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feature: Metadata Mapping pattern (#1932)
* metadata-mapping * Update README.md * add class diagram * update README.md * fix identation * Update pom.xml * fix indentation * fix ci * remove e.printstack * fix ci * update class diagram * fix ci * fix ci * fix sc * fix smells * Update DatabaseUtil.java * fix coverage * Update DatabaseUtil.java * Update DatabaseUtil.java * Update DatabaseUtil.java * Update metadata-mapping/README.md Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com> * fix review * fix review * Update App.java * Update App.java * fix review Co-authored-by: Ilkka Seppälä <iluwatar@users.noreply.github.com>
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DragonDreamer
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package com.iluwatar.metamapping;
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import com.iluwatar.metamapping.model.User;
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import com.iluwatar.metamapping.service.UserService;
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import com.iluwatar.metamapping.utils.DatabaseUtil;
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import java.util.List;
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import lombok.extern.slf4j.Slf4j;
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import org.hibernate.service.ServiceRegistry;
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/**
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* Metadata Mapping specifies the mapping
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* between classes and tables so that
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* we could treat a table of any database like a Java class.
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*
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* <p>With hibernate, we achieve list/create/update/delete/get operations:
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* 1)Create the H2 Database in {@link DatabaseUtil}.
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* 2)Hibernate resolve hibernate.cfg.xml and generate service like save/list/get/delete.
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* For learning metadata mapping pattern, we go deeper into Hibernate here:
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* a)read properties from hibernate.cfg.xml and mapping from *.hbm.xml
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* b)create session factory to generate session interacting with database
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* c)generate session with factory pattern
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* d)create query object or use basic api with session,
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* hibernate will convert all query to database query according to metadata
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* 3)We encapsulate hibernate service in {@link UserService} for our use.
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* @see org.hibernate.cfg.Configuration#configure(String)
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* @see org.hibernate.cfg.Configuration#buildSessionFactory(ServiceRegistry)
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* @see org.hibernate.internal.SessionFactoryImpl#openSession()
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*/
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@Slf4j
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public class App {
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/**
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* Program entry point.
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*
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* @param args command line args.
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* @throws Exception if any error occurs.
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*/
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public static void main(String[] args) throws Exception {
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// get service
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var userService = new UserService();
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// use create service to add users
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for (var user: generateSampleUsers()) {
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var id = userService.createUser(user);
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LOGGER.info("Add user" + user + "at" + id + ".");
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}
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// use list service to get users
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var users = userService.listUser();
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LOGGER.info(String.valueOf(users));
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// use get service to get a user
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var user = userService.getUser(1);
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LOGGER.info(String.valueOf(user));
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// change password of user 1
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user.setPassword("new123");
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// use update service to update user 1
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userService.updateUser(1, user);
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// use delete service to delete user 2
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userService.deleteUser(2);
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// close service
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userService.close();
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}
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/**
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* Generate users.
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*
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* @return list of users.
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*/
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public static List<User> generateSampleUsers() {
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final var user1 = new User("ZhangSan", "zhs123");
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final var user2 = new User("LiSi", "ls123");
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final var user3 = new User("WangWu", "ww123");
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return List.of(user1, user2, user3);
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}
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}
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package com.iluwatar.metamapping.model;
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import lombok.Getter;
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import lombok.Setter;
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import lombok.ToString;
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/**
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* User Entity.
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*/
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@Setter
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@Getter
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@ToString
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public class User {
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private Integer id;
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private String username;
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private String password;
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public User() {}
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/**
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* Get a user.
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* @param username user name
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* @param password user password
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*/
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public User(String username, String password) {
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this.username = username;
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this.password = password;
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}
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}
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package com.iluwatar.metamapping.service;
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import com.iluwatar.metamapping.model.User;
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import com.iluwatar.metamapping.utils.HibernateUtil;
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import java.util.ArrayList;
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import java.util.List;
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import lombok.extern.slf4j.Slf4j;
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import org.hibernate.HibernateException;
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import org.hibernate.SessionFactory;
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/**
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* Service layer for user.
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*/
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@Slf4j
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public class UserService {
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private static final SessionFactory factory = HibernateUtil.getSessionFactory();
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/**
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* List all users.
