#590 add explanation for event aggregator

.all-contributorsrc

@@ -1776,15 +1776,6 @@
       "contributions": [
         "code"
       ]
-    },
-    {
-      "login": "castleKing1997",
-      "name": "DragonDreamer",
-      "avatar_url": "https://avatars.githubusercontent.com/u/35420129?v=4",
-      "profile": "http://rosaecrucis.cn",
-      "contributions": [
-        "code"
-      ]
     }
   ],
   "contributorsPerLine": 7,

README.md

@@ -10,7 +10,7 @@
 [![Coverage](https://sonarcloud.io/api/project_badges/measure?project=iluwatar_java-design-patterns&metric=coverage)](https://sonarcloud.io/dashboard?id=iluwatar_java-design-patterns)
 [![Join the chat at https://gitter.im/iluwatar/java-design-patterns](https://badges.gitter.im/Join%20Chat.svg)](https://gitter.im/iluwatar/java-design-patterns?utm_source=badge&utm_medium=badge&utm_campaign=pr-badge&utm_content=badge)
 <!-- ALL-CONTRIBUTORS-BADGE:START - Do not remove or modify this section -->
-[![All Contributors](https://img.shields.io/badge/all_contributors-196-orange.svg?style=flat-square)](#contributors-)
+[![All Contributors](https://img.shields.io/badge/all_contributors-195-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
 <br/>
@@ -325,7 +325,6 @@ This project is licensed under the terms of the MIT license.
     <td align="center"><a href="https://github.com/interactwithankush"><img src="https://avatars.githubusercontent.com/u/18613127?v=4?s=100" width="100px;" alt=""/><br /><sub><b>interactwithankush</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=interactwithankush" title="Code">💻</a></td>
     <td align="center"><a href="https://github.com/yuhangbin"><img src="https://avatars.githubusercontent.com/u/17566866?v=4?s=100" width="100px;" alt=""/><br /><sub><b>CharlieYu</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=yuhangbin" title="Code">💻</a></td>
     <td align="center"><a href="https://github.com/Leisterbecker"><img src="https://avatars.githubusercontent.com/u/20650323?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Leisterbecker</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Leisterbecker" title="Code">💻</a></td>
-    <td align="center"><a href="http://rosaecrucis.cn"><img src="https://avatars.githubusercontent.com/u/35420129?v=4?s=100" width="100px;" alt=""/><br /><sub><b>DragonDreamer</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=castleKing1997" title="Code">💻</a></td>
   </tr>
 </table>
 

event-aggregator/README.md

@@ -9,6 +9,10 @@ tags:
  - Reactive
 ---
 
+## Name
+
+Event Aggregator
+
 ## Intent
 A system with lots of objects can lead to complexities when a
 client wants to subscribe to events. The client has to find and register for
@@ -17,6 +21,136 @@ requires a separate subscription. An Event Aggregator acts as a single source
 of events for many objects. It registers for all the events of the many objects
 allowing clients to register with just the aggregator.
 
