SpringMVC实现原理及详解

港控/mmm° 2022-05-24 02:39 243阅读 0赞

**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>
                    
                    <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>

**3、SpringMVC运行原理**

如图所示：

![70][]

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：**

![70 1][]

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：**

![70 2][]

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：**

![70 3][]

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：**

**![70 4][]**

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。

参考资料：http://elf8848.iteye.com/blog/875830

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