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* @return list of users
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*/
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public List<User> listUser() {
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LOGGER.info("list all users.");
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List<User> users = new ArrayList<>();
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try (var session = factory.openSession()) {
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var tx = session.beginTransaction();
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List<User> userIter = session.createQuery("FROM User").list();
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for (var iterator = userIter.iterator(); iterator.hasNext();) {
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users.add(iterator.next());
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}
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tx.commit();
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} catch (HibernateException e) {
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LOGGER.debug("fail to get users", e);
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}
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return users;
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}
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/**
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* Add a user.
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* @param user user entity
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* @return user id
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*/
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public int createUser(User user) {
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LOGGER.info("create user: " + user.getUsername());
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var id = -1;
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try (var session = factory.openSession()) {
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var tx = session.beginTransaction();
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id = (Integer) session.save(user);
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tx.commit();
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} catch (HibernateException e) {
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LOGGER.debug("fail to create user", e);
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}
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LOGGER.info("create user " + user.getUsername() + " at " + id);
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return id;
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}
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/**
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* Update user.
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* @param id user id
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* @param user new user entity
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*/
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public void updateUser(Integer id, User user) {
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LOGGER.info("update user at " + id);
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try (var session = factory.openSession()) {
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var tx = session.beginTransaction();
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user.setId(id);
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session.update(user);
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tx.commit();
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} catch (HibernateException e) {
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LOGGER.debug("fail to update user", e);
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}
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}
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/**
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* Delete user.
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* @param id user id
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*/
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public void deleteUser(Integer id) {
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LOGGER.info("delete user at: " + id);
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try (var session = factory.openSession()) {
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var tx = session.beginTransaction();
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var user = session.get(User.class, id);
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session.delete(user);
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tx.commit();
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} catch (HibernateException e) {
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LOGGER.debug("fail to delete user", e);
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}
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}
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/**
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* Get user.
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* @param id user id
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* @return deleted user
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*/
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public User getUser(Integer id) {
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LOGGER.info("get user at: " + id);
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User user = null;
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try (var session = factory.openSession()) {
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var tx = session.beginTransaction();
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user = session.get(User.class, id);
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tx.commit();
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} catch (HibernateException e) {
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LOGGER.debug("fail to get user", e);
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}
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return user;
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}
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/**
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* Close hibernate.
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*/
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public void close() {
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HibernateUtil.shutdown();
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}
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}
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package com.iluwatar.metamapping.utils;
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import java.sql.SQLException;
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import lombok.extern.slf4j.Slf4j;
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import org.h2.jdbcx.JdbcDataSource;
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/**
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* Create h2 database.
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*/
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@Slf4j
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public class DatabaseUtil {
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private static final String DB_URL = "jdbc:h2:mem:metamapping";
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private static final String CREATE_SCHEMA_SQL = "DROP TABLE IF EXISTS `user`;"
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+ "CREATE TABLE `user` (\n"
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+ " `id` int(11) NOT NULL AUTO_INCREMENT,\n"
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+ " `username` varchar(255) NOT NULL,\n"
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+ " `password` varchar(255) NOT NULL,\n"
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+ " PRIMARY KEY (`id`)\n"
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+ ");";
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/**
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* Hide constructor.
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*/
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private DatabaseUtil() {}
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/**
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* Create database.
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*/
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static {
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LOGGER.info("create h2 database");
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var source = new JdbcDataSource();
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source.setURL(DB_URL);
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try (var statement = source.getConnection().createStatement()) {
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statement.execute(CREATE_SCHEMA_SQL);
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} catch (SQLException e) {
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LOGGER.error("unable to create h2 data source", e);
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}
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}
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}
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@@ -0,0 +1,45 @@
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package com.iluwatar.metamapping.utils;
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import lombok.extern.slf4j.Slf4j;
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import org.hibernate.SessionFactory;
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import org.hibernate.cfg.Configuration;
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/**
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* Manage hibernate.
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*/
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@Slf4j
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public class HibernateUtil {
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private static final SessionFactory sessionFactory = buildSessionFactory();
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/**
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* Hide constructor.
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*/
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private HibernateUtil() {}
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/**
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* Build session factory.
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* @return session factory
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*/
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private static SessionFactory buildSessionFactory() {
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// Create the SessionFactory from hibernate.cfg.xml
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return new Configuration().configure().buildSessionFactory();
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}
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/**
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* Get session factory.
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* @return session factory
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*/
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public static SessionFactory getSessionFactory() {
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return sessionFactory;
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}
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/**
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* Close session factory.
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*/
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public static void shutdown() {
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// Close caches and connection pools
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getSessionFactory().close();
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}
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}
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