Create dynamic text image like as captcha

package com.barcode.demo;

import java.awt.Color;

import java.awt.Font;

import java.awt.GradientPaint;

import java.awt.Graphics2D;

import java.awt.image.BufferedImage;

import java.io.File;

import java.io.IOException;

import java.sql.Timestamp;

import java.util.Properties;

import javax.activation.DataHandler;

import javax.activation.DataSource;

import javax.activation.FileDataSource;

import javax.imageio.ImageIO;

import javax.mail.BodyPart;

import javax.mail.Message;

import javax.mail.PasswordAuthentication;

import javax.mail.Session;

import javax.mail.Transport;

import javax.mail.internet.InternetAddress;

import javax.mail.internet.MimeBodyPart;

import javax.mail.internet.MimeMessage;

import javax.mail.internet.MimeMultipart;

public class CreateCaptchaImage {

public static void main(String[] args) {

customCaptchaGeneration ();

}

/**

* Default constructor.

* @param title

* the frame title.

public static void customCaptchaGeneration() {

File file = null;

Timestamp timestamp = new Timestamp(System.currentTimeMillis());

try {

file = File

.createTempFile(timestamp.getTime() + "_Captcha", ".png");

} catch (IOException e) {

e.printStackTrace();

}

StringBuffer sb = createHtmlData();

sendEmailToRecepint(file, sb);

}

private static StringBuffer createHtmlData() {

StringBuffer sb = new StringBuffer();

sb.append("<html><head></head><body><table><tr><th></th><th></th><th></th><th></th><th></th><th></th><th></th></tr><tr>");

sb.append("<td rowspan=");

sb.append(10);

sb.append('"');

sb.append(" colspan=");

sb.append(3);

sb.append('"');

sb.append('>');

sb.append("<img src=");

sb.append("'");

sb.append("cid:ea-image");

sb.append("'");

sb.append("width=");

sb.append('"');

sb.append(200);

sb.append('"');

sb.append("height=");

sb.append('"');

sb.append(200);

sb.append('"');

sb.append('/');

sb.append('>');

sb.append("</td><th></th><th></th><th></th></tr></body></html>");

return sb;

/**

* <td rowspan="10" colspan="3">

* <img src='cid:ea-image'

* style="display: block; margin-left: auto; margin-right: auto;"

* width="200" height="200"/></td>

}

private static void sendEmailToRecepint(File file, StringBuffer sb) {

// Recipient's email ID needs to be mentioned.

String to = "kmandal@gmail.com";

// Sender's email ID needs to be mentioned

String from = "kmandal@kmical.com";

final String username = "kmandal";// change accordingly

final String password = "XXXXXXXXXXXXXXXX";// change accordingly

// Assuming you are sending email through relay.jangosmtp.net

String host = "XXXXXXXXXXXXXXXXXX";

Properties props = new Properties();

props.put("mail.smtp.auth", "true");

props.put("mail.smtp.starttls.enable", "true");

props.put("mail.smtp.host", host);

props.put("mail.smtp.port", "25");

Session session = Session.getInstance(props,

new javax.mail.Authenticator() {

protected PasswordAuthentication getPasswordAuthentication() {

return new PasswordAuthentication(username, password);

}

});

try {

// Create a default MimeMessage object.

Message message = new MimeMessage(session);

// Set From: header field of the header.

message.setFrom(new InternetAddress(from));

// Set To: header field of the header.

message.setRecipients(Message.RecipientType.TO,

InternetAddress.parse(to));

// Set Subject: header field

message.setSubject("Demo snapshot");

MimeMultipart multipart = new MimeMultipart();

BodyPart messageBodyPart = new MimeBodyPart();

messageBodyPart.setContent(sb.toString(), "text/HTML");

multipart.addBodyPart(messageBodyPart);

messageBodyPart = new MimeBodyPart();

createCaptchaImage(file);

DataSource fds = new FileDataSource(file);

messageBodyPart.setDataHandler(new DataHandler(fds));

