docs: update .all-contributorsrc [skip ci]

.all-contributorsrc

@@ -1767,24 +1767,6 @@
       "contributions": [
         "code"
       ]
-    },
-    {
-      "login": "Leisterbecker",
-      "name": "Leisterbecker",
-      "avatar_url": "https://avatars.githubusercontent.com/u/20650323?v=4",
-      "profile": "https://github.com/Leisterbecker",
-      "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-194-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
 <br/>
@@ -324,8 +324,6 @@ This project is licensed under the terms of the MIT license.
     <td align="center"><a href="https://github.com/Shrirang97"><img src="https://avatars.githubusercontent.com/u/28738668?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Shrirang</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/pulls?q=is%3Apr+reviewed-by%3AShrirang97" title="Reviewed Pull Requests">👀</a> <a href="https://github.com/iluwatar/java-design-patterns/commits?author=Shrirang97" title="Code">💻</a></td>
     <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/src/main/java/com/iluwatar/event/aggregator/App.java

@@ -49,28 +49,13 @@ public class App {
   public static void main(String[] args) {
 
     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 kingsHand = new KingsHand(kingJoffrey);
 
     var emitters = List.of(
         kingsHand,
-        baelish,
-        varys,
-        scout
+        new LordBaelish(kingsHand),
+        new LordVarys(kingsHand),
+        new Scout(kingsHand)
     );
 
     Arrays.stream(Weekday.values())

event-aggregator/src/main/java/com/iluwatar/event/aggregator/Event.java

@@ -31,7 +31,6 @@ import lombok.RequiredArgsConstructor;
 @RequiredArgsConstructor
 public enum Event {
 
-  WHITE_WALKERS_SIGHTED("White walkers sighted"),
   STARK_SIGHTED("Stark sighted"),
   WARSHIPS_APPROACHING("Warships approaching"),
   TRAITOR_DETECTED("Traitor detected");

event-aggregator/src/main/java/com/iluwatar/event/aggregator/EventEmitter.java

@@ -23,48 +23,31 @@
 
 package com.iluwatar.event.aggregator;
 
-import java.util.HashMap;
 import java.util.LinkedList;
 import java.util.List;
-import java.util.Map;
 
 /**
  * EventEmitter is the base class for event producers that can be observed.
  */
 public abstract class EventEmitter {
 
-  private final Map<Event, List<EventObserver>> observerLists;
+  private final List<EventObserver> observers;
 
   public EventEmitter() {
-    observerLists = new HashMap<>();
+    observers = new LinkedList<>();
   }
 
-  public EventEmitter(EventObserver obs, Event e) {
+  public EventEmitter(EventObserver obs) {
     this();
-    registerObserver(obs, e);
+    registerObserver(obs);
   }
 
-  /**
-  * Registers observer for specific event in the related list.
-  *
-  * @param obs the observer that observers this emitter
-  * @param e the specific event for that observation occurs
-  * */
-  public final void registerObserver(EventObserver obs, Event e) {
-    if (!observerLists.containsKey(e)) {
-      observerLists.put(e, new LinkedList<>());
-    }
-    if (!observerLists.get(e).contains(obs)) {
-      observerLists.get(e).add(obs);
-    }
+  public final void registerObserver(EventObserver obs) {
+    observers.add(obs);
   }
 
   protected void notifyObservers(Event e) {
-    if (observerLists.containsKey(e)) {
-      observerLists
-        .get(e)
-        .forEach(observer -> observer.onEvent(e));
-    }
+    observers.forEach(obs -> obs.onEvent(e));
   }
 
   public abstract void timePasses(Weekday day);

event-aggregator/src/main/java/com/iluwatar/event/aggregator/KingsHand.java

@@ -31,8 +31,8 @@ public class KingsHand extends EventEmitter implements EventObserver {
   public KingsHand() {
   }
 
-  public KingsHand(EventObserver obs, Event e) {
-    super(obs, e);
+  public KingsHand(EventObserver obs) {
+    super(obs);
   }
 
   @Override
@@ -42,5 +42,6 @@ public class KingsHand extends EventEmitter implements EventObserver {
 
   @Override
   public void timePasses(Weekday day) {
+    // NOP
   }
 }

event-aggregator/src/main/java/com/iluwatar/event/aggregator/LordBaelish.java

@@ -31,8 +31,8 @@ public class LordBaelish extends EventEmitter {
   public LordBaelish() {
   }
 
