xml
 * 以下配置的都是以前在web.xml中配置的
 */
public class WebAppInitializer extends AbstractAnnotationConfigDispatcherServletInitializer {
    /**
     * Spring的配置，目前不涉及Spring，这里设置为空
     */
    @Override
    protected Class<?>[] getRootConfigClasses() {
        return new Class<?>[0];
    }

    /**
     * SpringMVC的配置
     */
    @Override
    protected Class<?>[] getServletConfigClasses() {
        return new Class<?>[]{SpringMVCConfig.class};
    }

    /**
     * 用于配置DispatcherServlet的映射路径
     */
    @Override
    protected String[] getServletMappings() {
        return new String[]{"/"};
    }

    /**
     * 注册过滤器
     */
    @Override
    protected Filter[] getServletFilters() {
        // 字符编码过滤器
        CharacterEncodingFilter characterEncodingFilter = new CharacterEncodingFilter();
        characterEncodingFilter.setEncoding("UTF-8");
        characterEncodingFilter.setForceEncoding(true);
        // HiddenHttpMethodFilter 用于支持 PUT、DELETE 等 HTTP 请求
        HiddenHttpMethodFilter hiddenHttpMethodFilter = new HiddenHttpMethodFilter();
        return new Filter[]{characterEncodingFilter, hiddenHttpMethodFilter};
    }
}

// 将当前类标识为一个配置类
@Configuration
// 仅仅扫描@Controller、@RestController
@ComponentScan(
        value = "com.xc",
        includeFilters = {@ComponentScan.Filter(
                type = FilterType.ANNOTATION,
                classes = {Controller.class, RestController.class}
        )},
        // 默认扫描 @Component @Repository, @Service, or @Controller
        useDefaultFilters = false 
)
// mvc注解驱动
@EnableWebMvc
public class SpringMVCConfig implements WebMvcConfigurer {
    // 拦截器
    @Override
    public void addInterceptors(InterceptorRegistry registry) {
        MyInterceptor myInterceptor = new MyInterceptor();
        registry.addInterceptor(myInterceptor).addPathPatterns("/**");
    }
}

public class MyInterceptor implements HandlerInterceptor {
    @Override
    public boolean preHandle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception {
        System.out.println("处理器方法前调用");
        return true;
    }

    @Override
    public void postHandle(HttpServletRequest request, HttpServletResponse response, Object handler, ModelAndView modelAndView) throws Exception {
        System.out.println("处理器方法后调用");
    }

    @Override
    public void afterCompletion(HttpServletRequest request, HttpServletResponse response, Object handler, Exception ex) throws Exception {
        System.out.println("渲染完成后调用");
    }
}

// 接受User对象修改并返回
@PostMapping("/test")
@ResponseBody
public User test(@RequestBody User user) {
    // 修改名字为李四然后返回给前台
    user.setName("李四");
    System.out.println(user);
    return user;
}

// SpringServletContainerInitializer类
@HandlesTypes(WebApplicationInitializer.class)
public class SpringServletContainerInitializer implements ServletContainerInitializer {
	@Override
	public void onStartup(@Nullable Set<Class<?>> webAppInitializerClasses, ServletContext servletContext)
			throws ServletException {

		List<WebApplicationInitializer> initializers = Collections.emptyList();
		
		// 如果找不到WebApplicationInitializer的实现类，webAppInitializerClasses就为null
		if (webAppInitializerClasses != null) {
			initializers = new ArrayList<>(webAppInitializerClasses.size());
			for (Class<?> waiClass : webAppInitializerClasses) {
				// 判断实现类不是接口抽象类，即正常的接口实现类
				if (!waiClass.isInterface() && !Modifier.isAbstract(waiClass.getModifiers()) &&
						WebApplicationInitializer.class.isAssignableFrom(waiClass)) {
					try {
						// 反射创建对象，并添加到集合中，后面统一遍历调用onStartup方法
						initializers.add((WebApplicationInitializer)
								ReflectionUtils.accessibleConstructor(waiClass).newInstance());
					}
					catch (Throwable ex) {
						throw new ServletException("Failed to instantiate WebApplicationInitializer class", ex);
					}
				}
			}
		}
		
