Layer Supertype Pattern #1302

Implemented the Layer Supertype Pattern in Service Layer, updated README file and PUML class diagram to reflect the new changes.

Author: MeryAmr

service-layer/README.md

@@ -36,6 +36,18 @@ Wikipedia says
 
 > Service layer is an architectural pattern, applied within the service-orientation design paradigm, which aims to organize the services, within a service inventory, into a set of logical layers. Services that are categorized into a particular layer share functionality. This helps to reduce the conceptual overhead related to managing the service inventory, as the services belonging to the same layer address a smaller set of activities.
 
+## Application of Layer Supertype Pattern in This Example
+
+The `Layer Supertype` pattern is used in this implementation to provide a common base class for all entities (`BaseEntity`) and DAOs (`DaoBaseImpl`). This pattern helps reduce redundancy by defining shared properties and methods in a superclass that all child classes can inherit.
+
+### Layer Supertype in the Entity Layer
+
+The `BaseEntity` class serves as the common base class for all entities, providing shared attributes like `id`. This ensures consistent handling of these attributes across different entity classes like `Wizard`, `Spellbook`, and `Spell`.
+
+### Layer Supertype in the DAO Layer
+
+In the DAO layer, the `DaoBaseImpl` class acts as a common base implementation for all DAO classes, offering shared functionalities such as session handling and basic CRUD operations. By inheriting from `DaoBaseImpl`, specific DAO implementations like `WizardDaoImpl` can focus solely on their unique logic, while reusing common functionality.
+
 ## Programmatic Example of Service Layer Pattern in Java
 
 Our Java implementation uses the Service Layer pattern to streamline interactions between data access objects (DAOs) and the business logic, ensuring a clean separation of concerns.
@@ -88,32 +100,13 @@ Above the entity layer we have DAOs. For `Wizard` the DAO layer looks as follows
 
 ```java
 public interface WizardDao extends Dao<Wizard> {
-
-    Wizard findByName(String name);
+    
 }
 ```
 
 ```java
 public class WizardDaoImpl extends DaoBaseImpl<Wizard> implements WizardDao {
-
-    @Override
-    public Wizard findByName(String name) {
-        Transaction tx = null;
-        Wizard result;
-        try (var session = getSessionFactory().openSession()) {
-            tx = session.beginTransaction();
-            var criteria = session.createCriteria(persistentClass);
-            criteria.add(Restrictions.eq("name", name));
-            result = (Wizard) criteria.uniqueResult();
-            tx.commit();
-        } catch (Exception e) {
-            if (tx != null) {
-                tx.rollback();
-            }
-            throw e;
-        }
-        return result;
-    }
+    
 }
 ```
 
@@ -379,13 +372,19 @@ Implementing a Service Layer in Java
 * Enhances testability by isolating business logic.
 * Improves maintainability and flexibility of enterprise applications.
 
+Using the Layer Supertype pattern in conjunction:
+
+* Reduces boilerplate code by centralizing common logic.
+* Increases consistency across layers, simplifying debugging and enhancement.
+
 Trade-offs:
 
 * May introduce additional complexity by adding another layer to the application.
 * Can result in performance overhead due to the extra layer of abstraction.
 
 ## Related Java Design Patterns
 
+* [Layer Supertype](https://martinfowler.com/eaaCatalog/layerSupertype.html): Helps reduce duplication in entities and DAOs by centralizing common logic.
 * [Facade](https://java-design-patterns.com/patterns/facade/): Simplifies interactions with complex subsystems by providing a unified interface.
 * [DAO (Data Access Object)](https://java-design-patterns.com/patterns/dao/): Often used together with the Service Layer to handle data persistence.
 * [MVC (Model-View-Controller)](https://java-design-patterns.com/patterns/model-view-controller/): The Service Layer can be used to encapsulate business logic in the model component.
@@ -396,3 +395,4 @@ Trade-offs:
 * [Patterns of Enterprise Application Architecture](https://amzn.to/3WfKBPR)
 * [Spring in Action](https://amzn.to/4asnpSG)
 * [Service Layer (Martin Fowler)](http://martinfowler.com/eaaCatalog/serviceLayer.html)
+* [Layer Supertype (Martin Fowler)](https://martinfowler.com/eaaCatalog/layerSupertype.html)

