用画布的方式实现验证码

//用画布做一个验证码
@WebServlet("/image.do")
public class ImageCodeServlet extends HttpServlet {
    private static final long serialVersionUID = 1L;
    
    //设置画布的长宽以及验证码的字的个数
    static int width=100;
    static int height=40;
    static int size=4;
    
    static Random random=new Random();
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        //1 获取一个人画布
        /**
         * BufferedImage.TYPE_INT_RGB 画布的三原色
         */
        BufferedImage bi=new BufferedImage(width, height,BufferedImage.TYPE_INT_RGB );
    
        //2 获取画笔
        Graphics graphics=bi.getGraphics();
        
        //3 给画笔设置一个颜色
        graphics.setColor(getColor());
    
        //4 作画
        //4.1 画框 长宽；给画布填充一个背景色
        //画一个长方形 坐标从0-0开始
        graphics.fillRect(0, 0, width, height);
        
        //4.2 往框里面写字 写之前设置好的size次
        //设置会出现的字体
        String str="qwertyuidhjcnx12345689AGDFCZMW";
        char[]ch=str.toCharArray();
        StringBuilder sb=new StringBuilder();
        
        for (int i = 0; i < size; i++) {
            graphics.setColor(getFontColor());
            
            //写字的时候，Y坐标的位置：10-40 x坐标从5开始到95结束
            
            int index=random.nextInt(ch.length);
            
            graphics.drawString(ch[index]+"", i*15+random.nextInt(10), random.nextInt(25)+15);
        
            sb.append(ch[index]);
        }
        
        //4.3 添加干扰
        //添加点干扰
        for (int i = 0; i < 300; i++) {
            
            graphics.setColor(getColor());
            graphics.drawOval(random.nextInt(width), random.nextInt(height), 1, 1);
        }
        
        //添加线干扰
        graphics.setColor(getColor());
        graphics.clearRect(random.nextInt(width), random.nextInt(height), random.nextInt(50), 1);
        
        //把验证码的字符存储起来
        request.getSession().setAttribute("code",sb.toString());
        
        //5 将画好的图片，使用流输出到前台
        //将bi这个画笔以png的格式输出到前台
        ImageIO.write(bi,"png",response.getOutputStream());
        
    }

    //获取一个颜色对象，背景用浅色，文字用深色
    private Color getColor(){
        
        int x;
        int y;
        int z;
        
        do {
            x=random.nextInt(250);
            y=random.nextInt(250);
            z=random.nextInt(250);
        } while (!isDark(x, y, y));
        
        return new Color(x,y,z);
    }
    
    //字体用深色
        private Color getFontColor(){
            
            int x;
            int y;
            int z;
            
            do {
                x=random.nextInt(250);
                y=random.nextInt(250);
                z=random.nextInt(250);
            } while (isDark(x, y, y));
            
            return new Color(x,y,z);
        }
    
    
    /**
     * 根据RGB值判断 深色与浅色
     * @param r
     * @param g
     * @param b
     * @return
     */
    private boolean isDark(int r,int g,int b){
        if(r*0.299d + g*0.578d + b*0.114d >= 192){ //浅色
            return false;
        }else{  //深色
            return true;
        }
    }

    
    
    
    
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        doGet(request, response);
    }