追求無(wú)止境

以前，我們?cè)敿?xì)介紹了Spring的Controller技術(shù)。Spring的面向接口編程，使Controller的實(shí)現(xiàn)多種多樣。View技術(shù)也一樣。今天的分析先從在Controller中的ModelAndView開(kāi)始。

public class ModelAndView {     
  private Object view; //View實(shí)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;
}

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(zhǔn)備請(qǐng)求: 如果是JSP的視圖技術(shù)

     * 首先會(huì)把model設(shè)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?cè)賮?lái)看看View的實(shí)現(xiàn)繼承類(lèi)圖，可以看到Spring支持多種類(lèi)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

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(tài)屬性和model的屬性都添加到mergedModel里面。如果需要請(qǐng)求上下文，則將請(qǐng)求上下文添加到model中。

靜態(tài)屬性是繼承AbstractView進(jìn)行設(shè)置的屬性。而請(qǐng)求上下文如果設(shè)置的名字就會(huì)創(chuàng)建一個(gè)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(duì)響應(yīng)進(jìn)行預(yù)處理。最后調(diào)用子類(lèi)需要實(shí)現(xiàn)的函數(shù)renderMergedOutputModel。

對(duì)PDF和EXCEL格式我們暫且不管，且Spring支持多種視圖技術(shù)，這里我們主要關(guān)注JSTL技術(shù)，

接著我們來(lái)看AbstractUrlBasedView 類(lèi)。在AbstractUrlBasedView 只定義了一個(gè)url屬性。別的沒(méi)有什么特殊處理。

接著繼承AbstractUrlBasedView 的是InternalResourceView。他對(duì)renderMergedOutputModel進(jìn)行實(shí)現(xiàn)，實(shí)現(xiàn)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(shù)request
        HttpServletRequest requestToExpose = getRequestToExpose(request);

        // 將model的數(shù)據(jù)添加到request屬性中

        exposeModelAsRequestAttributes(model, requestToExpose);

        // 設(shè)置helper，如果存在的話
        exposeHelpers(requestToExpose);

        // 對(duì)繪制進(jìn)行預(yù)處理，從而獲得到要分發(fā)的url
        String dispatcherPath = prepareForRendering(requestToExpose, response);

        // 獲取請(qǐng)求分發(fā)對(duì)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);
        }
    }

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(duì)兩個(gè)方法進(jìn)行了覆蓋。第一個(gè)initServletContext，主要初始化了MessageResource

第二個(gè)exposeHelpers將messageSource放在了request里面。

這樣view的解析就結(jié)束了。接下來(lái)容器對(duì)jsp進(jìn)行解析，并進(jìn)行tag等的處理。然后將生成的頁(yè)面返回給客戶(hù)端。