+## Explanation
+
+Real-world example
+
+> King Joffrey sits on the iron throne and rules the seven kingdoms of Westeros. He receives most
+> of his critical information from King's Hand, the second in command. King's hand has many
+> close advisors himself, feeding him with relevant information about events occurring in the
+> kingdom.
+
+In Plain Words
+
+> Event Aggregator is an event mediator that collects events from multiple sources and delivers
+> them to registered observers.
+
+**Programmatic Example**
+
+In our programmatic example, we demonstrate the implementation of an event aggregator pattern. Some of
+the objects are event listeners, some are event emitters, and the event aggregator does both.
+
+```java
+public interface EventObserver {
+  void onEvent(Event e);
+}
+
+public abstract class EventEmitter {
+
+  private final Map<Event, List<EventObserver>> observerLists;
+
+  public EventEmitter() {
+    observerLists = new HashMap<>();
+  }
+
+  public final void registerObserver(EventObserver obs, Event e) {
+    ...
+  }
+
+  protected void notifyObservers(Event e) {
+    ...
+  }
+}
+```
+
+`KingJoffrey` is listening to events from `KingsHand`.
+
+```java
+@Slf4j
+public class KingJoffrey implements EventObserver {
+  @Override
+  public void onEvent(Event e) {
+    LOGGER.info("Received event from the King's Hand: {}", e.toString());
+  }
+}
+```
+
+`KingsHand` is listening to events from his subordinates `LordBaelish`, `LordVarys`, and `Scout`.
+Whatever he hears from them, he delivers to `KingJoffrey`.
+
+```java
+public class KingsHand extends EventEmitter implements EventObserver {
+
+  public KingsHand() {
+  }
+
+  public KingsHand(EventObserver obs, Event e) {
+    super(obs, e);
+  }
+
+  @Override
+  public void onEvent(Event e) {
+    notifyObservers(e);
+  }
+}
+```
+
+For example, `LordVarys` finds a traitor every Sunday and notifies the `KingsHand`.
+
+```java
+@Slf4j
+public class LordVarys extends EventEmitter implements EventObserver {
+  @Override
+  public void timePasses(Weekday day) {
+    if (day == Weekday.SATURDAY) {
+      notifyObservers(Event.TRAITOR_DETECTED);
+    }
+  }
+}
+```
+
+The following snippet demonstrates how the objects are constructed and wired together.
+
+```java
+    var kingJoffrey = new KingJoffrey();
+
+    var kingsHand = new KingsHand();
+    kingsHand.registerObserver(kingJoffrey, Event.TRAITOR_DETECTED);
+    kingsHand.registerObserver(kingJoffrey, Event.STARK_SIGHTED);
+    kingsHand.registerObserver(kingJoffrey, Event.WARSHIPS_APPROACHING);
+    kingsHand.registerObserver(kingJoffrey, Event.WHITE_WALKERS_SIGHTED);
+
+    var varys = new LordVarys();
+    varys.registerObserver(kingsHand, Event.TRAITOR_DETECTED);
+    varys.registerObserver(kingsHand, Event.WHITE_WALKERS_SIGHTED);
+
+    var scout = new Scout();
+    scout.registerObserver(kingsHand, Event.WARSHIPS_APPROACHING);
+    scout.registerObserver(varys, Event.WHITE_WALKERS_SIGHTED);
+
+    var baelish = new LordBaelish(kingsHand, Event.STARK_SIGHTED);
+
+    var emitters = List.of(
+        kingsHand,
+        baelish,
+        varys,
+        scout
+    );
+
+    Arrays.stream(Weekday.values())
+        .<Consumer<? super EventEmitter>>map(day -> emitter -> emitter.timePasses(day))
+        .forEachOrdered(emitters::forEach);
+```
+
+The console output after running the example.
+
+```
+18:21:52.955 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: Warships approaching
+18:21:52.960 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: White walkers sighted
+18:21:52.960 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: Stark sighted
+18:21:52.960 [main] INFO com.iluwatar.event.aggregator.KingJoffrey - Received event from the King's Hand: Traitor detected
+```
+
 ## Class diagram
 ![alt text](./etc/classes.png "Event Aggregator")
 
@@ -26,9 +160,13 @@ Use the Event Aggregator pattern when
 * Event Aggregator is a good choice when you have lots of objects that are
   potential event sources. Rather than have the observer deal with registering
   with them all, you can centralize the registration logic to the Event
-  Aggregator. As well as simplifying registration, a Event Aggregator also
+  Aggregator. As well as simplifying registration, an Event Aggregator also
   simplifies the memory management issues in using observers.
 
+## Related patterns
+
+* [Observer](https://java-design-patterns.com/patterns/observer/)
+
 ## Credits
 
 * [Martin Fowler - Event Aggregator](http://martinfowler.com/eaaDev/EventAggregator.html)

