feat: 동네 온도 랭킹 3위 조회

src/main/java/com/cake/pop/domain/letter/controller/LetterController.java

@@ -10,6 +10,7 @@
 import java.util.List;
 import lombok.RequiredArgsConstructor;
 import org.springframework.http.ResponseEntity;
+import org.springframework.security.core.annotation.AuthenticationPrincipal;
 import org.springframework.web.bind.annotation.GetMapping;
 import org.springframework.web.bind.annotation.PatchMapping;
 import org.springframework.web.bind.annotation.PathVariable;
@@ -45,15 +46,13 @@ public ResponseEntity<GetLetterResponse> getLetter(@PathVariable("letterId") Lon
     }
 
     @PostMapping("/storage")
-    public ResponseEntity<Void> createStorage(@RequestBody @Valid CreateStorageRequest request) {
-        Long userId = 1L;
+    public ResponseEntity<Void> createStorage(@AuthenticationPrincipal Long userId, @RequestBody @Valid CreateStorageRequest request) {
         letterService.createStorage(userId, request);
         return ResponseEntity.ok().build();
     }
 
     @GetMapping("/storages")
-    public ResponseEntity<List<SimpleLetterDto>> getStorages() {
-        Long userId = 1L;
+    public ResponseEntity<List<SimpleLetterDto>> getStorages(@AuthenticationPrincipal Long userId) {
         List<SimpleLetterDto> response = letterService.getStorages(userId);
         return ResponseEntity.ok(response);
     }

src/main/java/com/cake/pop/domain/letter/controller/MailboxController.java

@@ -0,0 +1,24 @@
+package com.cake.pop.domain.letter.controller;
+
+import com.cake.pop.domain.letter.dto.response.GetRankResponse;
+import com.cake.pop.domain.letter.service.MailboxService;
+import java.util.List;
+import lombok.RequiredArgsConstructor;
+import org.springframework.http.ResponseEntity;
+import org.springframework.web.bind.annotation.GetMapping;
+import org.springframework.web.bind.annotation.RequestMapping;
+import org.springframework.web.bind.annotation.RestController;
+
+@RestController
+@RequestMapping("/api/mailboxes")
+@RequiredArgsConstructor
+public class MailboxController {
+
+    private final MailboxService mailboxService;
+
+    @GetMapping("/rank")
+    public ResponseEntity<List<GetRankResponse>> getRanks(){
+        List<GetRankResponse> response = mailboxService.getRanks();
+        return ResponseEntity.ok(response);
+    }
+}

src/main/java/com/cake/pop/domain/letter/dto/response/GetRankResponse.java

@@ -0,0 +1,7 @@
+package com.cake.pop.domain.letter.dto.response;
+
+public record GetRankResponse(
+        String region,
+        Integer letterCount
+) {
+}

src/main/java/com/cake/pop/domain/letter/repository/MailboxRepository.java

@@ -4,6 +4,7 @@
 import com.cake.pop.entity.Mailbox;
 import com.cake.pop.entity.enums.Region;
 import com.cake.pop.global.exception.RestApiException;
+import java.util.List;
 import java.util.Optional;
 import org.springframework.data.jpa.repository.JpaRepository;
 import org.springframework.stereotype.Repository;
@@ -12,6 +13,8 @@
 public interface MailboxRepository extends JpaRepository<Mailbox, Long> {
     Optional<Mailbox> findFirstByRegion(Region region);
 
+    List<Mailbox> findTop3ByOrderByLetterCountDesc();
+
     default Mailbox getFirstByRegion(Region region) {
         return findFirstByRegion(region)
                 .orElseThrow(() -> new RestApiException(LetterErrorCode.MAILBOX_NOT_FOUND));

src/main/java/com/cake/pop/domain/letter/service/MailboxService.java

@@ -0,0 +1,28 @@
+package com.cake.pop.domain.letter.service;
+
+import com.cake.pop.domain.letter.dto.response.GetRankResponse;
+import com.cake.pop.domain.letter.repository.MailboxRepository;
+import com.cake.pop.entity.Mailbox;
+import java.util.List;
+import lombok.RequiredArgsConstructor;
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+@Transactional(readOnly = true)
+@Service
+@RequiredArgsConstructor
+public class MailboxService {
+
+    private final MailboxRepository mailboxRepository;
+
+    public List<GetRankResponse> getRanks() {
+        List<Mailbox> topMailboxes = mailboxRepository.findTop3ByOrderByLetterCountDesc();
+
+        return topMailboxes.stream()
+                .map(mailbox -> new GetRankResponse(
+                        mailbox.getRegion().getName(),
+                        mailbox.getLetterCount()
+                ))
+                .toList();
+    }
+}