-  public LordBaelish(EventObserver obs, Event e) {
-    super(obs, e);
+  public LordBaelish(EventObserver obs) {
+    super(obs);
   }
 
   @Override

event-aggregator/src/main/java/com/iluwatar/event/aggregator/LordVarys.java

@@ -23,19 +23,16 @@
 
 package com.iluwatar.event.aggregator;
 
-import lombok.extern.slf4j.Slf4j;
-
 /**
  * LordVarys produces events.
  */
-@Slf4j
-public class LordVarys extends EventEmitter implements EventObserver {
+public class LordVarys extends EventEmitter {
 
   public LordVarys() {
   }
 
-  public LordVarys(EventObserver obs, Event e) {
-    super(obs, e);
+  public LordVarys(EventObserver obs) {
+    super(obs);
   }
 
   @Override
@@ -44,10 +41,4 @@ public class LordVarys extends EventEmitter implements EventObserver {
       notifyObservers(Event.TRAITOR_DETECTED);
     }
   }
-
-
-  @Override
-  public void onEvent(Event e) {
-    notifyObservers(e);
-  }
 }

event-aggregator/src/main/java/com/iluwatar/event/aggregator/Scout.java

@@ -31,8 +31,8 @@ public class Scout extends EventEmitter {
   public Scout() {
   }
 
-  public Scout(EventObserver obs, Event e) {
-    super(obs, e);
+  public Scout(EventObserver obs) {
+    super(obs);
   }
 
   @Override
@@ -40,8 +40,5 @@ public class Scout extends EventEmitter {
     if (day == Weekday.TUESDAY) {
       notifyObservers(Event.WARSHIPS_APPROACHING);
     }
-    if (day == Weekday.WEDNESDAY) {
-      notifyObservers(Event.WHITE_WALKERS_SIGHTED);
-    }
   }
 }

event-aggregator/src/test/java/com/iluwatar/event/aggregator/EventEmitterTest.java

@@ -31,7 +31,6 @@ import static org.mockito.Mockito.verifyNoMoreInteractions;
 import static org.mockito.Mockito.verifyZeroInteractions;
 
 import java.util.Objects;
-import java.util.function.BiFunction;
 import java.util.function.Function;
 import java.util.function.Supplier;
 import org.junit.jupiter.api.Test;
@@ -47,7 +46,7 @@ abstract class EventEmitterTest<E extends EventEmitter> {
   /**
    * Factory used to create a new instance of the test object with a default observer
    */
-  private final BiFunction<EventObserver, Event, E> factoryWithDefaultObserver;
+  private final Function<EventObserver, E> factoryWithDefaultObserver;
 
   /**
    * Factory used to create a new instance of the test object without passing a default observer
@@ -68,7 +67,7 @@ abstract class EventEmitterTest<E extends EventEmitter> {
    * Create a new event emitter test, using the given test object factories, special day and event
    */
   EventEmitterTest(final Weekday specialDay, final Event event,
-                   final BiFunction<EventObserver, Event, E> factoryWithDefaultObserver,
+                   final Function<EventObserver, E> factoryWithDefaultObserver,
                    final Supplier<E> factoryWithoutDefaultObserver) {
 
     this.specialDay = specialDay;
@@ -130,8 +129,8 @@ abstract class EventEmitterTest<E extends EventEmitter> {
     final var observer2 = mock(EventObserver.class);
 
     final var emitter = this.factoryWithoutDefaultObserver.get();
-    emitter.registerObserver(observer1, event);
-    emitter.registerObserver(observer2, event);
+    emitter.registerObserver(observer1);
+    emitter.registerObserver(observer2);
 
     testAllDays(specialDay, event, emitter, observer1, observer2);
   }
@@ -147,9 +146,9 @@ abstract class EventEmitterTest<E extends EventEmitter> {
     final var observer1 = mock(EventObserver.class);
     final var observer2 = mock(EventObserver.class);
 