metadata-mapping/README.md

@@ -1,182 +0,0 @@
----
-layout: pattern
-title: Metadata Mapping
-folder: metadata-mapping
-permalink: /patterns/metadata-mapping/
-categories: Architectural
-language: en
-tags:
- - Data access
----
-
-## Intent
-
-Holds details of object-relational mapping in the metadata.
-
-## Explanation
-
-Real world example
-
-> Hibernate ORM Tool uses Metadata Mapping Pattern to specify the mapping between classes and tables either using XML or annotations in code. 
-
-In plain words
-
-> Metadata Mapping specifies the mapping between classes and tables so that we could treat a table of any database like a Java class.
-
-Wikipedia says
-
-> Create a "virtual [object database](https://en.wikipedia.org/wiki/Object_database)" that can be used from within the programming language.
-
-**Programmatic Example**
-
-We give an example about visiting the information of `USER` table in `h2` database. Firstly, we create `USER` table with `h2`:
-
-```java
-@Slf4j
-public class DatabaseUtil {
-  private static final String DB_URL = "jdbc:h2:mem:metamapping";
-  private static final String CREATE_SCHEMA_SQL = "DROP TABLE IF EXISTS `user`;"
-      + "CREATE TABLE `user` (\n"
-      + "  `id` int(11) NOT NULL AUTO_INCREMENT,\n"
-      + "  `username` varchar(255) NOT NULL,\n"
-      + "  `password` varchar(255) NOT NULL,\n"
-      + "  PRIMARY KEY (`id`)\n"
-      + ");";
-    
-  /**
-   * Create database.
-   */
-  static {
-    LOGGER.info("create h2 database");
-    var source = new JdbcDataSource();
-    source.setURL(DB_URL);
-    try (var statement = source.getConnection().createStatement()) {
-      statement.execute(CREATE_SCHEMA_SQL);
-    } catch (SQLException e) {
-      LOGGER.error("unable to create h2 data source", e);
-    }
-  }
-}
-```
-
-Correspondingly, here's the basic `User` entity.
-
-```java
-@Setter
-@Getter
-@ToString
-public class User {
-  private Integer id;
-  private String username;
-  private String password;
-    
-  /**
-   * Get a user.
-   * @param username user name
-   * @param password user password
-   */
-  public User(String username, String password) {
-    this.username = username;
-    this.password = password;
-  }
-}
-```
-
-Then we write a `xml` file to show the mapping between the table and the object:
-
-```xml
-<?xml version="1.0" encoding="utf-8"?>
-<!DOCTYPE hibernate-mapping PUBLIC
-    "-//Hibernate/Hibernate Mapping DTD//EN"
-    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
-
-<hibernate-mapping>
-  <class name="com.iluwatar.metamapping.model.User" table="user">
-    <id name="id" type="java.lang.Integer" column="id">
-      <generator class="native"/>
-    </id>
-    <property name="username" column="username" type="java.lang.String"/>
-    <property name="password" column="password" type="java.lang.String"/>
-  </class>
-</hibernate-mapping>
-```
-
-We use `Hibernate` to resolve the mapping and connect to our database, here's its configuration:
-
-```xml
-<?xml version="1.0" encoding="utf-8"?>
-<!DOCTYPE hibernate-configuration PUBLIC
-    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
-    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
-<hibernate-configuration>
-  <session-factory>
-    <!-- JDBC Database connection settings -->
-    <property name="connection.url">jdbc:h2:mem:metamapping</property>
-    <property name="connection.driver_class">org.h2.Driver</property>
-    <!-- JDBC connection pool settings ... using built-in test pool -->
-    <property name="connection.pool_size">1</property>
-    <!-- Select our SQL dialect -->
-    <property name="dialect">org.hibernate.dialect.H2Dialect</property>
-    <!-- Echo the SQL to stdout -->
-    <property name="show_sql">false</property>
-    <!-- Drop and re-create the database schema on startup -->
-    <property name="hbm2ddl.auto">create-drop</property>
-    <mapping resource="com/iluwatar/metamapping/model/User.hbm.xml" />
-  </session-factory>
-</hibernate-configuration>
-```
-
-Then we can get access to the table just like an object with `Hibernate`, here's some CRUDs:
-
-```java
-@Slf4j
-public class UserService {
-  private static final SessionFactory factory = HibernateUtil.getSessionFactory();
-
-  /**
-   * List all users.
-   * @return list of users
-   */
-  public List<User> listUser() {
-    LOGGER.info("list all users.");
-    List<User> users = new ArrayList<>();
-    try (var session = factory.openSession()) {
-      var tx = session.beginTransaction();
-      List<User> userIter = session.createQuery("FROM User").list();
-      for (var iterator = userIter.iterator(); iterator.hasNext();) {
-        users.add(iterator.next());
-      }
-      tx.commit();
-    } catch (HibernateException e) {
-      LOGGER.debug("fail to get users", e);
-    }
-    return users;
-  }
-  
-  // other CRUDs ->
-  ...
-    
-  public void close() {
-    HibernateUtil.shutdown();
-  }
-}
-```
-
-## Class diagram
-
-![metamapping](etc/metamapping.png)
-
-## Applicability
-
-Use the Metadata Mapping when:
-
-- you want reduce the amount of work needed to handle database mapping.
-
-## Known uses
-
-[Hibernate](https://hibernate.org/), [EclipseLink](https://www.eclipse.org/eclipselink/), [MyBatis](https://blog.mybatis.org/)......
-
-## Credits
-
-- [J2EE Design Patterns](https://www.amazon.com/gp/product/0596004273/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596004273&linkCode=as2&tag=javadesignpat-20&linkId=48d37c67fb3d845b802fa9b619ad8f31)
-

