The java captcha generates the concrete code

For your reference, the example code generated by java verification code is Shared as an example in this article. The details are as follows

package com.gonvan.component.captcha;
 
import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.IOException;
import java.util.HashMap;
import java.util.Map;
import java.util.Random;
 
import javax.imageio.ImageIO;
import javax.servlet.ServletOutputStream;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import javax.servlet.http.HttpSession;
 
/**
 * Created by yuerzm on 2016/3/14.
 */
public class CaptchaFactory {
 
  private static final char[]   CODE_SEQUENCE    = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789"
    .toCharArray();
  private static final int    DEFAULT_WIDTH    = 60;
  private static final int    DEFAULT_HEIGHT   = 20;
  private static final int    DEFAULT_CODE_LEN  = 4;
  private static final int    DEFAULT_CODE_X   = 13;
  private static final int    DEFAULT_CODE_Y   = 16;
  private static final int    DEFAULT_FONT_SIZE  = 18;
  private static final String   DEFAULT_FONT_FAMILY = "Times New Roman";
  private static CaptchaFactory  instance      = new CaptchaFactory();
  private int           width        = DEFAULT_WIDTH;            //  picture-defining width
  private int           height       = DEFAULT_HEIGHT;            //  picture-defining height
  private int           length       = DEFAULT_CODE_LEN;           //  Define the number of captchas to display on the image 
  private int           xx         = DEFAULT_CODE_X;            //  Define the captcha displayed on the image x coordinates 
  private int           yy         = DEFAULT_CODE_Y;            //  Define the captcha displayed on the image y coordinates 
  private int           fontSize      = DEFAULT_FONT_SIZE;          //  Define the font size to display the captcha on the image 
  private String         fontFamily     = DEFAULT_FONT_FAMILY;         //  Define the number of captchas to display on the image 
 
  private CaptchaFactory() {
  }
 
  public static CaptchaFactory getInstance() {
    return instance;
  }
 
  /**
   *  Configure wide high 
   *
   * @param w
   * @param h
   * @return
   */
  public CaptchaFactory configWidthAndHeight(int w, int h) {
    instance.width = w;
    instance.height = h;
    return instance;
  }
 
  /**
   *  Configuration coordinates 
   *
   * @param x
   * @param y
   * @return
   */
  public CaptchaFactory configXY(int x, int y) {
    instance.xx = x;
    instance.yy = y;
    return instance;
  }
 
  /**
   *  Configure font size 
   *
   * @param fontSize
   * @return
   */
  public CaptchaFactory configFontSize(int fontSize) {
    instance.fontSize = fontSize;
    return instance;
  }
 
  /**
   *  Configure the font 
   *
   * @param fontFamily
   * @return
   */
  public CaptchaFactory configFontSize(String fontFamily) {
    instance.fontFamily = fontFamily;
    return instance;
  }
 
  public void write(HttpServletRequest request, HttpServletResponse response) throws IOException {
    //  will 4 The numeric captcha is saved to Session In the. 
    Map captcha = generate();
    String randomCode = (String) captcha.get("captchaCode");
    BufferedImage buffImg = (BufferedImage) captcha.get("captchaImg");
 
    HttpSession session = request.getSession();
    session.setAttribute("code", randomCode);
 
    //  Disable image caching. 
    response.setHeader("Pragma", "no-cache");
    response.setHeader("Cache-Control", "no-cache");
    response.setDateHeader("Expires", 0);
    response.setContentType("image/jpeg");
 
    //  Output the image to Servlet In the output stream. 
    ServletOutputStream outputStream = response.getOutputStream();
    ImageIO.write(buffImg, "jpeg", outputStream);
    outputStream.close();
  }
 
  public Map<String, Object> generate() throws IOException {
    //  Define the image buffer
    BufferedImage buffImg = new BufferedImage(width, height, BufferedImage.TYPE_INT_RGB);
    Graphics gd = buffImg.getGraphics();
    //  Setting the background color 
    gd.setColor(getRandColor(200, 250));
    gd.fillRect(0, 0, width, height);
    //  Set the font size according to the height of the image. 
    gd.setFont(new Font(fontFamily, Font.PLAIN, fontSize));
 
    //  create 1 Random number generator class 
    Random random = new Random();
 
    //  Randomly generated 40 Interference line, so that the authentication code in the image is not easily detected by other programs. 
    gd.setColor(getRandColor(160, 200));
    for (int i = 0; i < 155; i++) {
      int x = random.nextInt(width);
      int y = random.nextInt(height);
      int xl = random.nextInt(12);
      int yl = random.nextInt(12);
      gd.drawLine(x, y, x + xl, y + yl);
    }
 
    // randomCode Used to save the randomly generated captcha for user authentication after login. 
    StringBuffer randomCode = new StringBuffer();
    int red = 0, green = 0, blue = 0;
 
    //  Randomly generated  length  Captcha. 
    for (int i = 0; i < length; i++) {
      //  Get the randomly generated captcha number. 
      String code = String.valueOf(CODE_SEQUENCE[random.nextInt(36)]);
      //  Generate a random color component to construct a color value, so that the color value of each number output will be different. 
      red = random.nextInt(110);
      green = random.nextInt(110);
      blue = random.nextInt(110);
 
      //  Draws the captcha into the image with randomly generated colors. 
      gd.setColor(new Color(red + 20, green + 20, blue + 20));
      gd.drawString(code, i * xx + 6, yy);
 
      //  Combine the generated random Numbers in 1 Up. 
      randomCode.append(code);
    }
    Map<String, Object> retval = new HashMap<>();
    retval.put("captchaCode", randomCode.toString());
    retval.put("captchaImg", buffImg);
    return retval;
  }
 
  /**
   *  Get a random color for a given range 
   *
   * @param fc
   *       The minimum value 
   * @param bc
   *       The maximum 
   * @return Color
   */
  private Color getRandColor(int fc, int bc) {
    Random random = new Random();
    if (fc > 255)
      fc = 255;
    if (bc > 255)
      bc = 255;
    int r = fc + random.nextInt(bc - fc);
    int g = fc + random.nextInt(bc - fc);
    int b = fc + random.nextInt(bc - fc);
    return new Color(r, g, b);
  }
}

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