JSP中验证码的使用

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;
import java.awt.image.*;
import java.awt.*;
import com.sun.image.codec.jpeg.*;

/**
 *
 * 在Web.xml中布署：
 
    CodePicServlet
    com.liuxu.servlet.CodePicServlet
 
 
    CodePicServlet
    /verifycode
 
 *
 * 在JSP中写上：
 *
 *
 * 在调用时，运行String random = (String) session.getAttribute("verifyCode");
 * 得到产生的验证码
 *
 */
public class CodePicServlet extends HttpServlet {
  //改成Servlet，就重写service方法就不会出现IllegalStateException异常了，不要写在JSP中
  protected void service(HttpServletRequest request,
      HttpServletResponse response) throws ServletException,
      IOException {
    String chose = "0123456789"; //abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ
    Random rand = new Random();
    HttpSession session = request.getSession(true);
    //设置显示内容
    response.setContentType("image/jpeg");
    //设置页面不缓存
    response.addHeader("pragma", "NO-cache");
    response.addHeader("Cache-Control", "no-cache");
    response.addDateHeader("Expries", 0);
    // 在内存中创建图象
    int width = 65, height = 20;
    BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    // 获取图形上下文
    Graphics g = image.getGraphics();
    //以下填充背景颜色
    g.setColor(new Color(51, 102, 255));
    g.fillRect(0, 0, width, height);
    //画边框
    // g.setColor(Color.BLACK);
    // g.drawRect(0, 0, width - 1, height - 1);
    // 随机产生很多条干扰线，使图象中的认证码不易被其它程序探测到
    for (int i = 0; i < 30; i++) {
      g.setColor(getRandColor(100, 150));
      int x = rand.nextInt(width);
      int y = rand.nextInt(height);
      int xl = rand.nextInt(10);
      int yl = rand.nextInt(10);
      g.drawLine(x, y, x + xl, y + yl);
    }
    //设置字体
    g.setFont(new Font("Times New Roman", Font.BOLD + Font.ITALIC, 16));
    //设置字体颜色
    g.setColor(Color.WHITE);
    // 取随机产生的认证码(4位数字)
    String sRand = "";
    for (int i = 0; i < 4; i++) {
      String ranChar = String.valueOf(chose.charAt(rand.nextInt(chose.length())));
      sRand += ranChar;
      //画一个出来
      g.drawString(ranChar, 14 * i + 6, 15);
    }
    //在session中会有一个代码的对象
    session.setAttribute("verifyCode", String.valueOf(sRand));
    // 图象生效
    g.dispose();
    ServletOutputStream outStream = response.getOutputStream();
    //将输出流建立成一个JPEG的文件编码
    JPEGImageEncoder encoder = JPEGCodec.createJPEGEncoder(outStream);
    encoder.encode(image);
    outStream.flush();
    outStream.close();
  }

  //给定范围获得随机颜色
  Color getRandColor(int beginColor, int endColor) {
    Random random = new Random();
    if (beginColor > 255) {
      beginColor = 255;
    }
    if (endColor > 255) {
      endColor = 255;
    }
    int r = beginColor + random.nextInt(endColor - beginColor);
    int g = beginColor + random.nextInt(endColor - beginColor);
    int b = beginColor + random.nextInt(endColor - beginColor);
    return new Color(r, g, b);
  }
}