利用servlet生成简单的验证码

在web.xml配置:

<servlet>   
    <servlet-name>image</servlet-name>   
    <servlet-class>org.test.web.AuthImage</servlet-class>   
</servlet>   
   
<servlet-mapping>   
    <servlet-name>image</servlet-name>   
 <url-pattern>/authImage</url-pattern>   
</servlet-mapping> 

 
其servlet源代码:

public class AuthImage extends HttpServlet    
{    
   
    private static final String CONTENT_TYPE = "text/html; charset=gb2312";    
    //设置字母的大小,大小    
    private Font mFont = new Font("Times New Roman", Font.PLAIN, 17);    
    public void init() throws ServletException    
    {    
        super.init();    
    }    
    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);    
    }    
   
    public void service(HttpServletRequest request, HttpServletResponse response) 
throws ServletException, IOException    
    {    
        response.setHeader("Pragma","No-cache");    
        response.setHeader("Cache-Control","no-cache");    
        response.setDateHeader("Expires", 0);    
        //表明生成的响应是图片    
        response.setContentType("image/jpeg");    
            
        int width=100, height=18;    
        BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);    
            
        Graphics g = image.getGraphics();    
        Random random = new Random();    
        g.setColor(getRandColor(200,250));    
        g.fillRect(1, 1, width-1, height-1);    
        g.setColor(new Color(102,102,102));    
        g.drawRect(0, 0, width-1, height-1);    
        g.setFont(mFont);    
   
        g.setColor(getRandColor(160,200));    
   
        //画随机线    
        for (int i=0;i<155;i++)    
        {    
            int x = random.nextInt(width - 1);    
            int y = random.nextInt(height - 1);    
            int xl = random.nextInt(6) + 1;    
            int yl = random.nextInt(12) + 1;    
            g.drawLine(x,y,x + xl,y + yl);    
        }    
   
        //从另一方向画随机线    
        for (int i = 0;i < 70;i++)    
        {    
            int x = random.nextInt(width - 1);    
            int y = random.nextInt(height - 1);    
            int xl = random.nextInt(12) + 1;    
            int yl = random.nextInt(6) + 1;    
            g.drawLine(x,y,x - xl,y - yl);    
        }    
   
        //生成随机数,并将随机数字转换为字母    
        String sRand="";    
        for (int i=0;i<6;i++)    
        {    
            int itmp = random.nextInt(26) + 65;    
            char ctmp = (char)itmp;    
            sRand += String.valueOf(ctmp);    
            g.setColor(new Color(20+random.nextInt(110),20+random.nextInt(110),20+random.nextInt(110)));    
            g.drawString(String.valueOf(ctmp),15*i+10,16);    
        }    
   
        HttpSession session = request.getSession(true);    
        session.setAttribute("rand",sRand);    
        g.dispose();    
        ImageIO.write(image, "JPEG", response.getOutputStream());    
    }    
    public void destroy()    
    {    
    }    
}   

在页面显示随机图片,可在JSP页面中增加如下代码即可:

<img src="authImage">