菜鸟之路——Spring MVC(二)再次深入
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Spring MVC 的核心类与接口:
- DispatcherServlet 前置控制器
- HandlerMapping 请求映射(到Controller)
HandlerMapping接口的实现类:
SimpleUrlHandlerMapping 通过配置文件,把一个URL映射到Controller
DefaultAnnotationHandlerMapping 通过注解,把一个URL映射到Controller类上
- HandlerAdapter 请求映射(到Controller类的方法上)
AnnotationMethodHandlerAdapter类,通过注解,把一个URL映射到Controller类的方法上
- Controller 控制器
由于我们使用了@Controller注解,添加了@Controller注解注解的类就可以担任控制器(Action)的职责,
所以我们并没有用到这个接口。
- HandlerIntercepter 拦截器
需要自己实现这个接口,来完成拦截的器的工作。
- ViewResolver 视图映射
UrlBasedViewResolver类 通过配置文件,把一个视图名交给到一个View来处理
InternalResourceViewResolver类,比上面的类,加入了JSTL的支持
- View 视图处理
启动过程
Spring MVC启动过程大致分为两个过程:
- ContextLoaderListener初始化,读取context-param中的contextConfigLocation指定的配置文件,创建ROOT Context,通过调用继承自ContextLoader的initWebApplicationContext方法实例化Spring IoC容器,并将此容器实例注册到ServletContext中。
- ContextLoaderListener初始化完毕后,开始初始化web.xml中配置的DispatcherServlet,DispatcherServlet的初始化又包括了视图管理器、异常处理器、映射管理等等。
/** * Initialize the strategy objects that this servlet uses. * <p>May be overridden in subclasses in order to initialize further strategy objects. */ protected void initStrategies(ApplicationContext context) { initMultipartResolver(context); initLocaleResolver(context); initThemeResolver(context); initHandlerMappings(context); initHandlerAdapters(context); initHandlerExceptionResolvers(context); initRequestToViewNameTranslator(context); initViewResolvers(context); initFlashMapManager(context); }
SpringMVC利用Spring的注入特性初始化资源文件,只需要调用setPropertyValues方法就可将contextConfigLocation属性设置到对应实例中,也就是以依赖注入的方式初始化属性。
时序图如下:
请求处理流程
官网上的图
涉及到核心类与接口的过程描述:
客户端浏览器发送http请求,被`DispatcherServlet`捕获,调用关键的doDispatch方法,遍历所有注册为`Controller`的bean,为请求寻找关联映射,其中遍历查找的函数getHandler和getHandlerAdapter的源码:
/** * Return the HandlerExecutionChain for this request. * <p>Tries all handler mappings in order. * @param request current HTTP request * @return the HandlerExecutionChain, or {@code null} if no handler could be found */ protected HandlerExecutionChain getHandler(HttpServletRequest request) throws Exception { for (HandlerMapping hm : this.handlerMappings) { if (logger.isTraceEnabled()) { logger.trace( "Testing handler map [" + hm + "] in DispatcherServlet with name '" + getServletName() + "'"); } HandlerExecutionChain handler = hm.getHandler(request); if (handler != null) { return handler; } } return null; } /** * Return the HandlerAdapter for this handler object. * @param handler the handler object to find an adapter for * @throws ServletException if no HandlerAdapter can be found for the handler. This is a fatal error. */ protected HandlerAdapter getHandlerAdapter(Object handler) throws ServletException { for (HandlerAdapter ha : this.handlerAdapters) { if (logger.isTraceEnabled()) { logger.trace("Testing handler adapter [" + ha + "]"); } if (ha.supports(handler)) { return ha; } } throw new ServletException("No adapter for handler [" + handler + "]: The DispatcherServlet configuration needs to include a HandlerAdapter that supports this handler"); }
找到匹配的映射后`HandlerAdapter`会依次调用preHandle、handle(返回ModelAndView)、postHandle方法,所有步骤完成后调用processDispatchResult函数处理结果,并返回View给客户端。postDispatchResult函数和其中调用的render函数源码如下:
/** * Handle the result of handler selection and handler invocation, which is * either a ModelAndView or an Exception to be resolved to a ModelAndView. */ private void processDispatchResult(HttpServletRequest request, HttpServletResponse response, HandlerExecutionChain mappedHandler, ModelAndView mv, Exception exception) throws Exception { boolean errorView = false; if (exception != null) { if (exception instanceof ModelAndViewDefiningException) { logger.debug("ModelAndViewDefiningException encountered", exception); mv = ((ModelAndViewDefiningException) exception).getModelAndView(); } else { Object handler = (mappedHandler != null ? mappedHandler.getHandler() : null); mv = processHandlerException(request, response, handler, exception); errorView = (mv != null); } } // Did the handler return a view to render? if (mv != null && !mv.wasCleared()) { render(mv, request, response); if (errorView) { WebUtils.clearErrorRequestAttributes(request); } } else { if (logger.isDebugEnabled()) { logger.debug("Null ModelAndView returned to DispatcherServlet with name '" + getServletName() + "': assuming HandlerAdapter completed request handling"); } } if (WebAsyncUtils.getAsyncManager(request).isConcurrentHandlingStarted()) { // Concurrent handling started during a forward return; } if (mappedHandler != null) { mappedHandler.triggerAfterCompletion(request, response, null); } } /** * Render the given ModelAndView. * <p>This is the last stage in handling a request. It may involve resolving the view by name. * @param mv the ModelAndView to render * @param request current HTTP servlet request * @param response current HTTP servlet response * @throws ServletException if view is missing or cannot be resolved * @throws Exception if there's a problem rendering the view */ protected void render(ModelAndView mv, HttpServletRequest request, HttpServletResponse response) throws Exception { // Determine locale for request and apply it to the response. Locale locale = this.localeResolver.resolveLocale(request); response.setLocale(locale); View view; if (mv.isReference()) { // We need to resolve the view name. view = resolveViewName(mv.getViewName(), mv.getModelInternal(), locale, request); if (view == null) { throw new ServletException("Could not resolve view with name '" + mv.getViewName() + "' in servlet with name '" + getServletName() + "'"); } } else { // No need to lookup: the ModelAndView object contains the actual View object. view = mv.getView(); if (view == null) { throw new ServletException("ModelAndView [" + mv + "] neither contains a view name nor a " + "View object in servlet with name '" + getServletName() + "'"); } } // Delegate to the View object for rendering. if (logger.isDebugEnabled()) { logger.debug("Rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'"); } try { if (mv.getStatus() != null) { response.setStatus(mv.getStatus().value()); } view.render(mv.getModelInternal(), request, response); } catch (Exception ex) { if (logger.isDebugEnabled()) { logger.debug("Error rendering view [" + view + "] in DispatcherServlet with name '" + getServletName() + "'", ex); } throw ex; } }
时序图如下
配置实例
这里放的是最简单的配置,可以通过这个简单的配置实例回顾一下上面的过程。
目录结构
-SpringMVCDemo
-src
-me.cyan
-WelcomeController
-web
-WEB-INF
-applicationContext.xml
-dispatcher-servlet.xml
-web.xml
-index.jsp
-pom.xml
pom.xml
引入的包
<?xml version="1.0" encoding="UTF-8"?><project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/maven-v4_0_0.xsd"> <modelVersion>4.0.0</modelVersion> <groupId>me.cyan</groupId> <artifactId>SpringMVCDemo</artifactId> <name>SpringMVCDemo</name> <packaging>war</packaging> <version>1.0.0</version> <properties> <spring-version>4.2.6.RELEASE</spring-version> </properties> <dependencies> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-context</artifactId> <version>${spring-version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-core</artifactId> <version>${spring-version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-web</artifactId> <version>${spring-version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-beans</artifactId> <version>${spring-version}</version> </dependency> <dependency> <groupId>commons-logging</groupId> <artifactId>commons-logging</artifactId> <version>1.2</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-webmvc</artifactId> <version>${spring-version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-aop</artifactId> <version>${spring-version}</version> </dependency> <dependency> <groupId>org.springframework</groupId> <artifactId>spring-expression</artifactId> <version>${spring-version}</version> </dependency> </dependencies></project>
web.xml
<?xml version="1.0" encoding="UTF-8"?><web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd" version="3.1"> <!--配置文件路径--> <context-param> <param-name>contextConfigLocation</param-name> <param-value>/WEB-INF/applicationContext.xml</param-value> </context-param> <listener> <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class> </listener> <!--SpringMVC核心servlet--> <servlet> <servlet-name>dispatcher</servlet-name> <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class> <load-on-startup>1</load-on-startup> </servlet> <servlet-mapping> <servlet-name>dispatcher</servlet-name> <url-pattern>/</url-pattern> </servlet-mapping></web-app>
dispatcher-servlet.xml
<?xml version="1.0" encoding="UTF-8"?><beans xmlns="http://www.springframework.org/schema/beans" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> <!-- 默认的注解映射的支持 --> <mvc:annotation-driven /> <!-- 自动扫描的包名 --> <context:component-scan base-package="me.cyan" /></beans>
WelcomeController
package me.cyan;import org.springframework.stereotype.Controller;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.ResponseBody;/** * Created by cyan on 16/5/23. */@Controllerpublic class welcomeController { @RequestMapping("/hello") public @ResponseBody String sayhello(){ return "hello Spring MVC!"; }}
- 菜鸟之路——Spring MVC(二)再次深入
- 菜鸟之路——Spring MVC(一)初探
- 菜鸟之路——Spring MVC(五)ViewResolver
- 菜鸟之路——Spring MVC(十)配置文件
- 菜鸟之路——Spring MVC(十五)事务管理
- 菜鸟之路——Spring MVC(十六)log4j
- 菜鸟之路——Spring MVC(十二)<mvc:annotation-driven/>做了什么
- 菜鸟之路——Spring MVC(十四)Spring AOP
- 菜鸟之路——Spring MVC(三)DispatcherServlet详解
- 菜鸟之路——Spring MVC(四)handlerMapping和handlerAdapter
- 菜鸟之路——Spring MVC(六)拦截器
- 菜鸟之路——Spring MVC(七)异常处理
- 菜鸟之路——Spring MVC(八)静态资源
- 菜鸟之路——Spring MVC(九)常用注解
- 菜鸟之路——Spring MVC(十一)ContextLoaderListener加载配置文件
- 菜鸟之路——Spring MVC(十三)本地化与国际化
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