AJAX 解决 JSP中JS向JAVA代码传参数问题！

以前也遇到过，当一个用户名输入框，失去焦点时，如何判断其 用户名是否存在？

 

因为它需要先JS触发，而调用逻辑去数据库对应ID。如此就需要 JS -> JAVA ？？

 

但又不想太复杂，又不想另外来个form提交；

 

突然看到了 AJAX，很好的实现：

 

<!-- 显示页面JSP --><SCRIPT LANGUAGE="JavaScript"><!--function isExist(desktopid){var xmlStr;//通过ajax判断用户ID是否可用if(desktopid == '' || desktopid == null){xmlStr = "<font class=/"notice_text/" color=/"red/">*请填写桌面ID</font>";}else{var xml=new ActiveXObject("Microsoft.XMLHTTP");var post="";var url="<%=request.getContextPath()%>/nportal/jsp/html/checkDesktopID.jsp?desktopId="+desktopid;xml.open("post",url,false); xml.setRequestHeader("context-type","text/xml;charset=gb2312"); xml.setRequestHeader("Content-Type","text/html;charset=gbk"); xml.send(post); xmlStr = xml.responseText; xmlStr = xmlStr.replace(/(^/s*)|(/s*$)/g, "");if(xmlStr == 'EXIST'){document.getElementById("desktopId").focus;document.getElementById("desktopId").selected=true;xmlStr = "<font class=/"notice_text/" color=/"red/">*桌面ID已经存在</font>";}else {xmlStr = "<font class=/"notice_text/" color=/"green/">*桌面ID可用</font>";}}document.getElementById('idMsg').innerHTML=xmlStr;document.getElementById('oidMsg').innerHTML="";}//--></SCRIPT><input name="desktopId" id="desktopId" onblur="isExist(this.value)" type="text" class="NCI_TEXT" size="30" maxlength="100"value=""<span id="idMsg"></span><span id="oidMsg" class="notice_text">－－请输入英文或者字符，并保证唯一</span></td></tr><!-- checkDesktopID.jsp --><%@page import="...."%><%@ page session="false" contentType="text/html;charset=GBK" %><%String desktopId = request.getParameter("desktopId");String xmlStr = "";if(desktopId != null){//判断桌面ID是否存在RemoteDesktopService remoteDesktopService = RemoteUMServiceLocator.getRemoteDesktopService();if (remoteDesktopService.getDesktopDTO(desktopId) == null) {xmlStr = "NOEXIST";}else{xmlStr = "EXIST";}}out.println(xmlStr);%>