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>