[FEAT] 이메일 알림 시스템 구현 (#90)

- 알림 관련 클래스 추가: NotificationType, NotificationEvent, TemplateProcessor
- Thymeleaf, AWS SES 의존성 추가 및 관련 설정 클래스 구현
- 알림 이벤트 리스너와 이메일 템플릿 추가, 사용자 승인/거절 API에 이메일 발송 로직 구현
- 알림 관련 에러 코드 및 커스텀 예외 클래스 추가, EmailService 예외 처리 개선
- 비동기 처리를 위한 AsyncConfig 추가

build.gradle

@@ -34,6 +34,9 @@ dependencies {
     // AWS SDK V2 for S3
     implementation platform('software.amazon.awssdk:bom:2.24.1')
     implementation 'software.amazon.awssdk:s3'
+    // AWS SDK V2 for SES
+    implementation 'software.amazon.awssdk:ses'
+    implementation 'org.springframework.boot:spring-boot-starter-thymeleaf'
     compileOnly 'org.projectlombok:lombok'
     runtimeOnly 'com.mysql:mysql-connector-j'
     annotationProcessor 'org.projectlombok:lombok'

src/main/java/com/example/epari/admin/controller/AdminUserManagementController.java

@@ -2,6 +2,7 @@
 
 import java.util.List;
 
+import org.springframework.context.ApplicationEventPublisher;
 import org.springframework.http.ResponseEntity;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PathVariable;
@@ -12,8 +13,11 @@
 
 import com.example.epari.admin.dto.ApprovalRequestDTO;
 import com.example.epari.admin.dto.CognitoUserDTO;
+import com.example.epari.admin.dto.RejectionRequestDTO;
 import com.example.epari.admin.service.AdminUserService;
 import com.example.epari.admin.service.CognitoService;
+import com.example.epari.global.event.NotificationEvent;
+import com.example.epari.global.event.NotificationType;
 
 import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
@@ -32,6 +36,8 @@ public class AdminUserManagementController {
 
 	private final AdminUserService adminUserService;
 
+	private final ApplicationEventPublisher eventPublisher;
+
 	/**
 	 * 임시 그룹에 속한 사용자를 조회하는 엔드포인트
 	 */
@@ -53,12 +59,17 @@ public ResponseEntity<Void> approveUser(
 			@RequestBody ApprovalRequestDTO request
 	) {
 		// 1. 백엔드 DB에 승인 상태 업데이트
-		adminUserService.approveUser(email, request);
+		String courseName = adminUserService.approveUser(email, request);
 
 		// 2. Cognito 그룹 변경
 		cognitoService.changeUserGroup(request.getUsername(), "STUDENT");
 
-		// 3. TODO 이메일 발송
+		// 3. 이메일 발송
+		NotificationEvent event = NotificationEvent.of(email, NotificationType.USER_APPROVED)
+				.addProperty("name", request.getName())
+				.addProperty("courseName", courseName);
+
+		eventPublisher.publishEvent(event);
 
 		return ResponseEntity.ok().build();
 	}
@@ -67,11 +78,19 @@ public ResponseEntity<Void> approveUser(
 	 * 임시 그룹에 속한 사용자를 반려하는 엔드포인트
 	 */
 	@PostMapping("/{userEmail}/reject")
-	public ResponseEntity<Void> rejectUser(@PathVariable("userEmail") String email) {
+	public ResponseEntity<Void> rejectUser(
+			@PathVariable("userEmail") String email,
+			@RequestBody RejectionRequestDTO request
+	) {
 		// 1. Cognito에서 사용자 삭제
 		cognitoService.deleteUser(email);
 
-		// 2. TODO 이메일 발송
+		// 2. 이메일 발송
+		NotificationEvent event = NotificationEvent.of(email, NotificationType.USER_REJECTED)
+				.addProperty("name", request.getName())
+				.addProperty("reason", request.getReason());
+
+		eventPublisher.publishEvent(event);
 
 		return ResponseEntity.ok().build();
 	}

src/main/java/com/example/epari/admin/dto/RejectionRequestDTO.java

@@ -0,0 +1,21 @@
+package com.example.epari.admin.dto;
+
+import lombok.AllArgsConstructor;
+import lombok.Data;
+import lombok.NoArgsConstructor;
+
+/**
+ * 사용자 반려 요청 DTO
+ */
+@Data
+@AllArgsConstructor
+@NoArgsConstructor
+public class RejectionRequestDTO {
+
+	private String username; // Cognito username
+
+	private String name;    // Username
+
+	private String reason;  // 반려 사유
+
+}

src/main/java/com/example/epari/admin/exception/NotificationException.java

@@ -0,0 +1,15 @@
+package com.example.epari.admin.exception;
+
+import com.example.epari.global.exception.BusinessBaseException;
+import com.example.epari.global.exception.ErrorCode;
+
+/**
+ * 알림 관련 커스텀 예외
+ */
+public class NotificationException extends BusinessBaseException {
+
+	public NotificationException(ErrorCode errorCode) {
+		super(errorCode);
+	}
+
+}

