UTF-8 encoding of application.properties attributes in Spring-Boot
<p>In my <code>application.properties</code> I add some custom attributes.</p>

<pre><code>custom.mail.property.subject-message=This is a ä ö ü ß problem
</code></pre>

<p>In this class I have the representation of the custom attributes.</p>

<pre><code>@Component
@ConfigurationProperties(prefix="custom.mail.property")
public class MailProperties {
    private String subjectMessage;
    public String getSubjectMessage() {
        return subjectMessage;
    }
    public void setSubjectMessage(String subjectMessage) {
        this.subjectMessage = subjectMessage;
    }
</code></pre>

<p>And here I use my <code>MailProperties</code>:</p>

<pre><code>@Service
public class SimpleUnknownResponseMessage extends MailProperties implements UnknownResponseMessage{

    private JavaMailSender javaMailSender;

    @Autowired
    public SimpleUnknownResponseMessage(JavaMailSender javaMailSender) {
        this.javaMailSender = javaMailSender;
    }

    @Override
    public void placeUnknownResponse(BookResponse bookResponse) {
        MimeMessage message = javaMailSender.createMimeMessage();
        try {
            MimeMessageHelper helper = new MimeMessageHelper(message, "UTF-8");
            helper.setSubject(this.getSubjectMessage());            
            javaMailSender.send(message);

        } catch (MessagingException e) {
            e.printStackTrace();
        }
    }
</code></pre>

<p><strong>While debugging I can see that my <code>this.getSubjectMessage()</code> variable has this value inside: <code>This is a Ã¤ Ã¶ Ã¼ Ã problem</code>. So before sending my mail I already have an UTF-8 encoding problem.</strong> </p>

<p>I already checked the encoding of the <code>application.properties</code> file and its UTF-8. </p>

<p>My IDE(STS/Eclipse) and the project properties are also set on UTF-8. </p>

<p><strong>How can I set the UTF-8 encoding for the text of my custom attributes in the <code>application.properties</code> file?</strong></p>