-    final var emitter = this.factoryWithDefaultObserver.apply(defaultObserver, event);
-    emitter.registerObserver(observer1, event);
-    emitter.registerObserver(observer2, event);
+    final var emitter = this.factoryWithDefaultObserver.apply(defaultObserver);
+    emitter.registerObserver(observer1);
+    emitter.registerObserver(observer2);
 
     testAllDays(specialDay, event, emitter, defaultObserver, observer1, observer2);
   }

event-aggregator/src/test/java/com/iluwatar/event/aggregator/KingsHandTest.java

@@ -55,11 +55,7 @@ class KingsHandTest extends EventEmitterTest<KingsHand> {
   @Test
   void testPassThrough() throws Exception {
     final var observer = mock(EventObserver.class);
-    final var kingsHand = new KingsHand();
-    kingsHand.registerObserver(observer, Event.STARK_SIGHTED);
-    kingsHand.registerObserver(observer, Event.WARSHIPS_APPROACHING);
-    kingsHand.registerObserver(observer, Event.TRAITOR_DETECTED);
-    kingsHand.registerObserver(observer, Event.WHITE_WALKERS_SIGHTED);
+    final var kingsHand = new KingsHand(observer);
 
     // The kings hand should not pass any events before he received one
     verifyZeroInteractions(observer);

event-aggregator/src/test/java/com/iluwatar/event/aggregator/ScoutTest.java

@@ -34,9 +34,7 @@ class ScoutTest extends EventEmitterTest<Scout> {
    * Create a new test instance, using the correct object factory
    */
   public ScoutTest() {
-
-      super(Weekday.TUESDAY, Event.WARSHIPS_APPROACHING, Scout::new, Scout::new);
-
+    super(Weekday.TUESDAY, Event.WARSHIPS_APPROACHING, Scout::new, Scout::new);
   }
 
 }

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>

unit-of-work/README.md

@@ -12,20 +12,20 @@ tags:
 
 ## Intent
 
-When a business transaction is completed, all the updates are sent as one big unit of work to be 
+When a business transaction is completed, all the the updates are sent as one big unit of work to be 
 persisted in one go to minimize database round-trips. 
 
 ## Explanation
 
-Real-world example
+Real world example
 
-> Arms dealer has a database containing weapon information. Merchants all over the town are 
-> constantly updating this information and it causes a high load on the database server. To make the 
+> We have a database containing student information. Administrators all over the country are 
+> constantly updating this information and it causes high load on the database server. To make the 
 > load more manageable we apply to Unit of Work pattern to send many small updates in batches.       
 
 In plain words
 
-> Unit of Work merges many small database updates in a single batch to optimize the number of 
+> Unit of Work merges many small database updates in single batch to optimize the number of 
 > round-trips. 
 
 [MartinFowler.com](https://martinfowler.com/eaaCatalog/unitOfWork.html) says
@@ -35,20 +35,37 @@ In plain words
 
 **Programmatic Example**
 
-Here's the `Weapon` entity that is being persisted in the database.
+Here's the `Student` entity that is being persisted to the database.
 
 ```java
-@Getter
-@RequiredArgsConstructor
-public class Weapon {
-    private final Integer id;
-    private final String name;
+public class Student {
+  private final Integer id;
+  private final String name;
+  private final String address;
+
+  public Student(Integer id, String name, String address) {
+    this.id = id;
+    this.name = name;
+    this.address = address;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public Integer getId() {
+    return id;
+  }
+
+  public String getAddress() {
+    return address;
+  }
 }
 ```
 
