Response生成注册验证码实现例子02

Servlet生成注册验证码图片CheckCodeServlet.java 示例2:

import java.awt.Color;  
import java.awt.Font;  
import java.awt.Graphics;  
import java.awt.image.BufferedImage;  
import java.io.ByteArrayOutputStream;  
import java.io.IOException;  
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;  
import javax.servlet.http.HttpSession;  
@SuppressWarnings("serial")  
public class CheckCodeServlet extends HttpServlet {  
    private static int WIDTH = 60;  
    private static int HEIGHT = 20;  
    public void doGet(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
        HttpSession session = request.getSession();  
        response.setContentType("image/jpeg");  
        ServletOutputStream sos = response.getOutputStream();  
        // 设置浏览器不要缓存此图片  
        response.setHeader("Pragma", "No-cache");  
        response.setHeader("Cache-Control", "no-cache");  
        response.setDateHeader("Expires", 0);  
        // 创建内存图象并获得其图形上下文  
        BufferedImage image =new BufferedImage(WIDTH, HEIGHT, BufferedImage.TYPE_INT_RGB);  
        Graphics g = image.getGraphics();  
        // 产生随机的认证码  
        char[] rands = generateCheckCode();  
        // 产生图像  
        drawBackground(g);  
        drawRands(g, rands);  
        // 结束图像的绘制过程，完成图像  
        g.dispose();  
        // 将图像输出到客户端  
        ByteArrayOutputStream bos = new ByteArrayOutputStream();  
        ImageIO.write(image, "JPEG", bos);  
        byte[] buf = bos.toByteArray();  
        response.setContentLength(buf.length);  
        // 下面的语句也可写成：bos.writeTo(sos);  
        sos.write(buf);  
        bos.close();  
        sos.close();  
        // 将当前验证码存入到Session中  
        session.setAttribute("check_code", new String(rands));  
        // 直接使用下面的代码将有问题，Session对象必须在提交响应前获得  
        // request.getSession().setAttribute("check_code",new String(rands));  
    }  
    private char[] generateCheckCode(){  
        // 定义验证码的字符表  
        String chars = "0123456789abcdefghijklmnopqrstuvwxyz";  
        char[] rands = new char[4];  
        for (int i = 0; i < 4; i++){  
            int rand = (int) (Math.random() * 36);  
            rands[i] = chars.charAt(rand);  
        }  
        return rands;  
    }  
    private void drawRands(Graphics g, char[] rands){  
        g.setColor(Color.BLACK);  
        g.setFont(new Font(null, Font.ITALIC | Font.BOLD, 18));  
        // 在不同的高度上输出验证码的每个字符  
        g.drawString("" + rands[0], 1, 17);  
        g.drawString("" + rands[1], 16, 15);  
        g.drawString("" + rands[2], 31, 18);  
        g.drawString("" + rands[3], 46, 16);  
        System.out.println(rands);  
    }  
    private void drawBackground(Graphics g){  
        // 画背景  
        g.setColor(new Color(0xDCDCDC));  
        g.fillRect(0, 0, WIDTH, HEIGHT);  
        // 随机产生120个干扰点  
        for (int i = 0; i < 120; i++){  
            int x = (int) (Math.random() * WIDTH);  
            int y = (int) (Math.random() * HEIGHT);  
            int red = (int) (Math.random() * 255);  
            int green = (int) (Math.random() * 255);  
            int blue = (int) (Math.random() * 255);  
            g.setColor(new Color(red, green, blue));  
            g.drawOval(x, y, 1, 0);  
        }  
    }  
}  

2,注册页面:check_code.html

 <h3>带有验证码的登录页面</h3>  
        <form action="servlet/LogonFormServlet" method="post">  
            用户名：<input type="text" name="name"><br>  
            密 码：<input type="password" name="pass"><br>  
            验证码：<input type="text" name="check_code">  
            <img src="servlet/CheckCodeServlet"><br>  
            <input type="submit" value="登录">  
        </form>  

3,验证注册信息页面:LogonFormServlet.java

import java.io.*;  
import javax.servlet.*;  
import javax.servlet.http.*;  
@SuppressWarnings("serial")  
public class LogonFormServlet extends HttpServlet {  
    public void service(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
        response.setContentType("text/html;charset=GB2312");  
        PrintWriter out = response.getWriter();  
        HttpSession session = request.getSession(false);  
        if (session == null)  
        {  
            out.println("验证码处理问题!");  
            return;  
        }  
        String savedCode = (String) session.getAttribute("check_code");  
        if (savedCode == null){  
            out.println("验证码处理问题!");  
            return;  
        }  
        String checkCode = request.getParameter("check_code");  
        if (!savedCode.equals(checkCode)){  
            // 验证码未通过，不从Session中清除原来的验证码，  
            // 以便用户可以后退回登录页面继续使用原来的验证码进行登录  
            out.println("验证码无效!");  
            return;  
        }  
        // 验证码检查通过后，从Session中清除原来的验证码，  
        // 以防用户后退回登录页面继续使用原来的验证码进行登录  
        session.removeAttribute("check_code");  
        out.println("验证码通过，服务器正在校验用户名和密码!");  
    }  
    public void doPost(HttpServletRequest request, HttpServletResponse response)  
            throws ServletException, IOException {  
  
        doGet(request, response);  
    }  
  
}