docs: fixes for yaml frontmatter

.all-contributorsrc

@@ -1631,33 +1631,6 @@
       "contributions": [
         "translation"
       ]
-    },
-    {
-      "login": "sims-keshri",
-      "name": "Simran Keshri",
-      "avatar_url": "https://avatars.githubusercontent.com/u/62168475?v=4",
-      "profile": "https://github.com/sims-keshri",
-      "contributions": [
-        "code"
-      ]
-    },
-    {
-      "login": "JCarlosR",
-      "name": "JCarlos",
-      "avatar_url": "https://avatars.githubusercontent.com/u/3101238?v=4",
-      "profile": "https://programacionymas.com",
-      "contributions": [
-        "translation"
-      ]
-    },
-    {
-      "login": "Dev-AliGhasemi",
-      "name": "Ali Ghasemi",
-      "avatar_url": "https://avatars.githubusercontent.com/u/60359433?v=4",
-      "profile": "https://www.mrmoshkel.ir",
-      "contributions": [
-        "code"
-      ]
     }
   ],
   "contributorsPerLine": 4,

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-182-orange.svg?style=flat-square)](#contributors-)
+[![All Contributors](https://img.shields.io/badge/all_contributors-179-orange.svg?style=flat-square)](#contributors-)
 <!-- ALL-CONTRIBUTORS-BADGE:END -->
 
 <br/>
@@ -343,11 +343,6 @@ This project is licensed under the terms of the MIT license.
     <td align="center"><a href="https://github.com/Conhan93"><img src="https://avatars.githubusercontent.com/u/71334757?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Conny Hansson</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Conhan93" title="Documentation">📖</a></td>
     <td align="center"><a href="http://muklasr.medium.com"><img src="https://avatars.githubusercontent.com/u/43443753?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Muklas Rahmanto</b></sub></a><br /><a href="#translation-muklasr" title="Translation">🌍</a></td>
     <td align="center"><a href="https://github.com/VxDxK"><img src="https://avatars.githubusercontent.com/u/38704817?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Vadim</b></sub></a><br /><a href="#translation-VxDxK" title="Translation">🌍</a></td>
-    <td align="center"><a href="https://github.com/sims-keshri"><img src="https://avatars.githubusercontent.com/u/62168475?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Simran Keshri</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=sims-keshri" title="Code">💻</a></td>
-  </tr>
-  <tr>
-    <td align="center"><a href="https://programacionymas.com"><img src="https://avatars.githubusercontent.com/u/3101238?v=4?s=100" width="100px;" alt=""/><br /><sub><b>JCarlos</b></sub></a><br /><a href="#translation-JCarlosR" title="Translation">🌍</a></td>
-    <td align="center"><a href="https://www.mrmoshkel.ir"><img src="https://avatars.githubusercontent.com/u/60359433?v=4?s=100" width="100px;" alt=""/><br /><sub><b>Ali Ghasemi</b></sub></a><br /><a href="https://github.com/iluwatar/java-design-patterns/commits?author=Dev-AliGhasemi" title="Code">💻</a></td>
   </tr>
 </table>
 

async-method-invocation/src/main/java/com/iluwatar/async/method/invocation/App.java

@@ -59,12 +59,9 @@ import lombok.extern.slf4j.Slf4j;
 @Slf4j
 public class App {
 
-  private static final String ROCKET_LAUNCH_LOG_PATTERN = "Space rocket <%s> launched successfully";
-
   /**
    * Program entry point.
    */
-
   public static void main(String[] args) throws Exception {
     // construct a new executor that will run async tasks
     var executor = new ThreadAsyncExecutor();
@@ -90,9 +87,9 @@ public class App {
     asyncResult5.await();
 
     // log the results of the tasks, callbacks log immediately when complete
-    log(String.format(ROCKET_LAUNCH_LOG_PATTERN, result1));
-    log(String.format(ROCKET_LAUNCH_LOG_PATTERN, result2));
-    log(String.format(ROCKET_LAUNCH_LOG_PATTERN, result3));
+    log("Space rocket <" + result1 + "> launch complete");
+    log("Space rocket <" + result2 + "> launch complete");
+    log("Space rocket <" + result3 + "> launch complete");
   }
 
   /**
@@ -105,7 +102,7 @@ public class App {
   private static <T> Callable<T> lazyval(T value, long delayMillis) {
     return () -> {
       Thread.sleep(delayMillis);
-      log(String.format(ROCKET_LAUNCH_LOG_PATTERN, value));
+      log("Space rocket <" + value + "> launched successfully");
       return value;
     };
   }

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

@@ -42,14 +42,6 @@ import lombok.extern.slf4j.Slf4j;
 @Slf4j
 public class App {
 
-  private static final String LITERAL_0 = "LITERAL 0";
-  private static final String HEALTH_PATTERN = "%s_HEALTH";
-  private static final String GET_AGILITY = "GET_AGILITY";
-  private static final String GET_WISDOM = "GET_WISDOM";
-  private static final String ADD = "ADD";
-  private static final String LITERAL_2 = "LITERAL 2";
-  private static final String DIVIDE = "DIVIDE";
-
   /**
    * Main app method.
    *
@@ -61,17 +53,17 @@ public class App {
         new Wizard(45, 7, 11, 0, 0),
         new Wizard(36, 18, 8, 0, 0));
 
-    vm.execute(InstructionConverterUtil.convertToByteCode(LITERAL_0));
-    vm.execute(InstructionConverterUtil.convertToByteCode(LITERAL_0));
-    vm.execute(InstructionConverterUtil.convertToByteCode(String.format(HEALTH_PATTERN, "GET")));
-    vm.execute(InstructionConverterUtil.convertToByteCode(LITERAL_0));
-    vm.execute(InstructionConverterUtil.convertToByteCode(GET_AGILITY));
-    vm.execute(InstructionConverterUtil.convertToByteCode(LITERAL_0));
-    vm.execute(InstructionConverterUtil.convertToByteCode(GET_WISDOM));
-    vm.execute(InstructionConverterUtil.convertToByteCode(ADD));
-    vm.execute(InstructionConverterUtil.convertToByteCode(LITERAL_2));
-    vm.execute(InstructionConverterUtil.convertToByteCode(DIVIDE));
-    vm.execute(InstructionConverterUtil.convertToByteCode(ADD));
-    vm.execute(InstructionConverterUtil.convertToByteCode(String.format(HEALTH_PATTERN, "SET")));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("GET_HEALTH"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("GET_AGILITY"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 0"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("GET_WISDOM"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("ADD"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("LITERAL 2"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("DIVIDE"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("ADD"));
+    vm.execute(InstructionConverterUtil.convertToByteCode("SET_HEALTH"));
   }
 }

caching/README.md

@@ -43,39 +43,29 @@ Wikipedia says:
 **Programmatic Example**
 
 Let's first look at the data layer of our application. The interesting classes are `UserAccount`
-which is a simple Java object containing the user account details, and `DbManager` which handles
-reading and writing of these objects to/from MongoDB database.
+which is a simple Java object containing the user account details, and `DbManager` interface which handles
+reading and writing of these objects to/from database.
 
 ```java
-@Setter
-@Getter
+@Data
 @AllArgsConstructor
 @ToString
+@EqualsAndHashCode
 public class UserAccount {
   private String userId;
   private String userName;
   private String additionalInfo;
 }
 
-@Slf4j
-public final class DbManager {
+public interface DbManager {
 
-  private static MongoClient mongoClient;
-  private static MongoDatabase db;
-
-  private DbManager() { /*...*/ }
-
-  public static void createVirtualDb() { /*...*/ }
-
-  public static void connect() throws ParseException { /*...*/ }
-
-  public static UserAccount readFromDb(String userId) { /*...*/ }
-
-  public static void writeToDb(UserAccount userAccount) { /*...*/ }
-
-  public static void updateDb(UserAccount userAccount) { /*...*/ }
-
-  public static void upsertDb(UserAccount userAccount) { /*...*/ }
+  void connect();
+  void disconnect();
+  
+  UserAccount readFromDb(String userId);
+  UserAccount writeToDb(UserAccount userAccount);
+  UserAccount updateDb(UserAccount userAccount);
+  UserAccount upsertDb(UserAccount userAccount);
 }
 ```
 
@@ -171,30 +161,43 @@ strategies.
 @Slf4j
 public class CacheStore {
 
+  private static final int CAPACITY = 3;
   private static LruCache cache;
+  private final DbManager dbManager;
 
   /* ... details omitted ... */
 
-  public static UserAccount readThrough(String userId) {
+  public UserAccount readThrough(final String userId) {
     if (cache.contains(userId)) {
-      LOGGER.info("# Cache Hit!");
+      LOGGER.info("# Found in Cache!");
       return cache.get(userId);
     }
-    LOGGER.info("# Cache Miss!");
-    UserAccount userAccount = DbManager.readFromDb(userId);
+    LOGGER.info("# Not found in cache! Go to DB!!");
+    UserAccount userAccount = dbManager.readFromDb(userId);
     cache.set(userId, userAccount);
     return userAccount;
   }
 
-  public static void writeThrough(UserAccount userAccount) {
+  public void writeThrough(final UserAccount userAccount) {
     if (cache.contains(userAccount.getUserId())) {
-      DbManager.updateDb(userAccount);
+      dbManager.updateDb(userAccount);
     } else {
-      DbManager.writeToDb(userAccount);
+      dbManager.writeToDb(userAccount);
     }
     cache.set(userAccount.getUserId(), userAccount);
   }
 
