JAVA架构-SpringMVC实现原理及解析
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);
}
}
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:
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:
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:
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:
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。
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