JSP编写验证码

index.html

<%@ page language="java" contentType="text/html; charset=utf-8"
    pageEncoding="utf-8"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Insert title here</title>
<script type="text/javascript">
             function reloadCode(){
                    var time = new Date().getTime();//根据时间的不同来刷新
                    document.getElementById("imagecode").src="<%=request.getContextPath() %>/servlet/ImageServlet?d="+time;
             }
       </script>
</head>
<body>
<form action="<%=request.getContextPath() %>/servlet/LoginServlet" method="get">
    验证码：<input type="text" name="checkcode"/>
    <img alt="验证码" id="imagecode" src="<%=request.getContextPath() %>/servlet/ImageServlet"/>
    <a href="javascript: reloadCode();">看不清楚</a><br>
    <input type="submit" value="提交">
    </form>
</body>
</html>

ImageServlet.java

import java.awt.Color;
import java.awt.Graphics;
import java.awt.Image;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;
import javax.imageio.ImageIO;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
public class ImageServlet extends HttpServlet{
       public void doGet(HttpServletRequest request,HttpServletResponse response) throws IOException{
             BufferedImage bi=new BufferedImage(68, 22, BufferedImage.TYPE_INT_RGB);
             Graphics g=bi.getGraphics();//获取画笔
             Color c=new Color(200,150,255);//颜色
             g.setColor(c);
             g.fillRect(0, 0, 68, 22);//框
             
             char[] ch="QWERTYUIOPASDFGHJKLZXCVBNM1234567890".toCharArray();
             //获取四个字符
             Random r=new Random();
             int len=ch.length,index;//设置范围
             StringBuffer sb=new StringBuffer();
             for (int i = 0; i <4; i++) {
                    index=r.nextInt(len);
                    g.setColor(new Color(r.nextInt(88),r.nextInt(188),r.nextInt(255)));//有字符后放在颜色上
                    g.drawString(ch[index]+"",(i*15)+3,18);//字符转字符串  画字符
                    sb.append(ch[index]);
             }//循环四次保存四次
             request.getSession().setAttribute("piccode", sb.toString());///字符保存到session里，要进行验证
             ImageIO.write(bi, "JPG",response.getOutputStream());
       }
}

LoginServlet.java

import java.io.IOException;
import java.io.PrintWriter;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

public class LoginServlet extends HttpServlet{
     public void doGet(HttpServletRequest request,HttpServletResponse response) throws IOException {
         String piccod=(String)request.getSession().getAttribute("piccode");//获得到原来的验证码信息
         String checkcode=request.getParameter("checkcode");//获取前台用户输入的数
         response.setContentType("text/html;charset=gbk");//防止乱码
         PrintWriter out=response.getWriter();//获得输出流
         if(piccod.equals(checkcode)){
             out.print("输入正确！");
         }else{
             out.print("输入错误！");
         }
         out.flush();//刷新
         out.close();
    }
}

web.xml

 <servlet>
       <servlet-name>ImageServlet</servlet-name>
       <servlet-class>com.moke.ImageServlet</servlet-class>
  </servlet>
  <servlet>
       <servlet-name>LoginServlet</servlet-name>
       <servlet-class>com.moke.LoginServlet</servlet-class>
  </servlet>
 
  <!-- 映射关系 -->
  <servlet-mapping>
       <servlet-name>ImageServlet</servlet-name>
       <url-pattern>/servlet/ImageServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
       <servlet-name>LoginServlet</servlet-name>
       <url-pattern>/servlet/LoginServlet</url-pattern>
  </servlet-mapping>

运行结果图：

ps:更新了web.xml记得从新启动服务器。

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