使用jsp生成验证码

<%@ page language="java" import="java.util.*" %>
<%
String path = request.getContextPath();
String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/";
%>
<%@ page contentType="image/JPEG"  
    import="java.awt.*,java.awt.image.*,java.util.*,javax.imageio.*"  
    pageEncoding="GBK"%> 
<%!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);   
    }%>  
  <%   
    //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 < 100; 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   
        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);   
    }   
  
    // 将认证码存入SESSION   
    session.setAttribute("code", sRand);   
  
    // 图象生效   
    g.dispose();   
  
    // 输出图象到页面   
    ImageIO.write(image, "JPEG", response.getOutputStream());  
    out.clear(); 
    out=pageContext.pushBody();//这两行代码不加会产生异常
    
%>