验证码

首先创建图片对象

设置好图片的宽度100和高度50
使用 BufferedImage创建图片对象

@WebServlet("/YanZhengServlet")
public class YanZhengServlet extends HttpServlet {
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {

        int width  = 100;
        int height = 50;
        BufferedImage image = new BufferedImage(width,height,BufferedImage.TYPE_INT_RGB);

        //将验证码输出到页面
        ImageIO.write(image,"jpg",response.getOutputStream());
    }

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        this.doPost(request, response);
    }
}

其次设置验证码的背景色

步骤：
1、获取画图工具对象Graphics g = image.getGraphics();
2、设置颜色 g.setColor(Color.PINK);
3、进行背景填充g.fillRect(0,0,width,height);

        Graphics g = image.getGraphics();
        g.setColor(Color.PINK);
        g.fillRect(0,0,width,height);

设置显示验证码

        g.setColor(Color.MAGENTA);
        g.drawString("A",20,25);
        g.drawString("B",40,25);
        g.drawString("C",60,25);
        g.drawString("D",80,25);

效果展示：

进阶操作：随机生成验证码

首先将字母大小写和数字都存在一个字符串中，然后随机生成一个index，获取对应的字符。再写入到验证码图片中。

        String S="ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789";

        for (int i = 1; i <= 4; i++) {
            Random random = new Random();
            int index = random.nextInt(S.length());
            char c = S.charAt(index);
            g.drawString(c+"",width/5*i,height/2);
        }

Random

混淆视觉（干扰线）

绘制一些线段来模拟遮挡验证码的混淆视觉效果

        g.setColor(Color.GREEN);
        for (int i = 0; i < 10; i++) {

            Random random = new Random();
            int x1 = random.nextInt(width);
            int x2 = random.nextInt(width);
            int y1 = random.nextInt(height);
            int y2 = random.nextInt(height);
            g.drawLine(x1,x2,y1,y2);
        }

效果展示：

效果