The attached file name was garbled in the Spring Boot email, so take measures

E-mail attachments are garbled

org.springframework.boot:spring-boot-starter-mail

When I sent the attached file using Spring's mail sending method, which is available on the Web and Qiita, the attached file name was garbled.

Apparently, it is OK if the file name is only in Japanese, but it seems that this garbled character occurs when the file identifier is entered (I have not investigated in detail here)

    private void sendMail(File file) throws MessagingException, URISyntaxException, IOException {
        JavaMailSender sender = this.getMailSender();
        
        MimeMessage message = sender.createMimeMessage();
        MimeMessageHelper helper = new MimeMessageHelper(message, true, StandardCharsets.UTF_8.name());
        
        String toAddr = this.mailToAddr;
        helper.setTo(toAddr);

        //Supports multiple CC addresses (separated by commas))
        if (!StringUtils.isEmpty(this.mailCcAddrs)) {
            String[] ccAddrArr = this.mailCcAddrs.split(",");
            helper.setTo(ccAddrArr);
        }
        String subject = "This is a test email"; 
        helper.setSubject(subject);
        
        //Email body template acquisition
        Path path = Paths.get(getClass().getClassLoader()
                .getResource("mail_template.txt").toURI());
                    
        Stream<String> lines = Files.lines(path);
        String template = lines.collect(Collectors.joining("\n"));
        String body = template.replace("[[Replace]]", toAddr);
        lines.close();
        helper.setText(body);
        
        //attaching file
        helper.addAttachment("The name of the attached file The attachment is a template.txt", file);
        
        sender.send(message);
    }

Fixed the following points

Process the file name of the attached file once

MimeUtility.encodeWord("file name");

Add mail settings to system properties

Change this property before creating your first MimeMessage instance

System.setProperty("mail.mime.splitlongparameters", "false");

Check the file name after the above correction