		// 集合为空，证明没找到实现类，直接返回
		if (initializers.isEmpty()) {
			servletContext.log("No Spring WebApplicationInitializer types detected on classpath");
			return;
		}
		
		// 排序，证明WebApplicationInitializer的实现类有先后顺序
		AnnotationAwareOrderComparator.sort(initializers);
		for (WebApplicationInitializer initializer : initializers) {
			// 调用WebApplicationInitializer接口实现类的onStartup方法
			initializer.onStartup(servletContext);
		}
	}
}

// WebApplicationInitializer接口
public interface WebApplicationInitializer {
	/**
	 * 初始化此Web应用程序所需的任何Servlet、过滤器、侦听器上下文参数和属性配置给定的ServletContext
	 */
	void onStartup(ServletContext servletContext) throws ServletException;
}

// AbstractDispatcherServletInitializer类的方法
protected void registerDispatcherServlet(ServletContext servletContext) {
	// 获取servlet名称,常量“dispatcher”
	String servletName = getServletName();
	// 创建一个web应用程序子容器
	WebApplicationContext servletAppContext = createServletApplicationContext();
	// 创建DispatcherServlet对象，将上下文设置到dispatcherServlet中
	FrameworkServlet dispatcherServlet = createDispatcherServlet(servletAppContext);
	// 设置servlet容器初始化参数（这里不设置一般默认为null）
 	dispatcherServlet.setContextInitializers(getServletApplicationContextInitializers());
	// 把servlet添加到Tomcat容器中
	ServletRegistration.Dynamic registration = servletContext.addServlet(servletName, dispatcherServlet);
	if (registration == null) {
		throw new IllegalStateException("Failed to register servlet with name '" + servletName + "'. " +
				"Check if there is another servlet registered under the same name.");
	}
	// 将前端控制器初始化提前到服务器启动时，否则调用时才会初始化
	registration.setLoadOnStartup(1);
	// 添加servlet映射，拦截请求
	// 调用自定义配置类重写的getServletMappings方法
	registration.addMapping(getServletMappings());
	// 设置是否支持异步，默认true
	registration.setAsyncSupported(isAsyncSupported());
	
	// 获取所有的过滤器getServletFilters方法
	// 调用自定义配置类重写的getServletMappings方法
	Filter[] filters = getServletFilters();
	if (!ObjectUtils.isEmpty(filters)) {
		for (Filter filter : filters) {
			registerServletFilter(servletContext, filter);
		}
	}
	// 空方法，可以再对dispatcherServlet进行处理
	customizeRegistration(registration);
}

// AbstractAnnotationConfigDispatcherServletInitializer类方法
protected WebApplicationContext createServletApplicationContext() {
	AnnotationConfigWebApplicationContext context = new AnnotationConfigWebApplicationContext();
	// 调用自定义配置类的设置子容器配置文件的方法
	Class<?>[] configClasses = getServletConfigClasses();
	if (!ObjectUtils.isEmpty(configClasses)) {
		context.register(configClasses);
	}
	return context;
}

// AbstractDispatcherServletInitializer类方法
protected FrameworkServlet createDispatcherServlet(WebApplicationContext servletAppContext) {
	return new DispatcherServlet(servletAppContext);
}

protected FilterRegistration.Dynamic registerServletFilter(ServletContext servletContext, Filter filter) {
	String filterName = Conventions.getVariableName(filter);
	Dynamic registration = servletContext.addFilter(filterName, filter);

	...

	registration.setAsyncSupported(isAsyncSupported());
	registration.addMappingForServletNames(getDispatcherTypes(), false, getServletName());
	return registration;
}

public interface WebMvcConfigurer {
	...
	