+  public void writeAround(final UserAccount userAccount) {
+    if (cache.contains(userAccount.getUserId())) {
+      dbManager.updateDb(userAccount);
+      // Cache data has been updated -- remove older
+      cache.invalidate(userAccount.getUserId());
+      // version from cache.
+    } else {
+      dbManager.writeToDb(userAccount);
+    }
+  }
+
   public static void clearCache() {
     if (cache != null) {
       cache.clear();
@@ -225,34 +228,39 @@ class.
 public final class AppManager {
 
   private static CachingPolicy cachingPolicy;
+  private final DbManager dbManager;
+  private final CacheStore cacheStore;
 
   private AppManager() {
   }
 
-  public static void initDb(boolean useMongoDb) { /* ... */ }
+  public void initDb() { /* ... */ }
 
   public static void initCachingPolicy(CachingPolicy policy) { /* ... */ }
 
   public static void initCacheCapacity(int capacity) { /* ... */ }
 
-  public static UserAccount find(String userId) {
-    if (cachingPolicy == CachingPolicy.THROUGH || cachingPolicy == CachingPolicy.AROUND) {
-      return CacheStore.readThrough(userId);
+  public UserAccount find(final String userId) {
+    LOGGER.info("Trying to find {} in cache", userId);
+    if (cachingPolicy == CachingPolicy.THROUGH
+            || cachingPolicy == CachingPolicy.AROUND) {
+      return cacheStore.readThrough(userId);
     } else if (cachingPolicy == CachingPolicy.BEHIND) {
-      return CacheStore.readThroughWithWriteBackPolicy(userId);
+      return cacheStore.readThroughWithWriteBackPolicy(userId);
     } else if (cachingPolicy == CachingPolicy.ASIDE) {
       return findAside(userId);
     }
     return null;
   }
 
-  public static void save(UserAccount userAccount) {
+  public void save(final UserAccount userAccount) {
+    LOGGER.info("Save record!");
     if (cachingPolicy == CachingPolicy.THROUGH) {
-      CacheStore.writeThrough(userAccount);
+      cacheStore.writeThrough(userAccount);
     } else if (cachingPolicy == CachingPolicy.AROUND) {
-      CacheStore.writeAround(userAccount);
+      cacheStore.writeAround(userAccount);
     } else if (cachingPolicy == CachingPolicy.BEHIND) {
-      CacheStore.writeBehind(userAccount);
+      cacheStore.writeBehind(userAccount);
     } else if (cachingPolicy == CachingPolicy.ASIDE) {
       saveAside(userAccount);
     }
@@ -272,24 +280,35 @@ Here is what we do in the main class of the application.
 @Slf4j
 public class App {
 
-  public static void main(String[] args) {
-    AppManager.initDb(false);
-    AppManager.initCacheCapacity(3);
-    var app = new App();
+  public static void main(final String[] args) {
+    boolean isDbMongo = isDbMongo(args);
+    if(isDbMongo){
+      LOGGER.info("Using the Mongo database engine to run the application.");
+    } else {
+      LOGGER.info("Using the 'in Memory' database to run the application.");
+    }
+    App app = new App(isDbMongo);
     app.useReadAndWriteThroughStrategy();
+    String splitLine = "==============================================";
+    LOGGER.info(splitLine);
     app.useReadThroughAndWriteAroundStrategy();
+    LOGGER.info(splitLine);
     app.useReadThroughAndWriteBehindStrategy();
+    LOGGER.info(splitLine);
     app.useCacheAsideStategy();
+    LOGGER.info(splitLine);
   }
 
   public void useReadAndWriteThroughStrategy() {
     LOGGER.info("# CachingPolicy.THROUGH");
-    AppManager.initCachingPolicy(CachingPolicy.THROUGH);
+    appManager.initCachingPolicy(CachingPolicy.THROUGH);
+
     var userAccount1 = new UserAccount("001", "John", "He is a boy.");
-    AppManager.save(userAccount1);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("001");
-    AppManager.find("001");
+
+    appManager.save(userAccount1);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("001");
+    appManager.find("001");
   }
 
