ajax+jsp实现无刷新验证码实例
3我们在做验证码的时候往往由于要反作弊，验证有时故意加入多的干扰因素，这时验证码显示不很清楚，用户经常输入错误。这样不但要重新刷新页面，导致用户没有看清楚验证码而重填而不是修改，而且如果没有用session保存下用户输入的其它数据的话(如姓名)，用户刚刚输入的内容也不存在了，这样给用户造成不好的体验。本例在原有验证方式基础之上增加一段js，通过xmlhttp来获取返回值，以此来验证是否有效，这样即使用户浏览器不支持js，也不会影响他的正常使用了。为了防止作弊，当用户连接3次输入错误时则重载一下图片，这样也利于用户因为图片上的验证码辨认不清而使终无法输入正确。本例还特别适合检验用户名是否有效，只要从后台做个sql查询，返回一个值或是xml即可。(这种例子太多 ，就在此不赘述了)。本例的优点在于非常方便用户输入，而且减少对服务器端的请求，可以说既改善用户体验而且略会节省带宽成本，但相应地要在页面上增加一段<%@ page contentType="text/html; charset=GBK" language="java" import="java.sql.*" errorPage="" pageEncoding="GBK"%>
<%
//set Chinese Char
//Cody by JarryLi@gmail.com;
//homepage:jiarry.126.com
request.setCharacterEncoding("GBK");
response.setCharacterEncoding("GBK");
response.setContentType("text/html; charset=GBK");
%>
<%
String num=request.getParameter("num");
String random=(String)session.getAttribute("random");if(num!=null&&random!=null)
{
if(!num.equals(random))
{
/*
out.println("<script>alert(验证码错误！请重试。)</script>");
out.println("<script>history.go(-1)</script>");
//response.sendRedirect("img.jsp");
*/
out.print("validate_failed:"+random);
}
else
{
//out.println("<center>验证成功！</center>");
out.print("validate_successful:"+random);
}
}
%>
<%@ page autoFlush="false"import="java.util.*,java.awt.*,java.awt.image.*,com.sun.image.codec.jpeg.*,java.util.*" %><%
//set Chinese Char
//Cody by JarryLi@gmail.com;
//homepage:jiarry.126.com
request.setCharacterEncoding("GBK");
response.setCharacterEncoding("GBK");
response.setContentType("text/html; charset=GBK");
%>
<%
String chose="0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";char display[]={0, ,0, ,0, ,0},ran[]={0,0,0,0},temp;Random rand=new Random();for(int i=0;i<4;i++)
{ temp=chose.charAt(rand.nextInt(chose.length())); display=temp; ran=temp;
}
String random=String.valueOf(display);session.setAttribute("random",String.valueOf(ran));
%>
<% out.clear();
response.setContentType("image/jpeg");
response.addHeader("pragma","NO-cache");
response.addHeader("Cache-Control","no-cache");
response.addDateHeader("Expries",0);
int width=80, height=30;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
Graphics g = image.getGraphics();
//以下填充背景颜色
g.setColor(Color.GREEN);
g.fillRect(0, 0, width, height);
//设置字体颜色
g.setColor(Color.RED);
Font font=new Font("Arial",Font.PLAIN,20);
g.setFont(font);
//g.drawString(random,5,14);
g.drawString(random,5,20);
g.dispose();
ServletOutputStream outStream = response.getOutputStream();
JPEGImageEncoder encoder =JPEGCodec.createJPEGEncoder(outStream);
encoder.encode(image);
outStream.close();
%>
/* namespacing object */
var net=new Object();
net.READY_STATE_UNINITIALIZED=0;
net.READY_STATE_LOADING=1;
net.READY_STATE_LOADED=2;
net.READY_STATE_INTERACTIVE=3;
net.READY_STATE_COMPLETE=4;
/*--- content loader object for cross-browser requests ---*/
net.ContentLoader=function(url,on_load,on_error,method,params,contentType){
this.req=null;
this.on_load=on_load;
this.on_error=(on_error) ? on_error : this.defaultError;
this.loadXMLDoc(url,method,params,contentType);
}
net.ContentLoader.prototype.loadXMLDoc=function(url,method,params,contentType){
if (!method)
{
method="GET";
}
if (!contentType && method=="POST")
{
contentType=application/x-www-form-urlencoded;
}
if (window.XMLHttpRequest)
{
this.req=new XMLHttpRequest();
}
else if (window.ActiveXObject)
{
//add try catch;
try {
this.req = new ActiveXObject("Msxml2.XMLHTTP");
}catch (e1){
try {
this.req = new ActiveXObject("Microsoft.XMLHTTP");
} catch (e2){
}
}
//
//this.req=new ActiveXObject("Microsoft.XMLHTTP");
}
if (this.req)
{
try
{
var loader=this;
this.req.onreadystatechange=function()
{
net.ContentLoader.onReadyState.call(loader);
}
this.req.open(method,url,true);
if (contentType)
{
this.req.setRequestHeader(Content-Type, contentType);
}
this.req.send(params);
}
catch (err)
{
this.on_error.call(this);
}
}
}
net.ContentLoader.onReadyState=function(){
var req=this.req;
var ready=req.readyState;
if (ready==net.READY_STATE_COMPLETE){
var httpStatus=req.status;
if (httpStatus==200 || httpStatus==0){
this.on_load.call(this);
}else{
this.on_error.call(this);
}
}
}
net.ContentLoader.prototype.defaultError=function(){
alert("error fetching data!"
+"
readyState:"+this.req.readyState
+"
status: "+this.req.status
+"
headers: "+this.req.getAllResponseHeaders());
} </p
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