[Feat] 이메일 템플릿 추가

build.gradle

@@ -139,6 +139,9 @@ dependencies {
     // Mail Service
     implementation 'org.springframework.boot:spring-boot-starter-mail'
 
+    // Thymeleaf (이메일 템플릿)
+    implementation 'org.springframework.boot:spring-boot-starter-thymeleaf'
+
     // Spring Security
     implementation 'org.springframework.boot:spring-boot-starter-security'
     testImplementation 'org.springframework.security:spring-security-test'

src/main/java/ku_rum/backend/domain/common/mail/application/MailSenderService.java

@@ -1,9 +1,11 @@
 package ku_rum.backend.domain.common.mail.application;
 
+import jakarta.mail.MessagingException;
+import jakarta.mail.internet.MimeMessage;
 import ku_rum.backend.global.exception.user.MailSendException;
 import lombok.RequiredArgsConstructor;
-import org.springframework.mail.SimpleMailMessage;
 import org.springframework.mail.javamail.JavaMailSender;
+import org.springframework.mail.javamail.MimeMessageHelper;
 import org.springframework.stereotype.Service;
 
 import static ku_rum.backend.global.support.status.BaseExceptionResponseStatus.MAIL_SEND_EXCEPTION;
@@ -13,19 +15,18 @@
 public class MailSenderService {
     private final JavaMailSender emailSender;
 
-    public void send(String toEmail, String title, String text) {
+    public void sendHtml(String toEmail, String title, String htmlContent) {
         try {
-            emailSender.send(createEmailForm(toEmail, title, text));
-        } catch (RuntimeException e) {
+            MimeMessage mimeMessage = emailSender.createMimeMessage();
+            MimeMessageHelper helper = new MimeMessageHelper(mimeMessage, true, "UTF-8");
+
+            helper.setTo(toEmail);
+            helper.setSubject(title);
+            helper.setText(htmlContent, true);
+
+            emailSender.send(mimeMessage);
+        } catch (MessagingException e) {
             throw new MailSendException(MAIL_SEND_EXCEPTION);
         }
     }
-
-    private SimpleMailMessage createEmailForm(String toEmail, String title, String text) {
-        SimpleMailMessage message = new SimpleMailMessage();
-        message.setTo(toEmail);
-        message.setSubject(title);
-        message.setText(text);
-        return message;
-    }
-}
+}

src/main/java/ku_rum/backend/domain/common/mail/application/MailService.java

@@ -4,13 +4,14 @@
 import ku_rum.backend.domain.common.mail.domain.repository.MailAuthRepository;
 import ku_rum.backend.domain.common.mail.dto.request.MailSendRequest;
 import ku_rum.backend.domain.common.mail.dto.request.MailVerificationRequest;
-import ku_rum.backend.domain.common.mail.dto.response.MailVerificationResponse;
 import ku_rum.backend.global.exception.user.MailSendException;
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 import org.springframework.scheduling.annotation.Async;
 import org.springframework.stereotype.Service;
 import org.springframework.transaction.annotation.Transactional;
+import org.thymeleaf.context.Context;
+import org.thymeleaf.spring6.SpringTemplateEngine;
 
 import java.time.Duration;
 
@@ -24,6 +25,7 @@
 public class MailService {
     private final MailSenderService mailSenderService;
     private final MailAuthRepository mailAuthRepository;
+    private final SpringTemplateEngine templateEngine;
 
     @Async
     @Transactional
@@ -34,10 +36,17 @@ public void sendCodeToEmail(final MailSendRequest request) {
                 request.email(),
                 MAIL_SEND_INFO.getCODE_LENGTH());
 
-        mailSenderService.send(request.email(), MAIL_SEND_INFO.getTITLE(), mailAuth.getAuthCode());
+        String htmlContent = createEmailContent(mailAuth.getAuthCode());
+        mailSenderService.sendHtml(request.email(), MAIL_SEND_INFO.getTITLE(), htmlContent);
         mailAuthRepository.save(mailAuth, Duration.ofMillis(MAIL_SEND_INFO.getAUTH_EXPIRED_MILLS()));
     }
 
+    private String createEmailContent(String code) {
+        Context context = new Context();
+        context.setVariable("code", code);
+        return templateEngine.process("email_template", context);
+    }
+
     private void deleteByEmail(MailSendRequest request) {
         mailAuthRepository.findByEmail(request.email())
                 .ifPresent(existingMailAuth -> {