   public void useReadThroughAndWriteAroundStrategy() { /* ... */ }
@@ -300,16 +319,6 @@ public class App {
 }
 ```
 
-Finally, here is some of the console output from the program.
-
-```
-12:32:53.845 [main] INFO com.iluwatar.caching.App - # CachingPolicy.THROUGH
-12:32:53.900 [main] INFO com.iluwatar.caching.App - 
---CACHE CONTENT--
-UserAccount(userId=001, userName=John, additionalInfo=He is a boy.)
-----
-```
-
 ## Class diagram
 
 ![alt text](./etc/caching.png "Caching")

caching/docker-compose.yml

@@ -0,0 +1,11 @@
+version: '3.7'
+services:
+  mongodb_container:
+    image: mongo:latest
+    environment:
+      MONGO_INITDB_ROOT_USERNAME: root
+      MONGO_INITDB_ROOT_PASSWORD: rootpassword
+    ports:
+      - 27017:27017
+    volumes:
+      - ./mongo-data/:/data/db

caching/pom.xml

@@ -39,19 +39,21 @@
       <scope>test</scope>
     </dependency>
     <dependency>
-      <groupId>org.mongodb</groupId>
-      <artifactId>mongodb-driver</artifactId>
-      <version>3.12.1</version>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-junit-jupiter</artifactId>
+      <version>3.12.4</version>
+      <scope>test</scope>
+    </dependency>
+    <dependency>
+      <groupId>org.mockito</groupId>
+      <artifactId>mockito-all</artifactId>
+      <version>1.10.19</version>
+      <scope>test</scope>
     </dependency>
     <dependency>
       <groupId>org.mongodb</groupId>
-      <artifactId>mongodb-driver-core</artifactId>
-      <version>3.0.4</version>
-    </dependency>
-    <dependency>
-      <groupId>org.mongodb</groupId>
-      <artifactId>bson</artifactId>
-      <version>3.0.4</version>
+      <artifactId>mongo-java-driver</artifactId>
+      <version>3.4.1</version>
     </dependency>
   </dependencies>
   <!--

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

@@ -1,58 +1,62 @@
-/*
- * 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.
- */
-
 package com.iluwatar.caching;
 
+import com.iluwatar.caching.database.DbManager;
+import com.iluwatar.caching.database.DbManagerFactory;
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * The Caching pattern describes how to avoid expensive re-acquisition of resources by not releasing
- * the resources immediately after their use. The resources retain their identity, are kept in some
- * fast-access storage, and are re-used to avoid having to acquire them again. There are four main
- * caching strategies/techniques in this pattern; each with their own pros and cons. They are;
- * <code>write-through</code> which writes data to the cache and DB in a single transaction,
- * <code>write-around</code> which writes data immediately into the DB instead of the cache,
- * <code>write-behind</code> which writes data into the cache initially whilst the data is only
- * written into the DB when the cache is full, and <code>cache-aside</code> which pushes the
- * responsibility of keeping the data synchronized in both data sources to the application itself.
- * The <code>read-through</code> strategy is also included in the mentioned four strategies --
- * returns data from the cache to the caller <b>if</b> it exists <b>else</b> queries from DB and
- * stores it into the cache for future use. These strategies determine when the data in the cache
- * should be written back to the backing store (i.e. Database) and help keep both data sources
- * synchronized/up-to-date. This pattern can improve performance and also helps to maintain
- * consistency between data held in the cache and the data in the underlying data store.
+ * The Caching pattern describes how to avoid expensive re-acquisition of
+ * resources by not releasing the resources immediately after their use.
+ * The resources retain their identity, are kept in some fast-access storage,
+ * and are re-used to avoid having to acquire them again. There are four main
+ * caching strategies/techniques in this pattern; each with their own pros and
+ * cons. They are <code>write-through</code> which writes data to the cache and
+ * DB in a single transaction, <code>write-around</code> which writes data
+ * immediately into the DB instead of the cache, <code>write-behind</code>
+ * which writes data into the cache initially whilst the data is only
+ * written into the DB when the cache is full, and <code>cache-aside</code>
+ * which pushes the responsibility of keeping the data synchronized in both
+ * data sources to the application itself. The <code>read-through</code>
+ * strategy is also included in the mentioned four strategies --
+ * returns data from the cache to the caller <b>if</b> it exists <b>else</b>
+ * queries from DB and stores it into the cache for future use. These strategies
+ * determine when the data in the cache should be written back to the backing
+ * store (i.e. Database) and help keep both data sources
+ * synchronized/up-to-date. This pattern can improve performance and also helps
+ * to maintainconsistency between data held in the cache and the data in
+ * the underlying data store.
  *
- * <p>In this example, the user account ({@link UserAccount}) entity is used as the underlying
- * application data. The cache itself is implemented as an internal (Java) data structure. It adopts
- * a Least-Recently-Used (LRU) strategy for evicting data from itself when its full. The four
- * strategies are individually tested. The testing of the cache is restricted towards saving and
- * querying of user accounts from the underlying data store ( {@link DbManager}). The main class (
- * {@link App} is not aware of the underlying mechanics of the application (i.e. save and query) and
- * whether the data is coming from the cache or the DB (i.e. separation of concern). The AppManager
- * ({@link AppManager}) handles the transaction of data to-and-from the underlying data store
- * (depending on the preferred caching policy/strategy).
+ * <p>In this example, the user account ({@link UserAccount}) entity is used
+ * as the underlying application data. The cache itself is implemented as an
+ * internal (Java) data structure. It adopts a Least-Recently-Used (LRU)
+ * strategy for evicting data from itself when its full. The four
+ * strategies are individually tested. The testing of the cache is restricted
+ * towards saving and querying of user accounts from the
+ * underlying data store( {@link DbManager}). The main class ( {@link App}
+ * is not aware of the underlying mechanics of the application
+ * (i.e. save and query) and whether the data is coming from the cache or the
+ * DB (i.e. separation of concern). The AppManager ({@link AppManager}) handles
+ * the transaction of data to-and-from the underlying data store (depending on
+ * the preferred caching policy/strategy).
  * <p>
- * <i>{@literal App --> AppManager --> CacheStore/LRUCache/CachingPolicy --> DBManager} </i>
+ * <i>{@literal App --> AppManager --> CacheStore/LRUCache/CachingPolicy -->
+ * DBManager} </i>
+ * </p>
+ *
+ * <p>
+ * There are 2 ways to launch the application.
+ *  - to use "in Memory" database.
+ *  - to use the MongoDb as a database
+ *
+ * To run the application with "in Memory" database, just launch it without parameters
+ * Example: 'java -jar app.jar'
+ *
+ * To run the application with MongoDb you need to be installed the MongoDb
+ * in your system, or to launch it in the docker container.
+ * You may launch docker container from the root of current module with command:
+ * 'docker-compose up'
+ * Then you can start the application with parameter --mongo
+ * Example: 'java -jar app.jar --mongo'
  * </p>
  *
  * @see CacheStore
@@ -61,23 +65,67 @@ import lombok.extern.slf4j.Slf4j;
  */
 @Slf4j
 public class App {
+  /**
+   * Constant parameter name to use mongoDB.
+   */
+  private static final String USE_MONGO_DB = "--mongo";
+  /**
+   * Application manager.
+   */
+  private final AppManager appManager;
+
+  /**
+   * Constructor of current App.
+   *
+   * @param isMongo boolean
+   */
+  public App(final boolean isMongo) {
+    DbManager dbManager = DbManagerFactory.initDb(isMongo);
+    appManager = new AppManager(dbManager);
+    appManager.initDb();
+  }
 
   /**
    * Program entry point.
    *
    * @param args command line args
    */
-  public static void main(String[] args) {
-    AppManager.initDb(false); // VirtualDB (instead of MongoDB) was used in running the JUnit tests
+  public static void main(final String[] args) {
+    // VirtualDB (instead of MongoDB) was used in running the JUnit tests
     // and the App class to avoid Maven compilation errors. Set flag to
     // true to run the tests with MongoDB (provided that MongoDB is
     // installed and socket connection is open).
-    AppManager.initCacheCapacity(3);
-    var app = new App();
+    boolean isDbMongo = isDbMongo(args);
+    if (isDbMongo) {
+      LOGGER.info("Using the Mongo database engine to run the application.");
+    } else {
+      LOGGER.info("Using the 'in Memory' database to run the application.");
+    }
+    App app = new App(isDbMongo);
     app.useReadAndWriteThroughStrategy();
+    String splitLine = "==============================================";
+    LOGGER.info(splitLine);
     app.useReadThroughAndWriteAroundStrategy();
+    LOGGER.info(splitLine);
     app.useReadThroughAndWriteBehindStrategy();
+    LOGGER.info(splitLine);
     app.useCacheAsideStategy();
+    LOGGER.info(splitLine);
+  }
+
+  /**
+   * Check the input parameters. if
+   *
+   * @param args input params
+   * @return true if there is "--mongo" parameter in arguments
+   */
+  private static boolean isDbMongo(final String[] args) {
+    for (String arg : args) {
+      if (arg.equals(USE_MONGO_DB)) {
+        return true;
+      }
+    }
+    return false;
   }
 
   /**
@@ -85,14 +133,14 @@ public class App {
    */
   public void useReadAndWriteThroughStrategy() {
     LOGGER.info("# CachingPolicy.THROUGH");
-    AppManager.initCachingPolicy(CachingPolicy.THROUGH);
+    appManager.initCachingPolicy(CachingPolicy.THROUGH);
 
     var userAccount1 = new UserAccount("001", "John", "He is a boy.");
 
-    AppManager.save(userAccount1);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("001");
-    AppManager.find("001");
+    appManager.save(userAccount1);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("001");
+    appManager.find("001");
   }
 
   /**
@@ -100,21 +148,21 @@ public class App {
    */
   public void useReadThroughAndWriteAroundStrategy() {
     LOGGER.info("# CachingPolicy.AROUND");
-    AppManager.initCachingPolicy(CachingPolicy.AROUND);
+    appManager.initCachingPolicy(CachingPolicy.AROUND);
 