	// 配置拦截器
	default void addInterceptors(InterceptorRegistry registry) {
	}

	// 配置跨域
	default void addCorsMappings(CorsRegistry registry) {
	}

	// 配置视图解析器
	default void configureViewResolvers(ViewResolverRegistry registry) {
	}
	
	// 配置方法参数解析器（解析@RequestBody就是通过HandlerMethodArgumentResolver接口实现的）
	default void addArgumentResolvers(List<HandlerMethodArgumentResolver> resolvers) {
	}

	// 配置方法返回值（解析@ResponseBody就是通过HandlerMethodReturnValueHandler接口实现的）
	default void addReturnValueHandlers(List<HandlerMethodReturnValueHandler> handlers) {
	}

	// 配置消息转换器（此时可能还没有转换器）
	default void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
	}
	
	// 扩展消息转换器（至少已存在默认转换器）
	default void extendMessageConverters(List<HttpMessageConverter<?>> converters) {
	}

	// 配置异常处理器
	default void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> resolvers) {
	}
	
	...
}

@Configuration(proxyBeanMethods = false)
public class DelegatingWebMvcConfiguration extends WebMvcConfigurationSupport {
	// WebMvcConfigurerComposite实现WebMvcConfigurer，内部有个WebMvcConfigurer集合
	private final WebMvcConfigurerComposite configurers = new WebMvcConfigurerComposite();

	// 注入一组WebMvcConfigurer，这些WebMvcConfigurer由开发人员提供，或者框架其他部分提供
	@Autowired(required = false)
	public void setConfigurers(List<WebMvcConfigurer> configurers) {
		if (!CollectionUtils.isEmpty(configurers)) {
			this.configurers.addWebMvcConfigurers(configurers);
		}
	}
	
	...
	
	// 如下方法都是重写父类WebMvcConfigurationSupport
	// 与WebMvcConfigurer接口中的方法一样，配置拦截器、跨域配置等
	@Override
	protected void configureDefaultServletHandling(DefaultServletHandlerConfigurer configurer) {
		this.configurers.configureDefaultServletHandling(configurer);
	}

	@Override
	protected void addInterceptors(InterceptorRegistry registry) {
		this.configurers.addInterceptors(registry);
	}

	@Override
	protected void addCorsMappings(CorsRegistry registry) {
		this.configurers.addCorsMappings(registry);
	}

	@Override
	protected void configureViewResolvers(ViewResolverRegistry registry) {
		this.configurers.configureViewResolvers(registry);
	}

	@Override
	protected void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
		this.configurers.configureMessageConverters(converters);
	}

	@Override
	protected void configureHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers) {
		this.configurers.configureHandlerExceptionResolvers(exceptionResolvers);
	}

	...
}

// WebMvcConfigurerComposite类
class WebMvcConfigurerComposite implements WebMvcConfigurer {
	private final List<WebMvcConfigurer> delegates = new ArrayList<>();
	
	@Override
	public void addInterceptors(InterceptorRegistry registry) {
		for (WebMvcConfigurer delegate : this.delegates) {
			delegate.addInterceptors(registry);
		}
	}
	@Override
	public void addCorsMappings(CorsRegistry registry) {
		for (WebMvcConfigurer delegate : this.delegates) {
			delegate.addCorsMappings(registry);
		}
	}
	@Override
	public void configureViewResolvers(ViewResolverRegistry registry) {
		for (WebMvcConfigurer delegate : this.delegates) {
			delegate.configureViewResolvers(registry);
		}
	}
	@Override
	public void configureMessageConverters(List<HttpMessageConverter<?>> converters) {
		for (WebMvcConfigurer delegate : this.delegates) {
			delegate.configureMessageConverters(converters);
		}
	}
}

public interface HandlerMapping {
	/**
	 * 获取执行器链（包括Handler和拦截器）
	 */
	@Nullable
	HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception;
}

public interface HandlerAdapter {

	/**
	 * 因为有多个HandlerMapping和HandlerAdapter
	 * 对于HandlerAdapter是否支持对应的HandlerMapping，通过此方法判断
	 */
	boolean supports(Object handler);

	/**
	 * 具体调用Hangder的方法
	 */
	@Nullable
	ModelAndView handle(HttpServletRequest request, HttpServletResponse response, Object handler) throws Exception;
}

// WebMvcConfigurationSupport类方法
@Bean
@SuppressWarnings("deprecation")
public RequestMappingHandlerMapping requestMappingHandlerMapping(
		@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,
		@Qualifier("mvcConversionService") FormattingConversionService conversionService,
		@Qualifier("mvcResourceUrlProvider") ResourceUrlProvider resourceUrlProvider) {
	// 创建RequestMappingHandlerMapping对象
	RequestMappingHandlerMapping mapping = createRequestMappingHandlerMapping();
	// 设置排序为0，以后会遍历所有HandlerMapping，排序0的话，则会先遍历
	// 简单说@RequestMaping注解使用概率大，先用RequestMappingHandlerMapping处理
	mapping.setOrder(0);
	// 设置所有的拦截器，并排序
	mapping.setInterceptors(getInterceptors(conversionService, resourceUrlProvider));
	mapping.setContentNegotiationManager(contentNegotiationManager);
	// 设置所有的跨域配置
	mapping.setCorsConfigurations(getCorsConfigurations());

