SpringMVC工作原理

MVC是一种设计模式

原理图如下

SpringMVC简单介绍

SpringMVC框架是以请求为驱动，围绕Select设计，建请求发给控制器，然后通过模型对象，分派器来展示请求结果试图。

其中核心类是DispatcherSelect,它是Servlet，顶层是实现的Select接口。

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>

SpringMVC 工作原理（重要）

简单来说：

客户端发送请求-> 前端控制器 DispatcherServlet 接受客户端请求 -> 找到处理器映射 HandlerMapping 解析请求对应的 Handler-> 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 -> 处理器返回一个模型视图 ModelAndView -> 视图解析器进行解析 -> 返回一个视图对象->前端控制器 DispatcherServlet 渲染数据（Moder）->将得到视图对象返回给用户

控制器，在DispatcherServlet的控制下Handler对具体的用户请求进行处理。由于Handler涉及到具体的用户业务请求，所以一般情况需要工程师根据业务需求开发Handler。

5、视图解析器View resolver(不需要工程师开发),由框架提供

作用：进行视图解析，根据逻辑视图名解析成真正的视图（view） View Resolver负责将处理结果生成View视图，View Resolver首先根据逻辑视图名解析成物理视图名即具体的页面地址，再生成View视图对象，最后对View进行渲染将处理结果通过页面展示给用户。 springmvc框架提供了很多的View视图类型，包括：jstlView、freemarkerView、pdfView等。一般情况下需要通过页面标签或页面模版技术将模型数据通过页面展示给用户，需要由工程师根据业务需求开发具体的页面。

6、视图View(需要工程师开发)

View是一个接口，实现类支持不同的View类型（jsp、freemarker、pdf...）

注意：处理器Handler（也就是我们平常说的Controller控制器）以及视图层view都是需要我们自己手动开发的。其他的一些组件比如：前端控制器DispatcherServlet、处理器映射器HandlerMapping、处理器适配器HandlerAdapter等等都是框架提供给我们的，不需要自己手动开发。

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);
    }
}