jsp生成好看的验证码

这是一个Servlet，名字是ImageServlet

package a;
 
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.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
public class ImageServlet extends HttpServlet {
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        request.setCharacterEncoding("utf-8");
         
        BufferedImage bfi = new BufferedImage(80,25,BufferedImage.TYPE_INT_RGB);
        Graphics g = bfi.getGraphics();
        g.fillRect(0, 0, 80, 25);
 
        //验证码字符范围
        char[] ch = "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789".toCharArray();
        Random r = new Random(); 
        int index;  
        StringBuffer sb = new StringBuffer(); //保存字符串
        for(int i=0; i<4; i++){
            index = r.nextInt(ch.length);
            g.setColor(new Color(r.nextInt(255),r.nextInt(255),r.nextInt(255)));
            Font font = new Font("宋体", 30, 20);
            g.setFont(font);
            g.drawString(ch[index]+"", (i*20)+2, 23);
            sb.append(ch[index]);
        }
         
        // 添加噪点
        int area = (int) (0.02 * 80 * 25);
        for(int i=0; i<area; ++i){
            int x = (int)(Math.random() * 80);
            int y = (int)(Math.random() * 25);
            bfi.setRGB(x, y, (int)(Math.random() * 255));
        }
         
      //设置验证码中的干扰线
        for (int i = 0; i < 6; i++) {  
              //随机获取干扰线的起点和终点
              int xstart = (int)(Math.random() * 80);
              int ystart = (int)(Math.random() * 25);
              int xend = (int)(Math.random() * 80);
              int yend = (int)(Math.random() * 25);
              g.setColor(interLine(1, 255));
              g.drawLine(xstart, ystart, xend, yend);
            }
        HttpSession session = request.getSession();  //保存到session
        session.setAttribute("verificationCode", sb.toString());
        ImageIO.write(bfi, "JPG", response.getOutputStream());  //写到输出流
    }
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        doGet(request, response);
    }
 
    private static Color interLine(int Low, int High){
        if(Low > 255)
            Low = 255;
        if(High > 255)
            High = 255;
        if(Low < 0)
            Low = 0;
        if(High < 0)
            High = 0;
        int interval = High - Low;
        int r = Low + (int)(Math.random() * interval);
        int g = Low + (int)(Math.random() * interval);
        int b = Low + (int)(Math.random() * interval);
        return new Color(r, g, b);
      }
}

接下来是一个jsp文件，先访问jsp文件。

<%@ 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=UTF-8">
<title>Insert title here</title>
</head>
<script type="text/javascript">
     function reload(){
        document.getElementById("image").src="<%=request.getContextPath() %>/imageServlet?date="+new Date().getTime();
        $("#checkcode").val("");   // 将验证码清空
    } 
      
     function verificationcode(){
         var text=$.trim($("#checkcode").val());
         $.post("${pageContext.request.contextPath}/verificationServlet",{op:text},function(data){
             data=parseInt($.trim(data));
             if(data>0){
                 $("#span").text("验证成功!").css("color","green");
             }else{
                 $("#span").text("验证失败!").css("color","red");
                 reload();  //验证失败后需要更换验证码
             }
         });
         $("#checkcode").val(""); // 将验证码清空
     }
</script>
 
<body>
     验证码：<input type="text" name="checkcode"  id="checkcode"/>
    <img  src="<%=request.getContextPath() %>/ImageServlet" alt="验证码" id="image" />
    <a href="reload();"><label>换一张</label></a><br>
    <input  type="button" value="提交"  onclick="verificationcode();">
    <span id="span"></span>
</body>
</html>