src/main/resources/templates/email_template.html

@@ -0,0 +1,92 @@
+<!DOCTYPE html>
+<html xmlns:th="http://www.thymeleaf.org">
+<head>
+    <meta charset="UTF-8"/>
+    <meta content="width=device-width, initial-scale=1.0" name="viewport"/>
+    <meta content="ie=edge" http-equiv="X-UA-Compatible"/>
+    <title>Kuroom 인증 메일</title>
+
+    <!-- sonar-ignore: external resource integrity not required for email template -->
+    <link href="https://fonts.googleapis.com/css2?family=Poppins:wght@300;400;500;600&display=swap" rel="stylesheet"/>
+</head>
+<body style="
+      margin: 0;
+      font-family: 'Poppins', sans-serif;
+      background: #ffffff;
+      font-size: 14px;">
+<div style="
+    max-width: 700px;
+    margin: 0 auto;
+    padding: 80px 30px 60px;
+    background: #f4f7ff;
+    font-size: 14px;
+    color: #434343;">
+
+    <header>
+        <table style="width: 100%;">
+            <tbody>
+            <tr style="height: 0;">
+                <td style="text-align: center;">
+                    <h2 style="margin: 0; font-size: 28px; font-weight: 600; color: #2d8c3c;">KUROOM</h2>
+                </td>
+            </tr>
+            </tbody>
+        </table>
+    </header>
+
+    <main>
+        <div style="
+            margin: 30px 0 0;
+            padding: 40px 20px 40px;
+            background: #ffffff;
+            border-radius: 30px;
+            text-align: center;">
+
+            <div style="width: 100%; max-width: 489px; margin: 0 auto;">
+                <h1 style="
+                    margin: 0;
+                    font-size: 24px;
+                    font-weight: 600;
+                    color: #1f1f1f;">
+                    이메일 인증
+                </h1>
+                <p style="
+                    margin: 17px 0 0;
+                    font-size: 16px;
+                    font-weight: 500;">
+                    건국대학교 학생들을 위한 서비스, 쿠룸
+                </p>
+                <p style="
+                margin: 17px 0 0;
+                font-weight: 500;
+                letter-spacing: 0.56px;">
+                    안녕하세요. 쿠룸입니다. <br/>
+                    앱으로 돌아가서 아래 인증 코드를 입력해주세요.<br/>
+                    해당 인증코드는 <span style="font-weight: 600; color: #1f1f1f;">3분간</span> 유효합니다.
+                </p>
+
+                <p id='code' style="
+                margin: 20px 0 0;
+                font-size: 30px;
+                font-weight: 600;
+                letter-spacing: 20px;
+                color: #2d8c3c;" th:text="${code}">
+                    123456
+                </p>
+            </div>
+            <div style="
+          width: 100%;
+          max-width: 490px;
+          margin: 20px auto 0;
+          text-align: center;
+          border-top: 1px solid #e6ebf1;">
+
+                <p style="margin: 16px 0 0; color: #434343;">
+                    Copyright © 2026 Kuroom. All rights reserved.
+                </p>
+            </div>
+        </div>
+    </main>
+</div>
+</body>
+</html>

src/test/java/ku_rum/backend/domain/common/mail/application/MailServiceTest.java

@@ -1,5 +1,16 @@
 package ku_rum.backend.domain.common.mail.application;
 
+import static org.junit.Assert.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.ArgumentMatchers.anyString;
+import static org.mockito.ArgumentMatchers.eq;
+import static org.mockito.BDDMockito.given;
+import static org.mockito.Mockito.times;
+import static org.mockito.Mockito.verify;
+
+import java.time.Duration;
+import java.util.Optional;
 import ku_rum.backend.domain.common.mail.domain.MailAuth;
 import ku_rum.backend.domain.common.mail.domain.repository.MailAuthRepository;
 import ku_rum.backend.domain.common.mail.dto.request.MailSendRequest;
@@ -11,31 +22,21 @@
 import org.mockito.InjectMocks;
 import org.mockito.Mock;
 import org.mockito.junit.jupiter.MockitoExtension;
-import org.springframework.mail.javamail.JavaMailSender;
-import org.springframework.test.context.ActiveProfiles;
-
-import java.time.Duration;
-import java.util.Optional;
+import org.thymeleaf.context.Context;
+import org.thymeleaf.spring6.SpringTemplateEngine;
 
-import static org.junit.Assert.assertThrows;
-import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
-import static org.mockito.ArgumentMatchers.any;
-import static org.mockito.BDDMockito.given;
-import static org.mockito.Mockito.*;
-
-@ActiveProfiles("test")
 @ExtendWith(MockitoExtension.class)
 class MailServiceTest {
 
-    @Mock
-    private JavaMailSender emailSender;
-
     @Mock
     private MailSenderService mailSenderService;
 
     @Mock
     private MailAuthRepository mailAuthRepository;
 
+    @Mock
+    private SpringTemplateEngine templateEngine;
+
     @InjectMocks
     private MailService mailService;
 
@@ -44,13 +45,16 @@ class MailServiceTest {
     void sendCodeToEmail_success() {
         // given
         MailSendRequest request = new MailSendRequest("test@example.com");
-        MailAuth mailAuth = MailAuth.create(request.email(), 6);
+        String htmlContent = "<html>테스트</html>";
+
+        given(templateEngine.process(eq("email_template"), any(Context.class))).willReturn(htmlContent);
 
         // when
         mailService.sendCodeToEmail(request);
 
         // then
-        verify(mailSenderService, times(1)).send(eq(request.email()), anyString(), anyString());
+        verify(templateEngine, times(1)).process(eq("email_template"), any(Context.class));
+        verify(mailSenderService, times(1)).sendHtml(eq(request.email()), anyString(), eq(htmlContent));
         verify(mailAuthRepository, times(1)).save(any(MailAuth.class), any(Duration.class));
     }