dynamicLists.html-优快云博客

本文链接：https://blog.youkuaiyun.com/iteye_9891/article/details/81692320

本文介绍了一个使用Ajax技术动态更新下拉列表的示例。通过监听用户选择的汽车年份和品牌，向服务器发送请求获取对应的车型列表，并更新第三个下拉列表。此示例展示了如何结合JavaScript与Servlet实现异步数据加载。

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例子来源：《Ajax 基础教程》金灵等译这本书非常不错

dynamicLists.html


<html>
<head>
<title>Dynamically Filling Lists</title>
<script type="text/javascript">
var xmlHttp;
function createXMLHttpRequest() {
	if (window.ActiveXObject) {
		xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
	}
	else if (window.XMLHttpRequest) {
		xmlHttp = new XMLHttpRequest();
	}
}

function refreshModelList() {
	var make = document.getElementById("make").value;
	var modelYear = document.getElementById("modelYear").value;

	if (make == "" || modelYear == "") {
		clearModelsList();
		return;
	}

	var url = "RefreshModelList?"
		+ createQueryString(make, modelYear) + "&ts=" + new Date().getTime();

	createXMLHttpRequest();
	xmlHttp.onreadystatechange = handleStateChange;
	xmlHttp.open("GET", url, true);
	xmlHttp.send(null);
}

function createQueryString(make, modelYear) {
	var queryString = "make=" + make + "&modelYear=" + modelYear;
	return queryString;
}

function handleStateChange() {
	if (xmlHttp.readyState == 4) {
		if (xmlHttp.status == 200) {
			updateModelsList();
		}
	}
}

function updateModelsList() {
	clearModelsList();

	var models = document.getElementById("models");
	var results = xmlHttp.responseXML.getElementsByTagName("model");
	var option = null;
	for (var i = 0; i < results.length; i++) {
		option = document.createElement("option");
		option.appendChild(document.createTextNode(results[i].firstChild.nodeValue));
		models.appendChild(option);
	}
}

function clearModelsList() {
	var models = document.getElementById("models");
	while (models.childNodes.length > 0) {
		models.removeChild(models.childNodes[0]);
	}
}
</script>
</head>
<body>
<h1>Select Model Year and Make</h1>

<form action="#">
	<span style="font-weight:bold;">Model Year:</span>
	<select id="modelYear" onchange="refreshModelList();">
		<option value="">Select One</option>
		<option value="2006">2006</option>
		<option value="1995">1995</option>
		<option value="1985">1985</option>
		<option value="1970">1970</option>
	</select>
	<br/><br/>
	<span style="font-weight:bold;">Make:</span>
	<select id="make" onchange="refreshModelList();">
		<option value="">Select One</option>
		<option value="Chevrolet">Chevrolet</option>
		<option value="Dodge">Dodge</option>
		<option value="Pontiac">Pontiac</option>
	</select>

	<br/><br/>
	<span style="font-weight:bold;">Models:</span>
	<br/>
	<select id="models" size="6" style="width:300px;">

	</select>

</form>
</body>
</html>

RefreshModelListServlet.java


package ajaxbook.chap4;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class RefreshModelListServlet extends HttpServlet {

	private static List availableModels = new ArrayList();

	protected void processRequest(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		response.setContentType("text/html;charset=UTF-8");

		int modelYear = Integer.parseInt(request.getParameter("modelYear"));
		String make = request.getParameter("make");

		StringBuffer results = new StringBuffer("<models>");
		MakeModelYear availableModel = null;
		for (Iterator it = availableModels.iterator(); it.hasNext();) {
			availableModel = (MakeModelYear) it.next();
			if (availableModel.modelYear == modelYear) {
				if (availableModel.make.equals(make)) {
					results.append("<model>");
					results.append(availableModel.model);
					results.append("</model>");
				}
			}
		}
		results.append("</models>");

		response.setContentType("text/xml");
		response.getWriter().write(results.toString());
	}

	protected void doGet(HttpServletRequest request,
			HttpServletResponse response) throws ServletException, IOException {
		processRequest(request, response);
	}

	public void init() throws ServletException {
		availableModels.add(new MakeModelYear(2006, "Dodge", "Charger1"));
		availableModels.add(new MakeModelYear(1995, "Dodge", "Charger2"));
		availableModels.add(new MakeModelYear(1985, "Dodge", "Charger3"));
		availableModels.add(new MakeModelYear(1970, "Dodge", "Charger4"));
		availableModels.add(new MakeModelYear(2006, "Dodge", "Charger5"));
		availableModels.add(new MakeModelYear(2006, "Dodge", "Charger6"));
		availableModels.add(new MakeModelYear(2006, "Dodge", "Charger7"));
		availableModels.add(new MakeModelYear(2006, "Dodge", "Charger8"));
	}

	private static class MakeModelYear {

		private int modelYear;
		private String make;
		private String model;

		public MakeModelYear(int modelYear, String make, String model) {
			this.modelYear = modelYear;
			this.make = make;
			this.model = model;
		}
	}

}