src/main/java/com/example/epari/admin/service/AdminUserService.java

@@ -33,7 +33,7 @@ public class AdminUserService {
 	 * 사용자 저장 및 과목 매핑 수행
 	 */
 	@Transactional
-	public void approveUser(String email, ApprovalRequestDTO request) {
+	public String approveUser(String email, ApprovalRequestDTO request) {
 		// 1. 사용자 저장
 		Student student = Student
 				.createStudent(email, "PASSWORD", request.getName(), "010-1234-5678");
@@ -45,6 +45,8 @@ public void approveUser(String email, ApprovalRequestDTO request) {
 				.orElseThrow(CourseNotFoundException::new);
 
 		courseStudentRepository.save(new CourseStudent(course, student));
+
+		return course.getName();
 	}
 
 }

src/main/java/com/example/epari/global/config/AsyncConfig.java

@@ -0,0 +1,10 @@
+package com.example.epari.global.config;
+
+import org.springframework.context.annotation.Configuration;
+import org.springframework.scheduling.annotation.EnableAsync;
+
+@Configuration
+@EnableAsync
+public class AsyncConfig {
+
+}

src/main/java/com/example/epari/global/config/ThymeleafConfig.java

@@ -0,0 +1,36 @@
+package com.example.epari.global.config;
+
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+import org.thymeleaf.spring6.SpringTemplateEngine;
+import org.thymeleaf.templateresolver.ClassLoaderTemplateResolver;
+import org.thymeleaf.templateresolver.ITemplateResolver;
+
+/**
+ * Thymeleaf 관련 설정 클래스
+ */
+@Configuration
+public class ThymeleafConfig {
+
+	@Bean
+	public SpringTemplateEngine emailTemplateEngine() {
+		SpringTemplateEngine templateEngine = new SpringTemplateEngine();
+
+		templateEngine.setTemplateResolver(emailTemplateResolver());
+
+		return templateEngine;
+	}
+
+	@Bean
+	public ITemplateResolver emailTemplateResolver() {
+		ClassLoaderTemplateResolver templateResolver = new ClassLoaderTemplateResolver();
+
+		templateResolver.setPrefix("mail-templates/");
+		templateResolver.setSuffix(".html");
+		templateResolver.setTemplateMode("HTML");
+		templateResolver.setCharacterEncoding("UTF-8");
+
+		return templateResolver;
+	}
+
+}

src/main/java/com/example/epari/global/config/aws/AwsSesConfig.java

@@ -0,0 +1,32 @@
+package com.example.epari.global.config.aws;
+
+import org.springframework.boot.context.properties.EnableConfigurationProperties;
+import org.springframework.context.annotation.Bean;
+import org.springframework.context.annotation.Configuration;
+
+import software.amazon.awssdk.auth.credentials.AwsBasicCredentials;
+import software.amazon.awssdk.auth.credentials.StaticCredentialsProvider;
+import software.amazon.awssdk.regions.Region;
+import software.amazon.awssdk.services.ses.SesClient;
+
+/**
+ * AWS SES 사용을 위한 설정 클래스
+ */
+@Configuration
+@EnableConfigurationProperties(AwsS3Properties.class)
+public class AwsSesConfig {
+
+	@Bean
+	public SesClient sesClient(AwsS3Properties properties) {
+		return SesClient.builder()
+				.region(Region.of(properties.getRegion()))
+				.credentialsProvider(StaticCredentialsProvider.create(
+						AwsBasicCredentials.create(
+								properties.getAccessKey(),
+								properties.getSecretKey()
+						)
+				))
+				.build();
+	}
+
+}

src/main/java/com/example/epari/global/event/NotificationEvent.java

@@ -0,0 +1,35 @@
+package com.example.epari.global.event;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import lombok.Builder;
+import lombok.Getter;
+
+/**
+ * 알림 이벤트 클래스
+ */
+@Getter
+@Builder
+public class NotificationEvent {
+
+	private String to;
+
+	private NotificationType type;
+
+	private Map<String, String> properties;
+
+	public static NotificationEvent of(String to, NotificationType type) {
+		return NotificationEvent.builder()
+				.to(to)
+				.type(type)
+				.properties(new HashMap<>())
+				.build();
+	}
+
+	public NotificationEvent addProperty(String key, String value) {
+		this.properties.put(key, value);
+		return this;
+	}
+
+}

src/main/java/com/example/epari/global/event/NotificationType.java

@@ -0,0 +1,23 @@
+package com.example.epari.global.event;
+
+import lombok.Getter;
+
+/**
+ * 알림 타입 Enum 클래스
+ */
+@Getter
+public enum NotificationType {
+
+	USER_APPROVED("사용자 승인", "user-approved.html"),
+	USER_REJECTED("사용자 반려", "user-rejected.html");
+
+	private final String description;
+
+	private final String templatePath;
+
+	NotificationType(String description, String templatePath) {
+		this.description = description;
+		this.templatePath = templatePath;
+	}
+
+}

