springMVC源码学习之addFlashAttribute源码分析

本文主要从falshMap初始化，存，取，消毁来进行源码分析，springmvc版本4.3.18。关于使用及验证请参考另一篇jsp取addFlashAttribute值深入理解即springMVC发redirect传隐藏参数

说明：在action中通过redirectAttributes.addFlashAttribute(userName,"mike")，retrun "redirect:indexTest.jsp",页面indexTest.jsp中打印该session的值发现有这组属性

org.springframework.web.servlet.support.SessionFlashMapManager.FLASH_MAPS==[FlashMap [attributes={userInfo=com.ccb.xx.vdo.UserInfo@2c367ad4, userID=ID001,userName=mike}, targetRequestPath=/project/page/public/indexTest.jsp, targetRequestParams={flag=[opening]}]],能过el表达式${sessionScope['org.springframework.web.servlet.support.SessionFlashMapManager.FLASH_MAPS'][0]['userId']}可取能值。

1.初始化和调用，首先是入springMVC 入口webmvc包中org.springframework.web.servlet.DispatcherServlet中的doService方法进行调用

public class DispatcherServlet extends FrameworkServlet
{
  private FlashMapManager flashMapManager;
 public static final String INPUT_FLASH_MAP_ATTRIBUTE = DispatcherServlet.class.getName() + ".INPUT_FLASH_MAP";
  protected void initStrategies(ApplicationContext context)
  {
    initMultipartResolver(context);
    initLocaleResolver(context);
    initThemeResolver(context);
    initHandlerMappings(context);
    initHandlerAdapters(context);
    initHandlerExceptionResolvers(context);
    initRequestToViewNameTranslator(context);
    initViewResolvers(context);
　　//初始化
    initFlashMapManager(context);
  }
  private void initFlashMapManager(ApplicationContext context)
  {
    try
    {
　　　　//同级目录下DispatcherServlet.properties中配置
　　　　//org.springframework.web.servlet.FlashMapManager=org.springframework.web.servlet.support.SessionFlashMapManager
　　　　//此处代码相当于this.flashMapManager=(FlashMapManager)new SessionFlashMapManager(),
　　　　//因SessionFlashMapManager extends AbstractFlashMapManager,此处会执行AbstractFlashMapManager.AbstractFlashMapManager()构造方法
　　　　//，并设置过期时间this.flashMapTimeout = ;
      this.flashMapManager = ((FlashMapManager)context.getBean("flashMapManager", FlashMapManager.class));
      if (this.logger.isDebugEnabled())
        this.logger.debug("Using FlashMapManager [" + this.flashMapManager + "]");

    }
    catch (NoSuchBeanDefinitionException ex)
    {
      this.flashMapManager = ((FlashMapManager)getDefaultStrategy(context, FlashMapManager.class));
      if (this.logger.isDebugEnabled())
        this.logger.debug("Unable to locate FlashMapManager with name 'flashMapManager': using default [" + this.flashMapManager + "]");
    }

  }

  protected void doService(HttpServletRequest request, HttpServletResponse response)
    throws Exception
  {
　　　//从session中获取及session中删除
　　　//此处执行的是模板类org.springframework.web.servlet.support.AbstractFlashMapManager中的retrieveAndUpdate方法
　　 FlashMap inputFlashMap = this.flashMapManager.retrieveAndUpdate(request, response);
    if (inputFlashMap != null)//转存request
      request.setAttribute(INPUT_FLASH_MAP_ATTRIBUTE, Collections.unmodifiableMap(inputFlashMap));

　　//下面解释在调用controller的方法时，将request中falshmap==>ModelMap中,ModelMap继承自LinkedHashMap
　　//在doDispatch中通过反射调用@RequestMapping修饰的方法，
 　　//HandlerAdapter ha = getHandlerAdapter(mappedHandler.getHandler());
　　// mv = ha.handle(processedRequest, response, mappedHandler.getHandler());
　　//HandlerAdapter是接口，模板类AbstractHandlerMethodAdapter具体handle（调用handleInternal）实现，
　　//实际调用子类RequestMappingHandlerAdapter.handleInternal(调用invokeHandlerMethod(request, response, handlerMethod))进行处理,
　　//在invokeHandlerMethod方法中，由下面代码将上面"转存request"放put到ModelMap中，所以jsp取addFlashAttribute值深入理解即springMVC发redirect传隐藏参数
　　//中3.2的model输出中有flashAttribute参数
    // ModelAndViewContainer mavContainer = new ModelAndViewContainer();
    // mavContainer.addAllAttributes(RequestContextUtils.getInputFlashMap(request));
    // modelFactory.initModel(webRequest, mavContainer, invocableMethod);
    // mavContainer.setIgnoreDefaultModelOnRedirect(this.ignoreDefaultModelOnRedirect);
　　 //invokeHandlerMethod详解SpringMVC源码分析（2）：分析HandlerAdapter.handle方法，了解handler方法的调用细节以及@ModelAttribute注解
　　 doDispatch(request, response);//最终由RequestMappingHandlerAdapter.invokeHandlerMethod(request, response, handlerMethod)进行处理
}
}

