feat(dao): add UserDao with Hibernate CRUD operations

second-part/hw-02/user-service/src/main/java/com/example/UserDao.java

@@ -0,0 +1,92 @@
+package com.example;
+
+import org.hibernate.HibernateException;
+import org.hibernate.Session;
+import org.hibernate.SessionFactory;
+import org.hibernate.Transaction;
+import org.hibernate.cfg.Configuration;
+
+public class UserDao {
+
+  private final SessionFactory sessionFactory;
+
+  public UserDao() {
+    sessionFactory =
+        new Configuration().configure().addAnnotatedClass(User.class).buildSessionFactory();
+  }
+
+  public User create(User user) {
+    Transaction transaction = null;
+
+    try (Session session = sessionFactory.openSession()) {
+      transaction = session.beginTransaction();
+
+      session.persist(user);
+
+      transaction.commit();
+
+      return user;
+    } catch (HibernateException e) {
+      handleException(transaction, e);
+      return null;
+    }
+  }
+
+  public User findById(Long id) {
+    try (Session session = sessionFactory.openSession()) {
+      return session.find(User.class, id);
+    } catch (HibernateException e) {
+      handleException(null, e);
+      return null;
+    }
+  }
+
+  public User update(User user) {
+    Transaction transaction = null;
+
+    try (Session session = sessionFactory.openSession()) {
+      transaction = session.beginTransaction();
+
+      User updatedUser = session.merge(user);
+
+      transaction.commit();
+
+      return updatedUser;
+    } catch (HibernateException e) {
+      handleException(transaction, e);
+      return null;
+    }
+  }
+
+  public void deleteById(Long id) {
+    Transaction transaction = null;
+
+    try (Session session = sessionFactory.openSession()) {
+      transaction = session.beginTransaction();
+
+      User user = session.find(User.class, id);
+
+      if (user != null) {
+        session.remove(user);
+      }
+
+      transaction.commit();
+    } catch (HibernateException e) {
+      handleException(transaction, e);
+    }
+  }
+
+  private void handleException(Transaction transaction, HibernateException e) {
+    if (transaction != null) {
+      try {
+        transaction.rollback();
+      } catch (HibernateException rollbackException) {
+        System.err.println("Ошибка при откате транзакции.");
+      }
+    }
+
+    System.err.println("Ошибка при работе с Hibernate: " + e.getMessage());
+
+    throw e;
+  }
+}