metadata-mapping/etc/metamapping.puml

@@ -1,32 +0,0 @@
-@startuml
-interface com.iluwatar.metamapping.service.UserService {
-+ List<User> listUser()
-+ int createUser(User)
-+ void updateUser(Integer,User)
-+ void deleteUser(Integer)
-+ User getUser(Integer)
-+ void close()
-}
-class com.iluwatar.metamapping.utils.DatabaseUtil {
-+ {static} void createDataSource()
-}
-class com.iluwatar.metamapping.model.User {
-- Integer id
-- String username
-- String password
-+ User(String username, String password)
-}
-class com.iluwatar.metamapping.utils.HibernateUtil {
-+ {static} SessionFactory getSessionFactory()
-+ {static} void shutdown()
-}
-class com.iluwatar.metamapping.App {
-+ {static} void main(String[])
-+ {static} List<User> generateSampleUsers()
-}
-
-com.iluwatar.metamapping.service.UserService <.. com.iluwatar.metamapping.App
-com.iluwatar.metamapping.model.User <.. com.iluwatar.metamapping.service.UserService
-com.iluwatar.metamapping.utils.HibernateUtil <.. com.iluwatar.metamapping.service.UserService
-com.iluwatar.metamapping.utils.DatabaseUtil <-- com.iluwatar.metamapping.utils.HibernateUtil
-@enduml

metadata-mapping/pom.xml

@@ -1,87 +0,0 @@
-<?xml version="1.0" encoding="UTF-8"?>
-<!--
-
-  The MIT License
-  Copyright © 2014-2021 Ilkka Seppälä
-
-  Permission is hereby granted, free of charge, to any person obtaining a copy
-  of this software and associated documentation files (the "Software"), to deal
-  in the Software without restriction, including without limitation the rights
-  to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
-  copies of the Software, and to permit persons to whom the Software is
-  furnished to do so, subject to the following conditions:
-
-  The above copyright notice and this permission notice shall be included in
-  all copies or substantial portions of the Software.
-
-  THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
-  IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
-  FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
-  AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
-  LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
-  OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
-  THE SOFTWARE.
-
--->
-<project xmlns="http://maven.apache.org/POM/4.0.0"
-     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
-     xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
-  <parent>
-    <artifactId>java-design-patterns</artifactId>
-    <groupId>com.iluwatar</groupId>
-    <version>1.26.0-SNAPSHOT</version>
-  </parent>
-  <modelVersion>4.0.0</modelVersion>
-
-  <artifactId>metadata-mapping</artifactId>
-  <dependencies>
-    <dependency>
-      <groupId>org.junit.jupiter</groupId>
-      <artifactId>junit-jupiter-engine</artifactId>
-      <scope>test</scope>
-    </dependency>
-    <dependency>
-      <groupId>com.h2database</groupId>
-      <artifactId>h2</artifactId>
-    </dependency>
-    <dependency>
-      <groupId>org.hibernate</groupId>
-      <artifactId>hibernate-core</artifactId>
-    </dependency>
-    <dependency>
-      <groupId>com.h2database</groupId>
-      <artifactId>h2</artifactId>
-    </dependency>
-    <dependency>
-      <groupId>javax.xml.bind</groupId>
-      <artifactId>jaxb-api</artifactId>
-    </dependency>
-    <dependency>
-      <groupId>com.sun.xml.bind</groupId>
-      <artifactId>jaxb-impl</artifactId>
-    </dependency>
-    <dependency>
-      <groupId>com.sun.istack</groupId>
-      <artifactId>istack-commons-runtime</artifactId>
-    </dependency>
-  </dependencies>
-  <build>
-    <plugins>
-      <plugin>
-        <groupId>org.apache.maven.plugins</groupId>
-        <artifactId>maven-assembly-plugin</artifactId>
-        <executions>
-          <execution>
-            <configuration>
-              <archive>
-                <manifest>
-                  <mainClass>com.iluwatar.metamapping.App</mainClass>
-                </manifest>
-              </archive>
-            </configuration>
-          </execution>
-        </executions>
-      </plugin>
-    </plugins>
-  </build>
-</project>

