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); %>