// ea-image is image file name

messageBodyPart.setHeader("Content-ID", "<ea-image>");

// add image to the multipart

multipart.addBodyPart(messageBodyPart);

// put everything together

message.setContent(multipart);

Transport.send(message);

} catch (Exception e) {

System.out.println("Error of file");

}

public static void createCaptchaImage(File file) {

Timestamp timestamp = new Timestamp(System.currentTimeMillis());

BufferedImage image = new BufferedImage(200, 40,

BufferedImage.TYPE_BYTE_INDEXED);

Graphics2D graphics = image.createGraphics();

// Set back ground of the generated image to white

graphics.setColor(Color.WHITE);

graphics.fillRect(0, 0, 200, 40);

// set gradient font of text to be converted to image

GradientPaint gradientPaint = new GradientPaint(10, 5, Color.BLUE, 20,

10, Color.LIGHT_GRAY, true);

graphics.setPaint(gradientPaint);

Font font = new Font("Comic Sans MS", Font.BOLD, 30);

graphics.setFont(font);

// write 'Hello World!' string in the image

graphics.drawString(String.valueOf(timestamp.getTime()), 5, 30);

// release resources used by graphics context

graphics.dispose();

try {

ImageIO.write(image, "png", file);

} catch (IOException e) {

// TODO Auto-generated catch block

e.printStackTrace();

}

The provided code generates a CAPTCHA image, embeds it into an email, and sends it as an attachment. Below is a step-by-step explanation of how this program works:

1. Generating the CAPTCHA Image

The program generates a simple image with the current timestamp. The createCaptchaImage function creates a BufferedImage and uses Graphics2D to write text (timestamp) on the image. This image is later saved as a PNG file.

2. Email Setup

The program uses JavaMail API to send an email. It configures SMTP properties (like host, port, and authentication), constructs a MimeMessage, and embeds the CAPTCHA image as an inline attachment. The image is referenced using Content-ID in the email body as cid:ea-image.

How the program works:

cutomCaptchaGeneration():

Ø This is the main function that starts the process.

Ø A temporary file is created to store the generated CAPTCHA image.

Ø HTML data with the image placeholder is created via createHtmlData().

Ø The email is sent with the generated CAPTCHA image using sendEmailToRecepint().

createHtmlData():

Ø Generates the HTML content with an image placeholder (cid:ea-image). This is the inline image reference used to embed the CAPTCHA image.

sendEmailToRecepint(File file, StringBuffer sb):

Ø Sets up email properties and authentication details.

Ø Composes the email body by adding the HTML content and embedding the image file.

Ø The image is attached to the email and referenced using the Content-ID (<ea-image>).

Ø The email is sent using Transport.send().

createCaptchaImage(File file):

Ø Creates the CAPTCHA image by generating a simple timestamp image.

Ø A gradient font effect is applied to the text.

Code Review and Suggestions:

Sensitive Information:

Ø Ensure that sensitive information like email username, password, and host are stored securely, such as in environment variables or a configuration file, rather than hardcoding them in the source code.

SMTP Settings:

Ø Replace the placeholders in SMTP configuration (host, username, password) with valid credentials.

Exception Handling:

Ø Improve the exception handling in sendEmailToRecepint() method by logging detailed errors instead of just printing "Error of file".

Temporary File Handling:

Ø The temporary file is created using File.createTempFile(), which is good for ensuring a unique filename, but it is also important to delete these temporary files after they are used.

Suggested Improvements:

Better CAPTCHA Design:

Ø Add random alphanumeric strings and distortions (e.g., lines, dots) to the CAPTCHA image to improve security and randomness.

HTML Email Template:

Ø The HTML email structure could be further enhanced with CSS for better styling and responsiveness.

Conclusion:

This is a basic implementation of a CAPTCHA generator and email sender. It demonstrates how to integrate image generation and sending the image inline within an HTML email using JavaMail. To make it production-ready, consider security improvements, better error handling, and enhanced CAPTCHA image generation.