service-layer/etc/service-layer.urm.puml

@@ -22,13 +22,15 @@ package com.iluwatar.servicelayer.common {
     + findAll() : List<E extends BaseEntity> {abstract}
     + merge(E extends BaseEntity) : E extends BaseEntity {abstract}
     + persist(E extends BaseEntity) {abstract}
+    + findByName(String) : E extends BaseEntity {abstract}
   }
   abstract class DaoBaseImpl<E extends BaseEntity> {
     # persistentClass : Class<E extends BaseEntity>
     + DaoBaseImpl<E extends BaseEntity>()
     + delete(entity : E extends BaseEntity)
     + find(id : Long) : E extends BaseEntity
     + findAll() : List<E extends BaseEntity>
+    + findByName(name : String) : E extends BaseEntity
     # getSessionFactory() : SessionFactory
     + merge(entity : E extends BaseEntity) : E extends BaseEntity
     + persist(entity : E extends BaseEntity)
@@ -71,11 +73,9 @@ package com.iluwatar.servicelayer.wizard {
     + toString() : String
   }
   interface WizardDao {
-    + findByName(String) : Wizard {abstract}
   }
   class WizardDaoImpl {
     + WizardDaoImpl()
-    + findByName(name : String) : Wizard
   }
 }
 package com.iluwatar.servicelayer.spellbook {
@@ -98,11 +98,9 @@ package com.iluwatar.servicelayer.spellbook {
     + toString() : String
   }
   interface SpellbookDao {
-    + findByName(String) : Spellbook {abstract}
   }
   class SpellbookDaoImpl {
     + SpellbookDaoImpl()
-    + findByName(name : String) : Spellbook
   }
 }
 package com.iluwatar.servicelayer.spell {
@@ -121,11 +119,9 @@ package com.iluwatar.servicelayer.spell {
     + toString() : String
   }
   interface SpellDao {
-    + findByName(String) : Spell {abstract}
   }
   class SpellDaoImpl {
     + SpellDaoImpl()
-    + findByName(name : String) : Spell
   }
 }
 package com.iluwatar.servicelayer.app {
@@ -142,18 +138,18 @@ MagicServiceImpl -->  "-spellbookDao" SpellbookDao
 MagicServiceImpl -->  "-spellDao" SpellDao
 Spellbook -->  "-spells" Spell
 Spellbook -->  "-wizards" Wizard
-DaoBaseImpl ..|> Dao 
-MagicServiceImpl ..|> MagicService 
-Spell --|> BaseEntity 
-SpellDao --|> Dao 
-SpellDaoImpl ..|> SpellDao 
-SpellDaoImpl --|> DaoBaseImpl 
-Spellbook --|> BaseEntity 
-SpellbookDao --|> Dao 
-SpellbookDaoImpl ..|> SpellbookDao 
-SpellbookDaoImpl --|> DaoBaseImpl 
-Wizard --|> BaseEntity 
-WizardDao --|> Dao 
-WizardDaoImpl ..|> WizardDao 
-WizardDaoImpl --|> DaoBaseImpl 
-@enduml
+DaoBaseImpl ..|> Dao
+MagicServiceImpl ..|> MagicService
+Spell --|> BaseEntity
+SpellDao --|> Dao
+SpellDaoImpl ..|> SpellDao
+SpellDaoImpl --|> DaoBaseImpl
+Spellbook --|> BaseEntity
+SpellbookDao --|> Dao
+SpellbookDaoImpl ..|> SpellbookDao
+SpellbookDaoImpl --|> DaoBaseImpl
+Wizard --|> BaseEntity
+WizardDao --|> Dao
+WizardDaoImpl ..|> WizardDao
+WizardDaoImpl --|> DaoBaseImpl
+@enduml

service-layer/src/main/java/com/iluwatar/servicelayer/common/Dao.java

@@ -42,4 +42,6 @@ public interface Dao<E extends BaseEntity> {
   void delete(E entity);
 
   List<E> findAll();
+
+  E findByName(String name);
 }

service-layer/src/main/java/com/iluwatar/servicelayer/common/DaoBaseImpl.java

@@ -74,6 +74,27 @@ public E find(Long id) {
     }
     return result;
   }
+  @Override
+  public E findByName(String name) {
+    Transaction tx = null;
+    E result;
+    try (var session = getSessionFactory().openSession()) {
+      tx = session.beginTransaction();
+      CriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();
+      CriteriaQuery<E> builderQuery = criteriaBuilder.createQuery(persistentClass);
+      Root<E> root = builderQuery.from(persistentClass);
+      builderQuery.select(root).where(criteriaBuilder.equal(root.get("name"), name));
+      Query<E> query = session.createQuery(builderQuery);
+      result = query.uniqueResult();
+      tx.commit();
+    } catch (Exception e) {
+      if (tx != null) {
+        tx.rollback();
+      }
+      throw e;
+    }
+    return result;
+  }
 