metadata-mapping/src/main/java/com/iluwatar/metamapping/App.java

@@ -1,72 +0,0 @@
-package com.iluwatar.metamapping;
-
-import com.iluwatar.metamapping.model.User;
-import com.iluwatar.metamapping.service.UserService;
-import com.iluwatar.metamapping.utils.DatabaseUtil;
-import java.util.List;
-import lombok.extern.slf4j.Slf4j;
-import org.hibernate.service.ServiceRegistry;
-
-/**
- * Metadata Mapping specifies the mapping
- * between classes and tables so that
- * we could treat a table of any database like a Java class.
- *
- * <p>With hibernate, we achieve list/create/update/delete/get operations:
- * 1)Create the H2 Database in {@link DatabaseUtil}.
- * 2)Hibernate resolve hibernate.cfg.xml and generate service like save/list/get/delete.
- *    For learning metadata mapping pattern, we go deeper into Hibernate here:
- * a)read properties from hibernate.cfg.xml and mapping from *.hbm.xml
- * b)create session factory to generate session interacting with database
- * c)generate session with factory pattern
- * d)create query object or use basic api with session,
- *      hibernate will convert all query to database query according to metadata
- * 3)We encapsulate hibernate service in {@link UserService} for our use.
- * @see org.hibernate.cfg.Configuration#configure(String)
- * @see org.hibernate.cfg.Configuration#buildSessionFactory(ServiceRegistry)
- * @see org.hibernate.internal.SessionFactoryImpl#openSession()
- */
-@Slf4j
-public class App {
-  /**
-   * Program entry point.
-   *
-   * @param args command line args.
-   * @throws Exception if any error occurs.
-   */
-  public static void main(String[] args)  throws Exception {
-    // get service
-    var userService = new UserService();
-    // use create service to add users
-    for (var user: generateSampleUsers()) {
-      var id = userService.createUser(user);
-      LOGGER.info("Add user" + user + "at" + id + ".");
-    }
-    // use list service to get users
-    var users = userService.listUser();
-    LOGGER.info(String.valueOf(users));
-    // use get service to get a user
-    var user = userService.getUser(1);
-    LOGGER.info(String.valueOf(user));
-    // change password of user 1
-    user.setPassword("new123");
-    // use update service to update user 1
-    userService.updateUser(1, user);
-    // use delete service to delete user 2
-    userService.deleteUser(2);
-    // close service
-    userService.close();
-  }
-
-  /**
-   * Generate users.
-   *
-   * @return list of users.
-   */
-  public static List<User> generateSampleUsers() {
-    final var user1 = new User("ZhangSan", "zhs123");
-    final var user2 = new User("LiSi", "ls123");
-    final var user3 = new User("WangWu", "ww123");
-    return List.of(user1, user2, user3);
-  }
-}

metadata-mapping/src/main/java/com/iluwatar/metamapping/model/User.java

@@ -1,29 +0,0 @@
-package com.iluwatar.metamapping.model;
-
-import lombok.Getter;
-import lombok.Setter;
-import lombok.ToString;
-
-/**
- * User Entity.
- */
-@Setter
-@Getter
-@ToString
-public class User {
-  private Integer id;
-  private String username;
-  private String password;
-
-  public User() {}
-
-  /**
-   * Get a user.
-   * @param username user name
-   * @param password user password
-   */
-  public User(String username, String password) {
-    this.username = username;
-    this.password = password;
-  }
-}