	// 省略各种匹配url的属性，如url正则匹配等等，我们这次只考虑url正常匹配
	...

	return mapping;
}

// WebMvcConfigurationSupport
protected final Object[] getInterceptors(
		FormattingConversionService mvcConversionService,
		ResourceUrlProvider mvcResourceUrlProvider) {

	if (this.interceptors == null) {
		InterceptorRegistry registry = new InterceptorRegistry();
		// 这里就是调用DelegatingWebMvcConfiguration重写的方法
		addInterceptors(registry);
		// 这是两个设置setAttribute值的拦截器，不用深入研究
		registry.addInterceptor(new ConversionServiceExposingInterceptor(mvcConversionService));
		registry.addInterceptor(new ResourceUrlProviderExposingInterceptor(mvcResourceUrlProvider));
		// 这里会将上面我们自己设置的拦截器包装一层返回
		this.interceptors = registry.getInterceptors();
	}
	return this.interceptors.toArray();
}

// WebMvcConfigurationSupport
protected final Map<String, CorsConfiguration> getCorsConfigurations() {
	if (this.corsConfigurations == null) {
		CorsRegistry registry = new CorsRegistry();
		addCorsMappings(registry);
		this.corsConfigurations = registry.getCorsConfigurations();
	}
	return this.corsConfigurations;
}

// RequestMappingHandlerMapping类方法
@Override
@SuppressWarnings("deprecation")
public void afterPropertiesSet() {
	// 创建RequestMappingInfo对象
	this.config = new RequestMappingInfo.BuilderConfiguration();
	this.config.setTrailingSlashMatch(useTrailingSlashMatch());
	this.config.setContentNegotiationManager(getContentNegotiationManager());

	if (getPatternParser() != null) {
		this.config.setPatternParser(getPatternParser());
		Assert.isTrue(!this.useSuffixPatternMatch && !this.useRegisteredSuffixPatternMatch,
				"Suffix pattern matching not supported with PathPatternParser.");
	}
	else {
		this.config.setSuffixPatternMatch(useSuffixPatternMatch());
		this.config.setRegisteredSuffixPatternMatch(useRegisteredSuffixPatternMatch());
		this.config.setPathMatcher(getPathMatcher());
	}
	// 调用父类实现的afterPropertiesSet方法
	super.afterPropertiesSet();
}

// AbstractHandlerMethodMapping类方法

/**
 * 在初始化时检测处理程序方法
 */
@Override
public void afterPropertiesSet() {
	initHandlerMethods();
}

/**
 * 扫描 ApplicationContext 中的 Bean，检测并注册处理程序方法
 */
protected void initHandlerMethods() {
	// 获取所有的bean对象并遍历
	for (String beanName : getCandidateBeanNames()) {
		if (!beanName.startsWith(SCOPED_TARGET_NAME_PREFIX)) {
			// 筛选候选的bean
			processCandidateBean(beanName);
		}
	}
	// getHandlerMethods()获取请求路径与具体Controller方法的映射关系
	handlerMethodsInitialized(getHandlerMethods());
}

// AbstractHandlerMethodMapping类方法
protected void processCandidateBean(String beanName) {
	Class<?> beanType = null;
	try {
		// 获取bean对象的Class类型
		beanType = obtainApplicationContext().getType(beanName);
	}
	catch (Throwable ex) {
		...
	}
	// 判断是否处理程序
	if (beanType != null && isHandler(beanType)) {
		// 查找处理程序的方法
		detectHandlerMethods(beanName);
	}
}

// RequestMappingHandlerMapping
@Override
protected boolean isHandler(Class<?> beanType) {
	return (AnnotatedElementUtils.hasAnnotation(beanType, Controller.class) ||
			AnnotatedElementUtils.hasAnnotation(beanType, RequestMapping.class));
}

