一个可以在JSP里面应用的验证码

  首先声明，这不是原创，而是从现有系统扒下来的一段验证码程序，至于出处已经无从考证，完全是想借助javaeye这个平台做一次搬运和备份，如果正好下面的代码正好能为你所使用，请对那位贡献了此段代码的人致敬。

生成验证码的JSP

<%@ page language="java" contentType="text/html;charset=UTF-8"%>
<%@ page import="java.awt.*,java.awt.image.*,java.util.*,com.sun.image.codec.jpeg.*"%>
<%
	request.setCharacterEncoding("UTF-8");
	response.setCharacterEncoding("UTF-8");
	response.setContentType("text/html; charset=UTF-8");

	String chose = "123456789abcdefghjkmnpqrstuvwxyzABCDEFGHJKLMNPQRSTUVWXYZ";

	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[i * 2] = temp;

		ran[i] = 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 = 65, height = 20;
	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.LIGHT_GRAY);
	g.fillRect(0, 0, width, height);
	//设置字体颜色
	g.setColor(Color.RED);
	Font font = new Font("Arial", Font.PLAIN, 17);
	g.setFont(font);
	g.drawString(random, 5, 15);
	Random r = new Random();
	for (int i = 0; i < 20; i++) {
		int x = r.nextInt(width);
		int y = r.nextInt(height);
		g.drawOval(x, y, 0, 0);
	}
	g.dispose();
	ServletOutputStream outStream = response.getOutputStream();
	JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(outStream);
	encoder.encode(image);
	outStream.close();
%>

在需要使用验证码的地方引入

<img src="random.jsp" id="random">

然后你可以判断用户输入的验证码，是否和保存在session.setAttribute("random", String.valueOf(ran));里面的验证码一致。