feature: #1299 Add Identity Map Pattern (#2094)

* #1299 IMPLEMENT IDENTITY MAP PATTERN. * #1299 Add docstrings, README, testCases and class diagram. * #1299 Update a comment string in DB implementation. * #1299 Fix code smells. * #1299 Fix code smells and add comments to App.java * #1299 Update constant name. * #1299 Remove java version dependency and update README.md. * #1299 Add lombok to PersonFinder.java. * #1299 Add dependency to maven-assembly-plugin. * #1299 Use java streams in PersonDbSimulatorImplementation.java. * #1299 Add print statements while returning the person object. * #1299 Update README.md. * #1299 Add puml file. * Update README.md
2026-05-16 20:59:07 +00:00 · 2022-11-10 06:55:44 +11:00
parent 3831a82b69
commit d2599a2904
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+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 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.identitymap;
+
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * The basic idea behind the Identity Map is to have a series of maps containing objects that have been pulled from the database.
+ * The below example demonstrates the identity map pattern by creating a sample DB.
+ * Since only 1 DB has been created we only have 1 map corresponding to it for the purpose of this demo.
+ * When you load an object from the database, you first check the map.
+ * If there’s an object in it that corresponds to the one you’re loading, you return it. If not, you go to the database,
+ * putting the objects on the map for future reference as you load them.
+ */
+@Slf4j
+public class App {
+  /**
+   * Program entry point.
+   *
+   * @param args command line args.
+   */
+  public static void main(String[] args) {
+
+    // Dummy Persons
+    Person person1 = new Person(1, "John", 27304159);
+    Person person2 = new Person(2, "Thomas", 42273631);
+    Person person3 = new Person(3, "Arthur", 27489171);
+    Person person4 = new Person(4, "Finn", 20499078);
+    Person person5 = new Person(5, "Michael", 40599078);
+
+    // Init database
+    PersonDbSimulatorImplementation db = new PersonDbSimulatorImplementation();
+    db.insert(person1);
+    db.insert(person2);
+    db.insert(person3);
+    db.insert(person4);
+    db.insert(person5);
+
+    // Init a personFinder
+    PersonFinder finder = new PersonFinder();
+    finder.setDb(db);
+
+    // Find persons in DataBase not the map.
+    LOGGER.info(finder.getPerson(2).toString());
+    LOGGER.info(finder.getPerson(4).toString());
+    LOGGER.info(finder.getPerson(5).toString());
+    // Find the person in the map.
+    LOGGER.info(finder.getPerson(2).toString());
+
+  }
+}
@@ -0,0 +1,31 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 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.identitymap;
+
+public class IdNotFoundException extends RuntimeException {
+  public IdNotFoundException(final String message) {
+    super(message);
+  }
+}
@@ -0,0 +1,77 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 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.identitymap;
+
+import java.util.HashMap;
+import java.util.Map;
+
+import lombok.Getter;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * This class stores the map into which we will be caching records after loading them from a DataBase.
+ * Stores the records as a Hash Map with the personNationalIDs as keys.
+ */
+@Slf4j
+@Getter
+public class IdentityMap {
+  private Map<Integer, Person> personMap = new HashMap<>();
+  /**
+   * Add person to the map.
+   */
+  public void addPerson(Person person) {
+    if (!personMap.containsKey(person.getPersonNationalId())) {
+      personMap.put(person.getPersonNationalId(), person);
+    } else { // Ensure that addPerson does not update a record. This situation will never arise in our implementation. Added only for testing purposes.
+      LOGGER.info("Key already in Map");
+    }
+  }
+
+  /**
+   * Get Person with given id.
+   *
+   * @param id : personNationalId as requested by user.
+   */
+  public Person getPerson(int id) {
+    Person person = personMap.get(id);
+    if (person == null) {
+      LOGGER.info("ID not in Map.");
+      return null;
+    }
+    LOGGER.info(person.toString());
+    return person;
+  }
+
+  /**
+   * Get the size of the map.
+   */
+  public int size() {
+    if (personMap == null) {
+      return 0;
+    }
+    return personMap.size();
+  }
+
+}
@@ -0,0 +1,57 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 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.identitymap;
+
+import java.io.Serializable;
+
+import lombok.AllArgsConstructor;
+import lombok.EqualsAndHashCode;
+import lombok.Getter;
+import lombok.Setter;
+
+/**
+ * Person definition.
+ */
+@EqualsAndHashCode(onlyExplicitlyIncluded = true)
+@Getter
+@Setter
+@AllArgsConstructor
+public final class Person implements Serializable {
+
+  private static final long serialVersionUID = 1L;
+
+  @EqualsAndHashCode.Include
+  private int personNationalId;
+  private String name;
+  private long phoneNum;
+
+  @Override
+  public String toString() {
+
+    return "Person ID is : " + personNationalId + " ; Person Name is : " + name + " ; Phone Number is :" + phoneNum;
+
+  }
+
+}
@@ -0,0 +1,36 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 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.identitymap;
+
+public interface PersonDbSimulator {
+  Person find(int personNationalID);
+
+  void insert(Person person);
+
+  void update(Person person);
+
+  void delete(int personNationalID);
+
+}
@@ -0,0 +1,108 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 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.identitymap;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Optional;
+
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * This is a sample database implementation. The database is in the form of an arraylist which stores records of
+ * different persons. The personNationalId acts as the primary key for a record.