// AbstractHandlerMethodMapping类方法
protected void detectHandlerMethods(Object handler) {
	Class<?> handlerType = (handler instanceof String ?
			obtainApplicationContext().getType((String) handler) : handler.getClass());

	if (handlerType != null) {
		// 类如果被代理，获取真正的类型
		Class<?> userType = ClassUtils.getUserClass(handlerType);
		Map<Method, T> methods = MethodIntrospector.selectMethods(userType,
				(MethodIntrospector.MetadataLookup<T>) method -> {
					try {
						return getMappingForMethod(method, userType);
					}
					catch (Throwable ex) {
						...
					}
				});
		...		
		
		// 注册Handler方法（将请求路径、RequestMappingInfo、Controller#Method统一放一起）
		methods.forEach((method, mapping) -> {
			Method invocableMethod = AopUtils.selectInvocableMethod(method, userType);
			registerHandlerMethod(handler, invocableMethod, mapping);
		});
	}
}
// RequestMappingHandlerMapping类方法
@Override
@Nullable
protected RequestMappingInfo getMappingForMethod(Method method, Class<?> handlerType) {
	RequestMappingInfo info = createRequestMappingInfo(method);
	...
	return info;
}

// AbstractHandlerMethodMapping的内部类MappingRegistry类方法
class MappingRegistry {

	private final Map<T, MappingRegistration<T>> registry = new HashMap<>();
	private final MultiValueMap<String, T> pathLookup = new LinkedMultiValueMap<>();
	private final Map<HandlerMethod, CorsConfiguration> corsLookup = new ConcurrentHashMap<>();
		
	public void register(T mapping, Object handler, Method method) {
		this.readWriteLock.writeLock().lock();
		try {
			// handler(Controller对象)与有@RequestMapping的Method组成对象HandlerMethod
			HandlerMethod handlerMethod = createHandlerMethod(handler, method);
			// 校验@RequestMapping注解内容是否注册过
			validateMethodMapping(handlerMethod, mapping);
			
			// 获取@RequestMapping注解映射的路径，因为可以设置多个，所以这里是集合
			Set<String> directPaths = AbstractHandlerMethodMapping.this.getDirectPaths(mapping);
			for (String path : directPaths) {
				this.pathLookup.add(path, mapping);
			}
	
			...
			
			// 获取@CrossOrigin获取CorsConfiguration，并初始化跨域的默认值，最后跨域配置添加到corsLookup
			CorsConfiguration corsConfig = initCorsConfiguration(handler, method, mapping);
			if (corsConfig != null) {
				corsConfig.validateAllowCredentials();
				this.corsLookup.put(handlerMethod, corsConfig);
			}
			
			// 各类属性配置组成对象MappingRegistration，然后添加到registry中
			this.registry.put(mapping,
					new MappingRegistration<>(mapping, handlerMethod, directPaths, name, corsConfig != null));
		}
		finally {
			this.readWriteLock.writeLock().unlock();
		}
	}
}

// AbstractHandlerMethodMapping类方法
public Map<T, HandlerMethod> getHandlerMethods() {
	this.mappingRegistry.acquireReadLock();
	try {
		return Collections.unmodifiableMap(
				this.mappingRegistry.getRegistrations().entrySet()
				.stream().collect(Collectors.toMap(
					Map.Entry::getKey, 
					entry -> entry.getValue().handlerMethod)
				));
	}
	finally {
		this.mappingRegistry.releaseReadLock();
	}
}

protected void handlerMethodsInitialized(Map<T, HandlerMethod> handlerMethods) {
	// 获取到上面拿到的值，打印数量
	int total = handlerMethods.size();
	if ((logger.isTraceEnabled() && total == 0) || (logger.isDebugEnabled() && total > 0) ) {
		logger.debug(total + " mappings in " + formatMappingName());
	}
}

// WebMvcConfigurationSupport类方法

private static final boolean jackson2Present;
// 加载对应的类，能加载成功方true，不能加载成功，表示没有这个类，没有导入包，返回false
jackson2Present = ClassUtils.isPresent("com.fasterxml.jackson.databind.ObjectMapper", classLoader) &&
				ClassUtils.isPresent("com.fasterxml.jackson.core.JsonGenerator", classLoader);


