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sessiona小案例之验证码

1.生成验证码

package web;import java.awt.Color;import java.awt.Font;import java.awt.Graphics;import java.awt.image.BufferedImage;import java.io.IOException;import java.io.OutputStream;import java.util.Random;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 CheckcodeServlet1 extends HttpServlet {		public void service(HttpServletRequest request, HttpServletResponse response)			throws ServletException, IOException {		System.out.println("checkcode...");		/*		 * 一,绘图		 */		//step1,内存映像对象(画布)		BufferedImage image = 			new BufferedImage(					80,30,					BufferedImage.TYPE_INT_RGB);		//step2,获得画笔		Graphics g = image.getGraphics();		//step3,给画笔设置颜色		g.setColor(new Color(255,255,255));		//step4,给画布设置背景颜色		g.fillRect(0, 0, 80, 30);		//step5,重新给笔设置颜色		Random r = new Random();		g.setColor(new Color(r.nextInt(255),				r.nextInt(255),r.nextInt(255)));		g.setFont(new Font(null,Font.ITALIC,24));		//step6,生成一个随机数(验证码)		String number = getNumber();		//将验证码绑订到session,用来验证。		HttpSession session =			request.getSession();		session.setAttribute("number", number);		//将验证码转换成图片		g.drawString(number, 2, 25);		//step7,加一些干扰线		for(int i = 0; i < 8; i ++){			g.setColor(new Color(r.nextInt(255),					r.nextInt(255),r.nextInt(255)));			g.drawLine(r.nextInt(80), 					r.nextInt(30), r.nextInt(80),					r.nextInt(30));		}		/*		 * 二,压缩图片并输出		 */		//设置服务器返回的数据类型(图片)		response.setContentType("image/jpeg");		//获得字节输出流		OutputStream ops = 			response.getOutputStream();		//压缩图片并输出		javax.imageio.ImageIO		.write(image, "jpeg", ops);		ops.close();			}		//长度为5个字符的验证码(这些字符要求从	//"A~Z,0~9"中选取,排除0,o,1,i)	private String getNumber() {		String number = "";		String chars = "ABCDEFGHJKLMNPQRSTU" +				"VWXYZ23456789";		Random r = new Random();		for(int i = 0; i < 5; i ++){			number += chars.charAt(					r.nextInt(chars.length()));		}		return number;	}}

代码：

        验证码:         换一张                  <%        String msg = (String)request.getAttribute("number_error");       %>       <%=(msg==null?"":msg) %>     /tr>

//number1  -- 系统生成的验证码HttpSession session = request.getSession();String number1 = (String)session.getAttribute("number");//number2  -- 表单提交的验证码String number2 = request.getParameter("number");if(!number1.equalsIgnoreCase(number2)){	request.setAttribute("number_error","验证码错误！");        request.getRequestDispatcher("regist.jsp").forward(request,response);	return ;}