web项目登陆页面添加验证码

1：首先编写一个普通的servlet生成随机图片

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.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import com.sun.image.codec.jpeg.JPEGCodec;
import com.sun.image.codec.jpeg.JPEGImageEncoder;

public class RandImgsServlet extends HttpServlet {
public void doGet(HttpServletRequest request,
HttpServletResponse response)throws ServletException, IOException {
String sRand = "";
int width = 60, height = 20;
BufferedImage image = new BufferedImage(width, height,
BufferedImage.TYPE_INT_RGB);
// 获取图形上下文
Graphics g = image.getGraphics();
// 生成随机类
Random random = new Random();
// 设定背景色
g.setColor(getRandColor(100, 250));
g.fillRect(0, 0, width, height);
// 设定字体
g.setFont(new Font("Comic Sans MS", Font.PLAIN, 15));
// 画边框
// g.setColor(new Color());
// g.drawRect(0,0,width-1,height-1);
// 随机产生155条干扰线，使图象中的认证码不易被其它程序探测到
g.setColor(getRandColor(160, 200));
for (int i = 0; i < 155; i++) {
int x = random.nextInt(width);
int y = random.nextInt(height);
int xl = random.nextInt(12);
int yl = random.nextInt(12);
g.drawLine(x, y, x + xl, y + yl);
}
// 取随机产生的认证码(4位数字)
// String rand = request.getParameter("rand");
// rand = rand.substring(0,rand.indexOf("."));
for (int i = 0; i < 4; i++) {
String rand = String.valueOf(random.nextInt(10));
sRand += rand;
// 将认证码显示到图象中
g.setColor(new Color(20 + random.nextInt(110), 20 + random
.nextInt(110), 20 + random.nextInt(110))); // 调用函数出来的颜色相同，可能是因为种子太接近，所以只能直接生成
g.drawString(rand, 13 * i + 6, 16);
}
// 图象生效
g.dispose();
request.getSession().setAttribute("sRandFont",sRand);
ServletOutputStream sos = response.getOutputStream();
JPEGImageEncoder code = JPEGCodec.createJPEGEncoder(sos);
code.encode(image);
}
public Color getRandColor(int fc, int bc) { // 给定范围获得随机颜色
Random random = new Random();
if (fc > 255)
fc = 255;
if (bc > 255)
bc = 255;
int r = fc + random.nextInt(bc - fc);
int g = fc + random.nextInt(bc - fc);
int b = fc + random.nextInt(bc - fc);
return new Color(r, g, b);
}
}
2：将这个servlet注册到web.xml中
<servlet>
<servlet-name>Vcode</servlet-name>
<servlet-class>com.framework.common.servlet.RandImgsServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>Vcode</servlet-name>
<url-pattern>/code.do</url-pattern>
</servlet-mapping>

3：在登录页面加入验证码输入框以及验证码图片

验证码
                    <span style="white-space:pre">	</span>
<img onclick="$(this).attr('src', 'code.do?ran=' + Math.random())" src="code.do"  title="点击刷新验证码"  class="vcodeImg">
<input  id="vcode" name="vcode">

4:最后在提交登录表单后，验证即可（生成的验证码，已经保存到session中）                    <span style="white-space:pre">	</span>