以前，我們詳細介紹了Spring的Controller技術。Spring的面向接口編程，使Controller的實現多種多樣。View技術也一樣。今天的分析先從在Controller中的ModelAndView開始。
public class ModelAndView {
private Object view; //View實例或者view的字符串
/** Model Map */
private ModelMap model; //model
/* * Convenient constructor when there is no model data to expose. * Can also be used in conjunction with <code>addObject</code>.
* @param view View object to render
* @see #addObject */
public ModelAndView(View view) {
this.view = view;
}
public ModelAndView(String viewName){
this.view = viewName;
}可以看到view實例可以指向一個View對象或者字符串。現在先看看View接口：
public interface View {
/**
* Return the content type of the view, if predetermined.
* <p>Can be used to check the content type upfront,
* before the actual rendering process.
* @return the content type String (optionally including a character set),
* or <code>null</code> if not predetermined.
*/
String getContentType();
/**
* 繪制視圖 * 繪制視圖的第一步是準備請求: 如果是JSP的視圖技術
* 首先會把model設為request的屬性。
* 第二步則是真正的繪制視圖
* @param model Map with name Strings as keys and corresponding model
* objects as values (Map can also be <code>null</code> in case of empty model)
* @param request current HTTP request
* @param response HTTP response we are building
* @throws Exception if rendering failed
*/
void render(Map model, HttpServletRequest request, HttpServletResponse response) throws Exception;
}
在這之后，我們再來看看View的實現繼承類圖，可以看到Spring支持多種類型視圖：
org.springframework.web.servlet.view.AbstractView (implements org.springframework.beans.factory.BeanNameAware, org.springframework.web.servlet.View)
- org.springframework.web.servlet.view.document.AbstractExcelView
- org.springframework.web.servlet.view.document.AbstractJExcelView
- org.springframework.web.servlet.view.document.AbstractPdfView
- org.springframework.web.servlet.view.AbstractUrlBasedView (implements org.springframework.beans.factory.InitializingBean)
- org.springframework.web.servlet.view.jasperreports.AbstractJasperReportsView
- org.springframework.web.servlet.view.jasperreports.AbstractJasperReportsSingleFormatView
- org.springframework.web.servlet.view.jasperreports.ConfigurableJasperReportsView
- org.springframework.web.servlet.view.jasperreports.JasperReportsCsvView
- org.springframework.web.servlet.view.jasperreports.JasperReportsHtmlView
- org.springframework.web.servlet.view.jasperreports.JasperReportsPdfView
- org.springframework.web.servlet.view.jasperreports.JasperReportsXlsView
- org.springframework.web.servlet.view.jasperreports.JasperReportsMultiFormatView
- org.springframework.web.servlet.view.document.AbstractPdfStamperView
- org.springframework.web.servlet.view.AbstractTemplateView
- org.springframework.web.servlet.view.freemarker.FreeMarkerView
- org.springframework.web.servlet.view.velocity.VelocityView
- org.springframework.web.servlet.view.velocity.VelocityToolboxView
- org.springframework.web.servlet.view.velocity.VelocityLayoutView
- org.springframework.web.servlet.view.InternalResourceView
- org.springframework.web.servlet.view.JstlView
- org.springframework.web.servlet.view.tiles.TilesView
- org.springframework.web.servlet.view.tiles.TilesJstlView
- org.springframework.web.servlet.view.RedirectView
- org.springframework.web.servlet.view.tiles2.TilesView
- org.springframework.web.servlet.view.xslt.XsltView
- org.springframework.web.servlet.view.xslt.AbstractXsltView
和Controller一樣，View的第一個實現也是AbstractView。所以先讓我們看看AbstractView對render函數的實現：
public void render(Map 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);
}
// Consolidate static and dynamic model attributes.