     var userAccount2 = new UserAccount("002", "Jane", "She is a girl.");
 
-    AppManager.save(userAccount2);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("002");
-    LOGGER.info(AppManager.printCacheContent());
-    userAccount2 = AppManager.find("002");
+    appManager.save(userAccount2);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("002");
+    LOGGER.info(appManager.printCacheContent());
+    userAccount2 = appManager.find("002");
     userAccount2.setUserName("Jane G.");
-    AppManager.save(userAccount2);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("002");
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("002");
+    appManager.save(userAccount2);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("002");
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("002");
   }
 
   /**
@@ -122,23 +170,31 @@ public class App {
    */
   public void useReadThroughAndWriteBehindStrategy() {
     LOGGER.info("# CachingPolicy.BEHIND");
-    AppManager.initCachingPolicy(CachingPolicy.BEHIND);
+    appManager.initCachingPolicy(CachingPolicy.BEHIND);
 
-    var userAccount3 = new UserAccount("003", "Adam", "He likes food.");
-    var userAccount4 = new UserAccount("004", "Rita", "She hates cats.");
-    var userAccount5 = new UserAccount("005", "Isaac", "He is allergic to mustard.");
+    var userAccount3 = new UserAccount("003",
+            "Adam",
+            "He likes food.");
+    var userAccount4 = new UserAccount("004",
+            "Rita",
+            "She hates cats.");
+    var userAccount5 = new UserAccount("005",
+            "Isaac",
+            "He is allergic to mustard.");
 
-    AppManager.save(userAccount3);
-    AppManager.save(userAccount4);
-    AppManager.save(userAccount5);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("003");
-    LOGGER.info(AppManager.printCacheContent());
-    UserAccount userAccount6 = new UserAccount("006", "Yasha", "She is an only child.");
-    AppManager.save(userAccount6);
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("004");
-    LOGGER.info(AppManager.printCacheContent());
+    appManager.save(userAccount3);
+    appManager.save(userAccount4);
+    appManager.save(userAccount5);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("003");
+    LOGGER.info(appManager.printCacheContent());
+    UserAccount userAccount6 = new UserAccount("006",
+            "Yasha",
+            "She is an only child.");
+    appManager.save(userAccount6);
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("004");
+    LOGGER.info(appManager.printCacheContent());
   }
 
   /**
@@ -146,20 +202,26 @@ public class App {
    */
   public void useCacheAsideStategy() {
     LOGGER.info("# CachingPolicy.ASIDE");
-    AppManager.initCachingPolicy(CachingPolicy.ASIDE);
-    LOGGER.info(AppManager.printCacheContent());
+    appManager.initCachingPolicy(CachingPolicy.ASIDE);
+    LOGGER.info(appManager.printCacheContent());
 
-    var userAccount3 = new UserAccount("003", "Adam", "He likes food.");
-    var userAccount4 = new UserAccount("004", "Rita", "She hates cats.");
-    var userAccount5 = new UserAccount("005", "Isaac", "He is allergic to mustard.");
-    AppManager.save(userAccount3);
-    AppManager.save(userAccount4);
-    AppManager.save(userAccount5);
+    var userAccount3 = new UserAccount("003",
+            "Adam",
+            "He likes food.");
+    var userAccount4 = new UserAccount("004",
+            "Rita",
+            "She hates cats.");
+    var userAccount5 = new UserAccount("005",
+            "Isaac",
+            "He is allergic to mustard.");
+    appManager.save(userAccount3);
+    appManager.save(userAccount4);
+    appManager.save(userAccount5);
 
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("003");
-    LOGGER.info(AppManager.printCacheContent());
-    AppManager.find("004");
-    LOGGER.info(AppManager.printCacheContent());
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("003");
+    LOGGER.info(appManager.printCacheContent());
+    appManager.find("004");
+    LOGGER.info(appManager.printCacheContent());
   }
 }

caching/src/main/java/com/iluwatar/caching/AppManager.java

@@ -23,65 +23,80 @@
 
 package com.iluwatar.caching;
 
-import java.text.ParseException;
+import com.iluwatar.caching.database.DbManager;
+
 import java.util.Optional;
+
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * AppManager helps to bridge the gap in communication between the main class and the application's
- * back-end. DB connection is initialized through this class. The chosen caching strategy/policy is
- * also initialized here. Before the cache can be used, the size of the cache has to be set.
- * Depending on the chosen caching policy, AppManager will call the appropriate function in the
- * CacheStore class.
+ * AppManager helps to bridge the gap in communication between the main class
+ * and the application's back-end. DB connection is initialized through this
+ * class. The chosen  caching strategy/policy is also initialized here.
+ * Before the cache can be used, the size of the  cache has to be set.
+ * Depending on the chosen caching policy, AppManager will call the
+ * appropriate function in the CacheStore class.
  */
 @Slf4j
-public final class AppManager {
+public class AppManager {
+  /**
+   * Caching Policy.
+   */
+  private CachingPolicy cachingPolicy;
+  /**
+   * Database Manager.
+   */
+  private final DbManager dbManager;
+  /**
+   * Cache Store.
+   */
+  private final CacheStore cacheStore;
 
-  private static CachingPolicy cachingPolicy;
-
-  private AppManager() {
+  /**
+   * Constructor.
+   *
+   * @param newDbManager database manager
+   */
+  public AppManager(final DbManager newDbManager) {
+    this.dbManager = newDbManager;
+    this.cacheStore = new CacheStore(newDbManager);
   }
 
   /**
-   * Developer/Tester is able to choose whether the application should use MongoDB as its underlying
-   * data storage or a simple Java data structure to (temporarily) store the data/objects during
-   * runtime.
+   * Developer/Tester is able to choose whether the application should use
+   * MongoDB as its underlying data storage or a simple Java data structure
+   * to (temporarily) store the data/objects during runtime.
    */
-  public static void initDb(boolean useMongoDb) {
-    if (useMongoDb) {
-      try {
-        DbManager.connect();
-      } catch (ParseException e) {
-        LOGGER.error("Error connecting to MongoDB", e);
-      }
-    } else {
-      DbManager.createVirtualDb();
-    }
+  public void initDb() {
+    dbManager.connect();
   }
 
   /**
    * Initialize caching policy.
+   *
+   * @param policy is a {@link CachingPolicy}
    */
-  public static void initCachingPolicy(CachingPolicy policy) {
+  public void initCachingPolicy(final CachingPolicy policy) {
     cachingPolicy = policy;
     if (cachingPolicy == CachingPolicy.BEHIND) {
-      Runtime.getRuntime().addShutdownHook(new Thread(CacheStore::flushCache));
+      Runtime.getRuntime().addShutdownHook(new Thread(cacheStore::flushCache));
     }
-    CacheStore.clearCache();
-  }
-
-  public static void initCacheCapacity(int capacity) {
-    CacheStore.initCapacity(capacity);
+    cacheStore.clearCache();
   }
 
   /**
    * Find user account.
+   *
+   * @param userId String
+   * @return {@link UserAccount}
    */
-  public static UserAccount find(String userId) {
-    if (cachingPolicy == CachingPolicy.THROUGH || cachingPolicy == CachingPolicy.AROUND) {
-      return CacheStore.readThrough(userId);
+  public UserAccount find(final String userId) {
+    LOGGER.info("Trying to find {} in cache", userId);
+    if (cachingPolicy == CachingPolicy.THROUGH
+            || cachingPolicy == CachingPolicy.AROUND) {
+      return cacheStore.readThrough(userId);
     } else if (cachingPolicy == CachingPolicy.BEHIND) {
-      return CacheStore.readThroughWithWriteBackPolicy(userId);
+      return cacheStore.readThroughWithWriteBackPolicy(userId);
     } else if (cachingPolicy == CachingPolicy.ASIDE) {
       return findAside(userId);
     }
@@ -90,41 +105,55 @@ public final class AppManager {
 
   /**
    * Save user account.
+   *
+   * @param userAccount {@link UserAccount}
    */
-  public static void save(UserAccount userAccount) {
+  public void save(final UserAccount userAccount) {
+    LOGGER.info("Save record!");
     if (cachingPolicy == CachingPolicy.THROUGH) {
-      CacheStore.writeThrough(userAccount);
+      cacheStore.writeThrough(userAccount);
     } else if (cachingPolicy == CachingPolicy.AROUND) {
-      CacheStore.writeAround(userAccount);
+      cacheStore.writeAround(userAccount);
     } else if (cachingPolicy == CachingPolicy.BEHIND) {
-      CacheStore.writeBehind(userAccount);
+      cacheStore.writeBehind(userAccount);
     } else if (cachingPolicy == CachingPolicy.ASIDE) {
       saveAside(userAccount);
     }
   }
 
-  public static String printCacheContent() {
-    return CacheStore.print();
+  /**
+   * Returns String.
+   *
+   * @return String
+   */
+  public String printCacheContent() {
+    return cacheStore.print();
   }
 
   /**
    * Cache-Aside save user account helper.
+   *
+   * @param userAccount {@link UserAccount}
    */
-  private static void saveAside(UserAccount userAccount) {
-    DbManager.updateDb(userAccount);
-    CacheStore.invalidate(userAccount.getUserId());
+  private void saveAside(final UserAccount userAccount) {
+    dbManager.updateDb(userAccount);
+    cacheStore.invalidate(userAccount.getUserId());
   }
 
   /**
    * Cache-Aside find user account helper.
+   *
+   * @param userId String
+   * @return {@link UserAccount}
    */
-  private static UserAccount findAside(String userId) {
-    return Optional.ofNullable(CacheStore.get(userId))
-        .or(() -> {
-          Optional<UserAccount> userAccount = Optional.ofNullable(DbManager.readFromDb(userId));
-          userAccount.ifPresent(account -> CacheStore.set(userId, account));
-          return userAccount;
-        })
-        .orElse(null);
+  private UserAccount findAside(final String userId) {
+    return Optional.ofNullable(cacheStore.get(userId))
+            .or(() -> {
+              Optional<UserAccount> userAccount =
+                      Optional.ofNullable(dbManager.readFromDb(userId));
+              userAccount.ifPresent(account -> cacheStore.set(userId, account));
+              return userAccount;
+            })
+            .orElse(null);
   }
 }

caching/src/main/java/com/iluwatar/caching/CacheStore.java

@@ -23,9 +23,11 @@
 
 package com.iluwatar.caching;
 
+import com.iluwatar.caching.database.DbManager;
 import java.util.List;
