Java Web实现登录验证码（Servlet+jsp）

1.生成验证码图片(Servlet)

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
 
import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;

/**
 * Servlet implementation class VerifyCode
 */
@WebServlet("/VerifyCode")
public class VerifyCode extends HttpServlet {
    private static final long serialVersionUID = 1L;
       
    /**
     * @see HttpServlet#HttpServlet()
     */
    public VerifyCode() {
        super();
        // TODO Auto-generated constructor stub
    }

    /**
     * @see HttpServlet#doGet(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // TODO Auto-generated method stub
        this.doPost(request, response);
    }

    /**
     * @see HttpServlet#doPost(HttpServletRequest request, HttpServletResponse response)
     */
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
        // 首先设置浏览器不缓存
        response.setHeader("cache-control", "no-cache"); 
        response.setHeader("Expire", "-1"); // >0为缓存 
        response.setHeader("pragma", "no-cache");
        // 存储正确的验证码
        String vali_code = "";
        String Vali_str = "abcdefghijklmnopqrstuvwsyz1234567890ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        Color[] colors =
            { Color.BLACK, Color.RED, Color.BLUE };
        // 1.创建图像
        int width = 110, height = 40;
        int x_offset = 5, y_offset = 28;
        BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_3BYTE_BGR);
        // 2.创建画布
        Graphics2D g = img.createGraphics();
        // 3.为画布添加背景颜色为亮灰色
        g.setColor(Color.LIGHT_GRAY);
        g.fillRect(0, 0, width, height);//fillRect是包括矩形框内部 
        // 4.为画布添加边框
        g.setColor(Color.BLUE);
        g.drawRect(0, 0, width - 1, height - 1);//drawRect是绘制矩形边框
        // 5.绘制干扰线
        for (int i = 0; i < 10; i++)
        {
            g.setColor(new Color(randNum(0, 255), randNum(0, 255), randNum(0, 255)));
            g.drawLine(randNum(0, width), randNum(0, height), randNum(0, width), randNum(0, height));
        }
        g.setFont(new Font("黑体", Font.BOLD, 20));
        for (int i = 0; i < 4; i++)
        {
            int r = randNum(-180, 180);
            String code = Vali_str.charAt(randNum(0, Vali_str.length() - 1)) + "";
            g.rotate(r / 180 * Math.PI);
            g.setColor(colors[randNum(0, colors.length)]);
            g.drawString(code, x_offset + i * 30, y_offset);
            g.rotate(-r / 180 * Math.PI);
            vali_code += code;
        }
 
        //将验证码的内容存储在HttpSession中        
        HttpSession session = request.getSession();        
        session.setAttribute("Valicode", vali_code);
 
        // 通过response的输出流打给浏览器
        ImageIO.write(img, "jpg", response.getOutputStream());
    }
    private Random random = new Random();
    //随机生成begin和end之间的一个int值 
    private int randNum(int begin, int end)
    {
        return random.nextInt(end - begin) + begin;
    }
}

2.JSP显示验证码

 <input type="text" placeholder="输入验证码" name="ValiImage" id="ValiImage" /><!-- 输入验证码文本 -->
<img src="VerifyCode" onclick="changeValiImage(this)"><!-- 验证码图片 -->

<script type="text/javascript">

		function changeValiImage(img){
				img.src = "VerifyCode?time=" + new Date().getTime();//刷新
		}
	
</script>

3.进行用户输入和正确验证码的比对

我在LoginServlet中

//1 获得用户输入的验证码
        String verifyCode = request.getParameter("ValiImage");
        //2 获得服务器session 存放数据 ,如果没有返回null
        String sessionCacheData = (String) request.getSession().getAttribute("Valicode");
        // *将服务器缓存session数据移除
        request.getSession().removeAttribute("Valicode");
        // ** 判断服务器是否存在
        if(sessionCacheData == null){
        	request.setAttribute("message", "请不要重复提交");
            request.getRequestDispatcher("login.jsp").forward(request, response);
            return;
        }
        //3 比较
        if(! sessionCacheData.equalsIgnoreCase(verifyCode)){
            //用户输入错误
            // * 存放request作用域
        	request.setAttribute("message", "验证码输入错误");
            // * 请求转发
            request.getRequestDispatcher("login.jsp").forward(request, response);        
            return;
        }
//接登录方法...