feat: mail send 기능 구현

build.gradle

@@ -97,6 +97,9 @@ dependencies {
 	// Google Firebase Admin
 	implementation 'com.google.firebase:firebase-admin:9.2.0'
 
+	// Spring Mail
+	implementation 'org.springframework.boot:spring-boot-starter-mail'
+
 }
 
 tasks.named('test') {

src/main/java/com/on/server/global/mail/MailController.java

@@ -0,0 +1,23 @@
+package com.on.server.global.mail;
+
+import lombok.RequiredArgsConstructor;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestHeader;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequiredArgsConstructor
+@RequestMapping("/api/v1/mail")
+public class MailController {
+
+    private final MailService mailService;
+
+    @GetMapping("/test")
+    public Integer sendAuthNumMail(
+            @RequestHeader String targetMailAddr
+    ) {
+        return mailService.sendAuthNumMail(targetMailAddr);
+    }
+
+}

src/main/java/com/on/server/global/mail/MailService.java

@@ -0,0 +1,57 @@
+package com.on.server.global.mail;
+
+import com.on.server.global.common.ResponseCode;
+import com.on.server.global.common.exceptions.InternalServerException;
+import com.on.server.global.util.StaticValue;
+import jakarta.mail.MessagingException;
+import jakarta.mail.internet.MimeMessage;
+import lombok.RequiredArgsConstructor;
+
+import org.springframework.beans.factory.annotation.Value;
+import org.springframework.context.annotation.Configuration;
+import org.springframework.mail.javamail.JavaMailSender;
+import org.springframework.stereotype.Service;
+
+@Service
+@Configuration
+@RequiredArgsConstructor
+public class MailService {
+
+    private final JavaMailSender javaMailSender;
+
+    @Value("${spring.mail.sender}")
+    private static String senderEmail;
+
+    public Integer sendAuthNumMail(String targetMailAddr) {
+        Integer number = createNumber();
+
+        MimeMessage message = CreateMail(
+                targetMailAddr,
+                StaticValue.AUTH_NUMBER_MAIL_SUBJECT,
+                StaticValue.AUTH_NUMBER_MAIL_BODY + "<h1>" + number + "</h1>"
+        );
+        javaMailSender.send(message);
+
+        return number;
+    }
+
+    private MimeMessage CreateMail(String targetMailAddr, String mailSubject, String mailBody) {
+        MimeMessage message = javaMailSender.createMimeMessage();
+
+        try {
+            message.setFrom(senderEmail);
+            message.setRecipients(MimeMessage.RecipientType.TO, targetMailAddr);
+            message.setSubject(mailSubject);
+            message.setText(mailBody,"UTF-8", "html");
+        } catch (MessagingException e) {
+            throw new InternalServerException(ResponseCode.INTERNAL_SERVER, "메일 내용 생성에 실패했습니다.");
+        }
+
+        return message;
+    }
+
+    private Integer createNumber() {
+        return (int)(Math.random() * (90000)) + 100000; // (int) Math.random() * (최댓값-최소값+1) + 최소값
+    }
+
+}

src/main/java/com/on/server/global/util/StaticValue.java

@@ -5,4 +5,7 @@ public class StaticValue {
     public final static Long JWT_ACCESS_TOKEN_VALID_TIME = 1000L * 60 * 60; // 1시간
     public final static Long JWT_REFRESH_TOKEN_VALID_TIME = 1000L * 60 * 60 * 24 * 14; // 2주
 
+    public final static String AUTH_NUMBER_MAIL_SUBJECT = "On: 이메일 인증";
+    public final static String AUTH_NUMBER_MAIL_BODY = "<h3>On: 이용에 감사드립니다.</h3><h3>아래 인증번호를 서비스에 입력해주시기 바랍니다.</h3><h3>감사합니다.</h3>";
+
 }