@Bean
public RequestMappingHandlerAdapter requestMappingHandlerAdapter(
		@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager,
		@Qualifier("mvcConversionService") FormattingConversionService conversionService,
		@Qualifier("mvcValidator") Validator validator) {
	// 创建RequestMappingHandlerAdapter对象
	RequestMappingHandlerAdapter adapter = createRequestMappingHandlerAdapter();
	adapter.setContentNegotiationManager(contentNegotiationManager);
	// 设置消息转换器
	adapter.setMessageConverters(getMessageConverters());
	adapter.setWebBindingInitializer(getConfigurableWebBindingInitializer(conversionService, validator));
	adapter.setCustomArgumentResolvers(getArgumentResolvers());
	adapter.setCustomReturnValueHandlers(getReturnValueHandlers());
	
	// 如果导入Jackson包，则添加
	if (jackson2Present) {
		// 处理jackson中的@JsonView的字段，过滤输出的字段，具体实现以后单独讲
		adapter.setRequestBodyAdvice(Collections.singletonList(new JsonViewRequestBodyAdvice()));
		adapter.setResponseBodyAdvice(Collections.singletonList(new JsonViewResponseBodyAdvice()));
	}

	// 省略异步配置，以后再研究
	...

	return adapter;
}

// WebMvcConfigurationSupport
protected final List<HttpMessageConverter<?>> getMessageConverters() {
	if (this.messageConverters == null) {
		this.messageConverters = new ArrayList<>();
		// 这里就是调用DelegatingWebMvcConfiguration重写的方法，配置消息转换器
		configureMessageConverters(this.messageConverters);
		if (this.messageConverters.isEmpty()) {
			// 如果上面没有添加消息转换器，这里添加默认的消息转换器
			addDefaultHttpMessageConverters(this.messageConverters);
		}
		// 这里就是调用DelegatingWebMvcConfiguration重写的方法，扩展消息转化器
		extendMessageConverters(this.messageConverters);
	}
	return this.messageConverters;
}

// WebMvcConfigurationSupport类方法
protected final void addDefaultHttpMessageConverters(List<HttpMessageConverter<?>> messageConverters) {
	// 默认消息转换器
	messageConverters.add(new ByteArrayHttpMessageConverter());
	messageConverters.add(new StringHttpMessageConverter());
	messageConverters.add(new ResourceHttpMessageConverter());
	messageConverters.add(new ResourceRegionHttpMessageConverter());

	...
	
	// jackson
	if (jackson2Present) {
		Jackson2ObjectMapperBuilder builder = Jackson2ObjectMapperBuilder.json();
		if (this.applicationContext != null) {
			builder.applicationContext(this.applicationContext);
		}
		messageConverters.add(new MappingJackson2HttpMessageConverter(builder.build()));
	}
	// Google Gson 库中的一个核心类，Java对象与JSON 格式字符串进行相互转换
	else if (gsonPresent) {
		messageConverters.add(new GsonHttpMessageConverter());
	}
	// JDK 类库JSON类
	else if (jsonbPresent) {
		messageConverters.add(new JsonbHttpMessageConverter());
	}

	...
}

// RequestMappingHandlerAdapter类方法
@Override
public void afterPropertiesSet() {
	// 初始化@ControllerAdvice
	initControllerAdviceCache();
	
	// 设置默认的方法参数解析器
	if (this.argumentResolvers == null) {
		List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
		this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
	}
	if (this.initBinderArgumentResolvers == null) {
		List<HandlerMethodArgumentResolver> resolvers = getDefaultInitBinderArgumentResolvers();
		this.initBinderArgumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
	}
	// 设置默认的返回值处理器
	if (this.returnValueHandlers == null) {
		List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
		this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
	}
}

// RequestMappingHandlerAdapter类方法
private void initControllerAdviceCache() {
	if (getApplicationContext() == null) {
		return;
	}
	
	// 获取所有@ControllerAdvice注解的bean，创建成ControllerAdviceBean对象的集合
	List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());

	List<Object> requestResponseBodyAdviceBeans = new ArrayList<>();

	for (ControllerAdviceBean adviceBean : adviceBeans) {
		Class<?> beanType = adviceBean.getBeanType();
		if (beanType == null) {
			throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
		}
		
		...		
		
