springmvc十六:视图解析

spring.xml配置视图解析器如下:

<?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:p="http://www.springframework.org/schema/p"xmlns:context="http://www.springframework.org/schema/context"xsi:schemaLocation="http://www.springframework.org/schema/beanshttp://www.springframework.org/schema/beans/spring-beans.xsdhttp://www.springframework.org/schema/contexthttp://www.springframework.org/schema/context/spring-context.xsdhttp://www.springframework.org/schema/mvchttp://www.springframework.org/schema/mvc/spring-mvc.xsd"><context:component-scan base-package="com.atchina"></context:component-scan><bean class="org.springframework.web.servlet.view.InternalResourceViewResolver"><property name="prefix" value="/WEB-INF/pages/"></property><property name="suffix" value=".jsp"></property></bean>
</beans>

方法执行后的返回值会作为页面地址参考，转发或者重定向到页面。

视图解析器可能会进行页面地址的拼串。

forward前缀指定一个转发操作

/***  forward:转发到一个页面*  /hello.jsp 转发当前项目下的hello.jsp*  *  forward:/hello.jsp, 视图解析器不会在这个返回值加前后缀*  forward:/hello.jsp 一定要加上/,如果不加/就是相对路径,容易出问题*/@RequestMapping("/hello3")public String hello3(){return "forward:/hello.jsp";}/***  forward:转发到一个请求*/@RequestMapping("/hello4")public String hello4(){return "forward:/hello3";}

重定向redirect

/***  重定向到hello.jsp页面 , 视图解析器不会在这个返回值加前后缀*  转发:   forward: 转发的路径*  重定向: redirect:重定向的路径*         /hello.jsp 代表就是从当前项目下开始,SpringMvc会为路径自动的拼接上项目名  */@RequestMapping("/hello5")public String hello5(){return "redirect:/hello.jsp";}/***  重定向一个请求*/@RequestMapping("/hello6")public String hello6(){return "redirect:/hello5";}

视图解析流程

1. 任何方法的返回值，最终都会被包装成ModelAndView对象。

2. 该方法处理视图渲染流程，将域中的数据在页面展示：页面就是用来渲染模型数据的。

processDispatchResult(processedRequest, response, mappedHandler, mv, dispatchException); // 来到页面的方法

3. 调用render(mv, request, response);渲染页面

4. View 和 ViewResolver

ViewResolver的作用是根据视图名(方法的返回值)得到View对象。

public interface ViewResolver {/*** Resolve the given view by name.* <p>Note: To allow for ViewResolver chaining, a ViewResolver should* return {@code null} if a view with the given name is not defined in it.* However, this is not required: Some ViewResolvers will always attempt* to build View objects with the given name, unable to return {@code null}* (rather throwing an exception when View creation failed).* @param viewName name of the view to resolve* @param locale Locale in which to resolve the view.* ViewResolvers that support internationalization should respect this.* @return the View object, or {@code null} if not found* (optional, to allow for ViewResolver chaining)* @throws Exception if the view cannot be resolved* (typically in case of problems creating an actual View object)*/View resolveViewName(String viewName, Locale locale) throws Exception;}

5. 怎么根据方法的返回值(视图名)得到View对象?

所有配置的视图解析器都会尝试根据视图名(方法的返回值)得到View(视图)对象；如果能得到View对象就返回，得不到就换下一个视图解析器。

protected View resolveViewName(String viewName, Map<String, Object> model, Locale locale,HttpServletRequest request) throws Exception {for (ViewResolver viewResolver : this.viewResolvers) {// ViewResolver视图解析器根据方法的返回值，得到一个View对象View view = viewResolver.resolveViewName(viewName, locale);if (view != null) {return view;}}return null;}

调用View对象的render方法

@Overridepublic void render(Map<String, ?> model, HttpServletRequest request, HttpServletResponse response) throws Exception {if (logger.isTraceEnabled()) {logger.trace("Rendering view with name '" + this.beanName + "' with model " + model +" and static attributes " + this.staticAttributes);}Map<String, Object> mergedModel = createMergedOutputModel(model, request, response);prepareResponse(request, response);// 渲染要给页面输出的所有数据renderMergedOutputModel(mergedModel, getRequestToExpose(request), response);}

InternalResourceView类

@Overrideprotected void renderMergedOutputModel(Map<String, Object> model, HttpServletRequest request, HttpServletResponse response) throws Exception {// Expose the model object as request attributes.// 将模型中的数据放在请求域中exposeModelAsRequestAttributes(model, request);// Expose helpers as request attributes, if any.exposeHelpers(request);// Determine the path for the request dispatcher.String dispatcherPath = prepareForRendering(request, response);// Obtain a RequestDispatcher for the target resource (typically a JSP).RequestDispatcher rd = getRequestDispatcher(request, dispatcherPath);if (rd == null) {throw new ServletException("Could not get RequestDispatcher for [" + getUrl() +"]: Check that the corresponding file exists within your web application archive!");}// If already included or response already committed, perform include, else forward.if (useInclude(request, response)) {response.setContentType(getContentType());if (logger.isDebugEnabled()) {logger.debug("Including resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");}rd.include(request, response);}else {// Note: The forwarded resource is supposed to determine the content type itself.if (logger.isDebugEnabled()) {logger.debug("Forwarding to resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");}rd.forward(request, response);}}

总结: 视图解析器只是为了得到视图对象；视图对象才能真正的转发(将模型数据全部放在请求域中)或者重定向到页面；视图对象才能真正的渲染视图。