+ * Operations :
+ * -> find (look for object with a particular ID)
+ * -> insert (insert record for a new person into the database)
+ * -> update (update the record of a person). To do this, create a new person instance with the same ID as the record you
+ * want to update. Then call this method with that person as an argument.
+ * -> delete (delete the record for a particular ID)
+ */
+@Slf4j
+public class PersonDbSimulatorImplementation implements PersonDbSimulator {
+
+  //This simulates a table in the database. To extend logic to multiple tables just add more lists to the implementation.
+  private List<Person> personList = new ArrayList<>();
+  static final String NOT_IN_DATA_BASE = " not in DataBase";
+  static final String ID_STR = "ID : ";
+
+  @Override
+  public Person find(int personNationalID) throws IdNotFoundException {
+    Optional<Person> elem = personList.stream().filter(p -> p.getPersonNationalId() == personNationalID).findFirst();
+    if (elem.isEmpty()) {
+      throw new IdNotFoundException(ID_STR + personNationalID + NOT_IN_DATA_BASE);
+    }
+    LOGGER.info(elem.get().toString());
+    return elem.get();
+  }
+
+  @Override
+  public void insert(Person person) {
+    Optional<Person> elem = personList.stream().filter(p -> p.getPersonNationalId() == person.getPersonNationalId()).findFirst();
+    if (elem.isPresent()) {
+      LOGGER.info("Record already exists.");
+      return;
+    }
+    personList.add(person);
+  }
+
+  @Override
+  public void update(Person person) throws IdNotFoundException {
+    Optional<Person> elem = personList.stream().filter(p -> p.getPersonNationalId() == person.getPersonNationalId()).findFirst();
+    if (elem.isPresent()) {
+      elem.get().setName(person.getName());
+      elem.get().setPhoneNum(person.getPhoneNum());
+      LOGGER.info("Record updated successfully");
+      return;
+    }
+    throw new IdNotFoundException(ID_STR + person.getPersonNationalId() + NOT_IN_DATA_BASE);
+  }
+
+  /**
+   * Delete the record corresponding to given ID from the DB.
+   *
+   * @param id : personNationalId for person whose record is to be deleted.
+   */
+  public void delete(int id) throws IdNotFoundException {
+    Optional<Person> elem = personList.stream().filter(p -> p.getPersonNationalId() == id).findFirst();
+    if (elem.isPresent()) {
+      personList.remove(elem.get());
+      LOGGER.info("Record deleted successfully.");
+      return;
+    }
+    throw new IdNotFoundException(ID_STR + id + NOT_IN_DATA_BASE);
+  }
+
+  /**
+   * Return the size of the database.
+   */
+  public int size() {
+    if (personList == null) {
+      return 0;
+    }
+    return personList.size();
+  }
+
+}
@@ -0,0 +1,69 @@
+/*
+ * This project is licensed under the MIT license. Module model-view-viewmodel is using ZK framework licensed under LGPL (see lgpl-3.0.txt).
+ *
+ * The MIT License
+ * Copyright © 2014-2022 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.identitymap;
+
+import lombok.Getter;
+import lombok.Setter;
+import lombok.extern.slf4j.Slf4j;
+
+/**
+ * Any object of this class stores a DataBase and an Identity Map. When we try to look for a key we first check if
+ * it has been cached in the Identity Map and return it if it is indeed in the map.
+ * If that is not the case then go to the DataBase, get the record, store it in the
+ * Identity Map and then return the record. Now if we look for the record again we will find it in the table itself which
+ * will make lookup faster.
+ */
+@Slf4j
+@Getter
+@Setter
+public class PersonFinder {
+  private static final long serialVersionUID = 1L;
+  //  Access to the Identity Map
+  private IdentityMap identityMap = new IdentityMap();
+  private PersonDbSimulatorImplementation db = new PersonDbSimulatorImplementation();
+  /**
+   * get person corresponding to input ID.
+   *
+   * @param key : personNationalId to look for.
+   */
+  public Person getPerson(int key) {
+    // Try to find person in the identity map
+    Person person = this.identityMap.getPerson(key);
+    if (person != null) {
+      LOGGER.info("Person found in the Map");
+      return person;
+    } else {
+      // Try to find person in the database
+      person = this.db.find(key);
+      if (person != null) {
+        this.identityMap.addPerson(person);
+        LOGGER.info("Person found in DB.");
+        return person;
+      }
+      LOGGER.info("Person with this ID does not exist.");
+      return null;
+    }
+  }
+}