运用Ajax通过select下拉框能得到数据

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Ajax XML Struts .net Bean

大伙应该在开发中遇到过这种情况，就是通过下拉框选择要显示的内容。如下图所示：

在没用到ajax技术时，我们可以使用两种方法来解决，一种就是选择后再次获得下拉框的数据，和显示的数据一起反映在页面上，这是最笨的方法，因为你选择多少次，下拉框的数据就要从数据库重复读取多少次。另外一种方法就是将页面分两桢，上桢是下拉框，下桢就是要读取的内容。这样做比第一种方法进步了不少，但是分桢对页面控制又有了要求。

使用Ajax正好结合了上面两种方法的优点。

下面就来看看我们是怎样实现的，我的实现平台是Struts+Spring+Hibernate，但与Ajax交道的也就是Struts，至于你后台怎样从数据库取得数据，就要看你的具体实现了：

JSP页面：

<%...@ page language="java" import="java.util.*,com.wehave.oa.labourset.model.MBm" pageEncoding="gb2312"%>
<%...@ taglib uri="struts-html" prefix="html" %>
<%...@ taglib uri="struts-bean" prefix="bean" %>
<%...@ taglib uri="struts-logic" prefix="logic" %>
<html>
<head>
<title>借阅信息</title>
<link rel="stylesheet" type="text/css" href="../css/table.css">
<link href="../css/style.css" rel="stylesheet" type="text/css"> 
<script src="../css/Alai_tc.js" language="JScript"></script> 
<!-- html:javascript formName="lendingCartForm"  method="validate"/-->
<script Language="JavaScript">...

function btn_AddFolder() ...{
    if(confirm("确定要归还吗？"))...{
        //if(document.lendingCartForm.onsubmit()){        
            document.forms[0].submit();
        //}
    }  
}

var req;
var dataDiv;
var dataTable;
var dataTableBody;
function Change_Select()
...{
    dataTableBody=document.getElementById("lendingcartDataBody");
    dataTable=document.getElementById("lendingcartData");
    dataDiv=document.getElementById("popup");
    
    var zhi=document.getElementById('tbEngineFilereadId').value;
    var url="returnBlueprintPage.go?method=getLendingCart&id="+zhi;
    
    if(zhi=="0")...{
        alert("请选择您要察看的信息");
                 return;
    }else...{
        if(window.XMLHttpRequest)
        ...{
            req=new XMLHttpRequest();
        }else if(window.ActiveXObject)
        ...{
            req=new ActiveXObject("Microsoft.XMLHTTP");
        }
        
        if(req)
        ...{
            req.open("GET",url,true);
            req.onreadystatechange=callback;
            req.send(null);
        }
    }
}

function callback()
...{
    if(req.readyState == 4)
    ...{
        if(req.status == 200)
        ...{
            //alert(req.responseText);
            document.getElementById("results").innerHTML=req.responseText;
        }else...{
            alert("Not able to retrieve description"+req.statusText);
        }
    }
}

</script>
</head>
<body class="bodycolor" topmargin="0" leftmargin="0">
    <html:form action="/updateLendingcarts" onsubmit="return validate(this)">    
    <table width="100%" background="../images/blank.gif" border="0" cellspacing="0" cellpadding="0">
        <tr><td height="7" colspan="2"></td></tr>
        <tr>
            <td width="45%" height="23" align="left"><strong>&nbsp;&nbsp; <img src="../images/small/page_tools_bar.gif" width="13" height="13"><span class="css3 STYLE20">&nbsp;&nbsp;借阅信息</span></strong></td>
            <td width="55%" align="right">
            <img name="aa" src="../images/xin_gh.gif" width="51" height="19" alt="" align="absmiddle"  onclick='btn_AddFolder()'  style="cursor:hand">&nbsp; 
            <img name="aa" src="../images/xin_gb.gif" width="51" height="19" alt="" align="absmiddle"  style="cursor:hand" onclick='javascript:window.close()'>&nbsp; 
            </td>
        </tr>
    </table>
    <table width="100%" border="1" cellpadding="0" cellspacing="0" style="border-collapse: collapse; border-top-width: 0" bordercolor="#426EB4">
        <tr>
            <td width="30%" class="td1_a"><span class="STYLE1">请选择借阅号</span></td>    
            <td width="70%">
            <html:select property="tbEngineFilereadId" onchange="Change_Select()" styleClass="SmallSelect">
                <html:option value="0">请选择&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</html:option>
                   <html:options collection="idlist" property="tbEngineFilereadId" labelProperty="tbEngineFilereadId"/>
            </html:select>
            </td>     
        </tr>
    </table>
     <div id="results"></div>
    <INPUT TYPE="hidden" name="method" value="doUpdateLendingcarts"> 
    </html:form>
    
