本文实例为大家分享了java实现图片验证码的具体代码，供大家参考，具体内容如下
目的:
1) 验证操作者是否是人
2) 防止表单重复提交
生成验证码的要点:
1) 使用java代码生成图片对象
BufferedImage
2) 使用Random生成随机字符串
3) 将图片对象用
ImageIO.write(图片对象, "jpeg|png", 响应字节输出流)
返回给客户端浏览器
验证验证码：
要点：
1) 将验证码文字存入session作用域
2) 表单提交时，对比session中的验证码和表单中的验证码
CaptchaUtils.java
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package cn.seeker.utils; import javax.imageio.ImageIO;import java.awt.*;import java.awt.image.BufferedImage;import java.io.FileNotFoundException;import java.io.FileOutputStream;import java.io.IOException;import java.io.OutputStream;import java.util.*;import java.util.List; public class CaptchaUtil { public static String [] fuhao = {"+","-","*","/"}; public static int num = 0; //生成随机算式 public static String random(){ List list = new ArrayList(); Random ran = new Random(); int n1 = ran.nextInt(10); int n2 = ran.nextInt(10); String f = fuhao[ran.nextInt(fuhao.length)]; StringBuilder sb = new StringBuilder(4); switch (f){ case "+": num = n1+n2; break; case "-": num =n1-n2; break; case "*": num = n1*n2; break; case "/": if(n2 == 0){ n2 = ran.nextInt(10)+1; num = n1/n2; }else{ num = n1/n2; } break; } sb.append(n1); sb.append(f); sb.append(n2); sb.append("="); return sb.toString(); } public static void outputImage(String str, OutputStream os){ Random ran = new Random(); //创建图片对象 BufferedImage img = new BufferedImage(100,40, BufferedImage.TYPE_INT_RGB); //获取画布 Graphics g = img.getGraphics(); //设置背景 g.setColor(Color.white); g.fillRect(0,0,100,40); //写字 g.setColor(Color.black); g.setFont(new Font("微软雅黑",Font.PLAIN,30)); g.drawString(str,10,40); //随机三条线 g.drawLine(ran.nextInt(100),ran.nextInt(40), ran.nextInt(100),ran.nextInt(40)); g.drawLine(ran.nextInt(100),ran.nextInt(40), ran.nextInt(100),ran.nextInt(40)); g.drawLine(ran.nextInt(100),ran.nextInt(40), ran.nextInt(100),ran.nextInt(40)); // 4. 输出结果 // 常见的压缩格式：jpeg(有损压缩), png(无损压缩) ... try { ImageIO.write(img, "png", os); } catch (IOException e) { e.printStackTrace(); } } } |
regist.jsp
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<%-- Created by IntelliJ IDEA. User: Administrator Date: 2018/10/14 Time: 15:43 To change this template use File | Settings | File Templates.--%><%@ page contentType="text/html;charset=UTF-8" language="java" %><html><head> <title>注册</title> <style> img { cursor: pointer} </style></head><body><form action="/regist" method="post"> <img src="/captcha.png" onclick="changeImg(this)"> 输入验证码：<input type="text" name="cap"> <input type="submit" value="提交"></form> <script> function changeImg(img) { // 浏览器有一个缓存特性, // 第一次从服务器获取图片，浏览器第二次发送请求时发现地址没有改变，就会使用第一次的图片，而不会真正发送请求 // 为了让浏览器每次都把请求发送给服务器，给一个时间参数 img.src = "/captcha.png?t="+new Date().getTime(); // 给src赋一个新值，就会向新值的地址发送一次请求 }</script></body></html> |
CaptchaServlet.java
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package cn.seeker.controller; import cn.seeker.utils.CaptchaUtil; 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 java.io.IOException; @WebServlet(urlPatterns = "/captcha.png")public class CaptchaServlet extends HttpServlet { @Override protected void service(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { response.setContentType("image/png"); //获取随机字符串 String random = CaptchaUtil.random(); //输出图片 CaptchaUtil.outputImage(random,response.getOutputStream()); //存入结果 request.getSession().setAttribute("res",CaptchaUtil.num); } } |
registServlet.jsp
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package cn.seeker.controller; 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 java.io.IOException; @WebServlet(urlPatterns = "/regist")public class registServlet extends HttpServlet { @Override protected void service(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { String cap = req.getParameter("cap"); Integer res = (Integer)req.getSession().getAttribute("res"); if(Integer.parseInt(cap) == res) { // 填写正确，注册成功 req.getSession().removeAttribute("res"); System.out.println("注册成功"); resp.sendRedirect("/index.jsp"); } else { req.setAttribute("error", "验证码不正确"); req.getRequestDispatcher("/jsp/regist.jsp").forward(req,resp); } }} |
以上就是本文的全部内容，希望对大家的学习有所帮助，也希望大家多多支持服务器之家。
原文链接：https://blog.csdn.net/qq_38454165/article/details/83097420
