SUN的《AJAX与J2EE》全文译了

                  if   ((targetId   !=   null)   &&   !users.containsKey(targetId.trim()))   {   
                          response.setContentType("text/xml");   
                          response.setHeader("Cache-Control",   "no-cache");   
                          response.getWriter().write("valid");     
                  }   else   {   
                          response.setContentType("text/xml");   
                          response.setHeader("Cache-Control",   "no-cache");   
                          response.getWriter().write("invalid");     
                  }   
          }   
  }   

  5.   The   ValidateServlet   returns   an   XML   document   containing   the   results.——ValidateServlet返回一个包含结果的XML文档。   
  ValidateServlet生成一个XML文档作为响应、更复杂的情况可能用到DOM、XSLT等。   

          response.setContentType("text/xml");   
          response.setHeader("Cache-Control",   "no-cache");   
          response.getWriter().write("invalid");