Implement Email Sending in Java


I wanted to reset the password in the Spring Boot project, but it is a memorandum that I tried to see if I could send the initialized password by email.

First of all, environment settings

The environment is IDE:Eclipse ** Version: Java8, springframework.boot version 2.3.0 **

Also, an SMTP server is required to send mail, but it seems that it can not actually be sent locally, so this time I will use Google's SMTP easily.

build what you need for build gradle


dependencies {
    implementation 'org.springframework.boot:spring-boot-starter-mail'
    //Commons for randomly generating password strings-Compile lang3
    compile group: 'org.apache.commons', name: 'commons-lang3', version: '3.10'


<!--Gmailsmtp settings-->

<!--Local smtp settings-->
<!-- -->
<!-- spring.mail.port=25 -->


Enter the sender's email address in username and the password of the google account with that email address in password. As mentioned in the comment, ** If you are in a local environment, set host to localhost and enter the default port number **.

Create view and controller

Create an input form that specifies the post method in html. If you enter an email address and press the send button, the email will be sent to that address. (Since it is not the main line, it is omitted)


import org.apache.commons.lang3.RandomStringUtils;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.mail.MailSender;
import org.springframework.mail.SimpleMailMessage;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestParam;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.ModelAndView;

import com.example.demo.entity.User;
import com.example.demo.service.UserService;

public class PassResetController {
	private UserService userService;
	private MailSender mailSender;

	public ModelAndView passResetPage(ModelAndView mav) {
		return mav;

	public ModelAndView passResetSend(@RequestParam(name = "email") String email,
																User user,
																ModelAndView mav) {
		SimpleMailMessage simpleMailMessage = new SimpleMailMessage();
        user = userService.findUserByEmail(email);
        if (user == null) {
        	simpleMailMessage.setSubject("Password reset notification");
            simpleMailMessage.setText("**Is a service\n\r\n\r" + email + "\n\r\n\r This account does not exist");
			return mav;
        String password = RandomStringUtils.randomAscii(8);;
        userService.accountEdit(user.getEmail(), password);
        simpleMailMessage.setSubject("Password reset notification");
        simpleMailMessage.setText("**Is a service\n\r\n\r" + email + "\n\r\n\r You have reset the password for this account.\n\r\n\r Reset password:" + password + "\n\r\n\r After logging in, please reset your password yourself.");
		return mav;

What you are doing with the post method

  1. Access the DB with the email address sent from view and search for users
  2. If the user does not exist, state in the body of the email that the account does not exist
  3. If the user exists, randomly generate a password (RandomStringutils.randomAscii) and change the password of the user in the DB
  4. Enter the changed password in plain text in the body of the email

It becomes the flow of.

Notes on this implementation

Actually, it would be better to use UUID instead of RandomStringUtils for security, but considering the handling of symbols etc., I thought that StringUtils would be easier, so I used this. Also, if you have set up 2-step authentication with your Google account, you will not be able to log in to the application, so you need to disable this in advance.


With this kind of feeling, security is awkward, but I think I managed to grasp the flow. I also tried it on a local SMTP server, but I was able to check the mail sent to the server in the same way (although the settings are slightly different), so I felt that this is a realistic range in the local environment. It was.

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