jsp验证码实现代码

1.后台java代码

package com.bobo.base.servlet;

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;

/**
 * <p>Title:用于产生校验码的servlet类</p>
 * <p>Description: 用于产生校验码的servlet类</p>
 * @author  
 * @version 1.0 2010-09-05
 */

@SuppressWarnings("serial")
public class CheckCodeServlet extends HttpServlet {
    
	public void doGet(HttpServletRequest request, HttpServletResponse response)
    throws ServletException, IOException {

    //设置页面不缓存
    response.setHeader("Pragma", "No-cache");
    response.setHeader("Cache-Control", "no-cache");
    response.setDateHeader("Expires", 0);

    // 在内存中创建图象
    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(200, 250));
    g.fillRect(0, 0, width, height);

    //设定字体
    g.setFont(new Font("Times New Roman", Font.PLAIN, 18));

    //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 sRand = "";
    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
        // 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.setColor(new Color(20 + random.nextInt(110), 20 + random.nextInt(110), 20 + random.nextInt(110)));
        g.drawString(rand, 13 * i + 6, 16);
    }

    // 将认证码存入SESSION
    request.getSession().setAttribute("checkCode", sRand);

    // 图象生效
    g.dispose();

    // 输出图象到页面
    ImageIO.write(image, "JPEG", response.getOutputStream());
}
 /**
  * 获取随机颜色
  * @param fc
  * @param bc
  * @return
  */	
private	Color getRandColor(int fc,int bc) {
	    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);
	}


}

<servlet>
    <servlet-name>checkCodeServlet</servlet-name>
    <servlet-class>com.bobo.base.servlet.CheckCodeServlet</servlet-class>
  </servlet>
  <servlet-mapping>
    <servlet-name>checkCodeServlet</servlet-name>
    <url-pattern>/checkCode.jpg</url-pattern>
  </servlet-mapping>

 <tr>
        <th>验证码:</th>
	<td><input  id="checkCode" name="checkCode" size="30" maxlength="6" type="text" value="" style="ime-mode:disabled"/><img src='checkCode.jpg' class="code" /></td> 
</tr>

session中拿到checkCode的值与jsp页面传入的值checkCode进行比较。