check spelling and update topic

* docs: update README.md [skip ci]

* docs: update .all-contributorsrc [skip ci]

Co-authored-by: allcontributors[bot] <46447321+allcontributors[bot]@users.noreply.github.com>

.all-contributorsrc

@@ -1776,6 +1776,15 @@
       "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-195-orange.svg?style=flat-square)](#contributors-)
+[![All Contributors](https://img.shields.io/badge/all_contributors-196-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
 <br/>
@@ -325,6 +325,7 @@ 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

@@ -0,0 +1,182 @@
+---
+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

@@ -0,0 +1,32 @@
+@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

@@ -0,0 +1,87 @@
+<?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

@@ -0,0 +1,72 @@
+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

@@ -0,0 +1,29 @@
+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

@@ -0,0 +1,114 @@
+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

@@ -0,0 +1,39 @@
+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

@@ -0,0 +1,45 @@
+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

@@ -0,0 +1,14 @@
+<?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

@@ -0,0 +1,20 @@
+<?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

@@ -0,0 +1,20 @@
+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

@@ -75,6 +75,7 @@
     <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>
@@ -227,6 +228,7 @@
     <module>lockable-object</module>
     <module>fanout-fanin</module>
     <module>domain-model</module>
+    <module>metadata-mapping</module>
   </modules>
   <repositories>
     <repository>
@@ -377,6 +379,11 @@
         <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>

thread-pool/README.md

@@ -18,11 +18,11 @@ threads and eliminating the latency of creating new threads.
 
 ## Explanation
 
-Real-world example
+Real world example
 
 > We have a large number of relatively short tasks at hand. We need to peel huge amounts of potatoes 
-> and serve a mighty amount of coffee cups. Creating a new thread for each task would be a waste so 
+> and serve mighty amount of coffee cups. Creating a new thread for each task would be a waste so we 
-> we establish a thread pool.       
+> establish a thread pool.       
 
 In plain words
 
@@ -99,7 +99,7 @@ public class PotatoPeelingTask extends Task {
 }
 ```
 
-Next, we present a runnable `Worker` class that the thread pool will utilize to handle all the potato 
+Next we present a runnable `Worker` class that the thread pool will utilize to handle all the potato 
 peeling and coffee making.
 
 ```java

throttling/README.md

@@ -16,12 +16,10 @@ Ensure that a given client is not able to access service resources more than the
 
 ## Explanation
 
-Real-world example
+Real world example
 
-> A young human and an old dwarf walk into a bar. They start ordering beers from the bartender.
+> A large multinational corporation offers API to its customers. The API is rate-limited and each 
-> The bartender immediately sees that the young human shouldn't consume too many drinks too fast
+> customer can only make certain amount of calls per second.      
-> and refuses to serve if enough time has not passed. For the old dwarf, the serving rate can
-> be higher.
 
 In plain words
 
@@ -35,25 +33,30 @@ In plain words
 
 **Programmatic Example**
 
-`BarCustomer` class presents the clients of the `Bartender` API. `CallsCount` tracks the number of 
+Tenant class presents the clients of the API. CallsCount tracks the number of API calls per tenant.
-calls per `BarCustomer`.
 
 ```java
-public class BarCustomer {
+public class Tenant {
 
-    @Getter
+  private final String name;
-    private final String name;
+  private final int allowedCallsPerSecond;
-    @Getter
-    private final int allowedCallsPerSecond;
 
-    public BarCustomer(String name, int allowedCallsPerSecond, CallsCount callsCount) {
+  public Tenant(String name, int allowedCallsPerSecond, CallsCount callsCount) {
-        if (allowedCallsPerSecond < 0) {
+    if (allowedCallsPerSecond < 0) {
-            throw new InvalidParameterException("Number of calls less than 0 not allowed");
+      throw new InvalidParameterException("Number of calls less than 0 not allowed");
-        }
-        this.name = name;
-        this.allowedCallsPerSecond = allowedCallsPerSecond;
-        callsCount.addTenant(name);
     }
+    this.name = name;
+    this.allowedCallsPerSecond = allowedCallsPerSecond;
+    callsCount.addTenant(name);
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public int getAllowedCallsPerSecond() {
+    return allowedCallsPerSecond;
+  }
 }
 
 @Slf4j
@@ -73,14 +76,14 @@ public final class CallsCount {
   }
 
   public void reset() {
+    LOGGER.debug("Resetting the map.");
     tenantCallsCount.replaceAll((k, v) -> new AtomicLong(0));
-    LOGGER.info("reset counters");
   }
 }
 ```
 