 import java.util.Optional;
 import java.util.stream.Collectors;
+
 import lombok.extern.slf4j.Slf4j;
 
 /**
@@ -33,16 +35,34 @@ import lombok.extern.slf4j.Slf4j;
  */
 @Slf4j
 public class CacheStore {
+  /**
+   * Cache capacity.
+   */
+  private static final int CAPACITY = 3;
 
-  private static LruCache cache;
+  /**
+   * Lru cache see {@link LruCache}.
+   */
+  private LruCache cache;
+  /**
+   * DbManager.
+   */
+  private final DbManager dbManager;
 
-  private CacheStore() {
+  /**
+   * Cache Store.
+   * @param dataBaseManager {@link DbManager}
+   */
+  public CacheStore(final DbManager dataBaseManager) {
+    this.dbManager = dataBaseManager;
+    initCapacity(CAPACITY);
   }
 
   /**
    * Init cache capacity.
+   * @param capacity int
    */
-  public static void initCapacity(int capacity) {
+  public void initCapacity(final int capacity) {
     if (cache == null) {
       cache = new LruCache(capacity);
     } else {
@@ -52,57 +72,64 @@ public class CacheStore {
 
   /**
    * Get user account using read-through cache.
+   * @param userId {@link String}
+   * @return {@link UserAccount}
    */
-  public static UserAccount readThrough(String userId) {
+  public UserAccount readThrough(final String userId) {
     if (cache.contains(userId)) {
-      LOGGER.info("# Cache Hit!");
+      LOGGER.info("# Found in Cache!");
       return cache.get(userId);
     }
-    LOGGER.info("# Cache Miss!");
-    UserAccount userAccount = DbManager.readFromDb(userId);
+    LOGGER.info("# Not found in cache! Go to DB!!");
+    UserAccount userAccount = dbManager.readFromDb(userId);
     cache.set(userId, userAccount);
     return userAccount;
   }
 
   /**
    * Get user account using write-through cache.
+   * @param userAccount {@link UserAccount}
    */
-  public static void writeThrough(UserAccount userAccount) {
+  public void writeThrough(final UserAccount userAccount) {
     if (cache.contains(userAccount.getUserId())) {
-      DbManager.updateDb(userAccount);
+      dbManager.updateDb(userAccount);
     } else {
-      DbManager.writeToDb(userAccount);
+      dbManager.writeToDb(userAccount);
     }
     cache.set(userAccount.getUserId(), userAccount);
   }
 
   /**
    * Get user account using write-around cache.
+   * @param userAccount {@link UserAccount}
    */
-  public static void writeAround(UserAccount userAccount) {
+  public void writeAround(final UserAccount userAccount) {
     if (cache.contains(userAccount.getUserId())) {
-      DbManager.updateDb(userAccount);
-      cache.invalidate(userAccount.getUserId()); // Cache data has been updated -- remove older
+      dbManager.updateDb(userAccount);
+      // Cache data has been updated -- remove older
+      cache.invalidate(userAccount.getUserId());
       // version from cache.
     } else {
-      DbManager.writeToDb(userAccount);
+      dbManager.writeToDb(userAccount);
     }
   }
 
   /**
    * Get user account using read-through cache with write-back policy.
+   * @param userId {@link String}
+   * @return {@link UserAccount}
    */
-  public static UserAccount readThroughWithWriteBackPolicy(String userId) {
+  public UserAccount readThroughWithWriteBackPolicy(final String userId) {
     if (cache.contains(userId)) {
-      LOGGER.info("# Cache Hit!");
+      LOGGER.info("# Found in cache!");
       return cache.get(userId);
     }
-    LOGGER.info("# Cache Miss!");
-    UserAccount userAccount = DbManager.readFromDb(userId);
+    LOGGER.info("# Not found in Cache!");
+    UserAccount userAccount = dbManager.readFromDb(userId);
     if (cache.isFull()) {
       LOGGER.info("# Cache is FULL! Writing LRU data to DB...");
       UserAccount toBeWrittenToDb = cache.getLruData();
-      DbManager.upsertDb(toBeWrittenToDb);
+      dbManager.upsertDb(toBeWrittenToDb);
     }
     cache.set(userId, userAccount);
     return userAccount;
@@ -110,12 +137,13 @@ public class CacheStore {
 
   /**
    * Set user account.
+   * @param userAccount {@link UserAccount}
    */
-  public static void writeBehind(UserAccount userAccount) {
+  public void writeBehind(final UserAccount userAccount) {
     if (cache.isFull() && !cache.contains(userAccount.getUserId())) {
       LOGGER.info("# Cache is FULL! Writing LRU data to DB...");
       UserAccount toBeWrittenToDb = cache.getLruData();
-      DbManager.upsertDb(toBeWrittenToDb);
+      dbManager.upsertDb(toBeWrittenToDb);
     }
     cache.set(userAccount.getUserId(), userAccount);
   }
@@ -123,7 +151,7 @@ public class CacheStore {
   /**
    * Clears cache.
    */
-  public static void clearCache() {
+  public void clearCache() {
     if (cache != null) {
       cache.clear();
     }
@@ -132,44 +160,51 @@ public class CacheStore {
   /**
    * Writes remaining content in the cache into the DB.
    */
-  public static void flushCache() {
+  public void flushCache() {
     LOGGER.info("# flushCache...");
     Optional.ofNullable(cache)
         .map(LruCache::getCacheDataInListForm)
         .orElse(List.of())
-        .forEach(DbManager::updateDb);
+        .forEach(dbManager::updateDb);
+    dbManager.disconnect();
   }
 
   /**
    * Print user accounts.
+   * @return {@link String}
    */
-  public static String print() {
+  public String print() {
     return Optional.ofNullable(cache)
         .map(LruCache::getCacheDataInListForm)
         .orElse(List.of())
         .stream()
         .map(userAccount -> userAccount.toString() + "\n")
-        .collect(Collectors.joining("", "\n--CACHE CONTENT--\n", "----\n"));
+        .collect(Collectors.joining("", "\n--CACHE CONTENT--\n", "----"));
   }
 
   /**
    * Delegate to backing cache store.
+   * @param userId {@link String}
+   * @return {@link UserAccount}
    */
-  public static UserAccount get(String userId) {
+  public UserAccount get(final String userId) {
     return cache.get(userId);
   }
 
   /**
    * Delegate to backing cache store.
+   * @param userId {@link String}
+   * @param userAccount {@link UserAccount}
    */
-  public static void set(String userId, UserAccount userAccount) {
+  public void set(final String userId, final UserAccount userAccount) {
     cache.set(userId, userAccount);
   }
 
   /**
    * Delegate to backing cache store.
+   * @param userId {@link String}
    */
-  public static void invalidate(String userId) {
+  public void invalidate(final String userId) {
     cache.invalidate(userId);
   }
 }

caching/src/main/java/com/iluwatar/caching/CachingPolicy.java

@@ -32,10 +32,25 @@ import lombok.Getter;
 @AllArgsConstructor
 @Getter
 public enum CachingPolicy {
+  /**
+   * Through.
+   */
   THROUGH("through"),
+  /**
+   * AROUND.
+   */
   AROUND("around"),
+  /**
+   * BEHIND.
+   */
   BEHIND("behind"),
+  /**
+   * ASIDE.
+   */
   ASIDE("aside");
 
+  /**
+   * Policy value.
+   */
   private final String policy;
 }

caching/src/main/java/com/iluwatar/caching/DbManager.java

@@ -1,172 +0,0 @@
-/*
- * 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.
- */
-
-package com.iluwatar.caching;
-
-import com.iluwatar.caching.constants.CachingConstants;
-import com.mongodb.MongoClient;
-import com.mongodb.client.MongoDatabase;
-import com.mongodb.client.model.UpdateOptions;
-import java.text.ParseException;
-import java.util.HashMap;
-import java.util.Map;
-import lombok.extern.slf4j.Slf4j;
-import org.bson.Document;
-
-/**
- * <p>DBManager handles the communication with the underlying data store i.e. Database. It contains
- * the implemented methods for querying, inserting, and updating data. MongoDB was used as the
- * database for the application.</p>
- *
- * <p>Developer/Tester is able to choose whether the application should use MongoDB as its
- * underlying data storage (connect()) or a simple Java data structure to (temporarily) store the
- * data/objects during runtime (createVirtualDB()).</p>
- */
-@Slf4j
-public final class DbManager {
-
-  private static MongoClient mongoClient;
-  private static MongoDatabase db;
-  private static boolean useMongoDB;
-
-  private static Map<String, UserAccount> virtualDB;
-  private static final String ERROR_MESSAGE_LOG = "Error connecting to MongoDB";
-
-  private DbManager() {
-  }
-
-  /**
-   * Create DB.
-   */
-  public static void createVirtualDb() {
-    useMongoDB = false;
-    virtualDB = new HashMap<>();
-  }
-
-  /**
-   * Connect to DB.
-   */
-  public static void connect() throws ParseException {
-    useMongoDB = true;
-    mongoClient = new MongoClient();
-    db = mongoClient.getDatabase("test");
-  }
-
-  /**
-   * Read user account from DB.
-   */
-  public static UserAccount readFromDb(String userId) {
-    if (!useMongoDB) {
-      if (virtualDB.containsKey(userId)) {
-        return virtualDB.get(userId);
-      }
-      return null;
-    }
-    if (db == null) {
-      try {
-        connect();
-      } catch (ParseException e) {
-        LOGGER.error(ERROR_MESSAGE_LOG, e);
-      }
-    }
-    var iterable = db
-        .getCollection(CachingConstants.USER_ACCOUNT)
-        .find(new Document(CachingConstants.USER_ID, userId));
-    if (iterable == null) {
-      return null;
-    }
-    Document doc = iterable.first();
-    String userName = doc.getString(CachingConstants.USER_NAME);
-    String appInfo = doc.getString(CachingConstants.ADD_INFO);
-    return new UserAccount(userId, userName, appInfo);
-  }
-
-  /**
-   * Write user account to DB.
-   */
-  public static void writeToDb(UserAccount userAccount) {
-    if (!useMongoDB) {
-      virtualDB.put(userAccount.getUserId(), userAccount);
-      return;
-    }
-    if (db == null) {
-      try {
-        connect();
-      } catch (ParseException e) {
-        LOGGER.error(ERROR_MESSAGE_LOG, e);
-      }
-    }
-    db.getCollection(CachingConstants.USER_ACCOUNT).insertOne(
-        new Document(CachingConstants.USER_ID, userAccount.getUserId())
-            .append(CachingConstants.USER_NAME, userAccount.getUserName())
-            .append(CachingConstants.ADD_INFO, userAccount.getAdditionalInfo())
-    );
-  }
-
-  /**
-   * Update DB.
-   */
-  public static void updateDb(UserAccount userAccount) {
-    if (!useMongoDB) {
-      virtualDB.put(userAccount.getUserId(), userAccount);
-      return;
-    }
-    if (db == null) {
-      try {
-        connect();
-      } catch (ParseException e) {
-        LOGGER.error(ERROR_MESSAGE_LOG, e);
-      }
-    }
-    db.getCollection(CachingConstants.USER_ACCOUNT).updateOne(
-        new Document(CachingConstants.USER_ID, userAccount.getUserId()),
-        new Document("$set", new Document(CachingConstants.USER_NAME, userAccount.getUserName())
