Posted on 2009-11-01 12:31
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Web开发技术
简单介绍一下Ajax应用程序的基本流程：
- 创建XMLHttpRequest对象；
- 从页面中获取获取需要的数据；
- 建立要连接的URL；
- 打开与服务器的连接；
- 设置服务器相应之后要调用的函数，即回调函数；
- 发送请求；
下面以一个简单的例子来演示一下，该例子要完成的功能是使用Ajax技术对输入的EMail地址进行简单校验，根据校验的结果，在页面显示相应的消息。
index.jsp
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
</head>
<script language="javascript">
var xmlHttp;
function sendreq(){
xmlHttp = createXMLHttpRequest(); //步骤1
var url = "AjaxServlet?email=" + document.getElementById("email").value;//步骤2，3
xmlHttp.open("GET", url); //步骤4
xmlHttp.onreadystatechange = handleStateChange; //步骤5
xmlHttp.send(null); //步骤6
}
function handleStateChange(){
if(xmlHttp.readyState == 4){
if(xmlHttp.status == 200){
document.getElementById("result").innerHTML=xmlHttp.responseText;
}
}
}
function createXMLHttpRequest(){
if (window.ActiveXObject){
xmlHttp = new ActiveXObject("Microsoft.XMLHTTP");
}
else if (window.XMLHttpRequest){
xmlHttp = new XMLHttpRequest();
}
return xmlHttp;
}
</script>
<body>
<label id="result"> </label><br>
Email:<input type="text" id="email" onblur="sendreq()" value="" />
<label id="result"> </label>
</body>
</html>
AjaxServlet.java
package servlet;
import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class AjaxServlet extends HttpServlet {
private static final long serialVersionUID = 7032718233562299325L;
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse response)
throws ServletException, IOException {
processRequest(req, response, "POST");
}
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse response)
throws ServletException, IOException {
processRequest(req, response, "GET");
}
private void processRequest(HttpServletRequest req,
HttpServletResponse response, String method) throws IOException {
String email = req.getParameter("email");
StringBuffer validator = new StringBuffer("");
validator.append(method);
response.setContentType("text/html;charset=UTF-8");
PrintWriter writer = response.getWriter();
if (email.indexOf("@") < 0) {
validator.append(":FAILURE!");
}else{
validator.append(":SUCCESS!");
}
writer.write(validator.toString());
writer.close();
}
}
GET和POST请求方式区别：
- POST方法将参数串放在请求体中发送；
- GET方法将参数串放在URL中发送；
如果数据处理不改变数据模型的状态，建议使用GET方式，如果需要改变数据模型的状态，建议使用POST方式；
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" 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">
<display-name>ajax</display-name>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<servlet>
<servlet-name>AjaxServlet</servlet-name>
<servlet-class>servlet.AjaxServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>AjaxServlet</servlet-name>
<url-pattern>/AjaxServlet</url-pattern>
</servlet-mapping>
</web-app>