   @Override
   public void persist(E entity) {

service-layer/src/main/java/com/iluwatar/servicelayer/spell/SpellDao.java

@@ -31,6 +31,5 @@
  */
 public interface SpellDao extends Dao<Spell> {
 
-  Spell findByName(String name);
 
 }

service-layer/src/main/java/com/iluwatar/servicelayer/spell/SpellDaoImpl.java

@@ -37,25 +37,4 @@
  */
 public class SpellDaoImpl extends DaoBaseImpl<Spell> implements SpellDao {
 
-  @Override
-  public Spell findByName(String name) {
-    Transaction tx = null;
-    Spell result;
-    try (var session = getSessionFactory().openSession()) {
-      tx = session.beginTransaction();
-      CriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();
-      CriteriaQuery<Spell> builderQuery = criteriaBuilder.createQuery(Spell.class);
-      Root<Spell> root = builderQuery.from(Spell.class);
-      builderQuery.select(root).where(criteriaBuilder.equal(root.get("name"), name));
-      Query<Spell> query = session.createQuery(builderQuery);
-      result = query.uniqueResult();
-      tx.commit();
-    } catch (Exception e) {
-      if (tx != null) {
-        tx.rollback();
-      }
-      throw e;
-    }
-    return result;
-  }
 }

service-layer/src/main/java/com/iluwatar/servicelayer/spellbook/SpellbookDao.java

@@ -31,6 +31,4 @@
  */
 public interface SpellbookDao extends Dao<Spellbook> {
 
-  Spellbook findByName(String name);
-
 }

service-layer/src/main/java/com/iluwatar/servicelayer/spellbook/SpellbookDaoImpl.java

@@ -37,26 +37,4 @@
  */
 public class SpellbookDaoImpl extends DaoBaseImpl<Spellbook> implements SpellbookDao {
 
-  @Override
-  public Spellbook findByName(String name) {
-    Transaction tx = null;
-    Spellbook result;
-    try (var session = getSessionFactory().openSession()) {
-      tx = session.beginTransaction();
-      CriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();
-      CriteriaQuery<Spellbook> builderQuery = criteriaBuilder.createQuery(Spellbook.class);
-      Root<Spellbook> root = builderQuery.from(Spellbook.class);
-      builderQuery.select(root).where(criteriaBuilder.equal(root.get("name"), name));
-      Query<Spellbook> query = session.createQuery(builderQuery);
-      result = query.uniqueResult();
-      tx.commit();
-    } catch (Exception e) {
-      if (tx != null) {
-        tx.rollback();
-      }
-      throw e;
-    }
-    return result;
-  }
-
 }

service-layer/src/main/java/com/iluwatar/servicelayer/wizard/WizardDao.java

@@ -31,6 +31,4 @@
  */
 public interface WizardDao extends Dao<Wizard> {
 
-  Wizard findByName(String name);
-
 }

service-layer/src/main/java/com/iluwatar/servicelayer/wizard/WizardDaoImpl.java

@@ -35,26 +35,4 @@
  * WizardDao implementation.
  */
 public class WizardDaoImpl extends DaoBaseImpl<Wizard> implements WizardDao {
-
-  @Override
-  public Wizard findByName(String name) {
-    Transaction tx = null;
-    Wizard result;
-    try (var session = getSessionFactory().openSession()) {
-      tx = session.beginTransaction();
-      CriteriaBuilder criteriaBuilder = session.getCriteriaBuilder();
-      CriteriaQuery<Wizard> builderQuery = criteriaBuilder.createQuery(Wizard.class);
-      Root<Wizard> root = builderQuery.from(Wizard.class);
-      builderQuery.select(root).where(criteriaBuilder.equal(root.get("name"), name));
-      Query<Wizard> query = session.createQuery(builderQuery);
-      result = query.uniqueResult();
-      tx.commit();
-    } catch (Exception e) {
-      if (tx != null) {
-        tx.rollback();
-      }
-      throw e;
-    }
-    return result;
-  }
 }