-            .append(CachingConstants.ADD_INFO, userAccount.getAdditionalInfo())));
-  }
-
-  /**
-   * Insert data into DB if it does not exist. Else, update it.
-   */
-  public static void upsertDb(UserAccount userAccount) {
-    if (!useMongoDB) {
-      virtualDB.put(userAccount.getUserId(), userAccount);
-      return;
-    }
-    if (db == null) {
-      try {
-        connect();
-      } catch (ParseException e) {
-        LOGGER.error(ERROR_MESSAGE_LOG, e);
-      }
-    }
-    db.getCollection(CachingConstants.USER_ACCOUNT).updateOne(
-        new Document(CachingConstants.USER_ID, userAccount.getUserId()),
-        new Document("$set",
-            new Document(CachingConstants.USER_ID, userAccount.getUserId())
-                .append(CachingConstants.USER_NAME, userAccount.getUserName())
-                .append(CachingConstants.ADD_INFO, userAccount.getAdditionalInfo())
-        ),
-        new UpdateOptions().upsert(true)
-    );
-  }
-}

caching/src/main/java/com/iluwatar/caching/LruCache.java

@@ -29,41 +29,83 @@ import java.util.List;
 import java.util.Map;
 import lombok.extern.slf4j.Slf4j;
 
+
 /**
- * Data structure/implementation of the application's cache. The data structure consists of a hash
- * table attached with a doubly linked-list. The linked-list helps in capturing and maintaining the
- * LRU data in the cache. When a data is queried (from the cache), added (to the cache), or updated,
- * the data is moved to the front of the list to depict itself as the most-recently-used data. The
- * LRU data is always at the end of the list.
+ * Data structure/implementation of the application's cache. The data structure
+ * consists of a hash table attached with a doubly linked-list. The linked-list
+ * helps in capturing and maintaining the LRU data in the cache. When a data is
+ * queried (from the cache), added (to the cache), or updated, the data is
+ * moved to the front of the list to depict itself as the most-recently-used
+ * data. The LRU data is always at the end of the list.
  */
 @Slf4j
 public class LruCache {
-
+  /**
+   * Static class Node.
+   */
   static class Node {
-    String userId;
-    UserAccount userAccount;
-    Node previous;
-    Node next;
+    /**
+     * user id.
+     */
+    private final String userId;
+    /**
+     * User Account.
+     */
+    private UserAccount userAccount;
+    /**
+     * previous.
+     */
+    private Node previous;
+    /**
+     * next.
+     */
+    private Node next;
 
-    public Node(String userId, UserAccount userAccount) {
-      this.userId = userId;
-      this.userAccount = userAccount;
+    /**
+     * Node definition.
+     *
+     * @param id      String
+     * @param account {@link UserAccount}
+     */
+    Node(final String id, final UserAccount account) {
+      this.userId = id;
+      this.userAccount = account;
     }
   }
 
-  int capacity;
-  Map<String, Node> cache = new HashMap<>();
-  Node head;
-  Node end;
+  /**
+   * Capacity of Cache.
+   */
+  private int capacity;
+  /**
+   * Cache {@link HashMap}.
+   */
+  private Map<String, Node> cache = new HashMap<>();
+  /**
+   * Head.
+   */
+  private Node head;
+  /**
+   * End.
+   */
+  private Node end;
 
-  public LruCache(int capacity) {
-    this.capacity = capacity;
+  /**
+   * Constructor.
+   *
+   * @param cap Integer.
+   */
+  public LruCache(final int cap) {
+    this.capacity = cap;
   }
 
   /**
    * Get user account.
+   *
+   * @param userId String
+   * @return {@link UserAccount}
    */
-  public UserAccount get(String userId) {
+  public UserAccount get(final String userId) {
     if (cache.containsKey(userId)) {
       var node = cache.get(userId);
       remove(node);
@@ -75,8 +117,10 @@ public class LruCache {
 
   /**
    * Remove node from linked list.
+   *
+   * @param node {@link Node}
    */
-  public void remove(Node node) {
+  public void remove(final Node node) {
     if (node.previous != null) {
       node.previous.next = node.next;
     } else {
@@ -91,8 +135,10 @@ public class LruCache {
 
   /**
    * Move node to the front of the list.
+   *
+   * @param node {@link Node}
    */
-  public void setHead(Node node) {
+  public void setHead(final Node node) {
     node.next = head;
     node.previous = null;
     if (head != null) {
@@ -106,8 +152,11 @@ public class LruCache {
 
   /**
    * Set user account.
+   *
+   * @param userAccount {@link UserAccount}
+   * @param userId      {@link String}
    */
-  public void set(String userId, UserAccount userAccount) {
+  public void set(final String userId, final UserAccount userAccount) {
     if (cache.containsKey(userId)) {
       var old = cache.get(userId);
       old.userAccount = userAccount;
@@ -127,25 +176,43 @@ public class LruCache {
     }
   }
 
-  public boolean contains(String userId) {
+  /**
+   * Check if Cache contains the userId.
+   *
+   * @param userId {@link String}
+   * @return boolean
+   */
+  public boolean contains(final String userId) {
     return cache.containsKey(userId);
   }
 
   /**
    * Invalidate cache for user.
+   *
+   * @param userId {@link String}
    */
-  public void invalidate(String userId) {
+  public void invalidate(final String userId) {
     var toBeRemoved = cache.remove(userId);
     if (toBeRemoved != null) {
-      LOGGER.info("# {} has been updated! Removing older version from cache...", userId);
+      LOGGER.info("# {} has been updated! "
+              + "Removing older version from cache...", userId);
       remove(toBeRemoved);
     }
   }
 
+  /**
+   * Check if the cache is full.
+   * @return boolean
+   */
   public boolean isFull() {
     return cache.size() >= capacity;
   }
 
+  /**
+   * Get LRU data.
+   *
+   * @return {@link UserAccount}
+   */
   public UserAccount getLruData() {
     return end.userAccount;
   }
@@ -161,6 +228,8 @@ public class LruCache {
 
   /**
    * Returns cache data in list form.
+   *
+   * @return {@link List}
    */
   public List<UserAccount> getCacheDataInListForm() {
     var listOfCacheData = new ArrayList<UserAccount>();
@@ -174,10 +243,14 @@ public class LruCache {
 
   /**
    * Set cache capacity.
+   *
+   * @param newCapacity int
    */
-  public void setCapacity(int newCapacity) {
+  public void setCapacity(final int newCapacity) {
     if (capacity > newCapacity) {
-      clear(); // Behavior can be modified to accommodate for decrease in cache size. For now, we'll
+      // Behavior can be modified to accommodate
+      // for decrease in cache size. For now, we'll
+      clear();
       // just clear the cache.
     } else {
       this.capacity = newCapacity;

caching/src/main/java/com/iluwatar/caching/UserAccount.java

@@ -24,19 +24,28 @@
 package com.iluwatar.caching;
 
 import lombok.AllArgsConstructor;
-import lombok.Getter;
-import lombok.Setter;
+import lombok.Data;
+import lombok.EqualsAndHashCode;
 import lombok.ToString;
 
 /**
  * Entity class (stored in cache and DB) used in the application.
  */
-@Setter
-@Getter
+@Data
 @AllArgsConstructor
 @ToString
+@EqualsAndHashCode
 public class UserAccount {
+  /**
+   * User Id.
+   */
   private String userId;
+  /**
+   * User Name.
+   */
   private String userName;
+  /**
+   * Additional Info.
+   */
   private String additionalInfo;
 }

caching/src/main/java/com/iluwatar/caching/constants/CachingConstants.java

@@ -26,11 +26,27 @@ package com.iluwatar.caching.constants;
 /**
  * Constant class for defining constants.
  */
-public class CachingConstants {
-
+public final class CachingConstants {
+  /**
+   * User Account.
+   */
   public static final String USER_ACCOUNT = "user_accounts";
+  /**
+   * User ID.
+   */
   public static final String USER_ID = "userID";
+  /**
+   * User Name.
+   */
   public static final String USER_NAME = "userName";
+  /**
+   * Additional Info.
+   */
   public static final String ADD_INFO = "additionalInfo";
 
+  /**
+   * Constructor.
+   */
+  private CachingConstants() {
+  }
 }

caching/src/main/java/com/iluwatar/caching/constants/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * Constants.
+ */
+package com.iluwatar.caching.constants;

caching/src/main/java/com/iluwatar/caching/database/DbManager.java

@@ -0,0 +1,52 @@
+package com.iluwatar.caching.database;
+
+import com.iluwatar.caching.UserAccount;
+
+/**
+ * <p>DBManager handles the communication with the underlying data store i.e.
+ * Database. It contains the implemented methods for querying, inserting,
+ * and updating data. MongoDB was used as the database for the application.</p>
+ */
+public interface DbManager {
+  /**
+   * Connect to DB.
+   */
+  void connect();
+
+  /**
+   * Disconnect from DB.
+   */
+  void disconnect();
+
+  /**
+   * Read from DB.
+   *
+   * @param userId {@link String}
+   * @return {@link UserAccount}
+   */
+  UserAccount readFromDb(String userId);
+
+  /**
+   * Write to DB.
+   *
+   * @param userAccount {@link UserAccount}
+   * @return {@link UserAccount}
+   */
+  UserAccount writeToDb(UserAccount userAccount);
+
+  /**
+   * Update record.
+   *
+   * @param userAccount {@link UserAccount}
+   * @return {@link UserAccount}
+   */
+  UserAccount updateDb(UserAccount userAccount);
+
+  /**
+   * Update record or Insert if not exists.
+   *
+   * @param userAccount {@link UserAccount}
+   * @return {@link UserAccount}
+   */
+  UserAccount upsertDb(UserAccount userAccount);
+}

caching/src/main/java/com/iluwatar/caching/database/DbManagerFactory.java

@@ -0,0 +1,25 @@
+package com.iluwatar.caching.database;
+
+/**
+ * Creates the database connection accroding the input parameter.
+ */
+public final class DbManagerFactory {
+  /**
+   * Private constructor.
+   */
+  private DbManagerFactory() {
+  }
+
+  /**
+   * Init database.
+   *
+   * @param isMongo boolean
+   * @return {@link DbManager}
+   */
+  public static DbManager initDb(final boolean isMongo) {
+    if (isMongo) {
+      return new MongoDb();
+    }
+    return new VirtualDb();
+  }
+}

caching/src/main/java/com/iluwatar/caching/database/MongoDb.java

@@ -0,0 +1,128 @@
+package com.iluwatar.caching.database;
+
+import static com.iluwatar.caching.constants.CachingConstants.ADD_INFO;
+import static com.iluwatar.caching.constants.CachingConstants.USER_ACCOUNT;
+import static com.iluwatar.caching.constants.CachingConstants.USER_ID;
+import static com.iluwatar.caching.constants.CachingConstants.USER_NAME;
+
+import com.iluwatar.caching.UserAccount;
+import com.iluwatar.caching.constants.CachingConstants;
+import com.mongodb.MongoClient;
+import com.mongodb.MongoClientOptions;
+import com.mongodb.MongoCredential;
