SpringMVC实现原理及详解

1、Spring mvc介绍

SpringMVC框架是以请求为驱动，围绕Servlet设计，将请求发给控制器，然后通过模型对象，分派器来展示请求结果视图。其中核心类是DispatcherServlet，它是一个Servlet，顶层是实现的Servlet接口。

2、SpringMVC使用

需要在web.xml中配置DispatcherServlet。并且需要配置spring监听器ContextLoaderListener

        <listener>
            <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
        </listener>        
        <servlet>
		<servlet-name>springmvc</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
                <!-- 如果不设置init-param标签，则必须在/WEB-INF/下创建xxx-servlet.xml文件，其中xxx是servlet-name中配置的名称。  -->
                <init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>classpath:spring/springmvc-servlet.xml</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>
	<servlet-mapping>
		<servlet-name>springmvc</servlet-name>
		<url-pattern>/</url-pattern>
	</servlet-mapping>

2.dispatchServlet继承关系

 

 

@Override
	protected void service(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		HttpMethod httpMethod = HttpMethod.resolve(request.getMethod());
		if (httpMethod == HttpMethod.PATCH || httpMethod == null) {
			processRequest(request, response);
		}
		else {
			super.service(request, response);
		}
	}

protected final void processRequest(HttpServletRequest request, HttpServletResponse response)
			throws ServletException, IOException {

		long startTime = System.currentTimeMillis();
		Throwable failureCause = null;

		LocaleContext previousLocaleContext = LocaleContextHolder.getLocaleContext();
		LocaleContext localeContext = buildLocaleContext(request);

		RequestAttributes previousAttributes = RequestContextHolder.getRequestAttributes();
		ServletRequestAttributes requestAttributes = buildRequestAttributes(request, response, previousAttributes);

		WebAsyncManager asyncManager = WebAsyncUtils.getAsyncManager(request);
		asyncManager.registerCallableInterceptor(FrameworkServlet.class.getName(), new RequestBindingInterceptor());
        
        //这里初始化一些上下文
		initContextHolders(request, localeContext, requestAttributes);

		try {
			doService(request, response);
		}
		catch (ServletException | IOException ex) {
			failureCause = ex;
			throw ex;
		}
		catch (Throwable ex) {
			failureCause = ex;
			throw new NestedServletException("Request processing failed", ex);
		}

		finally {
			resetContextHolders(request, previousLocaleContext, previousAttributes);
			if (requestAttributes != null) {
				requestAttributes.requestCompleted();
			}
			logResult(request, response, failureCause, asyncManager);
			publishRequestHandledEvent(request, response, startTime, failureCause);
		}
	}

private void initContextHolders(HttpServletRequest request,
			@Nullable LocaleContext localeContext, @Nullable RequestAttributes requestAttributes) {

		if (localeContext != null) {
			LocaleContextHolder.setLocaleContext(localeContext, this.threadContextInheritable);
		}
		if (requestAttributes != null) {
			RequestContextHolder.setRequestAttributes(requestAttributes, this.threadContextInheritable);
		}
	}

 org.springframework.web.context.request.RequestContextHolder

是一个非常实用的工具类，请求上下文工具，可以用他在任何地方获取请求的属性（请求头信息等等）

@Nullable
public static RequestAttributes getRequestAttributes() {
   RequestAttributes attributes = requestAttributesHolder.get();
   if (attributes == null) {
      attributes = inheritableRequestAttributesHolder.get();
   }
   return attributes;
}

 如果在项目中用到了多线程，那么需要做如下配置

@AutoWired
private  DispatcherServlet dispatchServlet；


@PostInstruct
private void init(){
    dispatchServlet.setThreadContextInheritable(true);
}

或者

// 将RequestAttributes对象设置为子线程共享
ServletRequestAttributes sra = (ServletRequestAttributes) RequestContextHolder.getRequestAttributes();
RequestContextHolder.setRequestAttributes(sra, true);

 