		// 筛选实现RequestBodyAdvice或ResponseBodyAdvice的adviceBean
		if (RequestBodyAdvice.class.isAssignableFrom(beanType) || ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
			requestResponseBodyAdviceBeans.add(adviceBean);
		}
	}

	if (!requestResponseBodyAdviceBeans.isEmpty()) {
		this.requestResponseBodyAdvice.addAll(0, requestResponseBodyAdviceBeans);
	}

	...
}

public static List<ControllerAdviceBean> findAnnotatedBeans(ApplicationContext context) {
	ListableBeanFactory beanFactory = context;
	if (context instanceof ConfigurableApplicationContext) {
		beanFactory = ((ConfigurableApplicationContext) context).getBeanFactory();
	}
	List<ControllerAdviceBean> adviceBeans = new ArrayList<>();
	// 遍历所有的bean对象
	for (String name : BeanFactoryUtils.beanNamesForTypeIncludingAncestors(beanFactory, Object.class)) {
		if (!ScopedProxyUtils.isScopedTarget(name)) {
			// 寻找有@ControllerAdvice注解
			ControllerAdvice controllerAdvice = beanFactory.findAnnotationOnBean(name, ControllerAdvice.class);
			if (controllerAdvice != null) {
				// 创建ControllerAdviceBean对象添加到集合中
				adviceBeans.add(new ControllerAdviceBean(name, beanFactory, controllerAdvice));
			}
		}
	}
	OrderComparator.sort(adviceBeans);
	return adviceBeans;
}

public interface RequestBodyAdvice {
	// 是否支持，自定义判断条件，如包含某个自定义注解等等
	// 该方法返回true时，才会进去下面的beforeBodyRead方法
	boolean supports(MethodParameter methodParameter, Type targetType,
			Class<? extends HttpMessageConverter<?>> converterType);

	// 请求体解析前处理，一般在此方法中对body数据进行修改
	HttpInputMessage beforeBodyRead(HttpInputMessage inputMessage, MethodParameter parameter,
			Type targetType, Class<? extends HttpMessageConverter<?>> converterType) throws IOException;
			
	// 请求体解析后处理，一般直接返回原实例
	Object afterBodyRead(Object body, HttpInputMessage inputMessage, MethodParameter parameter,
			Type targetType, Class<? extends HttpMessageConverter<?>> converterType);

	// 当body为empty时操作(body什么都不传才算，即使{}也不算空)
	@Nullable
	Object handleEmptyBody(@Nullable Object body, HttpInputMessage inputMessage, MethodParameter parameter,
			Type targetType, Class<? extends HttpMessageConverter<?>> converterType);

}

public interface ResponseBodyAdvice<T> {

	// 是否支持，自定义判断条件
	// 该方法返回true时，才会进去下面的 beforeBodyWrite方法
	boolean supports(MethodParameter returnType, Class<? extends HttpMessageConverter<?>> converterType);

	// 响应写入之前调用
	@Nullable
	T beforeBodyWrite(@Nullable T body, MethodParameter returnType, MediaType selectedContentType,
			Class<? extends HttpMessageConverter<?>> selectedConverterType,
			ServerHttpRequest request, ServerHttpResponse response);

}

public interface HandlerMethodArgumentResolver {

	/**
	 * 此解析器是否支持给定的方法参数
	 */
	boolean supportsParameter(MethodParameter parameter);

	/**
	 * 将方法参数解析为给定请求的参数值
	 */
	@Nullable
	Object resolveArgument(MethodParameter parameter, @Nullable ModelAndViewContainer mavContainer,
			NativeWebRequest webRequest, @Nullable WebDataBinderFactory binderFactory) throws Exception;

}

public interface HandlerMethodReturnValueHandler {

	/**
     * 此处理程序是否支持给定的方法返回类型
	 */
	boolean supportsReturnType(MethodParameter returnType);

	/**
	 * 通过向模型添加属性并设置视图或设置
	 */
	void handleReturnValue(@Nullable Object returnValue, MethodParameter returnType,
			ModelAndViewContainer mavContainer, NativeWebRequest webRequest) throws Exception;

