java_SpringMVC框架的实现原理及其详解

java_SpringMVC框架的实现原理及其详解

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

web.xml

<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>

3. SpringMVC运行原理

流程图：

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。
  1. HandlerMapping接口处理请求的映射
  2. HandlerMapping接口的实现类：
  3. SimpleUrlHandlerMapping类通过配置文件把URL映射到Controller类。
  4. DefaultAnnotationHandlerMapping类通过注解把URL映射到Controller类。
• 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。
  1. ViewResolver接口解析View视图。
  2. UrlBasedViewResolver类 通过配置文件，把一个视图名交给到一个View来处理。
• 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。