-The essence of the implementation is the `ArmsDealer` implementing the Unit of Work pattern. 
+The essence of the implementation is the `StudentRepository` implementing the Unit of Work pattern. 
 It maintains a map of database operations (`context`) that need to be done and when `commit` is 
-called it applies them in a single batch.
+called it applies them in single batch.
 
 ```java
 public interface IUnitOfWork<T> {
@@ -67,117 +84,96 @@ public interface IUnitOfWork<T> {
 }
 
 @Slf4j
-@RequiredArgsConstructor
-public class ArmsDealer implements IUnitOfWork<Weapon> {
+public class StudentRepository implements IUnitOfWork<Student> {
 
-    private final Map<String, List<Weapon>> context;
-    private final WeaponDatabase weaponDatabase;
+  private final Map<String, List<Student>> context;
+  private final StudentDatabase studentDatabase;
 
-    @Override
-    public void registerNew(Weapon weapon) {
-        LOGGER.info("Registering {} for insert in context.", weapon.getName());
-        register(weapon, UnitActions.INSERT.getActionValue());
+  public StudentRepository(Map<String, List<Student>> context, StudentDatabase studentDatabase) {
+    this.context = context;
+    this.studentDatabase = studentDatabase;
+  }
+
+  @Override
+  public void registerNew(Student student) {
+    LOGGER.info("Registering {} for insert in context.", student.getName());
+    register(student, IUnitOfWork.INSERT);
+  }
+
+  @Override
+  public void registerModified(Student student) {
+    LOGGER.info("Registering {} for modify in context.", student.getName());
+    register(student, IUnitOfWork.MODIFY);
+
+  }
+
+  @Override
+  public void registerDeleted(Student student) {
+    LOGGER.info("Registering {} for delete in context.", student.getName());
+    register(student, IUnitOfWork.DELETE);
+  }
+
+  private void register(Student student, String operation) {
+    var studentsToOperate = context.get(operation);
+    if (studentsToOperate == null) {
+      studentsToOperate = new ArrayList<>();
+    }
+    studentsToOperate.add(student);
+    context.put(operation, studentsToOperate);
+  }
+
+  @Override
+  public void commit() {
+    if (context == null || context.size() == 0) {
+      return;
+    }
+    LOGGER.info("Commit started");
+    if (context.containsKey(IUnitOfWork.INSERT)) {
+      commitInsert();
     }
 
-    @Override
-    public void registerModified(Weapon weapon) {
-        LOGGER.info("Registering {} for modify in context.", weapon.getName());
-        register(weapon, UnitActions.MODIFY.getActionValue());
-
+    if (context.containsKey(IUnitOfWork.MODIFY)) {
+      commitModify();
     }
-
-    @Override
-    public void registerDeleted(Weapon weapon) {
-        LOGGER.info("Registering {} for delete in context.", weapon.getName());
-        register(weapon, UnitActions.DELETE.getActionValue());
+    if (context.containsKey(IUnitOfWork.DELETE)) {
+      commitDelete();
     }
+    LOGGER.info("Commit finished.");
+  }
 
-    private void register(Weapon weapon, String operation) {
-        var weaponsToOperate = context.get(operation);
-        if (weaponsToOperate == null) {
-            weaponsToOperate = new ArrayList<>();
-        }
-        weaponsToOperate.add(weapon);
-        context.put(operation, weaponsToOperate);
+  private void commitInsert() {
+    var studentsToBeInserted = context.get(IUnitOfWork.INSERT);
+    for (var student : studentsToBeInserted) {
+      LOGGER.info("Saving {} to database.", student.getName());
+      studentDatabase.insert(student);
     }
+  }
 
-    /**
-     * All UnitOfWork operations are batched and executed together on commit only.
-     */
-    @Override
-    public void commit() {
-        if (context == null || context.size() == 0) {
-            return;
-        }
-        LOGGER.info("Commit started");
-        if (context.containsKey(UnitActions.INSERT.getActionValue())) {
-            commitInsert();
-        }
-
-        if (context.containsKey(UnitActions.MODIFY.getActionValue())) {
-            commitModify();
-        }
-        if (context.containsKey(UnitActions.DELETE.getActionValue())) {
-            commitDelete();
-        }
-        LOGGER.info("Commit finished.");
+  private void commitModify() {
+    var modifiedStudents = context.get(IUnitOfWork.MODIFY);
+    for (var student : modifiedStudents) {
+      LOGGER.info("Modifying {} to database.", student.getName());
+      studentDatabase.modify(student);
     }
+  }
 
-    private void commitInsert() {
-        var weaponsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
-        for (var weapon : weaponsToBeInserted) {
-            LOGGER.info("Inserting a new weapon {} to sales rack.", weapon.getName());
-            weaponDatabase.insert(weapon);
-        }
-    }
-
-    private void commitModify() {
-        var modifiedWeapons = context.get(UnitActions.MODIFY.getActionValue());
-        for (var weapon : modifiedWeapons) {
-            LOGGER.info("Scheduling {} for modification work.", weapon.getName());
-            weaponDatabase.modify(weapon);
-        }
-    }
-
-    private void commitDelete() {
-        var deletedWeapons = context.get(UnitActions.DELETE.getActionValue());
-        for (var weapon : deletedWeapons) {
-            LOGGER.info("Scrapping {}.", weapon.getName());
-            weaponDatabase.delete(weapon);
-        }
+  private void commitDelete() {
+    var deletedStudents = context.get(IUnitOfWork.DELETE);
+    for (var student : deletedStudents) {
+      LOGGER.info("Deleting {} to database.", student.getName());
+      studentDatabase.delete(student);
     }
+  }
 }
 ```
 