}

// WebMvcConfigurationSupport类方法
@Bean
public HandlerExceptionResolver handlerExceptionResolver(
		@Qualifier("mvcContentNegotiationManager") ContentNegotiationManager contentNegotiationManager) {
	// 创建空集合
	List<HandlerExceptionResolver> exceptionResolvers = new ArrayList<>();
	// 这里就是调用DelegatingWebMvcConfiguration重写的方法
	// 其实就是寻找WebMvcConfigurer实现类是否添加异常处理器
	configureHandlerExceptionResolvers(exceptionResolvers);
	if (exceptionResolvers.isEmpty()) {
		addDefaultHandlerExceptionResolvers(exceptionResolvers, contentNegotiationManager);
	}
	// 这里就是调用DelegatingWebMvcConfiguration重写的方法，扩展异常处理器
	extendHandlerExceptionResolvers(exceptionResolvers);
	HandlerExceptionResolverComposite composite = new HandlerExceptionResolverComposite();
	composite.setOrder(0);
	composite.setExceptionResolvers(exceptionResolvers);
	return composite;
}

protected final void addDefaultHandlerExceptionResolvers(List<HandlerExceptionResolver> exceptionResolvers,
		ContentNegotiationManager mvcContentNegotiationManager) {
	// 这个异常处理器内包含所有的自定义异常处理器
	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);
	}
	// 手动调用初始化接口的初始化方法
	exceptionHandlerResolver.afterPropertiesSet();
	exceptionResolvers.add(exceptionHandlerResolver);
	
	// ResponseStatus异常处理器
	ResponseStatusExceptionResolver responseStatusResolver = new ResponseStatusExceptionResolver();
	responseStatusResolver.setMessageSource(this.applicationContext);
	exceptionResolvers.add(responseStatusResolver);
	// 默认异常处理器
	exceptionResolvers.add(new DefaultHandlerExceptionResolver());
}

// ExceptionHandlerExceptionResolver类方法
@Override
public void afterPropertiesSet() {
	// 初始化异常处理增强类
	initExceptionHandlerAdviceCache();

	if (this.argumentResolvers == null) {
		List<HandlerMethodArgumentResolver> resolvers = getDefaultArgumentResolvers();
		this.argumentResolvers = new HandlerMethodArgumentResolverComposite().addResolvers(resolvers);
	}
	if (this.returnValueHandlers == null) {
		List<HandlerMethodReturnValueHandler> handlers = getDefaultReturnValueHandlers();
		this.returnValueHandlers = new HandlerMethodReturnValueHandlerComposite().addHandlers(handlers);
	}
}

// ExceptionHandlerExceptionResolver类方法
private void initExceptionHandlerAdviceCache() {
	if (getApplicationContext() == null) {
		return;
	}
	// 获取所有@ControllerAdvice注解的bean，创建成ControllerAdviceBean，添加到集合中
	List<ControllerAdviceBean> adviceBeans = ControllerAdviceBean.findAnnotatedBeans(getApplicationContext());
	for (ControllerAdviceBean adviceBean : adviceBeans) {
		Class<?> beanType = adviceBean.getBeanType();
		if (beanType == null) {
			throw new IllegalStateException("Unresolvable type for ControllerAdviceBean: " + adviceBean);
		}
		// 筛选方法上@ExceptionHandler注解
		ExceptionHandlerMethodResolver resolver = new ExceptionHandlerMethodResolver(beanType);
		if (resolver.hasExceptionMappings()) {
			this.exceptionHandlerAdviceCache.put(adviceBean, resolver);
		}
		if (ResponseBodyAdvice.class.isAssignableFrom(beanType)) {
			this.responseBodyAdvice.add(adviceBean);
		}
	}
}

// ExceptionHandlerMethodResolver类属性和方法
public static final MethodFilter EXCEPTION_HANDLER_METHODS = method ->
		AnnotatedElementUtils.hasAnnotation(method, ExceptionHandler.class);

public ExceptionHandlerMethodResolver(Class<?> handlerType) {
	for (Method method : MethodIntrospector.selectMethods(handlerType, EXCEPTION_HANDLER_METHODS)) {
		for (Class<? extends Throwable> exceptionType : detectExceptionMappings(method)) {
			addExceptionMapping(exceptionType, method);
		}
	}
}