3、SpringMVC运行原理

如图所示：

流程说明：

（1）客户端（浏览器）发送请求，直接请求到DispatcherServlet。

（2）DispatcherServlet根据请求信息调用HandlerMapping，解析请求对应的Handler。

（3）解析到对应的Handler后，开始由HandlerAdapter适配器处理。

（4）HandlerAdapter会根据Handler来调用真正的处理器开处理请求，并处理相应的业务逻辑。

（5）处理器处理完业务后，会返回一个ModelAndView对象，Model是返回的数据对象，View是个逻辑上的View。

（6）ViewResolver会根据逻辑View查找实际的View。

（7）DispaterServlet把返回的Model传给View。

（8）通过View返回给请求者（浏览器）

4、DispatcherServlet详细解析

首先看下源码：

package org.springframework.web.servlet;
 
@SuppressWarnings("serial")
public class DispatcherServlet extends FrameworkServlet {
 
	public static final String MULTIPART_RESOLVER_BEAN_NAME = "multipartResolver";
	public static final String LOCALE_RESOLVER_BEAN_NAME = "localeResolver";
	public static final String THEME_RESOLVER_BEAN_NAME = "themeResolver";
	public static final String HANDLER_MAPPING_BEAN_NAME = "handlerMapping";
	public static final String HANDLER_ADAPTER_BEAN_NAME = "handlerAdapter";
	public static final String HANDLER_EXCEPTION_RESOLVER_BEAN_NAME = "handlerExceptionResolver";
	public static final String REQUEST_TO_VIEW_NAME_TRANSLATOR_BEAN_NAME = "viewNameTranslator";
	public static final String VIEW_RESOLVER_BEAN_NAME = "viewResolver";
	public static final String FLASH_MAP_MANAGER_BEAN_NAME = "flashMapManager";
	public static final String WEB_APPLICATION_CONTEXT_ATTRIBUTE = DispatcherServlet.class.getName() + ".CONTEXT";
	public static final String LOCALE_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".LOCALE_RESOLVER";
	public static final String THEME_RESOLVER_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_RESOLVER";
	public static final String THEME_SOURCE_ATTRIBUTE = DispatcherServlet.class.getName() + ".THEME_SOURCE";
	public static final String INPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".INPUT_FLASH_MAP";
	public static final String OUTPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".OUTPUT_FLASH_MAP";
	public static final String FLASH_MAP_MANAGER_ATTRIBUTE = DispatcherServlet.class.getName() + ".FLASH_MAP_MANAGER";
	public static final String EXCEPTION_ATTRIBUTE = DispatcherServlet.class.getName() + ".EXCEPTION";
	public static final String PAGE_NOT_FOUND_LOG_CATEGORY = "org.springframework.web.servlet.PageNotFound";
	private static final String DEFAULT_STRATEGIES_PATH = "DispatcherServlet.properties";
	protected static final Log pageNotFoundLogger = LogFactory.getLog(PAGE_NOT_FOUND_LOG_CATEGORY);
	private static final Properties defaultStrategies;
	static {
		try {
			ClassPathResource resource = new ClassPathResource(DEFAULT_STRATEGIES_PATH, DispatcherServlet.class);
			defaultStrategies = PropertiesLoaderUtils.loadProperties(resource);
		}
		catch (IOException ex) {
			throw new IllegalStateException("Could not load 'DispatcherServlet.properties': " + ex.getMessage());
		}
	}
 
	/** Detect all HandlerMappings or just expect "handlerMapping" bean? */
	private boolean detectAllHandlerMappings = true;
 
	/** Detect all HandlerAdapters or just expect "handlerAdapter" bean? */
	private boolean detectAllHandlerAdapters = true;
 
	/** Detect all HandlerExceptionResolvers or just expect "handlerExceptionResolver" bean? */
	private boolean detectAllHandlerExceptionResolvers = true;
 
	/** Detect all ViewResolvers or just expect "viewResolver" bean? */
	private boolean detectAllViewResolvers = true;
 
