validation.html
例子来源：《Ajax 基础教程》 金灵 等译 这本书非常不错validation.html
<html><head><title>Using Ajax for validation</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 validate() {createXMLHttpRequest();var date = document.getElementById("birthDate");var url = "ValidationServlet?birthDate=" + escape(date.value);xmlHttp.onreadystatechange = callback;xmlHttp.open("GET", url, true);xmlHttp.send(null);}function callback() {if(xmlHttp.readyState == 4) {if(xmlHttp.status == 200) {var mes = xmlHttp.responseXML.getElementsByTagName("message").firstChild.data;var val = xmlHttp.responseXML.getElementsByTagName("passed").firstChild.data;setMessage(mes, val);}}}function setMessage(message, isValid) {var messageArea = document.getElementById("dateMessage");var fontColor = "red";if (isValid == "true") {fontColor = "gree";}messageArea.innerHTML = "<font color=" + fontColor + ">" + message + " </font>";}</script></head><body><h1>Ajax Validation Example</h1>Birth date: <input type="text" size="10" id="birthDate" onchange="validate();" /><div id="dateMessage"></div></body></html>
ValidationServlet.java
package ajaxbook.chap4;import java.io.IOException;import java.io.PrintWriter;import java.text.ParseException;import java.text.SimpleDateFormat;import javax.servlet.ServletException;import javax.servlet.http.HttpServlet;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;public class ValidationServlet extends HttpServlet {protected void doGet(HttpServletRequest request,HttpServletResponse response) throws ServletException, IOException {PrintWriter out = response.getWriter();boolean passed = validateDate(request.getParameter("birthDate"));response.setContentType("text/xml");response.setHeader("Cache-Control", "no-cache");String message = "You have entered an invalid date.";if (passed) {message = "You have entered a valid date.";}out.println("<response>");out.println("<passed>" + Boolean.toString(passed) + "</passed>");out.println("<message>" + message + "</message>");out.println("</response>");out.println();out.close();}private boolean validateDate(String date) {boolean isValid = true;if (date != null) {SimpleDateFormat formatter = new SimpleDateFormat("yyyyMMdd");try {formatter.parse(date);} catch (ParseException e) {System.out.println(e.toString());isValid = false;}} else {isValid = false;}return isValid;}}
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