利用jaxp、dom实现ajax xml 响应

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在某些情况下用 jaxp dom api 实现ajax xml响应会是一个很好的选择,可以简化程序.需要用到的jar包

javax.xml.parsers.*;
org.w3c.dom.*;
javax.xml.transform.*;
javax.xml.transform.stream.*;
javax.xml.transform.dom.*;

前两个包用来创建xml文档,后面几个用来转换到输出流. 以下用先简要说明，然后贴出一个完整实例

创建新文档

DocumentBuilderFactory factory = DocumentBuilderFactory. newInstance();
DocumentBuilder builder = factory.newDocumentBuilder();

Document doc = builder.newDocument();
创建root元素或其它元素 Element root = doc.createElement("selects");

doc.appendChild(root);
Element的appendChild()方法用来添加子元素

创建文本结点 doc.createTextNode(String textNode)

在servlet中通过以下方法转换到输出流
Transformer t = TransformerFactory.newInstance().newTransformer();
t.transform(new DOMSource(doc), new StreamResult(response.getWriter()));

一、 web.inf 文件配置一个servlet
<?xml version="1.0" encoding="ISO-8859-1"?>

<web-app 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"
version="2.4">

<display-name>Welcome to Tomcat</display-name>
<description>
Welcome to Tomcat
</description>

<servlet>
  <servlet-name>SelectServlet</servlet-name>
  <servlet-class>drownmenu.SelectServlet</servlet-class>
</servlet>
<servlet-mapping>
  <servlet-name>SelectServlet</servlet-name>
  <url-pattern>/SelectServlet</url-pattern>
</servlet-mapping>
</web-app>

二、JSP页面
<%@ page language="java" contentType="text/html; charset=utf-8"%>

<html>
<head>
<title>Ajax 联动下拉框</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<SCRIPT type="text/javascript">

        var req;
        window.onload=function(){
        }
        function Change_Select()
        {
            var zhi=document.getElementById('state').value;
            var url="/Tajax/SelectServlet?id="+escape(zhi);
            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)
                {
                    parseMessage();
                }else{
                    alert("Not able to retrieve description"+req.statusText);
                }
            }
        }
        function parseMessage()
        {
            var xmlDoc=req.responseXML.documentElement;
            var xSel=xmlDoc.getElementsByTagName('select');
            var select_root=document.getElementById('city');
            select_root.options.length=0;
            for(var i=0;i< xSel.length;i++)
            {
                var xValue=xSel[i].childNodes[0].firstChild.nodeValue;
                var xText=xSel[i].childNodes[1].firstChild.nodeValue;
                var option=new Option(xText,xValue);
                try{
                    select_root.add(option);
                }catch(e){
                }
            }
        }

</script>
</head>

<body>
<div align="center">
<form name="form1" method="post" action="">
<TABLE width="70%" boder="0" cellspacing="0">
<TR>
<TD align="center">Ajax 联动下拉框</TD>
</TR>
<TR>
<TD>请选择省份:

<SELECT name="state" id="state" onChange="Change_Select()">
<OPTION value="0">未选择</OPTION>
<OPTION value="1">湖南</OPTION>
<OPTION value="2">湖北</OPTION>
</SELECT>

请选择城市:
<SELECT name="city" id="city">
<OPTION value="0">未选择</OPTION>
</SELECT>
</TD>
</TR>
<TR><td> </td></TR>
</TABLE>
</form>
</div>
</body>
</html>

三、 SelectServlet 类
package drownmenu;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import javax.xml.parsers.*;
import org.w3c.dom.*;
import javax.xml.transform.*;
import javax.xml.transform.stream.*;
import javax.xml.transform.dom.*;

public class SelectServlet extends HttpServlet {

//Initialize global variables
public void init() throws ServletException {
}

//Process the HTTP Get request
public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
    String targetId = request.getParameter("id").toString();
    response.setCharacterEncoding("UTF-8");
    response.setContentType("application/xml");
    try {
       DocumentBuilderFactory factory = DocumentBuilderFactory. newInstance();
       DocumentBuilder builder = factory.newDocumentBuilder();
       Document doc = builder.newDocument();

       Element root = doc.createElement("selects");
       doc.appendChild(root);

/*
String xml_start="<selects>";
String xml_end="</selects>";
String xml="";
*/

if (targetId.equalsIgnoreCase("0")) {
    makeElement(doc, root, new String[] {"未选择"});
   // xml = "<select><value>0</value><text>Unbounded</text></select>";
}
if (targetId.equalsIgnoreCase("1")) {
   makeElement(doc, root, new String[] {"长沙","岳阳"});

/* xml ="<select><value>1</value><text>Mana Burn</text></select>";
xml +="<select><value>2</value><text>Death Coil</text></select>";
xml +="<select><value>3</value><text>Unholy Aura</text></select>";
xml +="<select><value>4</value><text>Unholy Fire</text></select>";
*/
}

if (targetId.equalsIgnoreCase("2")) {
    makeElement(doc, root, new String[] {"武汉","石堰","襄樊","孝感"});
/*
xml ="<select><value>1</value><text>Corprxplode</text></select>";
xml +="<select><value>2</value><text>Raise Dead</text></select>";
xml +="<select><value>3</value><text>Brilliance Aura</text></select>";
xml +="<select><value>4</value><text>Aim Aura</text></select>";
*/
} //else {
    // makeElement(doc, root, new String[] {"何畅1", "何畅2", "何畅3"});
/*
xml ="<select><value>1</value><text>Rain of Chaos</text></select>";
xml +="<select><value>2</value><text>Finger of Death</text></select>";
xml += "<select><value>3</value><text>Bash</text></select>";
xml +="<select><value>4</value><text>Summon Doom</text></select>";
*/
// }

    Transformer t = TransformerFactory.newInstance().newTransformer();
     t.transform(new DOMSource(doc), new StreamResult(response.getWriter()));

  } catch (Exception ex) {
      throw new ServletException(ex.toString());
}
   // String last_xml = xml_start + xml + xml_end;
    // response.getWriter().write(last_xml);
}

private void makeElement(Document doc, Element root, String[] name) throws　 DOMException {
   if (name == null) {
     return;
   }

for (int i = 0; i < name.length; i++) {
Element selectElement = doc.createElement("select");
root.appendChild(selectElement);

   Element valueElement = doc.createElement("value");
   Element textElement = doc.createElement("text");
   int t=i+1;
   Text valueText = doc.createTextNode(""+t);
   Text textText = doc.createTextNode(name[i]);
    valueElement.appendChild(valueText);
    textElement.appendChild(textText);
    selectElement.appendChild(valueElement);
    selectElement.appendChild(textElement);
   }

}

//Process the HTTP Post request
public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
doGet(request, response);
}

//Clean up resources
public void destroy() {
}
}

运行图：