feat: Create PetService class

src/main/java/com/udacity/jdnd/course3/critter/pet/PetService.java

@@ -0,0 +1,36 @@
+package com.udacity.jdnd.course3.critter.pet;
+
+import org.springframework.stereotype.Service;
+import org.springframework.transaction.annotation.Transactional;
+
+import java.util.ArrayList;
+import java.util.List;
+
+@Service
+@Transactional
+public class PetService {
+
+    private final PetRepository petRepository;
+
+    public PetService(PetRepository petRepository) {
+        this.petRepository = petRepository;
+    }
+
+    public Pet savePet(Pet pet) {
+        return petRepository.save(pet);
+    }
+
+    public Pet getPetById(Long petId) {
+        return petRepository.findById(petId).orElseThrow(RuntimeException::new);
+    }
+
+    public List<Pet> getAllPets() {
+        List<Pet> pets = new ArrayList<>();
+        petRepository.findAll().forEach(pets::add);
+        return pets;
+    }
+
+    public List<Pet> getPetsByOwner(Long ownerId) {
+        return petRepository.findAllByOwnerId(ownerId);
+    }
+}