-Next, the service that the tenants are calling is introduced. To track the call count, a throttler 
+Next we introduce the service that the tenants are calling. To track the call count we use the 
-timer is used.
+throttler timer.
 
 ```java
 public interface Throttler {
@@ -108,103 +111,71 @@ public class ThrottleTimerImpl implements Throttler {
     }, 0, throttlePeriod);
   }
 }
-```
 
-`Bartender` offers the `orderDrink` service to the `BarCustomer`s. The customers probably don't
+class B2BService {
-know that the beer serving rate is limited by their appearances.
 
-```java
+  private static final Logger LOGGER = LoggerFactory.getLogger(B2BService.class);
-class Bartender {
+  private final CallsCount callsCount;
 
-    private static final Logger LOGGER = LoggerFactory.getLogger(Bartender.class);
+  public B2BService(Throttler timer, CallsCount callsCount) {
-    private final CallsCount callsCount;
+    this.callsCount = callsCount;
+    timer.start();
+  }
 
-    public Bartender(Throttler timer, CallsCount callsCount) {
+  public int dummyCustomerApi(Tenant tenant) {
-        this.callsCount = callsCount;
+    var tenantName = tenant.getName();
-        timer.start();
+    var count = callsCount.getCount(tenantName);
+    LOGGER.debug("Counter for {} : {} ", tenant.getName(), count);
+    if (count >= tenant.getAllowedCallsPerSecond()) {
+      LOGGER.error("API access per second limit reached for: {}", tenantName);
+      return -1;
     }
+    callsCount.incrementCount(tenantName);
+    return getRandomCustomerId();
+  }
 
-    public int orderDrink(BarCustomer barCustomer) {
+  private int getRandomCustomerId() {
-        var tenantName = barCustomer.getName();
+    return ThreadLocalRandom.current().nextInt(1, 10000);
-        var count = callsCount.getCount(tenantName);
+  }
-        if (count >= barCustomer.getAllowedCallsPerSecond()) {
-            LOGGER.error("I'm sorry {}, you've had enough for today!", tenantName);
-            return -1;
-        }
-        callsCount.incrementCount(tenantName);
-        LOGGER.debug("Serving beer to {} : [{} consumed] ", barCustomer.getName(), count+1);
-        return getRandomCustomerId();
-    }
-
-    private int getRandomCustomerId() {
-        return ThreadLocalRandom.current().nextInt(1, 10000);
-    }
 }
 ```
 
