四位验证码
Java文件生成随机四位验证码代码及教程
package cn.itcast.chapter06.session.example; import sun.net.www.content.text.Generic; import javax.imageio.ImageIO; import javax.servlet.Servlet; import javax.servlet.ServletException; import javax.servlet.ServletOutputStream; 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 java.awt.*; import java.awt.image.BufferedImage; import java.io.ByteArrayOutputStream; import java.io.IOException; @WebServlet("/check") public class ChesckServlet extends HttpServlet { private static int WIDTH=60; private static int HEIGHT=20; @Override protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { HttpSession session =req.getSession(); resp.setContentType("image/jpeg"); ServletOutputStream sos = resp.getOutputStream(); //静止缓存此图片 resp.setHeader("pragma","No-cache"); resp.setHeader("Cache-Control","no-cache"); resp.setDateHeader("Expires",0); //创建内存，并获取图像上下文 BufferedImage image = new BufferedImage(WIDTH,HEIGHT,BufferedImage.TYPE_INT_RGB); Graphics g = image.getGraphics(); //产生随机验证码 char[]rands = generateCheckCode(); //产生图像 drawBcakground(g); drawRands(g, rands); //结束绘图过程，完成图像 g.dispose(); //将图像发给客户端 ByteArrayOutputStream bos = new ByteArrayOutputStream(); ImageIO.write(image, "JPEG",bos); byte[]buf =bos.toByteArray(); resp.setContentLength(buf.length); //将下面的语句也改为bos.weiteTo(sos) sos.write(buf); bos.close(); sos.close(); session .setAttribute("check_code",new String(rands) ); } private char[] generateCheckCode() { //定义验证码的字符表 String chars = "0123456789zxcvbnmlkjhgfdsaqwertyuiop"; char[] rands = new char[4]; for (int i = 0; i < 4; i++) { int rand = (int)(Math.random()*36); rands[i] = chars.charAt(rand); } return rands; } private void drawRands(Graphics g, char [] rands){ g.setColor(Color.BLACK); g.setFont(new Font(null,Font.ITALIC|Font.BOLD,18)); //在不同高度输出验证码 g.drawString(""+rands[0],1,7); g.drawString(""+rands[1],16,15); g.drawString(""+rands[2],31,18); g.drawString(""+rands[3],46,16); System.out.println(rands); } private void drawBcakground(Graphics g){ g.setColor(new Color(0xDCDCDC)); g.fillRect(0, 0, WIDTH,HEIGHT); //产生120个干扰点 for(int i=0;i<100;i++){ int x = (int)(Math.random()*WIDTH ); int y = (int)(Math.random()*HEIGHT); int red = (int)(Math.random()*225); int green = (int)(Math.random()*225); int blue = (int)(Math.random()*225); g.setColor(new Color(red,green,blue)); g.drawOval(x,y,1,0); } } @Override protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { doGet(req,resp); } }代码不懂查看此处资料（（Tomcat资料一）Servlet资料总结）
问题现状
验证码图片加载不出来原因如下：
一、HTML代码错误
<form name = "reg" action="/login" method="post"> <meta charset="UTF-8"> 账号：<input type="text" name="username"/><br> 密码：<input type="password" name="passward"/><br> 验证码：<input type="text" name="check_code"> <img src="/chapter06/CheckServlet"><br> <input type="submit" value="提交" id="bt"> </form>正确的代码
<form name = "reg" action="/login" method="post"> <meta charset="UTF-8"> 账号：<input type="text" name="username"/><br> 密码：<input type="password" name="passward"/><br> 验证码：<input type="text" name="check_code"> <img src="/check"> <input type="submit" value="提交" id="bt"> </form>< img src="/check" >此处的路由对应上方Java文件的路由
对于客户端来说，由java文件生成的图片需要访问Java文件，而客户端不能直接访问Java文件，如果要访问Java文件需要配置路由，配置路由方法（点击查看）二、Java代码书写错误
代码见上方第一个标题
三、过滤器没有排除加载的资源路径
if (uri.contains("/login.html")||uri.contains("/login")||uri.contains("/index.html")||uri.contains("/check")){// 排除资源 chain.doFilter(req,resp);其中uri.contains("/check")就是验证码的路径
正常页面
java 小demo — 随机生成四位验证码
import javax.swing.*; import java.awt.*; import java.util.Random; /** * @author yk.ddm * @createDate 2021-01-05 12:18 */ public class Test { public static void main(String[] args) { JFrame jf = new JFrame(); JPanel jPanel = new Mypanel(); jf.add(jPanel); jf.setSize(200,100); jf.setLocationRelativeTo(null); jf.setVisible(true); Mypanel mypanel =new Mypanel(); Test05 t = new Test05(); String s = t.getNumber(); } } class Mypanel extends JPanel{ static String s; @Override public void paint(Graphics g) { //设置验证码的宽高 int width = 160; int height = 40; g.setColor(Color.LIGHT_GRAY);//背景颜色 g.fillRect(0, 0, width -1, height -1);//背景填充 g.setColor(Color.BLACK);//边框颜色 g.drawRect(0, 0, width -1, height -1);//绘制边框 //绘制干扰点 Random random = new Random(); for (int i = 0; i < 100; i++) { int x = random.nextInt(width) - 2; int y = random.nextInt(height) - 2; g.drawOval(x, y, 2, 2); } //开始对验证码字体进行设置 g.setFont(new Font("黑体",Font.BOLD,32));//字体 g.setColor(Color.BLUE);//颜色 //设置一个数组来当验证码的词库 char [] arr = ("0123456789").toCharArray(); //实例化一个StringBuilder对象来生成随机验证码 StringBuilder sb = new StringBuilder(); //循环生成4个随机数 for (int i = 0; i < 4; i++) { //生成一个随机位置 int position = random.nextInt(arr.length); //获取到这个位置的字符 char c = arr[position]; //将字符添加到StringBuilder对象里面,并且加一个空格保持间隔 sb.append(c+""); } //写入验证码，调用sb的toString()方法将其转换为一个String对象进行写入 g.drawString(sb.toString(), 20, 30); //新建一个String类型的变量来存储已经好了的验证码，用来判断用户输入的验证码是否正确 String s = sb.toString(); this.s = sb.toString(); // Mypanel.s = sb.toString(); System.out.println(Mypanel.s); // System.out.println(s); Test05 t = new Test05(); t.setNumber(s); } } class Test05 { String Number ; public String getNumber() { return Number; } public void setNumber(String number) { Number = number; } }
验证码在平时用到的很多，简单记录一下生成四位随机验证码的核心代码：
生成四位验证码（数字与字母混合）
String str="ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"; StringBuilder sb=new StringBuilder(4); for(int i=0;i<4;i++) { char ch=str.charAt(new Random().nextInt(str.length())); sb.append(ch); } System.out.println(sb.toString());
public static void main(String[] args) { // TODO 自动生成的方法存根 Random r=new Random(); String str="0123456789abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";//列出所有的字母数字 for(int i=0;i<4;i++)//循环4次，输出四个数 { int a=r.nextInt(62);//从0-61中随机一个数，作为字符串的索引 System.out.println(str.substring(a,a+1));//从字符串中利用索引找到输出它 }
转载于:https://www.cnblogs.com/jskbk/p/5483097.html
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