Implemented service, repository and controller for each entity

src/main/java/com/faf223/expensetrackerfaf/service/ExpenseService.java

@@ -0,0 +1,19 @@
+package com.faf223.expensetrackerfaf.service;
+
+import com.faf223.expensetrackerfaf.model.Expense;
+import com.faf223.expensetrackerfaf.repository.ExpenseRepository;
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.stereotype.Service;
+
+import java.util.List;
+
+@Service
+public class ExpenseService {
+
+    @Autowired
+    private ExpenseRepository expenseRepository;
+
+    public List<Expense> getExpensesByUserId(String userUuid) {
+        return expenseRepository.findByUserUserUuid(userUuid);
+    }
+}