Complete example of random verification code function (Java implementation)

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Simple examples of implementing random verification code function in Java

Nowadays, the registration, login or information release modules of many systems have added random code functions to avoid the use of automatic registration programs or automatic publishing programs.

The verification code actually randomly selects some characters and displays them on the page in the form of pictures. If the characters on the pictures need to be submitted at the same time during the submission operation, if the submitted characters are different from those saved in the server session, The submitted information is considered invalid. In order to prevent automatic programs from analyzing and parsing images, some interference lines are usually randomly generated on the image or characters are distorted, making automatic recognition more difficult.

Here, we use servlet to implement the random verification code.

Implementation code:

package com.servlet;

import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.image.BufferedImage;
import java.util.Random;
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 javax.servlet.http.HttpSession;

/**
 * 生成随机验证码
 * @author bitiliu
 *
 */
public class ValidateCodeServlet extends HttpServlet 
{

 private static final long serialVersionUID = 1L;
 
 //验证码图片的宽度。
  private int width=60;
  //验证码图片的高度。
  private int height=20;
  //验证码字符个数
  private int codeCount=4;
  
  
  private int x=0;
  //字体高度
  private int fontHeight;  
  private int codeY;
  
  char[] codeSequence = { 'A', 'B', 'C', 'D', 'E', 'F', 'G', 'H', 'I', 'J',
  'K', 'L', 'M', 'N', 'O', 'P', 'Q', 'R', 'S', 'T', 'U', 'V', 'W',
  'X', 'Y', 'Z', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9' };
  
  /**
   * 初始化验证图片属性
   */
  public void init() throws ServletException
 {
   //从web.xml中获取初始信息
   //宽度
 String strWidth=this.getInitParameter("width");
 //高度
 String strHeight=this.getInitParameter("height");
 //字符个数
 String strCodeCount=this.getInitParameter("codeCount"); 
 
 //将配置的信息转换成数值
 try
 {
  if(strWidth!=null && strWidth.length()!=0)
  {
  width=Integer.parseInt(strWidth);
  }
  if(strHeight!=null && strHeight.length()!=0)
  {
  height=Integer.parseInt(strHeight);
  }
  if(strCodeCount!=null && strCodeCount.length()!=0)
  {
  codeCount=Integer.parseInt(strCodeCount);
  }
 }
 catch(NumberFormatException e)
 {}
 
 x=width/(codeCount+1);
 fontHeight=height-2;
 codeY=height-4;
 
 }
  
  protected void service(HttpServletRequest req, HttpServletResponse resp)
  throws ServletException, java.io.IOException {
   
   //定义图像buffer
 BufferedImage buffImg = new BufferedImage(
width, height,BufferedImage.TYPE_INT_RGB);
 Graphics2D g = buffImg.createGraphics();

 //创建一个随机数生成器类
 Random random = new Random();

 //将图像填充为白色
 g.setColor(Color.WHITE);
 g.fillRect(0, 0, width, height);

 //创建字体，字体的大小应该根据图片的高度来定。
 Font font = new Font("Fixedsys", Font.PLAIN, fontHeight);
 //设置字体。
 g.setFont(font);

 //画边框。
 g.setColor(Color.BLACK);
 g.drawRect(0, 0, width - 1, height - 1);

 //随机产生160条干扰线，使图象中的认证码不易被其它程序探测到。
 g.setColor(Color.BLACK);
 for(int i = 0; i < 160; i++) 
 {
  int x = random.nextInt(width);
  int y = random.nextInt(height);
  int xl = random.nextInt(12);
  int yl = random.nextInt(12);
  g.drawLine(x, y, x + xl, y + yl);
 }

 //randomCode用于保存随机产生的验证码，以便用户登录后进行验证。
 StringBuffer randomCode = new StringBuffer();
 int red = 0, green = 0, blue = 0;

 //随机产生codeCount数字的验证码。
 for (int i = 0; i < codeCount; i++) {
  //得到随机产生的验证码数字。
  String strRand = String.valueOf(codeSequence[random.nextInt(36)]);
  //产生随机的颜色分量来构造颜色值，这样输出的每位数字的颜色值都将不同。
  red = random.nextInt(255);
  green = random.nextInt(255);
  blue = random.nextInt(255);

  //用随机产生的颜色将验证码绘制到图像中。
  g.setColor(new Color(red, green, blue));
  g.drawString(strRand, (i + 1) * x, codeY);

  //将产生的四个随机数组合在一起。
  randomCode.append(strRand);
 }
 // 将四位数字的验证码保存到Session中。
 HttpSession session = req.getSession();
 session.setAttribute("validateCode", randomCode.toString());

 // 禁止图像缓存。
 resp.setHeader("Pragma", "no-cache");
 resp.setHeader("Cache-Control", "no-cache");
 resp.setDateHeader("Expires", 0);

 resp.setContentType("image/jpeg");

 //将图像输出到Servlet输出流中。
 ServletOutputStream sos = resp.getOutputStream();
 ImageIO.write(buffImg, "jpeg", sos);
 sos.close();
 }

}

Need to declare servlet in web.xml

<servlet>
 <servlet-name>ValidateCodeServlet</servlet-name>
 <servlet-class>com.servlet.ValidateCodeServlet</servlet-class>
 <init-param>
 <param-name>width</param-name>
 <param-value>200</param-value>
 </init-param>
 <init-param>
 <param-name>height</param-name>
 <param-value>80</param-value>
 </init-param>
 <init-param>
 <param-name>codeCount</param-name>
 <param-value>5</param-value>
 </init-param>
 </servlet>

 <servlet-mapping>  
 <servlet-name>ValidateCodeServlet</servlet-name>  
 <url-pattern>/validateCodeServlet</url-pattern>  
 </servlet-mapping>

The page that needs to be referenced can be like this Write:

<ccid_file values="validateCodeServlet" width="100/" />

After the user submits, the verification code entered by the user can be compared with the string saved in the session to achieve the verification effect.

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