+import com.mongodb.ServerAddress;
+import com.mongodb.client.MongoDatabase;
+import com.mongodb.client.model.UpdateOptions;
+import java.util.List;
+import lombok.extern.slf4j.Slf4j;
+import org.bson.Document;
+
+/**
+ * Implementation of DatabaseManager.
+ * implements base methods to work with MongoDb.
+ */
+@Slf4j
+public class MongoDb implements DbManager {
+  private static final String DATABASE_NAME = "admin";
+  private static final String MONGO_USER = "root";
+  private static final String MONGO_PASSWORD = "rootpassword";
+  private MongoClient client;
+  private MongoDatabase db;
+
+  /**
+   * Connect to Db. Check th connection
+   */
+  @Override
+  public void connect() {
+    MongoCredential mongoCredential = MongoCredential.createCredential(MONGO_USER,
+                    DATABASE_NAME,
+                    MONGO_PASSWORD.toCharArray());
+    MongoClientOptions options = MongoClientOptions.builder().build();
+    client = new MongoClient(new ServerAddress(), List.of(mongoCredential), options);
+    db = client.getDatabase(DATABASE_NAME);
+  }
+
+  @Override
+  public void disconnect() {
+    client.close();
+  }
+
+  /**
+   * Read data from DB.
+   *
+   * @param userId {@link String}
+   * @return {@link UserAccount}
+   */
+  @Override
+  public UserAccount readFromDb(final String userId) {
+    var iterable = db
+            .getCollection(CachingConstants.USER_ACCOUNT)
+            .find(new Document(USER_ID, userId));
+    if (iterable.first() == null) {
+      return null;
+    }
+    Document doc = iterable.first();
+    if (doc != null) {
+      String userName = doc.getString(USER_NAME);
+      String appInfo = doc.getString(ADD_INFO);
+      return new UserAccount(userId, userName, appInfo);
+    } else {
+      return null;
+    }
+  }
+
+  /**
+   * Write data to DB.
+   *
+   * @param userAccount {@link UserAccount}
+   * @return {@link UserAccount}
+   */
+  @Override
+  public UserAccount writeToDb(final UserAccount userAccount) {
+    db.getCollection(USER_ACCOUNT).insertOne(
+            new Document(USER_ID, userAccount.getUserId())
+                    .append(USER_NAME, userAccount.getUserName())
+                    .append(ADD_INFO, userAccount.getAdditionalInfo())
+    );
+    return userAccount;
+  }
+
+  /**
+   * Update DB.
+   *
+   * @param userAccount {@link UserAccount}
+   * @return {@link UserAccount}
+   */
+  @Override
+  public UserAccount updateDb(final UserAccount userAccount) {
+    Document id = new Document(USER_ID, userAccount.getUserId());
+    Document dataSet = new Document(USER_NAME, userAccount.getUserName())
+            .append(ADD_INFO, userAccount.getAdditionalInfo());
+    db.getCollection(CachingConstants.USER_ACCOUNT)
+            .updateOne(id, new Document("$set", dataSet));
+    return userAccount;
+  }
+
+  /**
+   * Update data if exists.
+   *
+   * @param userAccount {@link UserAccount}
+   * @return {@link UserAccount}
+   */
+  @Override
+  public UserAccount upsertDb(final UserAccount userAccount) {
+    String userId = userAccount.getUserId();
+    String userName = userAccount.getUserName();
+    String additionalInfo = userAccount.getAdditionalInfo();
+    db.getCollection(CachingConstants.USER_ACCOUNT).updateOne(
+            new Document(USER_ID, userId),
+            new Document("$set",
+                    new Document(USER_ID, userId)
+                            .append(USER_NAME, userName)
+                            .append(ADD_INFO, additionalInfo)
+            ),
+            new UpdateOptions().upsert(true)
+    );
+    return userAccount;
+  }
+}

caching/src/main/java/com/iluwatar/caching/database/VirtualDb.java

@@ -0,0 +1,78 @@
+package com.iluwatar.caching.database;
+
+import com.iluwatar.caching.UserAccount;
+
+import java.util.HashMap;
+import java.util.Map;
+
+/**
+ * Implementation of DatabaseManager.
+ * implements base methods to work with hashMap as database.
+ */
+public class VirtualDb implements DbManager {
+  /**
+   * Virtual DataBase.
+   */
+  private Map<String, UserAccount> db;
+
+  /**
+   * Creates new HashMap.
+   */
+  @Override
+  public void connect() {
+    db = new HashMap<>();
+  }
+
+  @Override
+  public void disconnect() {
+    db = null;
+  }
+
+  /**
+   * Read from Db.
+   *
+   * @param userId {@link String}
+   * @return {@link UserAccount}
+   */
+  @Override
+  public UserAccount readFromDb(final String userId) {
+    if (db.containsKey(userId)) {
+      return db.get(userId);
+    }
+    return null;
+  }
+
+  /**
+   * Write to DB.
+   *
+   * @param userAccount {@link UserAccount}
+   * @return {@link UserAccount}
+   */
+  @Override
+  public UserAccount writeToDb(final UserAccount userAccount) {
+    db.put(userAccount.getUserId(), userAccount);
+    return userAccount;
+  }
+
+  /**
+   * Update reecord in DB.
+   *
+   * @param userAccount {@link UserAccount}
+   * @return {@link UserAccount}
+   */
+  @Override
+  public UserAccount updateDb(final UserAccount userAccount) {
+    return writeToDb(userAccount);
+  }
+
+  /**
+   * Update.
+   *
+   * @param userAccount {@link UserAccount}
+   * @return {@link UserAccount}
+   */
+  @Override
+  public UserAccount upsertDb(final UserAccount userAccount) {
+    return updateDb(userAccount);
+  }
+}

caching/src/main/java/com/iluwatar/caching/database/package-info.java

@@ -0,0 +1,4 @@
+/**
+ * Database classes.
+ */
+package com.iluwatar.caching.database;

caching/src/main/java/com/iluwatar/caching/package-info.java

@@ -0,0 +1,20 @@
+/**
+ * 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.
+ */
+package com.iluwatar.caching;

caching/src/test/java/com/iluwatar/caching/AppTest.java

@@ -25,25 +25,21 @@ package com.iluwatar.caching;
 
 import org.junit.jupiter.api.Test;
 
-import java.io.IOException;
-
 import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
 
 /**
  * Tests that Caching example runs without errors.
  */
 class AppTest {
-
   /**
    * Issue: Add at least one assertion to this test case.
-   *
+   * <p>
    * Solution: Inserted assertion to check whether the execution of the main method in {@link App}
    * throws an exception.
    */
 
   @Test
   void shouldExecuteApplicationWithoutException() {
-
     assertDoesNotThrow(() -> App.main(new String[]{}));
   }
 }

caching/src/test/java/com/iluwatar/caching/CachingTest.java

@@ -23,11 +23,11 @@
 
 package com.iluwatar.caching;
 
-import static org.junit.jupiter.api.Assertions.assertNotNull;
-
 import org.junit.jupiter.api.BeforeEach;
 import org.junit.jupiter.api.Test;
 
+import static org.junit.jupiter.api.Assertions.assertNotNull;
+
 /**
  * Application test
  */
@@ -43,32 +43,30 @@ class CachingTest {
     // to avoid Maven compilation errors. Set flag to true to run the
     // tests with MongoDB (provided that MongoDB is installed and socket
     // connection is open).
-    AppManager.initDb(false);
-    AppManager.initCacheCapacity(3);
-    app = new App();
+    app = new App(false);
   }
 
   @Test
   void testReadAndWriteThroughStrategy() {
-	assertNotNull(app);
+    assertNotNull(app);
     app.useReadAndWriteThroughStrategy();
   }
 
   @Test
   void testReadThroughAndWriteAroundStrategy() {
-	assertNotNull(app);
+    assertNotNull(app);
     app.useReadThroughAndWriteAroundStrategy();
   }
 
   @Test
   void testReadThroughAndWriteBehindStrategy() {
-	assertNotNull(app);
+    assertNotNull(app);
     app.useReadThroughAndWriteBehindStrategy();
   }
 
   @Test
   void testCacheAsideStrategy() {
-	assertNotNull(app);
+    assertNotNull(app);
     app.useCacheAsideStategy();
   }
 }

caching/src/test/java/com/iluwatar/caching/database/MongoDbTest.java

@@ -0,0 +1,84 @@
+package com.iluwatar.caching.database;
+
+import com.iluwatar.caching.UserAccount;
+import com.iluwatar.caching.constants.CachingConstants;
+import com.mongodb.client.FindIterable;
+import com.mongodb.client.MongoCollection;
+import com.mongodb.client.MongoDatabase;
+import org.bson.Document;
+import org.junit.jupiter.api.BeforeEach;
+import org.junit.jupiter.api.Test;
+import org.mockito.Mock;
+import org.mockito.internal.util.reflection.Whitebox;
+
+import static com.iluwatar.caching.constants.CachingConstants.ADD_INFO;
+import static com.iluwatar.caching.constants.CachingConstants.USER_ID;
+import static com.iluwatar.caching.constants.CachingConstants.USER_NAME;
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.mockito.ArgumentMatchers.any;
+import static org.mockito.Mockito.*;
+
+class MongoDbTest {
+  private static final String ID = "123";
+  private static final String NAME = "Some user";
+  private static final String ADDITIONAL_INFO = "Some app Info";
+
+  @Mock
+  MongoDatabase db;
+  private MongoDb mongoDb = new MongoDb();
+
+  private UserAccount userAccount;
+
+  @BeforeEach
+  void init() {
+    db = mock(MongoDatabase.class);
+    Whitebox.setInternalState(mongoDb, "db", db);
+    userAccount = new UserAccount(ID, NAME, ADDITIONAL_INFO);
+
+
+  }
+
+  @Test
+  void connect() {
+    assertDoesNotThrow(() -> mongoDb.connect());
+  }
+
+  @Test
+  void readFromDb() {
+    Document document = new Document(USER_ID, ID)
+            .append(USER_NAME, NAME)
+            .append(ADD_INFO, ADDITIONAL_INFO);
+    MongoCollection<Document> mongoCollection = mock(MongoCollection.class);
+    when(db.getCollection(CachingConstants.USER_ACCOUNT)).thenReturn(mongoCollection);
+
+    FindIterable<Document> findIterable = mock(FindIterable.class);
+    when(mongoCollection.find(any(Document.class))).thenReturn(findIterable);
+
+    when(findIterable.first()).thenReturn(document);
+
+    assertEquals(mongoDb.readFromDb(ID),userAccount);
+  }
+
+  @Test
+  void writeToDb() {
+    MongoCollection<Document> mongoCollection = mock(MongoCollection.class);
+    when(db.getCollection(CachingConstants.USER_ACCOUNT)).thenReturn(mongoCollection);
+    doNothing().when(mongoCollection).insertOne(any(Document.class));
+    assertDoesNotThrow(()-> {mongoDb.writeToDb(userAccount);});
+  }
+
+  @Test
+  void updateDb() {
+    MongoCollection<Document> mongoCollection = mock(MongoCollection.class);
+    when(db.getCollection(CachingConstants.USER_ACCOUNT)).thenReturn(mongoCollection);
+    assertDoesNotThrow(()-> {mongoDb.updateDb(userAccount);});
+  }
+
+  @Test
+  void upsertDb() {
+    MongoCollection<Document> mongoCollection = mock(MongoCollection.class);
+    when(db.getCollection(CachingConstants.USER_ACCOUNT)).thenReturn(mongoCollection);
+    assertDoesNotThrow(()-> {mongoDb.upsertDb(userAccount);});
+  }
+}

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

@@ -26,9 +26,9 @@ package com.iluwatar.factory;