	/** Throw a NoHandlerFoundException if no Handler was found to process this request? **/
	private boolean throwExceptionIfNoHandlerFound = false;
 
	/** Perform cleanup of request attributes after include request? */
	private boolean cleanupAfterInclude = true;
 
	/** MultipartResolver used by this servlet */
	private MultipartResolver multipartResolver;
 
	/** LocaleResolver used by this servlet */
	private LocaleResolver localeResolver;
 
	/** ThemeResolver used by this servlet */
	private ThemeResolver themeResolver;
 
	/** List of HandlerMappings used by this servlet */
	private List<HandlerMapping> handlerMappings;
 
	/** List of HandlerAdapters used by this servlet */
	private List<HandlerAdapter> handlerAdapters;
 
	/** List of HandlerExceptionResolvers used by this servlet */
	private List<HandlerExceptionResolver> handlerExceptionResolvers;
 
	/** RequestToViewNameTranslator used by this servlet */
	private RequestToViewNameTranslator viewNameTranslator;
 
	private FlashMapManager flashMapManager;
 
	/** List of ViewResolvers used by this servlet */
	private List<ViewResolver> viewResolvers;
 
	public DispatcherServlet() {
		super();
	}
 
	public DispatcherServlet(WebApplicationContext webApplicationContext) {
		super(webApplicationContext);
	}
 
	@Override
	protected void onRefresh(ApplicationContext context) {
		initStrategies(context);
	}
 
	protected void initStrategies(ApplicationContext context) {
		initMultipartResolver(context);
		initLocaleResolver(context);
		initThemeResolver(context);
		initHandlerMappings(context);
		initHandlerAdapters(context);
		initHandlerExceptionResolvers(context);
		initRequestToViewNameTranslator(context);
		initViewResolvers(context);
		initFlashMapManager(context);
	}
}

DispatcherServlet类中的属性beans：

HandlerMapping：用于handlers映射请求和一系列的对于拦截器的前处理和后处理，大部分用@Controller注解。

HandlerAdapter：帮助DispatcherServlet处理映射请求处理程序的适配器，而不用考虑实际调用的是 哪个处理程序。

HandlerExceptionResolver：处理映射异常。

ViewResolver：根据实际配置解析实际的View类型。

LocaleResolver：解决客户正在使用的区域设置以及可能的时区，以便能够提供国际化视野。

ThemeResolver：解决Web应用程序可以使用的主题，例如提供个性化布局。

MultipartResolver：解析多部分请求，以支持从HTML表单上传文件。

FlashMapManager：存储并检索可用于将一个请求属性传递到另一个请求的input和output的FlashMap，通常用于重定向。

在Web MVC框架中，每个DispatcherServlet都拥自己的WebApplicationContext，它继承了ApplicationContext。WebApplicationContext包含了其上下文和Servlet实例之间共享的所有的基础框架beans。

• HandlerMapping：

HandlerMapping接口处理请求的映射

HandlerMapping接口的实现类：

SimpleUrlHandlerMapping类通过配置文件把URL映射到Controller类。

DefaultAnnotationHandlerMapping类通过注解把URL映射到Controller类。

• HandlerAdapter：

 

HandlerAdapter接口-处理请求映射

AnnotationMethodHandlerAdapter：通过注解，把请求URL映射到Controller类的方法上。

• HandlerExceptionResolver：

HandlerExceptionResolver接口-异常处理接口

SimpleMappingExceptionResolver通过配置文件进行异常处理。

AnnotationMethodHandlerExceptionResolver：通过注解进行异常处理。

• ViewResolver：

ViewResolver接口解析View视图。

UrlBasedViewResolver类 通过配置文件，把一个视图名交给到一个View来处理。

参考：

SpringMVC简介及工作原理 - 拯代码 - 博客园

SpringMVC实现原理及详解_yanweihpu的博客-优快云博客_springmvc原理