-Here is how the whole app is put together.
+Finally, here's how we use the `StudentRepository` and `commit` the transaction.
 
 ```java
-// create some weapons
-var enchantedHammer = new Weapon(1, "enchanted hammer");
-var brokenGreatSword = new Weapon(2, "broken great sword");
-var silverTrident = new Weapon(3, "silver trident");
-
-// create repository
-var weaponRepository = new ArmsDealer(new HashMap<String, List<Weapon>>(), new WeaponDatabase());
-
-// perform operations on the weapons
-weaponRepository.registerNew(enchantedHammer);
-weaponRepository.registerModified(silverTrident);
-weaponRepository.registerDeleted(brokenGreatSword);
-weaponRepository.commit();
-```
-
-Here is the console output.
-
-```
-21:39:21.984 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering enchanted hammer for insert in context.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering silver trident for modify in context.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Registering broken great sword for delete in context.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Commit started
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Inserting a new weapon enchanted hammer to sales rack.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Scheduling silver trident for modification work.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Scrapping broken great sword.
-21:39:21.989 [main] INFO com.iluwatar.unitofwork.ArmsDealer - Commit finished.
+    studentRepository.registerNew(ram);
+    studentRepository.registerModified(shyam);
+    studentRepository.registerDeleted(gopi);
+    studentRepository.commit();
 ```
 
 ## Class diagram
@@ -190,7 +186,7 @@ Use the Unit Of Work pattern when
 
 * To optimize the time taken for database transactions.
 * To send changes to database as a unit of work which ensures atomicity of the transaction.
-* To reduce the number of database calls.
+* To reduce number of database calls.
 
 ## Tutorials
 

unit-of-work/etc/unit-of-work.ucls

@@ -1,7 +1,7 @@
 <?xml version="1.0" encoding="UTF-8"?>
 <class-diagram version="1.2.1" icons="true" always-add-relationships="false" generalizations="true" realizations="true" 
   associations="true" dependencies="false" nesting-relationships="true" router="FAN">  
-  <class id="1" language="java" name="com.iluwatar.unitofwork.WeaponDatabase" project="unit-of-work"
+  <class id="1" language="java" name="com.iluwatar.unitofwork.StudentDatabase" project="unit-of-work" 
     file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentDatabase.java" binary="false" corner="BOTTOM_RIGHT">    
     <position height="-1" width="-1" x="170" y="406"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 
@@ -28,7 +28,7 @@
       <operations public="true" package="true" protected="true" private="true" static="true"/>    
     </display>  
   </class>  
-  <class id="4" language="java" name="com.iluwatar.unitofwork.ArmsDealer" project="unit-of-work"
+  <class id="4" language="java" name="com.iluwatar.unitofwork.StudentRepository" project="unit-of-work" 
     file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentRepository.java" binary="false" 
     corner="BOTTOM_RIGHT">    
     <position height="-1" width="-1" x="377" y="166"/>    
@@ -38,7 +38,7 @@
       <operations public="true" package="true" protected="true" private="true" static="true"/>    
     </display>  
   </class>  
-  <class id="5" language="java" name="com.iluwatar.unitofwork.Weapon" project="unit-of-work"
+  <class id="5" language="java" name="com.iluwatar.unitofwork.Student" project="unit-of-work" 
     file="/unit-of-work/src/main/java/com/iluwatar/unitofwork/Student.java" binary="false" corner="BOTTOM_RIGHT">    
     <position height="-1" width="-1" x="696" y="130"/>    
     <display autosize="true" stereotype="true" package="true" initial-value="false" signature="true" 

unit-of-work/src/main/java/com/iluwatar/unitofwork/App.java

@@ -27,7 +27,7 @@ import java.util.HashMap;
 import java.util.List;
 
