Ajax二级联动菜单实现原理及代码

t request, HttpServletResponse response)
throws ServletException, IOException
{
// response.setCharacterEncoding("GBK");
response.setContentType("text/xml");
response.setHeader("Cache-Control", "no-cache");
request.setCharacterEncoding("GBK");
response.setCharacterEncoding("UTF-8");
String targetId = request.getParameter("id").toString();
System.out.println(targetId);
// 获得请求中参数为id的值
String xml_start = "<selects>";
String xml_end = "</selects>";
String xml = "";
if (targetId.equalsIgnoreCase("0"))
{
xml = "<select><value>0</value><text>请选择</text></select>";
} else if (targetId.equalsIgnoreCase("1"))
{
xml = "<select><value>1</value><text>昌平</text></select>";
xml += "<select><value>2</value><text>丰台</text></select>";
xml += "<select><value>3</value><text>海淀</text></select>";
xml += "<select><value>4</value><text>朝阳</text></select>";
} else if (targetId.equalsIgnoreCase("2"))
{
xml = "<select><value>1</value><text>塘沽区</text></select>";
xml += "<select><value>2</value><text>汉沽区</text></select>";
xml += "<select><value>3</value><text>大港区</text></select>";
xml += "<select><value>4</value><text>东丽区</text></select>";
} else
{// 如果是3,则返回下面的字符
xml = "<select><value>1</value><text>济南</text></select>";
xml += "<select><value>2</value><text>青岛</text></select>";
xml += "<select><value>3</value><text>淄博</text></select>";
xml += "<select><value>4</value><text>枣庄</text></select>";
}
String last_xml = xml_start + xml + xml_end;
response.getWriter().write(last_xml);
}
public void doPost(HttpServletRequest request, HttpServletResponse response)
throws ServletException, IOException
{
doGet(request, response);
}
public void init() throws ServletException
{
}
}

web.xml:
复制代码 代码如下:
<?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>SelectServlet</servlet-name>
<servlet-class>com.SelectServlet</servlet-class>
</servlet>
<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>