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#84 Documented the Layers example
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‎layers/src/main/java/com/iluwatar/layers/App.java‎

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import java.util.Arrays;
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/**
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*
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* <p>
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* Multilayered architecture is an architectural style where software responsibilities are
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* divided among the different layers of the application.
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* </p>
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*
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* <p>
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* This example demonstrates a traditional 3-layer architecture consisting of data access
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* layer, business layer and presentation layer.
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* </p>
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*
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* <p>
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* The data access layer is formed of Spring Data repositories <code>CakeDao</code>, <code>CakeToppingDao</code> and
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* <code>CakeLayerDao</code>. The repositories can be used for CRUD operations on cakes, cake toppings
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* and cake layers respectively.
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* </p>
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*
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* <p>
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* The business layer is built on top of the data access layer. <code>CakeBakingService</code> offers
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* methods to retrieve available cake toppings and cake layers and baked cakes. Also the
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* service is used to create new cakes out of cake toppings and cake layers.
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* </p>
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*
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* <p>
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* The presentation layer is built on the business layer and in this example it simply lists
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* the cakes that have been baked.
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* </p>
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*
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* <p>
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* We have applied so called strict layering which means that the layers can only access
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* the classes directly beneath them. This leads the solution to create an additional set of
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* DTOs (<code>CakeInfo</code>, <code>CakeToppingInfo</code>, <code>CakeLayerInfo</code>)
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* to translate data between layers. In other words, <code>CakeBakingService</code> cannot
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* return entities (<code>Cake</code>, <code>CakeTopping</code>, <code>CakeLayer</code>)
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* directly since these reside on data access layer but instead translates these into business
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* layer DTOs (<code>CakeInfo</code>, <code>CakeToppingInfo</code>, <code>CakeLayerInfo</code>)
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* and returns them instead. This way the presentation layer does not have any knowledge of
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* other layers than the business layer and thus is not affected by changes to them.
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* </p>
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*
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* @see Cake
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* @see CakeTopping
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* @see CakeLayer
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* @see CakeDao
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* @see CakeToppingDao
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* @see CakeLayerDao
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* @see CakeBakingService
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* @see CakeInfo
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* @see CakeToppingInfo
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* @see CakeLayerInfo
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*
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*/
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public class App {
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private static CakeBakingService cakeBakingService = new CakeBakingServiceImpl();
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/**
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* Application entry point
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* @param args Command line parameters
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*/
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public static void main(String[] args) {
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// initialize example data
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cakeView.render();
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}
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/**
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* Initializes the example data
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* @param cakeBakingService
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*/
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private static void initializeData(CakeBakingService cakeBakingService) {
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cakeBakingService.saveNewLayer(new CakeLayerInfo("chocolate", 1200));
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cakeBakingService.saveNewLayer(new CakeLayerInfo("banana", 900));

‎layers/src/main/java/com/iluwatar/layers/Cake.java‎

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import javax.persistence.OneToMany;
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import javax.persistence.OneToOne;
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/**
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*
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* Cake entity
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*
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*/
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@Entity
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public class Cake {
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‎layers/src/main/java/com/iluwatar/layers/CakeBakingException.java‎

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package com.iluwatar.layers;
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/**
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*
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* Custom exception used in cake baking
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*
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*/
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public class CakeBakingException extends Exception {
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private static final long serialVersionUID = 1L;
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public CakeBakingException() {
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}
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‎layers/src/main/java/com/iluwatar/layers/CakeBakingService.java‎

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import java.util.List;
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/**
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*
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* Service for cake baking operations
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*
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*/
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public interface CakeBakingService {
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/**
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* Bakes new cake according to parameters
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* @param cakeInfo
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* @throws CakeBakingException
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*/
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void bakeNewCake(CakeInfo cakeInfo) throws CakeBakingException;
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/**
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* Get all cakes
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* @return
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*/
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List<CakeInfo> getAllCakes();
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/**
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* Store new cake topping
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* @param toppingInfo
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*/
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void saveNewTopping(CakeToppingInfo toppingInfo);
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/**
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* Get available cake toppings
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* @return
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*/
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List<CakeToppingInfo> getAvailableToppings();
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/**
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* Add new cake layer
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* @param layerInfo
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*/
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void saveNewLayer(CakeLayerInfo layerInfo);
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/**
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* Get available cake layers
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* @return
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*/
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List<CakeLayerInfo> getAvailableLayers();
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}

‎layers/src/main/java/com/iluwatar/layers/CakeBakingServiceImpl.java‎

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import org.springframework.stereotype.Service;
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import org.springframework.transaction.annotation.Transactional;
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/**
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*
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* Implementation of CakeBakingService
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*
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*/
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@Service
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@Transactional
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public class CakeBakingServiceImpl implements CakeBakingService {

‎layers/src/main/java/com/iluwatar/layers/CakeDao.java‎

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import org.springframework.data.repository.CrudRepository;
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import org.springframework.stereotype.Repository;
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/**
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*
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* CRUD repository for cakes
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*
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*/
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@Repository
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public interface CakeDao extends CrudRepository<Cake, Long> {
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‎layers/src/main/java/com/iluwatar/layers/CakeInfo.java‎

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import java.util.List;
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import java.util.Optional;
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/**
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*
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* DTO for cakes
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*
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*/
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public class CakeInfo {
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public final Optional<Long> id;

‎layers/src/main/java/com/iluwatar/layers/CakeLayer.java‎

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import javax.persistence.Id;
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import javax.persistence.ManyToOne;
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/**
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*
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* CakeLayer entity
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*
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*/
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@Entity
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public class CakeLayer {
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‎layers/src/main/java/com/iluwatar/layers/CakeLayerDao.java‎

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import org.springframework.data.repository.CrudRepository;
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import org.springframework.stereotype.Repository;
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/**
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*
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* CRUD repository for cake layers
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*
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*/
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@Repository
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public interface CakeLayerDao extends CrudRepository<CakeLayer, Long> {
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‎layers/src/main/java/com/iluwatar/layers/CakeLayerInfo.java‎

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import java.util.Optional;
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/**
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*
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* DTO for cake layers
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*
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*/
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public class CakeLayerInfo {
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public final Optional<Long> id;

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