Map mergedModel = new HashMap(this.staticAttributes.size() + (model != null ? model.size() : 0));
mergedModel.putAll(this.staticAttributes);
if (model != null) {
mergedModel.putAll(model);
}
// Expose RequestContext?
if (this.requestContextAttribute != null) {
mergedModel.put(this.requestContextAttribute, createRequestContext(request, mergedModel));
}
prepareResponse(request, response);
renderMergedOutputModel(mergedModel, request, response);
}
第一步，將靜態屬性和model的屬性都添加到mergedModel里面。如果需要請求上下文，則將請求上下文添加到model中。
靜態屬性是繼承AbstractView進行設置的屬性。而請求上下文如果設置的名字就會創建一個request上下文。在requestContext中定義了一些包括本地化和主題的處理工具。
第二步，對響應進行預處理。最后調用子類需要實現的函數renderMergedOutputModel。
對PDF和EXCEL格式我們暫且不管，且Spring支持多種視圖技術，這里我們主要關注JSTL技術，
接著我們來看AbstractUrlBasedView 類。在AbstractUrlBasedView 只定義了一個url屬性。別的沒有什么特殊處理。
接著繼承AbstractUrlBasedView 的是InternalResourceView。他對renderMergedOutputModel進行實現，實現如下:
/**
* Render the internal resource given the specified model.
* This includes setting the model as request attributes.
*/
protected void renderMergedOutputModel(
Map model, HttpServletRequest request, HttpServletResponse response) throws Exception {
// 獲取要暴露的request，一般都是傳入的參數request
HttpServletRequest requestToExpose = getRequestToExpose(request);
// 將model的數據添加到request屬性中
exposeModelAsRequestAttributes(model, requestToExpose);
// 設置helper，如果存在的話
exposeHelpers(requestToExpose);
// 對繪制進行預處理，從而獲得到要分發的url
String dispatcherPath = prepareForRendering(requestToExpose, response);
// 獲取請求分發對象
RequestDispatcher rd = requestToExpose.getRequestDispatcher(dispatcherPath);
if (rd == null) {
throw new ServletException(
"Could not get RequestDispatcher for [" + getUrl() + "]: check that this file exists within your WAR");
}
// 決定使用RequestDispatcher的include方法還是forward方法
if (useInclude(requestToExpose, response)) {
response.setContentType(getContentType());
if (logger.isDebugEnabled()) {
logger.debug("Including resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");
}
rd.include(requestToExpose, response);
}
else {
// Note: The forwarded resource is supposed to determine the content type itself.
exposeForwardRequestAttributes(requestToExpose);
if (logger.isDebugEnabled()) {
logger.debug("Forwarding to resource [" + getUrl() + "] in InternalResourceView '" + getBeanName() + "'");
}
rd.forward(requestToExpose, response);
}
}
可以看到InternalResourceView對請求進行了轉發。轉發到url上。最后我們看看JSTLView的實現：
public class JstlView extends InternalResourceView {
private MessageSource messageSource;
public JstlView() {
}
public JstlView(String url) {
super(url);
}
public JstlView(String url, MessageSource messageSource) {
this(url);
this.messageSource = messageSource;
}
protected void initServletContext(ServletContext servletContext) {
if (this.messageSource != null) {
this.messageSource = JstlUtils.getJstlAwareMessageSource(servletContext, this.messageSource);
}
super.initServletContext(servletContext);
}
protected void exposeHelpers(HttpServletRequest request) throws Exception {
if (this.messageSource != null) {
JstlUtils.exposeLocalizationContext(request, this.messageSource);
}
else {
JstlUtils.exposeLocalizationContext(new RequestContext(request, getServletContext()));
}
}
}
在InternalResourceView 中，基本上所有的處理都差不多了。在JSTLView對兩個方法進行了覆蓋。第一個initServletContext，主要初始化了MessageResource
第二個exposeHelpers將messageSource放在了request里面。
這樣view的解析就結束了。接下來容器對jsp進行解析，并進行tag等的處理。然后將生成的頁面返回給客戶端。