AbstractFlashMapManager源码如下，

retrieveAndUpdate调用实现子类的retrieveFlashMaps取session中的flashmap,调用子类updateFlashMaps删除session的方法

public abstract class AbstractFlashMapManager
  implements FlashMapManager
{
 public final FlashMap retrieveAndUpdate(HttpServletRequest request, HttpServletResponse response)
  {//从session中取SessionFlashMapManager.FLASH_MAPS
    List allFlashMaps = retrieveFlashMaps(request);
    if (CollectionUtils.isEmpty(allFlashMaps)) {
      return null;
    }

    if (this.logger.isDebugEnabled())
      this.logger.debug("Retrieved FlashMap(s): " + allFlashMaps);

    List mapsToRemove = getExpiredFlashMaps(allFlashMaps);
　　//此处match返回SessionFlashMapManager.FLASH_MAPS值，值的结构如（[FlashMap [attributes={userInfo=com.ccb.xx.vdo.UserInfo@2c367ad4, userId=ID001,
　　//userName=mike}, targetRequestPath=/project/page/public/indexTest.jsp, targetRequestParams={flag=[opening]}]]）
　　//虽然此时request attribute为空，
　　//但实际执行此函数的spring-web包中org.springframework.web.util.UrlPathHelper中方法
　　//getOriginatingRequestUri(request)代码“if (uri == null) uri = request.getRequestURI()”
　　//代码可取到值，与SessionFlashMapManager.FLASH_MAPS中的targetRequestPath值相等
    FlashMap match = getMatchingFlashMap(allFlashMaps, request);
    if (match != null) {//将FLASH_MAPS加入待删除列表，后续请空allFlashMaps，再清空session该项的值
      mapsToRemove.add(match);
    }

    if (!(mapsToRemove.isEmpty())) {
      if (this.logger.isDebugEnabled())
        this.logger.debug("Removing FlashMap(s): " + mapsToRemove);

      Object mutex = getFlashMapsMutex(request);
      if (mutex != null) {
        synchronized (mutex) {
          allFlashMaps = retrieveFlashMaps(request);
          if (allFlashMaps != null) {
　　　　　　　　//将SessionFlashMapManager.FLASH_MAPS从allFlashMaps中删除
            allFlashMaps.removeAll(mapsToRemove);
　　　　　　　　//此时allFlashMaps中SessionFlashMapManager.FLASH_MAPS为空，下面方法将其从session中删除
            updateFlashMaps(allFlashMaps, request, response);
          }
        }
      }
      else {
        allFlashMaps.removeAll(mapsToRemove);
　　　　
        updateFlashMaps(allFlashMaps, request, response);
      }
    }

    return match;
  }
//具体实现在SessionFlashMapManager中

　 protected abstract List<FlashMap> retrieveFlashMaps(HttpServletRequest paramHttpServletRequest);

  protected abstract void updateFlashMaps(List<FlashMap> paramList, HttpServletRequest paramHttpServletRequest, HttpServletResponse paramHttpServletResponse); 

}

实现类SessionFlashMapManager中重写retrieveFlashMaps和updateFlashMaps

public class SessionFlashMapManager extends AbstractFlashMapManager
{
  private static final String FLASH_MAPS_SESSION_ATTRIBUTE = SessionFlashMapManager.class.getName() + ".FLASH_MAPS";

  protected List<FlashMap> retrieveFlashMaps(HttpServletRequest request)
  {
    HttpSession session = request.getSession(false);
    return ((session != null) ? (List)session.getAttribute(FLASH_MAPS_SESSION_ATTRIBUTE) : null);
  }

  protected void updateFlashMaps(List<FlashMap> flashMaps, HttpServletRequest request, HttpServletResponse response)
  {//flashMaps中SessionFlashMapManager.FLASH_MAPS为空，（!(flashMaps.isEmpty())) ? flashMaps : null)整个表达式返回null
　　//即实现falshMaps中值为空，清空sesssion中该项的目的
    WebUtils.setSessionAttribute(request, FLASH_MAPS_SESSION_ATTRIBUTE, (!(flashMaps.isEmpty())) ? flashMaps : null);
  }

  protected Object getFlashMapsMutex(HttpServletRequest request)
  {
    return WebUtils.getSessionMutex(request.getSession());
  }
}

spring-web包org.springframework.web.util.WebUtils中WebUtils.setSessionAttribute

public static void setSessionAttribute(HttpServletRequest request, String name, Object value)
  {
    Assert.notNull(request, "Request must not be null");
    if (value != null) {
      request.getSession().setAttribute(name, value);
    }
    else {//进入此步
      HttpSession session = request.getSession(false);
      if (session != null)
        session.removeAttribute(name);//删除falshmap
    }
  }

接口类org.springframework.web.servlet.FlashMapManager

public abstract interface FlashMapManager
{
  public abstract FlashMap retrieveAndUpdate(HttpServletRequest paramHttpServletRequest, HttpServletResponse paramHttpServletResponse);

  public abstract void saveOutputFlashMap(FlashMap paramFlashMap, HttpServletRequest paramHttpServletRequest, HttpServletResponse paramHttpServletResponse);
}