纯JSP+DWR实现三级联动下拉选择菜单实现技巧

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网上看到一些例子，对于一个简单的三级联动，都加上什么Struts, Hibernate诸如此类的框架。这个Ajax联动殊不知和这些框架有什么关系，一个小Demo干嘛整得那么大。

今天我做了一个dwr+jsp做的例子。
web.xml:

 
<?xml version="1.0" encoding="UTF-8"?> 
<web-app version="2.4" xmlns="http://java.sun.com/xml/ns/j2ee" 
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee 
http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> 
<servlet> 
<servlet-name>dwr-invoker</servlet-name> 
<servlet-class> 
org.directwebremoting.servlet.DwrServlet 
</servlet-class> 
<init-param> 
<param-name>debug</param-name> 
<param-value>true</param-value> 
</init-param> 
</servlet> 
<servlet> 
<servlet-name>SelectServlet</servlet-name> 
<servlet-class>com.action.SelectServlet</servlet-class> 
</servlet> 
<servlet-mapping> 
<servlet-name>dwr-invoker</servlet-name> 
<url-pattern>/dwr/*</url-pattern> 
</servlet-mapping> 
<servlet-mapping> 
<servlet-name>SelectServlet</servlet-name> 
<url-pattern>/select</url-pattern> 
</servlet-mapping> 
<welcome-file-list> 
<welcome-file>index.jsp</welcome-file> 
</welcome-file-list> 
</web-app> 

dwr.xml:

复制代码代码如下:

 
<?xml version="1.0" encoding="UTF-8"?> 
<!DOCTYPE dwr PUBLIC "-//GetAhead Limited//DTD Direct Web Remoting 
2.0//EN" "http://www.getahead.ltd.uk/dwr/dwr20.dtd"> 
<dwr> 
<!-- 没有它DWR什么也做不了 --> 
<allow> 
<create creator="new" javascript="menu"> 
<param name="class" value="com.dao.CountryDAO" /> 
</create> 
<!-- 要转换的Bean --> 
<convert converter="bean" match="com.vo.Country" /> 
<convert converter="bean" match="com.vo.Province" /> 
<convert converter="bean" match="com.vo.City" /> 
</allow> 
</dwr> 

test.jsp:

复制代码代码如下:

 
<%@ page language="java" import="java.util.*,com.vo.*" 
pageEncoding="GBK"%> 
<%@ taglib uri="http://java.sun.com/jstl/core" prefix="c"%> 
<html> 
<head> 
<title>DWR三级联动</title> 
<script type='text/javascript' 
src='/mutiplyMenu/dwr/interface/menu.js'></script> 
<script type='text/javascript' src='/mutiplyMenu/dwr/engine.js'></script> 
<script type='text/javascript' src='/mutiplyMenu/dwr/util.js'></script> 
</head> 
<body> 
<script type="text/javascript"> 
//根据国家id查询所属省或州 
function queryProvince() 
{ 
var countryId = $("country").value; 
//默认为不选择 
if(countryId == 0) 
{ 
${"province"}.options.length=0; 
${"city"}.options.length=0; 
} 
else 
{ 
menu.queryProvinceById(countryId,provinceCallback); 
} 
} 
//根据国家id查询所属省或州的回调函数 
function provinceCallback(provinces) 
{ 
${"province"}.options.length=0; 
//每次获得新的数据的时候先把每二个下拉框架的长度清0 
for(var i=0;i< provinces.length;i ++){ 
var value = provinces[i].id; 
var text = provinces[i].provinceName; 
var option = new Option(text, value); 
//根据每组value和text标记的值创建一个option对象 
try{ 
$("province").add(option);//将option对象添加到第二个下拉框中 
}catch(e){ 
} 
} 
//同时关联第三级 
var provinceId = ${"province"}.value; 
menu.queryCityById(provinceId,cityCallback); 
} 
//查询所属城市 
function queryCity() 
{ 
var provinceId = $("province").value; 
menu.queryCityById(provinceId,cityCallback); 
} 
//查询所属城市回调函数 
function cityCallback(citys) 
{ 
//每次获得新的数据的时候先把每三个下拉框架的长度清0 
${"city"}.options.length=0; 
for(var i=0;i< citys.length;i ++){ 
var value = citys[i].id; 
var text = citys[i].cityName; 
var option = new Option(text, value); 
//根据每组value和text标记的值创建一个option对象 
try{ 
$("city").add(option);//将option对象添加到第三个下拉框中 
}catch(e){ 
} 
} 
} 
function change1() 
{ 
queryProvince(); 
} 
function change2() 
{ 
queryCity(); 
} 
</script> 
<div align="center"> 
<h3> 
<br> 
</h3> 
<h3> 
DWR三级联动演示 
</h3> 
<!-- 我都奇怪了，我的<c>标签在这里不能用 --> 
<select id="country" onchange="change1();"> 
<option selected="selected" value="0"> 
请选择 
</option> 
<% 
@SuppressWarnings("unchecked") 
List list = (List) request.getAttribute("countrys"); 
for (int i = 0; i < list.size(); i++) 
{ 
Country temp = (Country) list.get(i); 
%> 
<option value="<%=temp.getId()%>"><%=temp.getCountryName()%></option> 
<% 
} 
%> 
</select> 
<select id="province" onchange="change2();"> 
</select> 
<select id="city"> 
</select> 
</div> 
</body> 
</html> 