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>

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);

}

}

作者：Java高级架构
链接：https://www.jianshu.com/p/4c7ed36430cb