src/main/java/com/example/epari/global/exception/ErrorCode.java

@@ -69,7 +69,11 @@ public enum ErrorCode {
 	// Cognito 관련 에러 코드 (CGT)
 	COGNITO_USER_FETCH_ERROR(HttpStatus.INTERNAL_SERVER_ERROR, "CGT-001", "사용자 정보 조회에 실패했습니다."),
 	COGNITO_USER_NOT_FOUND(HttpStatus.INTERNAL_SERVER_ERROR, "CGT-002", "사용자 정보를 찾을 수 없습니다."),
-	COGNITO_USER_DELETE_ERROR(HttpStatus.INTERNAL_SERVER_ERROR, "CGT-003", "사용자를 삭제하는 도중 오류가 발생했습니다.");
+	COGNITO_USER_DELETE_ERROR(HttpStatus.INTERNAL_SERVER_ERROR, "CGT-003", "사용자를 삭제하는 도중 오류가 발생했습니다."),
+
+	// 알림 관련 에러 코드 (NTF)
+	NOTIFICATION_SEND_FAILED(HttpStatus.INTERNAL_SERVER_ERROR, "NTF-001", "알림 발송에 실패했습니다."),
+	SES_SERVICE_ERROR(HttpStatus.INTERNAL_SERVER_ERROR, "NTF-002", "이메일 서비스 연동 중 오류가 발생했습니다.");
 
 	private final HttpStatus status;
 

src/main/java/com/example/epari/global/notification/EmailService.java

@@ -0,0 +1,73 @@
+package com.example.epari.global.notification;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.stereotype.Service;
+
+import com.example.epari.admin.exception.NotificationException;
+import com.example.epari.global.event.NotificationEvent;
+import com.example.epari.global.exception.ErrorCode;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+import software.amazon.awssdk.services.ses.SesClient;
+import software.amazon.awssdk.services.ses.model.Body;
+import software.amazon.awssdk.services.ses.model.Content;
+import software.amazon.awssdk.services.ses.model.Destination;
+import software.amazon.awssdk.services.ses.model.Message;
+import software.amazon.awssdk.services.ses.model.SendEmailRequest;
+import software.amazon.awssdk.services.ses.model.SesException;
+
+/**
+ * 이메일 전송을 담당하는 서비스 클래스
+ */
+@Slf4j
+@Service
+@RequiredArgsConstructor
+public class EmailService {
+
+	private final SesClient sesClient;
+
+	private final TemplateProcessor templateProcessor;
+
+	@Value("${aws.ses.source.email}")
+	private String sender;
+
+	/**
+	 * 이벤트를 기반으로 이메일을 발송
+	 */
+	public void sendEmail(NotificationEvent event) {
+		try {
+			String content = templateProcessor.processTemplate(
+					event.getType(),
+					event.getProperties()
+			);
+
+			SendEmailRequest request = SendEmailRequest.builder()
+					.source(sender)
+					.destination(Destination.builder()
+							.toAddresses(event.getTo())
+							.build())
+					.message(Message.builder()
+							.subject(Content.builder()
+									.data(event.getType().getDescription())
+									.build())
+							.body(Body.builder()
+									.html(Content.builder()
+											.data(content)
+											.build())
+									.build())
+							.build())
+					.build();
+
+			sesClient.sendEmail(request);
+			log.info("Email sent successfully to: {}", event.getTo());
+		} catch (SesException e) {
+			log.error("AWS SES error for: {}", event.getTo(), e);
+			throw new NotificationException(ErrorCode.SES_SERVICE_ERROR);
+		} catch (Exception e) {
+			log.error("Notification failed for: {}", event.getTo(), e);
+			throw new NotificationException(ErrorCode.NOTIFICATION_SEND_FAILED);
+		}
+	}
+
+}

src/main/java/com/example/epari/global/notification/NotificationEventListener.java

@@ -0,0 +1,33 @@
+package com.example.epari.global.notification;
+
+import org.springframework.context.event.EventListener;
+import org.springframework.scheduling.annotation.Async;
+import org.springframework.stereotype.Component;
+
+import com.example.epari.global.event.NotificationEvent;
+
+import lombok.RequiredArgsConstructor;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * 알림 이벤트를 Listen하는 이벤트 리스너 클래스
+ */
+@Component
+@RequiredArgsConstructor
+@Slf4j
+public class NotificationEventListener {
+
+	private final EmailService emailService;
+
+	/**
+	 * NotificationEvent를 처리하는 메서드
+	 * emailService.sendEmail 메서드 호출
+	 */
+	@Async
+	@EventListener
+	public void handleNotificationEvent(NotificationEvent event) {
+		log.info("Received notification event for: {}", event.getTo());
+		emailService.sendEmail(event);
+	}
+
+}