日期验证

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日期验证。

这个例子的HTML很简单（见代码清单4-1）。其中有一个标准的输入框，相应的onchange()事件（当然，可以使用你认为合适的任何事件）会触发验证方法。可以看到，要调用标准的createXMLHttpRequest()方法，然后把输入值发送到ValidationServlet servlet。callback()函数从服务器得到结果，然后委托给setMessage()方法，这个方法会检查值以确定用什么颜色显示消息。

代码清单4-1 validation.html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" >

<html>

<head>

<title>Using Ajax for validation</title>

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.open("GET", url, true);

xmlHttp.onreadystatechange = callback;

xmlHttp.send(null);

}

function callback() {

if (xmlHttp.readyState == 4) {

if (xmlHttp.status == 200) {

var mes =

xmlHttp.responseXML

.getElementsByTagName("message")[0].firstChild.data;

var val =

xmlHttp.responseXML

.getElementsByTagName("passed")[0].firstChild.data;

setMessage(mes, val);

}

function setMessage(message, isValid) {

var messageArea = document.getElementById("dateMessage");

var fontColor = "red";

if (isValid == "true") {

fontColor = "green";

}

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();"/>

</body>

</html>

服务器端代码也很简单（见代码清单4-2）。为简单起见，这里把验证代码放在servlet中，而在生产环境中很可能会把验证代码委托给验证服务。

代码清单4-2 ValidationServlet.java

package ajaxbook.chap4;

import java.io.*;

import java.text.ParseException;

import java.text.SimpleDateFormat;

import javax.servlet.*;

import javax.servlet.http.*;

public class ValidationServlet extends HttpServlet {

/** Handles the HTTP <code>GET</code> method.

* @param request servlet request

* @param response servlet response

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.close();

}

/**

* Checks to see whether the argument is a valid date.

* A null date is considered invalid. This method

* used the default data formatter and lenient

* parsing.

* @param date a String representing the date to check

* @return message a String representing the outcome of the check

private boolean validateDate(String date) {

boolean isValid = true;

if(date != null) {

SimpleDateFormat formatter= new SimpleDateFormat("MM/dd/yyyy");

try {

formatter.parse(date);

} catch (ParseException pe) {

System.out.println(pe.toString());

isValid = false;

}

} else {

isValid = false;

}

return isValid;

}

运行这个例子会得到图4-1和图4-2所示的结果。

图4-1 输入非法的日期

图4-2 输入合法的日期