</body>
</html>

页面内容看上去很多，其实关键代码并不多：

首先我们的获得下拉框的数据，并在页面上反映出来：

<html:select property="tbEngineFilereadId" onchange="Change_Select()" styleClass="SmallSelect">
             <html:option value="0">请选择&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;</html:option>
             <html:options collection="idlist" property="tbEngineFilereadId" labelProperty="tbEngineFilereadId"/>
   </html:select>

当选择下拉框时，就会触动"Change_Select()"事件：

var req;
var dataDiv;
var dataTable;
var dataTableBody;
function Change_Select()
...{
    dataTableBody=document.getElementById("lendingcartDataBody");
    dataTable=document.getElementById("lendingcartData");
    dataDiv=document.getElementById("popup");
    
    var zhi=document.getElementById('tbEngineFilereadId').value;
    var url="returnBlueprintPage.go?method=getLendingCart&id="+zhi;
    
    if(zhi=="0")...{
        alert("请选择您要察看的信息");
                 return;
    }else...{
        if(window.XMLHttpRequest)
        ...{
            req=new XMLHttpRequest();
        }else if(window.ActiveXObject)
        ...{
            req=new ActiveXObject("Microsoft.XMLHTTP");
        }
        
        if(req)
        ...{
            req.open("GET",url,true);
            req.onreadystatechange=callback;
            req.send(null);
        }
    }
}

function callback()
...{
    if(req.readyState == 4)
    ...{
        if(req.status == 200)
        ...{
            //alert(req.responseText);
            document.getElementById("results").innerHTML=req.responseText;
        }else...{
            alert("Not able to retrieve description"+req.statusText);
        }
    }
}

这个js代码也不难，关键就在于"document.getElementById("results").innerHTML=req.responseText;"
我没有用JS来拼出页面，是考虑到页面的安全性问题，所以我采取了在后台拼出页面的做法。

最后看看action是怎样实现的：

/** *//** 
     * 根据借阅号获得借阅信息 
     */
    public ActionForward getLendingCart(
            ActionMapping mapping,
            ActionForm form,
            HttpServletRequest req,
            HttpServletResponse res)...{
        
        String readID=(String)req.getParameter("id");
        
        TbEngineFileread tef=lendingCartsService.getLendingCartbyID(readID);
        
        MYhb yhb=lendingCartsService.getBM(tef.getTbEngineFilereadJyr());
        String jyrname=yhb.getMYhbXm();
        String jyrbmid=yhb.getMBm().getMBmBmbh();
        String jyrbmname=yhb.getMBm().getMBmMc();
    
        MYhb yhb1=lendingCartsService.getBM(tef.getTbEngineFilereadDjr());
        String djrname=yhb1.getMYhbXm();
        String djrbmid=yhb1.getMBm().getMBmBmbh();
        String djrbmname=yhb1.getMBm().getMBmMc();
        
        String date=tef.getTbEngineFilereadGetTime().substring(0,11);
        
        String redate="";
        if(tef.getTbEngineFilereadEndTime()!=null)...{
            redate=tef.getTbEngineFilereadEndTime().substring(0,11);
        }
        
