ImageIO生成验证码

     public static void main(String[] args) throws Exception {
         //编写验证案例效果
         String letter = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
         Random random = new Random();

         //建立图像，定义尺寸，格式
         int w = 160;    //图像的宽
         int h = 60;     //图像的高
         int len = 4;
         BufferedImage bd = new BufferedImage(w, h, BufferedImage.TYPE_INT_ARGB);

         //建立画笔
         Graphics2D g = bd.createGraphics();
         //设置线条平滑
         g.setRenderingHint(RenderingHints.KEY_TEXT_ANTIALIASING,
                 RenderingHints.VALUE_TEXT_ANTIALIAS_GASP);
         g.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                 RenderingHints.VALUE_ANTIALIAS_ON);
         g.setRenderingHint(RenderingHints.KEY_STROKE_CONTROL,
                 RenderingHints.VALUE_STROKE_DEFAULT);

         g.setColor(new Color(251, 251, 251, 200));
         g.fillRect(0, 0, w, h);

         Font font = new Font("宋体", Font.BOLD, 35);
         g.setFont(font);

         StringBuilder su = new StringBuilder(len);
         //画字
         for (int i = 0; i < len; i++) {
             Color c = new Color(random.nextInt(256), random.nextInt(256), random.nextInt(256), random.nextInt(100) + 100);
             g.setColor(c);

             int x = i*35+5;
             int y = random.nextInt(25)+28;

             font = font.deriveFont(random.nextInt(553),random.nextInt(18)+30);  //设置验证码的字体
             g.setFont(font);

             String t = String.valueOf(letter.charAt(random.nextInt(letter.length())));
             su.append(t);

             double radianPercent = Math.PI*(random.nextInt(35)/180D);
             if (random.nextBoolean())
                 radianPercent = -radianPercent;
             g.rotate(radianPercent,x,y);
             g.drawString(t,x,y);
             g.rotate(-radianPercent,x,y);

         }
         System.out.println(su);
//04增加干扰文字
         for(int i=0;i<15;i++){
             Color c = new
                     Color(random.nextInt(256),random.nextInt(256),random.nextInt(256),random.nextInt(120
             )+120);
             g.setColor(c);
             int x = random.nextInt(w);
             int y = random.nextInt(h);
             font = font.deriveFont(random.nextInt(3),random.nextInt(8)+10);
             g.setFont(font);
             String t =
                     String.valueOf(letter.charAt(random.nextInt(letter.length())));
             g.drawString(t,x,y);
         }
//干扰图形
         for (int i=0;i<10;i++){
             Color c = new
                     Color(random.nextInt(256),random.nextInt(256),random.nextInt(256),random.nextInt(20)
                     +20);
             g.setColor(c);
             int x = random.nextInt(w);
             int y = random.nextInt(h);
             int ss = random.nextInt(30)+10;
             g.fillOval(x,y,ss,ss);
         }
         g.dispose(); //关闭画笔
         ImageIO.write(bd, "png", new File("image.png"));
     }