metadata-mapping/src/main/java/com/iluwatar/metamapping/service/UserService.java

@@ -1,114 +0,0 @@
-package com.iluwatar.metamapping.service;
-
-import com.iluwatar.metamapping.model.User;
-import com.iluwatar.metamapping.utils.HibernateUtil;
-import java.util.ArrayList;
-import java.util.List;
-import lombok.extern.slf4j.Slf4j;
-import org.hibernate.HibernateException;
-import org.hibernate.SessionFactory;
-
-/**
- * Service layer for user.
- */
-@Slf4j
-public class UserService {
-  private static final SessionFactory factory = HibernateUtil.getSessionFactory();
-
-  /**
-   * List all users.
-   * @return list of users
-   */
-  public List<User> listUser() {
-    LOGGER.info("list all users.");
-    List<User> users = new ArrayList<>();
-    try (var session = factory.openSession()) {
-      var tx = session.beginTransaction();
-      List<User> userIter = session.createQuery("FROM User").list();
-      for (var iterator = userIter.iterator(); iterator.hasNext();) {
-        users.add(iterator.next());
-      }
-      tx.commit();
-    } catch (HibernateException e) {
-      LOGGER.debug("fail to get users", e);
-    }
-    return users;
-  }
-
-  /**
-   * Add a user.
-   * @param user user entity
-   * @return user id
-   */
-  public int createUser(User user) {
-    LOGGER.info("create user: " + user.getUsername());
-    var id = -1;
-    try (var session = factory.openSession()) {
-      var tx = session.beginTransaction();
-      id = (Integer) session.save(user);
-      tx.commit();
-    } catch (HibernateException e) {
-      LOGGER.debug("fail to create user", e);
-    }
-    LOGGER.info("create user " + user.getUsername() + " at " + id);
-    return id;
-  }
-
-  /**
-   * Update user.
-   * @param id user id
-   * @param user new user entity
-   */
-  public void updateUser(Integer id, User user) {
-    LOGGER.info("update user at " + id);
-    try (var session = factory.openSession()) {
-      var tx = session.beginTransaction();
-      user.setId(id);
-      session.update(user);
-      tx.commit();
-    } catch (HibernateException e) {
-      LOGGER.debug("fail to update user", e);
-    }
-  }
-
-  /**
-   * Delete user.
-   * @param id user id
-   */
-  public void deleteUser(Integer id) {
-    LOGGER.info("delete user at: " + id);
-    try (var session = factory.openSession()) {
-      var tx = session.beginTransaction();
-      var user = session.get(User.class, id);
-      session.delete(user);
-      tx.commit();
-    } catch (HibernateException e) {
-      LOGGER.debug("fail to delete user", e);
-    }
-  }
-
-  /**
-   * Get user.
-   * @param id user id
-   * @return deleted user
-   */
-  public User getUser(Integer id) {
-    LOGGER.info("get user at: " + id);
-    User user = null;
-    try (var session = factory.openSession()) {
-      var tx = session.beginTransaction();
-      user = session.get(User.class, id);
-      tx.commit();
-    } catch (HibernateException e) {
-      LOGGER.debug("fail to get user", e);
-    }
-    return user;
-  }
-
-  /**
-   * Close hibernate.
-   */
-  public void close() {
-    HibernateUtil.shutdown();
-  }
-}

metadata-mapping/src/main/java/com/iluwatar/metamapping/utils/DatabaseUtil.java

@@ -1,39 +0,0 @@
-package com.iluwatar.metamapping.utils;
-
-import java.sql.SQLException;
-import lombok.extern.slf4j.Slf4j;
-import org.h2.jdbcx.JdbcDataSource;
-
-/**
- * Create h2 database.
- */
-@Slf4j
-public class DatabaseUtil {
-  private static final String DB_URL = "jdbc:h2:mem:metamapping";
-  private static final String CREATE_SCHEMA_SQL = "DROP TABLE IF EXISTS `user`;"
-      + "CREATE TABLE `user` (\n"
-      + "  `id` int(11) NOT NULL AUTO_INCREMENT,\n"
-      + "  `username` varchar(255) NOT NULL,\n"
-      + "  `password` varchar(255) NOT NULL,\n"
-      + "  PRIMARY KEY (`id`)\n"
-      + ");";
-
-  /**
-   * Hide constructor.
-   */
-  private DatabaseUtil() {}
-
-  /**
-   * Create database.
-   */
-  static {
-    LOGGER.info("create h2 database");
-    var source = new JdbcDataSource();
-    source.setURL(DB_URL);
-    try (var statement = source.getConnection().createStatement()) {
-      statement.execute(CREATE_SCHEMA_SQL);
-    } catch (SQLException e) {
-      LOGGER.error("unable to create h2 data source", e);
-    }
-  }
-}