 /**
- * {@link App} Application demonstrating unit of work pattern.
+ * {@link App} Application for managing student data.
  */
 public class App {
   /**
@@ -37,19 +37,17 @@ public class App {
    */
 
   public static void main(String[] args) {
-    // create some weapons
-    var enchantedHammer = new Weapon(1, "enchanted hammer");
-    var brokenGreatSword = new Weapon(2, "broken great sword");
-    var silverTrident = new Weapon(3, "silver trident");
+    var ram = new Student(1, "Ram", "Street 9, Cupertino");
+    var shyam = new Student(2, "Shyam", "Z bridge, Pune");
+    var gopi = new Student(3, "Gopi", "Street 10, Mumbai");
 
-    // create repository
-    var weaponRepository = new ArmsDealer(new HashMap<String, List<Weapon>>(),
-            new WeaponDatabase());
+    var context = new HashMap<String, List<Student>>();
+    var studentDatabase = new StudentDatabase();
+    var studentRepository = new StudentRepository(context, studentDatabase);
 
-    // perform operations on the weapons
-    weaponRepository.registerNew(enchantedHammer);
-    weaponRepository.registerModified(silverTrident);
-    weaponRepository.registerDeleted(brokenGreatSword);
-    weaponRepository.commit();
+    studentRepository.registerNew(ram);
+    studentRepository.registerModified(shyam);
+    studentRepository.registerDeleted(gopi);
+    studentRepository.commit();
   }
 }

unit-of-work/src/main/java/com/iluwatar/unitofwork/Student.java

@@ -27,12 +27,14 @@ import lombok.Getter;
 import lombok.RequiredArgsConstructor;
 
 /**
- * {@link Weapon} is an entity.
+ * {@link Student} is an entity.
  */
 @Getter
 @RequiredArgsConstructor
-public class Weapon {
+public class Student {
 
   private final Integer id;
   private final String name;
+  private final String address;
+
 }

unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentDatabase.java

@@ -24,19 +24,19 @@
 package com.iluwatar.unitofwork;
 
 /**
- * Act as database for weapon records.
+ * Act as Database for student records.
  */
-public class WeaponDatabase {
+public class StudentDatabase {
 
-  public void insert(Weapon weapon) {
+  public void insert(Student student) {
     //Some insert logic to DB
   }
 
-  public void modify(Weapon weapon) {
+  public void modify(Student student) {
     //Some modify logic to DB
   }
 
-  public void delete(Weapon weapon) {
+  public void delete(Student student) {
     //Some delete logic to DB
   }
 }

unit-of-work/src/main/java/com/iluwatar/unitofwork/StudentRepository.java

@@ -30,41 +30,41 @@ import lombok.RequiredArgsConstructor;
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * {@link ArmsDealer} Weapon repository that supports unit of work for weapons.
+ * {@link StudentRepository} Student database repository. supports unit of work for student data.
  */
 @Slf4j
 @RequiredArgsConstructor
-public class ArmsDealer implements IUnitOfWork<Weapon> {
+public class StudentRepository implements IUnitOfWork<Student> {
 
-  private final Map<String, List<Weapon>> context;
-  private final WeaponDatabase weaponDatabase;
+  private final Map<String, List<Student>> context;
+  private final StudentDatabase studentDatabase;
 
   @Override
-  public void registerNew(Weapon weapon) {
-    LOGGER.info("Registering {} for insert in context.", weapon.getName());
-    register(weapon, UnitActions.INSERT.getActionValue());
+  public void registerNew(Student student) {
+    LOGGER.info("Registering {} for insert in context.", student.getName());
+    register(student, UnitActions.INSERT.getActionValue());
   }
 
   @Override
-  public void registerModified(Weapon weapon) {
-    LOGGER.info("Registering {} for modify in context.", weapon.getName());
-    register(weapon, UnitActions.MODIFY.getActionValue());
+  public void registerModified(Student student) {
+    LOGGER.info("Registering {} for modify in context.", student.getName());
+    register(student, UnitActions.MODIFY.getActionValue());
 
   }
 
   @Override
-  public void registerDeleted(Weapon weapon) {
-    LOGGER.info("Registering {} for delete in context.", weapon.getName());
-    register(weapon, UnitActions.DELETE.getActionValue());
+  public void registerDeleted(Student student) {
+    LOGGER.info("Registering {} for delete in context.", student.getName());
+    register(student, UnitActions.DELETE.getActionValue());
   }
 
