/**  * <p>  * Process an <code>HttpServletRequest</code> and create the corresponding  * <code>HttpServletResponse</code>.  * </p>  *   * @param request  *            The servlet request we are processing  * @param response  *            The servlet response we are creating  *   * @exception IOException  *                if an input/output error occurs  * @exception ServletException  *                if a processing exception occurs  */ public void process(HttpServletRequest request, HttpServletResponse response)   throws IOException, ServletException {   /*   * 如果request请求是POST方法并且contentType为"multipart/form-data",则标准request将被转换成   * org.apache.struts.upload.MultipartRequestWrapper.它是HttpServletRequest的一个子类,然后   * 返回MultipartRequestWrapper;如果request请求是GET方法或contentType不是"multipart/form-data",   * 则传入的request被原样返回.   */  request = processMultipart(request);   /*   * 获取request的路径信息.用于选取合适的action.   */  String path = processPath(request, response);  if (path == null) {   return;  }  if (log.isDebugEnabled()) {   log.debug("Processing a '" + request.getMethod() + "' for path '"     + path + "'");  }   /*   * 根据<controller>元素的locale属性配置,决定是否将一个Locale对象保存到用户的HttpSession中.   */  processLocale(request, response);   // Set the content type and no-caching headers if requested  // 确定contentType，预设是 text/html  processContent(request, response);  // 判断<controller>属性nocache是否被设定  // 若是，在 response 中加入header参数,包括Pragma, Cache-Control, and  // Expires以防止浏览器网页被快取  processNoCache(request, response);   /*   * processPreprocess(request, response)前置处理，预设返回   * true，子类可以重新定义它以决定要不要继续处理下面的代码   * 因为此方法在Action被调用前执行,所以比较适合在此处检查用户session里是否含有合适的session值,   * 如果此方法返回true,则继续执行,否则终止process()   */  if (!processPreprocess(request, response)) {   return;  }   /*   * 從URI路徑確定ActionMapping 如果没有找到ActionMapping,则一个错误的response将被返回   */  ActionMapping mapping = processMapping(request, response, path);  if (mapping == null) {   return;  }   // Check for any role required to perform this action  // 安全角色认证  if (!processRoles(request, response, mapping)) {   return;  }   /*   * 处理ActionForm，如果没有就新增一个，之后一直使用它 Call the processActionForm() method to   * determine if an ActionForm is configured for the ActionMapping. If an   * ActionForm has been configured for the mapping, an attempt will be   * made to find an existing instance in the appropriate scope. Once an   * ActionForm is either found or created, it will be stored within the   * proper scope using a key that is configured in the name attribute for   * the mapping. If a new ActionForm instance needs to be created, the   * reset() method will be called on it.   */  ActionForm form = processActionForm(request, response, mapping);   // 将表单的域值填入ActionForm  processPopulate(request, response, form, mapping);   /*   * The processValidate() method is called and if an ActionForm has been   * configured and if the validate attribute is set to true for the   * mapping, then call the validate() method on the ActionForm. If the   * validate() method detects errors, it will store an ActionErrors   * object into the request scope and the request is automatically   * forwarded to the resource specified by the input attribute for the   * mapping. If no errors were detected from the validate() method or   * there wasn’t an ActionForm for the mapping, processing of the request   * will continue.   */  if (!processValidate(request, response, form, mapping)) {   return;  }   /*   * 判断 <action> 卷标的 forward 或 include 卷标是不是被设定 这两个卷标在设定一个路径，其与 type   * 属性是互斥的，当设定 其中一个属性时，调用 RequestDispatcher 的 forward() 或 include()   * ，其作用与设定ForwardAction或IncludeAction相同 直接绕送而不再使用Action对象进行接下来的处理   */  if (!processForward(request, response, mapping)) {   return;  }  if (!processInclude(request, response, mapping)) {   return;  }   // 处理Action，如果没有就生成一个，之后一直使用它  Action action = processActionCreate(request, response, mapping);  if (action == null) {   return;  }   // 呼叫Action的execute()或perform()方法，并返回ActionForward  ActionForward forward = processActionPerform(request, response, action,    form, mapping);   // 跳转到processActionPerform()方法返回的ActionForward  processForwardConfig(request, response, forward);  }  

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