验证码

package cn.meeting.utils;

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.imageio.ImageIO;
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 ImgServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;

    protected void doGet(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        // 1:声明高宽
        int width = 60;
        int height = 30;
        // 2:定义内存中的图片
        BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        // 4:获取G
        Graphics g = img.getGraphics();
        // 5:设置背景为white
        g.setColor(Color.WHITE);
        g.fillRect(0, 0, width, height);
        g.setFont(new Font("宋体", Font.BOLD, 18));
        //
        Random r = new Random();
        StringBuilder stringBuilder = new StringBuilder();
        String str="";
        for (int i = 0; i < 4; i++) {
            //int a = r.nextInt(10);   生成数字验证码
            
            //生成字母验证码
             /*int t = r.nextInt(2);
             char a = t ==0? (char)(r.nextInt(26)+'a'):(char)(r.nextInt(26)+'A');
             stringBuilder.append(a);*/
            
            str = getRandomChar();
            stringBuilder.append(str);
            g.setColor(new Color(r.nextInt(256), r.nextInt(256), r.nextInt(256)));
            g.drawString("" + str, i * 15, 10 + r.nextInt(20));
        }

        //------将验证码保存到session中去
        
        HttpSession session = request.getSession();
        session.setAttribute("randomNum", str);
        
        for (int i = 0; i < 8; i++) {
            g.setColor(new Color(r.nextInt(256), r.nextInt(256), r.nextInt(256)));
            g.drawLine(r.nextInt(width), r.nextInt(height), r.nextInt(width), r.nextInt(height));
        }

        //
        g.dispose();

        // 设置输出的类型
        response.setContentType("image/jpg");
        OutputStream out = response.getOutputStream();
        // 使用ImageIO
        ImageIO.write(img, "JPEG", out);
    }
    
    /*
     * 生成验证码的方法
     */
     public static String getRandomChar() { 
         int index = (int) Math.round(Math.random() * 2); 
         String randChar = ""; 
         switch (index) { 
         case 0://大写字符 
             randChar = String.valueOf((char)Math.round(Math.random() * 25 + 65)); 
             break; 
         case 1://小写字符 
             randChar = String.valueOf((char)Math.round(Math.random() * 25 + 97)); 
             break; 
         default://数字 
             randChar = String.valueOf(Math.round(Math.random() * 9)); 
             break; 
         } 
         return randChar; 
     } 
}