metadata-mapping/src/main/java/com/iluwatar/metamapping/utils/HibernateUtil.java

@@ -1,45 +0,0 @@
-package com.iluwatar.metamapping.utils;
-
-import lombok.extern.slf4j.Slf4j;
-import org.hibernate.SessionFactory;
-import org.hibernate.cfg.Configuration;
-
-/**
- * Manage hibernate.
- */
-@Slf4j
-public class HibernateUtil {
-
-  private static final SessionFactory sessionFactory = buildSessionFactory();
-
-  /**
-   * Hide constructor.
-   */
-  private HibernateUtil() {}
-
-  /**
-   * Build session factory.
-   * @return session factory
-   */
-  private static SessionFactory buildSessionFactory() {
-    // Create the SessionFactory from hibernate.cfg.xml
-    return new Configuration().configure().buildSessionFactory();
-  }
-
-  /**
-   * Get session factory.
-   * @return session factory
-   */
-  public static SessionFactory getSessionFactory() {
-    return sessionFactory;
-  }
-
-  /**
-   * Close session factory.
-   */
-  public static void shutdown() {
-    // Close caches and connection pools
-    getSessionFactory().close();
-  }
-
-}

metadata-mapping/src/main/resources/com/iluwatar/metamapping/model/User.hbm.xml

@@ -1,14 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!DOCTYPE hibernate-mapping PUBLIC
-    "-//Hibernate/Hibernate Mapping DTD//EN"
-    "http://www.hibernate.org/dtd/hibernate-mapping-3.0.dtd">
-
-<hibernate-mapping>
-  <class name="com.iluwatar.metamapping.model.User" table="user">
-    <id name="id" type="java.lang.Integer" column="id">
-      <generator class="native"/>
-    </id>
-    <property name="username" column="username" type="java.lang.String"/>
-    <property name="password" column="password" type="java.lang.String"/>
-  </class>
-</hibernate-mapping>

metadata-mapping/src/main/resources/hibernate.cfg.xml

@@ -1,20 +0,0 @@
-<?xml version="1.0" encoding="utf-8"?>
-<!DOCTYPE hibernate-configuration PUBLIC
-    "-//Hibernate/Hibernate Configuration DTD 3.0//EN"
-    "http://hibernate.sourceforge.net/hibernate-configuration-3.0.dtd">
-<hibernate-configuration>
-  <session-factory>
-    <!-- JDBC Database connection settings -->
-    <property name="connection.url">jdbc:h2:mem:metamapping</property>
-    <property name="connection.driver_class">org.h2.Driver</property>
-    <!-- JDBC connection pool settings ... using built-in test pool -->
-    <property name="connection.pool_size">1</property>
-    <!-- Select our SQL dialect -->
-    <property name="dialect">org.hibernate.dialect.H2Dialect</property>
-    <!-- Echo the SQL to stdout -->
-    <property name="show_sql">false</property>
-    <!-- Drop and re-create the database schema on startup -->
-    <property name="hbm2ddl.auto">create-drop</property>
-    <mapping resource="com/iluwatar/metamapping/model/User.hbm.xml" />
-  </session-factory>
-</hibernate-configuration>

metadata-mapping/src/test/java/com/iluwatar/metamapping/AppTest.java

@@ -1,20 +0,0 @@
-package com.iluwatar.metamapping;
-
-import org.junit.jupiter.api.Test;
-import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
-
-/**
- * Tests that metadata mapping example runs without errors.
- */
-class AppTest {
-  /**
-   * Issue: Add at least one assertion to this test case.
-   *
-   * Solution: Inserted assertion to check whether the execution of the main method in {@link App#main(String[])}
-   * throws an exception.
-   */
-  @Test
-  void shouldExecuteMetaMappingWithoutException() {
-    assertDoesNotThrow(() -> App.main(new String[]{}));
-  }
-}

pom.xml

@@ -75,7 +75,6 @@
     <license-maven-plugin.version>3.0</license-maven-plugin.version>
     <urm-maven-plugin.version>1.4.8</urm-maven-plugin.version>
     <commons-io.version>2.7</commons-io.version>
-    <istack-commons-runtime.version>4.0.1</istack-commons-runtime.version>
     <!-- SonarCloud -->
     <sonar.host.url>https://sonarcloud.io</sonar.host.url>
     <sonar.organization>iluwatar</sonar.organization>
@@ -228,7 +227,6 @@
     <module>lockable-object</module>
     <module>fanout-fanin</module>
     <module>domain-model</module>
-    <module>metadata-mapping</module>
   </modules>
   <repositories>
     <repository>
@@ -379,11 +377,6 @@
         <artifactId>commons-io</artifactId>
         <version>${commons-io.version}</version>
       </dependency>
-      <dependency>
-        <groupId>com.sun.istack</groupId>
-        <artifactId>istack-commons-runtime</artifactId>
-        <version>${istack-commons-runtime.version}</version>
-      </dependency>
     </dependencies>
   </dependencyManagement>
   <dependencies>