-  private void register(Weapon weapon, String operation) {
-    var weaponsToOperate = context.get(operation);
-    if (weaponsToOperate == null) {
-      weaponsToOperate = new ArrayList<>();
+  private void register(Student student, String operation) {
+    var studentsToOperate = context.get(operation);
+    if (studentsToOperate == null) {
+      studentsToOperate = new ArrayList<>();
     }
-    weaponsToOperate.add(weapon);
-    context.put(operation, weaponsToOperate);
+    studentsToOperate.add(student);
+    context.put(operation, studentsToOperate);
   }
 
   /**
@@ -90,26 +90,26 @@ public class ArmsDealer implements IUnitOfWork<Weapon> {
   }
 
   private void commitInsert() {
-    var weaponsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
-    for (var weapon : weaponsToBeInserted) {
-      LOGGER.info("Inserting a new weapon {} to sales rack.", weapon.getName());
-      weaponDatabase.insert(weapon);
+    var studentsToBeInserted = context.get(UnitActions.INSERT.getActionValue());
+    for (var student : studentsToBeInserted) {
+      LOGGER.info("Saving {} to database.", student.getName());
+      studentDatabase.insert(student);
     }
   }
 
   private void commitModify() {
-    var modifiedWeapons = context.get(UnitActions.MODIFY.getActionValue());
-    for (var weapon : modifiedWeapons) {
-      LOGGER.info("Scheduling {} for modification work.", weapon.getName());
-      weaponDatabase.modify(weapon);
+    var modifiedStudents = context.get(UnitActions.MODIFY.getActionValue());
+    for (var student : modifiedStudents) {
+      LOGGER.info("Modifying {} to database.", student.getName());
+      studentDatabase.modify(student);
     }
   }
 
   private void commitDelete() {
-    var deletedWeapons = context.get(UnitActions.DELETE.getActionValue());
-    for (var weapon : deletedWeapons) {
-      LOGGER.info("Scrapping {}.", weapon.getName());
-      weaponDatabase.delete(weapon);
+    var deletedStudents = context.get(UnitActions.DELETE.getActionValue());
+    for (var student : deletedStudents) {
+      LOGGER.info("Deleting {} to database.", student.getName());
+      studentDatabase.delete(student);
     }
   }
 }

unit-of-work/src/test/java/com/iluwatar/unitofwork/StudentRepositoryTest.java

@@ -36,102 +36,102 @@ import java.util.Map;
 import org.junit.jupiter.api.Test;
 
 /**
- * tests {@link ArmsDealer}
+ * tests {@link StudentRepository}
  */
 
-class ArmsDealerTest {
-  private final Weapon weapon1 = new Weapon(1, "battle ram");
-  private final Weapon weapon2 = new Weapon(1, "wooden lance");
+class StudentRepositoryTest {
+  private final Student student1 = new Student(1, "Ram", "street 9, cupertino");
+  private final Student student2 = new Student(1, "Sham", "Z bridge, pune");
 
-  private final Map<String, List<Weapon>> context = new HashMap<>();
-  private final WeaponDatabase weaponDatabase = mock(WeaponDatabase.class);
-  private final ArmsDealer armsDealer = new ArmsDealer(context, weaponDatabase);;
+  private final Map<String, List<Student>> context = new HashMap<>();
+  private final StudentDatabase studentDatabase = mock(StudentDatabase.class);
+  private final StudentRepository studentRepository = new StudentRepository(context, studentDatabase);;
 
   @Test
   void shouldSaveNewStudentWithoutWritingToDb() {
-    armsDealer.registerNew(weapon1);
-    armsDealer.registerNew(weapon2);
+    studentRepository.registerNew(student1);
+    studentRepository.registerNew(student2);
 
     assertEquals(2, context.get(UnitActions.INSERT.getActionValue()).size());
-    verifyNoMoreInteractions(weaponDatabase);
+    verifyNoMoreInteractions(studentDatabase);
   }
 
   @Test
   void shouldSaveDeletedStudentWithoutWritingToDb() {
-    armsDealer.registerDeleted(weapon1);
-    armsDealer.registerDeleted(weapon2);
+    studentRepository.registerDeleted(student1);
+    studentRepository.registerDeleted(student2);
 
     assertEquals(2, context.get(UnitActions.DELETE.getActionValue()).size());
-    verifyNoMoreInteractions(weaponDatabase);
+    verifyNoMoreInteractions(studentDatabase);
   }
 