-Now it is possible to see the full example in action. `BarCustomer` young human is rate-limited to 2 
+Now we are ready to see the full example in action. Tenant Adidas is rate-limited to 5 calls per 
-calls per second and the old dwarf to 4.
+second and Nike to 6.
 
 ```java
-public static void main(String[] args) {
+  public static void main(String[] args) {
     var callsCount = new CallsCount();
-    var human = new BarCustomer("young human", 2, callsCount);
+    var adidas = new Tenant("Adidas", 5, callsCount);
-    var dwarf = new BarCustomer("dwarf soldier", 4, callsCount);
+    var nike = new Tenant("Nike", 6, callsCount);
 
     var executorService = Executors.newFixedThreadPool(2);
-
+    executorService.execute(() -> makeServiceCalls(adidas, callsCount));
-    executorService.execute(() -> makeServiceCalls(human, callsCount));
+    executorService.execute(() -> makeServiceCalls(nike, callsCount));
-    executorService.execute(() -> makeServiceCalls(dwarf, callsCount));
-
     executorService.shutdown();
+    
     try {
-        executorService.awaitTermination(10, TimeUnit.SECONDS);
+      executorService.awaitTermination(10, TimeUnit.SECONDS);
     } catch (InterruptedException e) {
-        LOGGER.error("Executor service terminated: {}", e.getMessage());
+      LOGGER.error("Executor Service terminated: {}", e.getMessage());
     }
-}
+  }
 
-private static void makeServiceCalls(BarCustomer barCustomer, CallsCount callsCount) {
+  private static void makeServiceCalls(Tenant tenant, CallsCount callsCount) {
-    var timer = new ThrottleTimerImpl(1000, callsCount);
+    var timer = new ThrottleTimerImpl(10, callsCount);
-    var service = new Bartender(timer, callsCount);
+    var service = new B2BService(timer, callsCount);
     // Sleep is introduced to keep the output in check and easy to view and analyze the results.
-    IntStream.range(0, 50).forEach(i -> {
+    IntStream.range(0, 20).forEach(i -> {
-        service.orderDrink(barCustomer);
+      service.dummyCustomerApi(tenant);
-        try {
+      try {
-            Thread.sleep(100);
+        Thread.sleep(1);
-        } catch (InterruptedException e) {
+      } catch (InterruptedException e) {
-            LOGGER.error("Thread interrupted: {}", e.getMessage());
+        LOGGER.error("Thread interrupted: {}", e.getMessage());
-        }
+      }
     });
-}
+  }
 ```
 
-An excerpt from the example's console output:
-
-```
-18:46:36.218 [Timer-0] INFO com.iluwatar.throttling.CallsCount - reset counters
-18:46:36.218 [Timer-1] INFO com.iluwatar.throttling.CallsCount - reset counters
-18:46:36.242 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [1 consumed] 
-18:46:36.242 [pool-1-thread-1] DEBUG com.iluwatar.throttling.Bartender - Serving beer to young human : [1 consumed] 
-18:46:36.342 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [2 consumed] 
-18:46:36.342 [pool-1-thread-1] DEBUG com.iluwatar.throttling.Bartender - Serving beer to young human : [2 consumed] 
-18:46:36.443 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
-18:46:36.443 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [3 consumed] 
-18:46:36.544 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
-18:46:36.544 [pool-1-thread-2] DEBUG com.iluwatar.throttling.Bartender - Serving beer to dwarf soldier : [4 consumed] 
-18:46:36.645 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
-18:46:36.645 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
-18:46:36.745 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
-18:46:36.745 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
-18:46:36.846 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
-18:46:36.846 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
-18:46:36.947 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
-18:46:36.947 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
-18:46:37.048 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
-18:46:37.048 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
-18:46:37.148 [pool-1-thread-1] ERROR com.iluwatar.throttling.Bartender - I'm sorry young human, you've had enough for today!
-18:46:37.148 [pool-1-thread-2] ERROR com.iluwatar.throttling.Bartender - I'm sorry dwarf soldier, you've had enough for today!
-```
 
 ## Class diagram
 
@@ -214,7 +185,7 @@ An excerpt from the example's console output:
 
 The Throttling pattern should be used:
 
-* When service access needs to be restricted not to have high impact on the performance of the service.
+* When a service access needs to be restricted to not have high impacts on the performance of the service.
 * When multiple clients are consuming the same service resources and restriction has to be made according to the usage per client.
 
 ## Credits

throttling/src/main/java/com/iluwatar/throttling/App.java

@@ -34,11 +34,11 @@ import lombok.extern.slf4j.Slf4j;
  * complete service by users or a particular tenant. This can allow systems to continue to function
  * and meet service level agreements, even when an increase in demand places load on resources.
  * <p>
- * In this example there is a {@link Bartender} serving beer to {@link BarCustomer}s. This is a time
+ * In this example we have ({@link App}) as the initiating point of the service. This is a time
  * based throttling, i.e. only a certain number of calls are allowed per second.
  * </p>
- * ({@link BarCustomer}) is the service tenant class having a name and the number of calls allowed.
+ * ({@link Tenant}) is the Tenant POJO class with which many tenants can be created ({@link
- * ({@link Bartender}) is the service which is consumed by the tenants and is throttled.
+ * B2BService}) is the service which is consumed by the tenants and is throttled.
  */
 @Slf4j
 public class App {
@@ -50,35 +50,33 @@ public class App {
    */
   public static void main(String[] args) {
     var callsCount = new CallsCount();
-    var human = new BarCustomer("young human", 2, callsCount);
+    var adidas = new Tenant("Adidas", 5, callsCount);
-    var dwarf = new BarCustomer("dwarf soldier", 4, callsCount);
+    var nike = new Tenant("Nike", 6, callsCount);
 
