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SpringMVC架構實現原理

一、SpringMVC介紹

        Spring mvc是一個基於mvc的web框架。其中核心類是DispatcherServlet,它是一個Servlet,頂層是實現的Servlet介面。

        Spring mvc是spring框架的一個模組,springmvc和spring無需通過中間整合層進行整合。

二、SpringMVC使用

        需要在web.xml中配置DispatcherServlet。並且需要配置spring監聽器ContextLoaderListener

<?xml version="1.0" encoding="UTF-8"?> <!-- 當前的XML文件版本與字元編碼 -->
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns="http://java.sun.com/xml/ns/javaee"  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee  http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" id="WebApp_ID" version="3.0">
  <display-name>SpringMVC</display-name>
  
  <!-- SpringMVC前段控制器 -->
	<servlet>
		<servlet-name>springmvc</servlet-name>
		<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
		
		<!-- contextConfigLocation配置SpringMVC載入的配置檔案(配置處理器對映器、介面卡等等) 
			 如果不配置ContextConfigLocation,預設載入的是/WEB-INF/servlet名稱-servlet.xml(springmvc-servlet.xml)
		-->
		<init-param>
			<param-name>contextConfigLocation</param-name>
			<param-value>classpath:springmvc-config.xml</param-value>
		</init-param>
		<load-on-startup>1</load-on-startup>
	</servlet>
	
	<servlet-mapping>
		<servlet-name>springmvc</servlet-name>
		<!--
			第一種:*.action,訪問以.action結尾由DispatcherServlet進行解析
			第二種:/,所以訪問的地址都由DispatcherServlet進行解析,對於靜態檔案的配置不讓DispatcherServlet解析
			第三種:/*,這樣配置不對
		-->
		<url-pattern>*.action</url-pattern>
	</servlet-mapping>
	
</web-app>

三、SpringMVC執行原理

1、 執行流程圖:

2、流程說明:

(1)客戶端(瀏覽器)傳送請求,直接請求到DispatcherServlet。(請求DispatcherServlet)

(2)DispatcherServlet根據請求資訊呼叫HandlerMapping,解析請求對應的Handler。(查詢@Controller)

(3)解析到對應的Handler後,開始由HandlerAdapter介面卡處理。(查詢@RequestMapping)

(4)HandlerAdapter會根據Handler來呼叫真正的處理器開處理請求,並處理相應的業務邏輯。(處理方法)

(5)處理器處理完業務後,會返回一個ModelAndView物件,Model是返回的資料物件,View是個邏輯上的View。(返回處理結果)

(6)ViewResolver會根據邏輯View查詢實際的View。(邏輯檢視解析為真正的檢視)

(7)DispatcherServlet把返回的Model傳給View。(DispatcherServlet試圖渲染)

(8)通過View返回給請求者(瀏覽器)

四、DispatcherServlet詳細解析

原始碼分析:

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類中的屬性beans:

1、HandlerMapping:

        用於handlers對映請求和一系列的對於攔截器的前處理和後處理,大部分用@Controller註解。

        HandlerMapping介面的實現類:

                SimpleUrlHandlerMapping類通過配置檔案把URL對映到Controller類。

                DefaultAnnotationHandlerMapping類通過註解把URL對映到Controller類。

2、HandlerAdapter:

       幫助DispatcherServlet處理對映請求處理程式的介面卡,而不用考慮實際呼叫的是 哪個處理程式。

        AnnotationMethodHandlerAdapter:通過註解,把請求URL對映到Controller類的方法上。

3、HandlerExceptionResolver:

        處理對映異常。

        SimpleMappingExceptionResolver通過配置檔案進行異常處理。

        AnnotationMethodHandlerExceptionResolver:通過註解進行異常處理。

4、ViewResolver:

        根據實際配置解析實際的View型別。

        UrlBasedViewResolver類 通過配置檔案,把一個檢視名交給到一個View來處理。

5、LocaleResolver:

        解決客戶正在使用的區域設定以及可能的時區,以便能夠提供國際化視野。

6、ThemeResolver:

        解決Web應用程式可以使用的主題,例如提供個性化佈局。

7、MultipartResolver:

        解析多部分請求,以支援從HTML表單上傳檔案。

8、FlashMapManager:

        儲存並檢索可用於將一個請求屬性傳遞到另一個請求的input和output的FlashMap,通常用於重定向。