 import lombok.extern.slf4j.Slf4j;
 
 /**
- * Factory is an object for creating other objects. It provides a static method to 
+ * Factory is an object for creating other objects, it providing Providing a static method to 
  * create and return objects of varying classes, in order to hide the implementation logic 
- * and makes client code focus on usage rather than objects initialization and management.
+ * and makes client code focus on usage rather then objects initialization and management.
  *
  * <p>In this example an alchemist manufactures coins. CoinFactory is the factory class and it
  * provides a static method to create different types of coins.

localization/es/README.md

@@ -34,13 +34,13 @@ Todos los diseños deben ser lo más simples posible. Deberías comenzar con los
 Una vez que esté familiarizado con estos conceptos, puedes comenzar a profundizar con los
 [patrones de diseño disponibles](https://java-design-patterns.com/patterns/) por cualquiera de los siguientes enfoques
 
- - Buscar un patrón específico por su nombre. ¿No puedes encontrar uno? Informa de un nuevo patrón [aquí](https://github.com/iluwatar/java-design-patterns/issues).
+ - Buscar un patrón específico por su nombre. ¿No puedes encontrar uno? Informe un nuevo patrón [aquí](https://github.com/iluwatar/java-design-patterns/issues).
  - Usando etiquetas como `Performance`, `Gang of Four` ó `Data access`.
  - Usando categorías de patrones, `Creational`, `Behavioral` y otras.
 
-Esperamos que las soluciones orientadas a objetos presentadas en este sitio te resulten útiles en sus arquitecturas y se divierta aprendiéndolas tanto como nosotros desarrollándolas.
+Esperamos que las soluciones orientadas a objetos presentadas en este sitio le resulten útiles en sus arquitecturas y se divierta aprendiéndolas tanto como nosotros desarrollándolas.
 
-# Cómo contribuir
+# Como contribuir
 
 Si estás dispuesto a contribuir al proyecto encontrarás la información relevante en nuestra [wiki del desarrollador](https://github.com/iluwatar/java-design-patterns/wiki). Te ayudaremos y responderemos tus preguntas en la [sala de chat de Gitter](https://gitter.im/iluwatar/java-design-patterns).
 

monitor/README.md

@@ -1,71 +0,0 @@
----
-layout: pattern
-title: Monitor
-folder: monitor
-permalink: /patterns/monitor/
-categories: Concurrency
-language: en
-tags:
- - Performance
----
-
-## Intent
-Monitor pattern is used to create thread-safe objects and prevent conflicts between threads in concurrent applications.
-
-## Explanation
-
-In plain words
-
-> Monitor pattern is used to enforce single-threaded access to data. Only one thread at a time is allowed to execute code within the monitor object.
-
-Wikipedia says
-
-> In concurrent programming (also known as parallel programming), a monitor is a synchronization construct that allows threads to have both mutual exclusion and the ability to wait (block) for a certain condition to become false. Monitors also have a mechanism for signaling other threads that their condition has been met.
-
-**Programmatic Examples**
-
-Consider there is a bank that transfers money from an account to another account with transfer method . it is `synchronized` mean just one thread can access to this method because if many threads access to it and transfer money from an account to another account in same time balance changed !   
- 
-```
-class Bank {
-
-     private int[] accounts;
-     Logger logger;
- 
-     public Bank(int accountNum, int baseAmount, Logger logger) {
-         this.logger = logger;
-         accounts = new int[accountNum];
-         Arrays.fill(accounts, baseAmount);
-     }
- 
-     public synchronized void transfer(int accountA, int accountB, int amount) {
-         if (accounts[accountA] >= amount) {
-             accounts[accountB] += amount;
-             accounts[accountA] -= amount;
-             logger.info("Transferred from account :" + accountA + " to account :" + accountB + " , amount :" + amount + " . balance :" + getBalance());
-         }
-     }
-```
-
-getBalance always return total amount and the total amount should be same after each transfers 
-
-```
-     private synchronized int getBalance() {
-         int balance = 0;
-         for (int account : accounts) {
-             balance += account;
-         }
-         return balance;
-     }
- }
-```
-
-## Class diagram
-![alt text](./etc/monitor.urm.png "Monitor class diagram")
-
-## Applicability
-Use the Monitor pattern when
-
-* we have a shared resource and there is critical section .
-* you want to create thread-safe objects .
-* you want to achieve mutual exclusion in high level programming language .

monitor/etc/monitor.urm.puml

@@ -1,12 +0,0 @@
-@startuml
-Main - Bank : use
-class Main{
-    + main(args : String[]) : void
-}
-class Bank{
-    - accounts : int[]
-    + Bank (accountNum : int , baseAccount : int)
-    + transfer(accountA : int , accountB : int , amount : int) : void {synchronized}
-    - getBalance() : void {synchronized}
-}
-@enduml

monitor/pom.xml

@@ -1,59 +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">
-    <modelVersion>4.0.0</modelVersion>
-    <parent>
-        <artifactId>java-design-patterns</artifactId>
-        <groupId>com.iluwatar</groupId>
-        <version>1.24.0-SNAPSHOT</version>
-    </parent>
-    <artifactId>monitor</artifactId>
-    <dependencies>
-        <dependency>
-            <groupId>org.junit.jupiter</groupId>
-            <artifactId>junit-jupiter-engine</artifactId>
-            <scope>test</scope>
-        </dependency>
-    </dependencies>
-    <build>
-        <plugins>
-            <!-- Maven assembly plugin is invoked with default setting which we have
-                in parent pom and specifying the class having main method -->
-            <plugin>
-                <groupId>org.apache.maven.plugins</groupId>
-                <artifactId>maven-assembly-plugin</artifactId>
-                <executions>
-                    <execution>
-                        <configuration>
-                            <archive>
-                                <manifest>
-                                    <mainClass>com.iluwatar.abstractdocument.Main</mainClass>
-                                </manifest>
-                            </archive>
-                        </configuration>
-                    </execution>
-                </executions>
-            </plugin>
-        </plugins>
-    </build>
-</project>

monitor/src/main/java/com/iluwatar/monitor/Bank.java

@@ -1,37 +0,0 @@
-package com.iluwatar.monitor;
-
-import java.util.Arrays;
-import java.util.logging.Logger;
-
-// Bank class implements the Monitor pattern
-public class Bank {
-
-    private int[] accounts;
-    Logger logger;
-
-    public Bank(int accountNum, int baseAmount, Logger logger) {
-        this.logger = logger;
-        accounts = new int[accountNum];
-        Arrays.fill(accounts, baseAmount);
-    }
-
-    public synchronized void transfer(int accountA, int accountB, int amount) {
-        if (accounts[accountA] >= amount) {
-            accounts[accountB] += amount;
-            accounts[accountA] -= amount;
-            logger.info("Transferred from account :" + accountA + " to account :" + accountB + " , amount :" + amount + " . balance :" + getBalance());
-        }
-    }
-
-    public synchronized int getBalance() {
-        int balance = 0;
-        for (int account : accounts) {
-            balance += account;
-        }
-        return balance;
-    }
-
-    public int[] getAccounts() {
-        return accounts;
-    }
-}

monitor/src/main/java/com/iluwatar/monitor/Main.java

@@ -1,60 +0,0 @@
-/*
- * 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.
- */
-
-package com.iluwatar.monitor;
-
-import java.util.*;
-import java.util.concurrent.ExecutorService;
-import java.util.concurrent.Executors;
-import java.util.logging.Logger;
-
-/**
- * <p>The Monitor pattern is used in concurrent algorithms to achieve mutual exclusion.</p>
- *
- * <p>Bank is a simple class that transfers money from an account to another account using
- * {@link Bank#transfer}. It can also return the balance of the bank account stored in the bank.</p>
- *
- * <p>Main class uses ThreadPool to run threads that do transactions on the bank accounts.</p>
- */
-
-public class Main {
-
-    public static void main(String[] args) {
-        Logger logger = Logger.getLogger("monitor");
-        var bank = new Bank(4, 1000, logger);
-        Runnable runnable = () -> {
-            try {
-                Thread.sleep((long) (Math.random() * 1000));
-                Random random = new Random();
-                for (int i = 0; i < 1000000; i++)
-                    bank.transfer(random.nextInt(4), random.nextInt(4), (int) (Math.random() * 1000));
-            } catch (InterruptedException e) {
-                logger.info(e.getMessage());
-            }
-        };
-        ExecutorService executorService = Executors.newFixedThreadPool(5);
-        for (int i = 0; i < 5; i++) {
-            executorService.execute(runnable);
-        }
-    }
-}

monitor/src/main/test/java/com/iluwater/java/BankTest.java

@@ -1,55 +0,0 @@
-package com.iluwater.java;
-
-import com.iluwatar.monitor.Bank;
-import org.junit.jupiter.api.AfterAll;
-import org.junit.jupiter.api.BeforeAll;
-import org.junit.jupiter.api.Test;
-
-import static org.junit.jupiter.api.Assertions.*;
-import static org.junit.jupiter.api.Assumptions.*;
-
-import java.util.logging.Logger;
-
-public class BankTest {
-
-    private static Bank bank;
-    private static final int ACCOUNT_NUM = 4;
-    private static final int BASE_AMOUNT = 1000;
-    private static final Logger LOGGER = Logger.getLogger("monitor");
-
-    @BeforeAll
-    public static void Setup() {
-        bank = new Bank(ACCOUNT_NUM, BASE_AMOUNT, LOGGER);
-    }
-
-    @Test
-    public void GetAccountHaveNotBeNull() {
-        assertNotNull(bank.getAccounts());
-    }
-
-    @Test
-    public void LengthOfAccountsHaveToEqualsToAccountNumConstant() {
-        assumeTrue(bank.getAccounts() != null);
-        assertEquals(ACCOUNT_NUM, bank.getAccounts().length);
-    }
-
-    @Test
-    public void TransferMethodHaveToTransferAmountFromAnAccountToOtherAccount() {
-        bank.transfer(0, 1, 1000);
-        int accounts[] = bank.getAccounts();
-        assertEquals(0, accounts[0]);
-        assertEquals(2000, 2000);
-    }
-
-    @Test
-    public void BalanceHaveToBeOK() {
-        assertEquals(4000, bank.getBalance());
-    }
-
-
-    @AfterAll
-    public static void TearDown() {
-        bank = null;
-    }
-
-}