   @Test
   void shouldSaveModifiedStudentWithoutWritingToDb() {
-    armsDealer.registerModified(weapon1);
-    armsDealer.registerModified(weapon2);
+    studentRepository.registerModified(student1);
+    studentRepository.registerModified(student2);
 
     assertEquals(2, context.get(UnitActions.MODIFY.getActionValue()).size());
-    verifyNoMoreInteractions(weaponDatabase);
+    verifyNoMoreInteractions(studentDatabase);
   }
 
   @Test
   void shouldSaveAllLocalChangesToDb() {
-    context.put(UnitActions.INSERT.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.MODIFY.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.DELETE.getActionValue(), List.of(weapon1));
+    context.put(UnitActions.INSERT.getActionValue(), List.of(student1));
+    context.put(UnitActions.MODIFY.getActionValue(), List.of(student1));
+    context.put(UnitActions.DELETE.getActionValue(), List.of(student1));
 
-    armsDealer.commit();
+    studentRepository.commit();
 
-    verify(weaponDatabase, times(1)).insert(weapon1);
-    verify(weaponDatabase, times(1)).modify(weapon1);
-    verify(weaponDatabase, times(1)).delete(weapon1);
+    verify(studentDatabase, times(1)).insert(student1);
+    verify(studentDatabase, times(1)).modify(student1);
+    verify(studentDatabase, times(1)).delete(student1);
   }
 
   @Test
   void shouldNotWriteToDbIfContextIsNull() {
-    var weaponRepository = new ArmsDealer(null, weaponDatabase);
+    var studentRepository = new StudentRepository(null, studentDatabase);
 
-    weaponRepository.commit();
+    studentRepository.commit();
 
-    verifyNoMoreInteractions(weaponDatabase);
+    verifyNoMoreInteractions(studentDatabase);
   }
 
   @Test
   void shouldNotWriteToDbIfNothingToCommit() {
-    var weaponRepository = new ArmsDealer(new HashMap<>(), weaponDatabase);
+    var studentRepository = new StudentRepository(new HashMap<>(), studentDatabase);
 
-    weaponRepository.commit();
+    studentRepository.commit();
 
-    verifyNoMoreInteractions(weaponDatabase);
+    verifyNoMoreInteractions(studentDatabase);
   }
 
   @Test
   void shouldNotInsertToDbIfNoRegisteredStudentsToBeCommitted() {
-    context.put(UnitActions.MODIFY.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.DELETE.getActionValue(), List.of(weapon1));
+    context.put(UnitActions.MODIFY.getActionValue(), List.of(student1));
+    context.put(UnitActions.DELETE.getActionValue(), List.of(student1));
 
-    armsDealer.commit();
+    studentRepository.commit();
 
-    verify(weaponDatabase, never()).insert(weapon1);
+    verify(studentDatabase, never()).insert(student1);
   }
 
   @Test
   void shouldNotModifyToDbIfNotRegisteredStudentsToBeCommitted() {
-    context.put(UnitActions.INSERT.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.DELETE.getActionValue(), List.of(weapon1));
+    context.put(UnitActions.INSERT.getActionValue(), List.of(student1));
+    context.put(UnitActions.DELETE.getActionValue(), List.of(student1));
 
-    armsDealer.commit();
+    studentRepository.commit();
 
-    verify(weaponDatabase, never()).modify(weapon1);
+    verify(studentDatabase, never()).modify(student1);
   }
 
   @Test
   void shouldNotDeleteFromDbIfNotRegisteredStudentsToBeCommitted() {
-    context.put(UnitActions.INSERT.getActionValue(), List.of(weapon1));
-    context.put(UnitActions.MODIFY.getActionValue(), List.of(weapon1));
+    context.put(UnitActions.INSERT.getActionValue(), List.of(student1));
+    context.put(UnitActions.MODIFY.getActionValue(), List.of(student1));
 
-    armsDealer.commit();
+    studentRepository.commit();
 
-    verify(weaponDatabase, never()).delete(weapon1);
+    verify(studentDatabase, never()).delete(student1);
   }
 }