JS代码function getXMLRequest(){
var request;
try{
//for火狐等浏览器
request = new XMLHttpRequest();
}catch(e){
try{
//for IE
request = new ActiveXObject("Microsoft.XMLHttp");
}catch(e){
alert("您的浏览器不支持AJAX!!!");
return null; }
}
return request;
}
function checkcode(){
alert(1);
var request = getXMLRequest();//得到XMLHttpRequest对象
alert(2);
//将请求发送出去
request.open("GET","ImageAction",true);
alert(3);
request.onreadystatechange = function(){
if(request.readyState == 4){
alert("进来了");
document.getElementById("code").src = "ImageAction";//改变验证码图片
}
}
alert(4);
request.send(null);
alert(5);
}
<input type="text" name="checkCode" style="width: 50%">
<img id="code" src="ImageAction">
<a href="#" onclick="checkcode()">看不清,换一张</a>
var request;
try{
//for火狐等浏览器
request = new XMLHttpRequest();
}catch(e){
try{
//for IE
request = new ActiveXObject("Microsoft.XMLHttp");
}catch(e){
alert("您的浏览器不支持AJAX!!!");
return null; }
}
return request;
}
function checkcode(){
alert(1);
var request = getXMLRequest();//得到XMLHttpRequest对象
alert(2);
//将请求发送出去
request.open("GET","ImageAction",true);
alert(3);
request.onreadystatechange = function(){
if(request.readyState == 4){
alert("进来了");
document.getElementById("code").src = "ImageAction";//改变验证码图片
}
}
alert(4);
request.send(null);
alert(5);
}
<input type="text" name="checkCode" style="width: 50%">
<img id="code" src="ImageAction">
<a href="#" onclick="checkcode()">看不清,换一张</a>
package com.wnkj.user.action;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ImageAction extends HttpServlet {
/**
* 执行登陆的业务处理
* @param request:发送上来的请求
* @return destJsp:目标URL
*/
public void service(HttpServletRequest request,
HttpServletResponse response) throws IOException,ServletException{
//设置页面不缓存
response.setHeader("Pragma", "No-cache");
response.setHeader("Cache-Control", "no-cache");
response.setDateHeader("Expires", 0);
//在内存中创建图象
int width = 60, height = 20;
BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
//获取图形上下文
Graphics g = image.getGraphics();
//生成随机类
Random random = new Random();
//设定背景色
g.setColor(getRandColor(220, 250));
g.fillRect(0, 0, width, height);
//设定字体
g.setFont(new Font("Times New Roman", Font.PLAIN, 18));
//画边框
//g.drawRect(0,0,width-1,height-1);
g.draw3DRect(0,0,width-1,height-1,true);
//随机产生155条干扰线,使图象中的认证码不易被其它程序探测到
g.setColor(getRandColor(160, 200));
for (int i = 0; i < 155; i++) {
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(12);
int yl = random.nextInt(12);
g.drawLine(x, y, x + xl, y + yl);
}
// 取随机产生的认证码(6位数字)
String sRand = "";
String s = "012345678901234567890123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ012345678901234567890123456789abcdefghijklmnopqrstuvwxyz";
for (int i = 0; i < 4; i++) {
char rand =s.charAt(random.nextInt(s.length()));
sRand += rand;
// 将认证码显示到图象中
g.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110)));
//调用函数出来的颜色相同,可能是因为种子太接近,所以只能直接生成
g.drawString(String.valueOf(rand), 13 * i + 6, 16);
}
g.drawOval(0,12,60,11);
// 将认证码存入SESSION
request.getSession().setAttribute("rand", sRand);
System.out.println(sRand+"验证码");
// 图象生效
g.dispose();
ServletOutputStream output;
try {
output = response.getOutputStream();
// 输出图象到页面
ImageIO.write(image, "JPEG", output);
} catch (IOException e) {
e.printStackTrace();
}
}
/**
* 生成随机颜色
*/
private Color getRandColor(int fc, int bc) {
Random random = new Random();
if (fc > 255)
fc = 255;
if (bc > 255)
bc = 255;
int r = fc + random.nextInt(bc - fc);
int g = fc + random.nextInt(bc - fc);
int b = fc + random.nextInt(bc - fc);
return new Color(r, g, b);
}
}
我刚才发现了 验证码换了 但是前台图片没换
到底怎么回事?
最原始的ajax就是这么写的
再不换就加个随机时间
也有可能是浏览器缓存了