1、在访问登录页面时，需要生产验证码。从而防止用户使用程序恶意操作。
2、验证码的本质是图片。
3、生成验证码的工具Servlet，直接复制粘贴即可使用
import java.awt.Color; import java.awt.Font; import java.awt.Graphics; 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; @WebServlet("/check") public class CheckCodes extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doPost(request,response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //设定长和宽 int height = 25; int width = 80; String data = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789abcdefghijklmnopqrstuvwxyz"; Random random = new Random(); //创建一个图片 BufferedImage image = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB); //获得画板 Graphics g = image.getGraphics(); //填充一个矩形 g.setColor(Color.RED); g.fillRect(0, 0, width, height); g.setColor(Color.WHITE); g.fillRect(1, 1, width-2, height-2); //设置字体 g.setFont(new Font("宋体", Font.BOLD|Font.ITALIC, 25)); //写随机字 String code=""; for(int i = 0 ; i < 4 ; i ++){ // 设置颜色--随机数 g.setColor(new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255))); // 获得随机字 int index = random.nextInt(data.length()); String str = data.substring(index, index + 1); code += str; // 写入 g.drawString(str, width / 6 * (i + 1), 20); } //利用会话跟踪技术，将验证码传入作用域，可以用于验证用户登录 HttpSession session = request.getSession(); session.setAttribute("code", code); //干扰线 for(int i = 0 ; i < 3 ; i ++){ // 设置颜色--随机数 g.setColor(new Color(random.nextInt(255), random.nextInt(255), random.nextInt(255))); // 随机绘制先 g.drawLine(random.nextInt(width), random.nextInt(height), random.nextInt(width),random.nextInt(height)); // 随机点 g.drawOval(random.nextInt(width), random.nextInt(height), 2, 2); } //将图片返回给浏览器 ImageIO.write(image, "jpg", response.getOutputStream()); } }
4、网页调用
<!DOCTYPE html> <html> <head> <meta charset="UTF-8"> <title>Insert title here</title> <script type="text/javascript"> function checkcodeChange(){ //最后加随机属性是为了刷新路径，不然不会重复刷新验证码 document.getElementById("checkcode").src="check?test="+Math.random(); } </script> </head> <body> <h1 style="color:red;">${error}</h1> <form action="login" method="post"> 用户名：<input type="text" name="username"/><br/> 密 码：<input type="text" name="password" /><br/> 验证码：<input type="text" name="checkcode" size="4"/> <img src="check" onclick="checkcodeChange()"id="checkcode"/><br/> <input type="submit" value="提交"/> </form> </body> </html>
5、登录验证代码
import java.io.IOException; 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; import com.bean.User; @WebServlet("/login") public class LoginServlet extends HttpServlet { protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { this.doPost(request, response); } protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("text/html;charset=utf-8"); String username = request.getParameter("username"); String password = request.getParameter("password"); String checkcode = request.getParameter("checkcode"); HttpSession session = request.getSession(); String code = (String)session.getAttribute("code"); if(!checkcode.equalsIgnoreCase(code)) { session.setAttribute("error", "验证码错误"); response.sendRedirect("login.html"); return; } if ("root".equals(username) && "1234".equals(password)) { User user = new User(username, password); session.setAttribute("user", user); response.sendRedirect("aaa/main.jsp"); } else { session.setAttribute("error", "账户名或密码错误"); response.sendRedirect("login.html"); } } }