        res.setContentType("text/xml;charset=GB2312");
        res.setHeader("Cache-Control","no-cache");
        String xml="";
        xml+="<table width='100%' border='1' cellpadding='0' cellspacing='0' style='border-collapse: collapse; border-top-width: 0' bordercolor='#426EB4'>";
        xml+="<tbody>";
        xml+="<tr>";
        xml+="<td width='20%' class='td1_a'><span class='STYLE1'>档案分类ID</span></td>";
        xml+="<td width='30%'>"+"<input type='text' name='tbEngineFilereadSortId' class='smallInput' size='15' maxlength='15' value="+tef.getTbEngineFilereadSortId()+" readonly='true'>"+"</td>";
        xml+="<td width='20%' class='td1_a'><span class='STYLE1'>机械设备ID</span></td>";
        xml+="<td width='30%'>"+"<input type='text' name='tbEngineFilereadEgineId' class='smallInput' size='15' maxlength='15' value="+tef.getTbEngineFilereadEgineId()+" readonly='true'>"+"</td>";
        xml+="</tr>";
        xml+="<tr>";
        xml+="<td width='20%' class='td1_a'><span class='STYLE1'>蓝图ID</span></td>";
        xml+="<td width='30%'>"+"<input type='text' name='tbEngineFilereadBluePrintId' class='smallInput' size='15' maxlength='15' value="+tef.getTbEngineFilereadBluePrintId()+" readonly='true'>"+"</td>";
        xml+="<td width='20%' class='td1_a'><span class='STYLE1'>备注</span></td>";
        xml+="<td width='30%'>"+"<input type='text' name='tbEngineFilereadMemo' class='smallInput' size='15' maxlength='15' value="+tef.getTbEngineFilereadMemo()+" >"+"</td>";
        xml+="</tr>";
        xml+="<tr>";
        xml+="<td width='20%' class='td1_a'><span class='STYLE1'>借阅时间</span></td>";
        xml+="<td width='30%'>"+"<input type='text' name='tbEngineFilereadGetTime' class='smallInput' size='15' maxlength='15' value="+date+" readonly='true'>"+"</td>";
        xml+="<td width='20%' class='td1_a'><span class='STYLE1'>归还时间</span></td>";
        xml+="<td width='30%'>";
        xml+="<input type='text' name='tbEngineFilereadEndTime' class='smallInput' size='15' maxlength='15' value="+redate+">";    
        xml+="<img src='../js/date/img.gif' id='f_trigger_c' style='cursor: pointer; border: 1px solid red;'  title='Date selector' onmouseover="this.style.background='red';" onmouseout="this.style.background=''" />";    
        xml+="<script type="text/javascript"> ";
        xml+="Calendar.setup({ inputField     :    "tbEngineFilereadEndTime",  ifFormat       :    "%Y-%m-%d", button         :    "f_trigger_c",  align          :    "Tl", singleClick    :    "true" });";
        xml+="</"+"script>";
        xml+="</td>";
        xml+="</tr>";
        xml+="<tr>";
        xml+="<td width='20%' class='td1_a'><span class='STYLE1'>借阅人</span></td>";
        xml+="<td width='30%'>"+"<input type='hidden' name='tbEngineFilereadJyr' value="+tef.getTbEngineFilereadJyr()+" >";
        xml+="<input type='text' name='tbEngineFilereadJyrmc' class='smallInput' size='15' maxlength='15' value="+jyrname+" readonly='true'>"+"</td>";
        xml+="<td width='20%' class='td1_a'><span class='STYLE1'>借阅人部门</span></td>";
        xml+="<td width='30%'>"+"<input type='hidden' name='tbEngineFilereadJyrbm' value="+jyrbmid+" >";
        xml+="<input type='text' name='tbEngineFilereadJyrbmmc' class='smallInput' size='15' maxlength='15' value="+jyrbmname+" readonly='true'>"+"</td>";
        xml+="</tr>";
        xml+="<tr>";
        xml+="<td width='20%' class='td1_a'><span class='STYLE1'>登记人</span></td>";
        xml+="<td width='30%'>"+"<input type='hidden' name='tbEngineFilereadDjr' value="+tef.getTbEngineFilereadDjr()+" >";
        xml+="<input type='text' name='tbEngineFilereadDjrmc' class='smallInput' size='15' maxlength='15' value="+djrname+" readonly='true'>"+"</td>";
        xml+="<td width='20%' class='td1_a'><span class='STYLE1'>登记人部门</span></td>";
        xml+="<td width='30%'>"+"<input type='hidden' name='tbEngineFilereadDjrbm' value="+djrbmid+" >";
        xml+="<input type='text' name='tbEngineFilereadDjrbmmc' class='smallInput' size='15' maxlength='15' value="+djrbmname+" readonly='true'>"+"</td>";
        xml+="</tr>";
        xml+="</tbody>";
        xml+="</table>";
        try ...{
            res.getWriter().write(xml);
        } catch (IOException e) ...{
            // TODO 自动生成 catch 块
            e.printStackTrace();
        }
        return null;
    }

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