java语言使用servlet生成随机四个字符的验证码案例带源码及解析

首先使用maven搭建web项目导入一下servlet依赖

 <!-- servlet依赖的jar包start -->
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>javax.servlet-api</artifactId>
      <version>3.1.0</version>
    </dependency>
    <!-- servlet依赖的jar包start -->
    <!-- jsp依赖jar包start -->
    <dependency>
      <groupId>javax.servlet.jsp</groupId>
      <artifactId>javax.servlet.jsp-api</artifactId>
      <version>2.3.1</version>
    </dependency>
    <!-- jsp依赖jar包end -->
    <!--jstl标签依赖的jar包start -->
    <dependency>
      <groupId>javax.servlet</groupId>
      <artifactId>jstl</artifactId>
      <version>1.2</version>
    </dependency>
    <!--jstl标签依赖的jar包end -->

第二步前端页面有点简陋自己用到时改一下根据自己的页面就行了，页面代码

<%--
  Created by IntelliJ IDEA.
  User: Lenovo
  Date: 2020/2/8
  Time: 15:28
  To change this template use File | Settings | File Templates.
--%>
<%@ page contentType="text/html;charset=UTF-8" language="java" %>
<html>
<title>验证码</title>
<style type="text/css">
    .code_a {
        color: #0000ff;
        font-size: 12px;
        text-decoration: none;
        cursor: pointer;
    }

    #imgCode {
        cursor: pointer;
    }
</style>
<body>
<div id="codeform">
    <form action="" method="post">
        <label>验证码:</label>
        <input type="text" id="code" placeholder="输入验证码"/>
        <%--此处src的名称codeImage与web.xml中配置的<url-pattern>/codeImage</url-pattern>名称相同--%>
        <img src="codeImage" id="imgCode" align="center"/>
        <a class="code_a">看不清!切换一张</a><br>
        <input type="submit" value="登录">
    </form>
</div>

<div style="color: #ff0000;">${errmsg}</div>
</body>
</html>

最重要的配置web.xml配置此处小心

<!DOCTYPE web-app PUBLIC
 "-//Sun Microsystems, Inc.//DTD Web Application 2.3//EN"
 "http://java.sun.com/dtd/web-app_2_3.dtd" >

<web-app>
  <display-name>Archetype Created Web Application</display-name>
 <servlet>
     <!--名字随便起为了方便与类名相同-->
   <servlet-name>codeServlet</servlet-name>
     <!--servlet类所在的位置即生成验证码代码的类-->
   <servlet-class>demo1.servlet.CodeServlet</servlet-class>
 </servlet>
  <servlet-mapping>
      <!--与上面的<servlet-name></servlet-name>名字相同此处-->
    <servlet-name>codeServlet</servlet-name>
      <!--生成验证码的servlet路由路径此处与页面处 <img src="codeImage" id="imgCode" align="center"/>src的名称保持相同否则报错-->
    <url-pattern>/codeImage</url-pattern>
  </servlet-mapping>
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>

</web-app>

生成验证码的servlet代码

package demo1.servlet;

import javax.imageio.ImageIO;
import javax.servlet.ServletException;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.Random;

/**
 * package_name:demo1.servlet
 * Author:徐亚远
 * Date:2020/2/8 15:20
 * 项目名:code-projects
 * Desription:
 **/
public class CodeServlet extends HttpServlet {
    private int width = 100; //宽度
    private int height = 40; //高度
    private int fontsize = 22; //字体大小
    private Random random = new Random(); //随机数对象
    private String str = "0123456789qazwsxedcrfvtgbyhnujmikolpQAZWSXEDCRFVTGBYHNUJMIKOLP"; //从str中随机生成字符
    //返回一个四个字符的字符串
    public String randomCode(){

        String code = "";
        for (int i = 0;i<4;i++){
            code += str.charAt(random.nextInt(str.length()));
        }
        return code;
    }

    //返回随机颜色
    private Color randColor() {
        int r = random.nextInt(256);
        int g = random.nextInt(256);
        int b = random.nextInt(256);
        return new Color(r, g, b);
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        this.doPost(req, resp);
    }

    @Override
    protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
        //一:创建画板:new Bufferedimage（）
        BufferedImage img = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
        //二:创建画笔:画板.getGaphics()
        Graphics2D pen = (Graphics2D) img.getGraphics();
        //三:随机生成内容:不同颜色的字符
        String code = randomCode();
        //四:绘制内容:画笔.drawString()
        // 4.1设置绘制区域
        pen.fillRect(0, 0, width, height);
        //4.2设置字体
        pen.setFont(new Font("微软雅黑", Font.BOLD, fontsize));
        //4.3生成随机内容
        for (int i = 0; i < code.length(); i++) {
            pen.setColor(randColor());
            //绘制字符
            pen.drawString(code.charAt(i) + "", 5 + i * fontsize, (fontsize + height) / 2);
        }
        //4.4绘制噪音线

        //五:存为图片发送:ImageIo.wreite(画板,图片类型，输出流)
        ServletOutputStream out = resp.getOutputStream();
        ImageIO.write(img, "png", out);
        out.flush();
        out.close();
    }
}

目录结构
在这里插入图片描述
生成验证码的效果

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java语言使用servlet生成随机四个字符的验证码案例带源码及解析

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