     var executorService = Executors.newFixedThreadPool(2);
 
-    executorService.execute(() -> makeServiceCalls(human, callsCount));
+    executorService.execute(() -> makeServiceCalls(adidas, callsCount));
-    executorService.execute(() -> makeServiceCalls(dwarf, callsCount));
+    executorService.execute(() -> makeServiceCalls(nike, callsCount));
 
     executorService.shutdown();
     try {
-      if (!executorService.awaitTermination(10, TimeUnit.SECONDS)) {
+      executorService.awaitTermination(10, TimeUnit.SECONDS);
-        executorService.shutdownNow();
-      }
     } catch (InterruptedException e) {
-      executorService.shutdownNow();
+      LOGGER.error("Executor Service terminated: {}", e.getMessage());
     }
   }
 
   /**
-   * Make calls to the bartender.
+   * Make calls to the B2BService dummy API.
    */
-  private static void makeServiceCalls(BarCustomer barCustomer, CallsCount callsCount) {
+  private static void makeServiceCalls(Tenant tenant, CallsCount callsCount) {
-    var timer = new ThrottleTimerImpl(1000, callsCount);
+    var timer = new ThrottleTimerImpl(10, callsCount);
-    var service = new Bartender(timer, callsCount);
+    var service = new B2BService(timer, callsCount);
     // Sleep is introduced to keep the output in check and easy to view and analyze the results.
-    IntStream.range(0, 50).forEach(i -> {
+    IntStream.range(0, 20).forEach(i -> {
-      service.orderDrink(barCustomer);
+      service.dummyCustomerApi(tenant);
       try {
-        Thread.sleep(100);
+        Thread.sleep(1);
       } catch (InterruptedException e) {
         LOGGER.error("Thread interrupted: {}", e.getMessage());
       }

throttling/src/main/java/com/iluwatar/throttling/B2BService.java

@@ -29,32 +29,33 @@ import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 /**
- * Bartender is a service which accepts a BarCustomer (tenant) and throttles
+ * A service which accepts a tenant and throttles the resource based on the time given to the
- * the resource based on the time given to the tenant.
+ * tenant.
  */
-class Bartender {
+class B2BService {
 
-  private static final Logger LOGGER = LoggerFactory.getLogger(Bartender.class);
+  private static final Logger LOGGER = LoggerFactory.getLogger(B2BService.class);
   private final CallsCount callsCount;
 
-  public Bartender(Throttler timer, CallsCount callsCount) {
+  public B2BService(Throttler timer, CallsCount callsCount) {
     this.callsCount = callsCount;
     timer.start();
   }
 
   /**
-   * Orders a drink from the bartender.
+   * Calls dummy customer api.
+   *
    * @return customer id which is randomly generated
    */
-  public int orderDrink(BarCustomer barCustomer) {
+  public int dummyCustomerApi(Tenant tenant) {
-    var tenantName = barCustomer.getName();
+    var tenantName = tenant.getName();
     var count = callsCount.getCount(tenantName);
-    if (count >= barCustomer.getAllowedCallsPerSecond()) {
+    LOGGER.debug("Counter for {} : {} ", tenant.getName(), count);
-      LOGGER.error("I'm sorry {}, you've had enough for today!", tenantName);
+    if (count >= tenant.getAllowedCallsPerSecond()) {
+      LOGGER.error("API access per second limit reached for: {}", tenantName);
       return -1;
     }
     callsCount.incrementCount(tenantName);
-    LOGGER.debug("Serving beer to {} : [{} consumed] ", barCustomer.getName(), count + 1);
     return getRandomCustomerId();
   }
 

throttling/src/main/java/com/iluwatar/throttling/CallsCount.java

@@ -69,7 +69,7 @@ public final class CallsCount {
    * Resets the count of all the tenants in the map.
    */
   public void reset() {
+    LOGGER.debug("Resetting the map.");
     tenantCallsCount.replaceAll((k, v) -> new AtomicLong(0));
-    LOGGER.info("reset counters");
   }
 }

throttling/src/main/java/com/iluwatar/throttling/Tenant.java

@@ -25,26 +25,22 @@ package com.iluwatar.throttling;
 
 import java.security.InvalidParameterException;
 
-import lombok.Getter;
-
 /**
- * BarCustomer is a tenant with a name and a number of allowed calls per second.
+ * A Pojo class to create a basic Tenant with the allowed calls per second.
  */
-public class BarCustomer {
+public class Tenant {
 
-  @Getter
   private final String name;
-  @Getter
   private final int allowedCallsPerSecond;
 
   /**
    * Constructor.
    *
-   * @param name Name of the BarCustomer
+   * @param name                  Name of the tenant
-   * @param allowedCallsPerSecond The number of calls allowed for this particular tenant.
+   * @param allowedCallsPerSecond The number of calls allowed for a particular tenant.
    * @throws InvalidParameterException If number of calls is less than 0, throws exception.
    */
-  public BarCustomer(String name, int allowedCallsPerSecond, CallsCount callsCount) {
+  public Tenant(String name, int allowedCallsPerSecond, CallsCount callsCount) {
     if (allowedCallsPerSecond < 0) {
       throw new InvalidParameterException("Number of calls less than 0 not allowed");
     }
@@ -52,4 +48,12 @@ public class BarCustomer {
     this.allowedCallsPerSecond = allowedCallsPerSecond;
     callsCount.addTenant(name);
   }
+
+  public String getName() {
+    return name;
+  }
+
+  public int getAllowedCallsPerSecond() {
+    return allowedCallsPerSecond;
+  }
 }

throttling/src/test/java/com/iluwatar/throttling/B2BServiceTest.java

@@ -32,18 +32,19 @@ import org.junit.jupiter.api.Test;
 /**
  * B2BServiceTest class to test the B2BService
  */
-public class BartenderTest {
+public class B2BServiceTest {
 
   private final CallsCount callsCount = new CallsCount();
 
   @Test
   void dummyCustomerApiTest() {
-    var tenant = new BarCustomer("pirate", 2, callsCount);
+    var tenant = new Tenant("testTenant", 2, callsCount);
     // In order to assure that throttling limits will not be reset, we use an empty throttling implementation
-    var timer = (Throttler) () -> {};
+    var timer = (Throttler) () -> {
-    var service = new Bartender(timer, callsCount);
+    };
+    var service = new B2BService(timer, callsCount);
 
-    IntStream.range(0, 5).mapToObj(i -> tenant).forEach(service::orderDrink);
+    IntStream.range(0, 5).mapToObj(i -> tenant).forEach(service::dummyCustomerApi);
     var counter = callsCount.getCount(tenant.getName());
     assertEquals(2, counter, "Counter limit must be reached");
   }

throttling/src/test/java/com/iluwatar/throttling/TenantTest.java

@@ -23,21 +23,20 @@
 
 package com.iluwatar.throttling;
 
-import org.junit.jupiter.api.Test;
+import static org.junit.jupiter.api.Assertions.assertThrows;
 
 import java.security.InvalidParameterException;
-
+import org.junit.jupiter.api.Test;
-import static org.junit.jupiter.api.Assertions.assertThrows;
 
 /**
  * TenantTest to test the creation of Tenant with valid parameters.
  */
-public class BarCustomerTest {
+public class TenantTest {
 
   @Test
   void constructorTest() {
     assertThrows(InvalidParameterException.class, () -> {
-      new BarCustomer("sirBrave", -1, new CallsCount());
+      new Tenant("FailTenant", -1, new CallsCount());
     });
   }
 }

trampoline/README.md

@@ -17,19 +17,19 @@ and to interleave the execution of functions without hard coding them together.
 ## Explanation
 
 Recursion is a frequently adopted technique for solving algorithmic problems in a divide and conquer
-style. For example calculating fibonacci accumulating sum and factorials. In these kinds of problems 
+style. For example, calculating Fibonacci accumulating sum and factorials. In these kinds of 
-recursion is more straightforward than their loop counterpart. Furthermore recursion may need less 
+problems, recursion is more straightforward than its loop counterpart. Furthermore, recursion may 
-code and looks more concise. There is a saying that every recursion problem can be solved using 
+need less code and looks more concise. There is a saying that every recursion problem can be solved 
-a loop with the cost of writing code that is more difficult to understand.
+using a loop with the cost of writing code that is more difficult to understand.
 
-However recursion type solutions have one big caveat. For each recursive call it typically needs 
+However, recursion-type solutions have one big caveat. For each recursive call, it typically needs 
 an intermediate value stored and there is a limited amount of stack memory available. Running out of 
 stack memory creates a stack overflow error and halts the program execution.
 
-Trampoline pattern is a trick that allows us define recursive algorithms in Java without blowing the 
+Trampoline pattern is a trick that allows defining recursive algorithms in Java without blowing the 
 stack. 
 
-Real world example
+Real-world example
 
 > A recursive Fibonacci calculation without the stack overflow problem using the Trampoline pattern.       
 
@@ -105,24 +105,26 @@ public interface Trampoline<T> {
 Using the `Trampoline` to get Fibonacci values.
 
 ```java
-  public static Trampoline<Integer> loop(int times, int prod) {
+public static void main(String[] args) {
+    LOGGER.info("Start calculating war casualties");
+    var result = loop(10, 1).result();
+    LOGGER.info("The number of orcs perished in the war: {}", result);
+}
+
+public static Trampoline<Integer> loop(int times, int prod) {
     if (times == 0) {
-      return Trampoline.done(prod);
+        return Trampoline.done(prod);
     } else {
-      return Trampoline.more(() -> loop(times - 1, prod * times));
+        return Trampoline.more(() -> loop(times - 1, prod * times));
     }
-  }
+}
-  
-  log.info("start pattern");
-  var result = loop(10, 1).result();
-  log.info("result {}", result);
 ```
 
 Program output:
 
 ```
-start pattern
+19:22:24.462 [main] INFO com.iluwatar.trampoline.TrampolineApp - Start calculating war casualties
-result 3628800
+19:22:24.472 [main] INFO com.iluwatar.trampoline.TrampolineApp - The number of orcs perished in the war: 3628800
 ```
 
 ## Class diagram
@@ -133,8 +135,8 @@ result 3628800
 
 Use the Trampoline pattern when
 
-* For implementing tail recursive function. This pattern allows to switch on a stackless operation.
+* For implementing tail-recursive functions. This pattern allows to switch on a stackless operation.
-* For interleaving the execution of two or more functions on the same thread.
+* For interleaving execution of two or more functions on the same thread.
 
 ## Known uses
 

trampoline/src/main/java/com/iluwatar/trampoline/Trampoline.java

@@ -107,6 +107,4 @@ public interface Trampoline<T> {
       }
     };
   }
-
-
 }

trampoline/src/main/java/com/iluwatar/trampoline/TrampolineApp.java

@@ -39,9 +39,9 @@ public class TrampolineApp {
    * Main program for showing pattern. It does loop with factorial function.
    */
   public static void main(String[] args) {
-    LOGGER.info("start pattern");
+    LOGGER.info("Start calculating war casualties");
     var result = loop(10, 1).result();
-    LOGGER.info("result {}", result);
+    LOGGER.info("The number of orcs perished in the war: {}", result);
 
   }
 
@@ -55,5 +55,4 @@ public class TrampolineApp {
       return Trampoline.more(() -> loop(times - 1, prod * times));
     }
   }
-
 }