#1569 DTO pattern implementation using Enums (#1570)

* #1569 DTO pattern implemented using Enums

* #1569 DTO pattern implemented using Enums

* #1569 adding some java docs

* #1569 some changes in java doc and code style

* #1569 some changes in java doc and code style

* #1569 some changes in java doc and code style

* #1569 some changes in java doc and code style

* #1569 adding suggested extra line

* #1569 license added to pom.xml

* #1569 more checkstyle problems resolved

* #1569 more checkstyle problems resolved

* #1569 more checkstyle problems resolved
Co-authored-by: Nsiavashsoleymani <siavash.soleimani@snapp.cab>
Co-authored-by: NSubhrodip Mohanta <subhrodipmohanta@gmail.com>

data-transfer-object-enum-impl/README.md

+---
+layout: pattern
+title: Data Transfer Object
+folder: data-transfer-object
+permalink: /patterns/data-transfer-object/
+categories: Architectural
+tags:
+ - Performance
+---
+
+## Intent
+
+Pass data with multiple attributes in one shot from client to server, to avoid multiple calls to 
+remote server. 
+
+## Explanation
+
+Real world example
+
+> We need to fetch information about customers from remote database. Instead of querying the 
+> attributes one at a time, we use DTOs to transfer all the relevant attributes in a single shot.     
+
+In plain words
+
+> Using DTO relevant information can be fetched with a single backend query. 
+
+Wikipedia says
+
+> In the field of programming a data transfer object (DTO) is an object that carries data between 
+> processes. The motivation for its use is that communication between processes is usually done 
+> resorting to remote interfaces (e.g. web services), where each call is an expensive operation. 
+> Because the majority of the cost of each call is related to the round-trip time between the client 
+> and the server, one way of reducing the number of calls is to use an object (the DTO) that 
+> aggregates the data that would have been transferred by the several calls, but that is served by 
+> one call only.
+
+## Class diagram
+
+![alt text](./etc/dto-enum-uml.png "data-transfer-object")
+
+## Applicability
+
+Use the Data Transfer Object pattern when:
+
+* The client is asking for multiple information. And the information is related.
+* When you want to boost the performance to get resources.
+* You want reduced number of remote calls.
+
+## Credits
+
+* [Design Pattern - Transfer Object Pattern](https://www.tutorialspoint.com/design_pattern/transfer_object_pattern.htm)
+* [Data Transfer Object](https://msdn.microsoft.com/en-us/library/ff649585.aspx)
+* [J2EE Design Patterns](https://www.amazon.com/gp/product/0596004273/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0596004273&linkCode=as2&tag=javadesignpat-20&linkId=f27d2644fbe5026ea448791a8ad09c94)
+* [Patterns of Enterprise Application Architecture](https://www.amazon.com/gp/product/0321127420/ref=as_li_tl?ie=UTF8&camp=1789&creative=9325&creativeASIN=0321127420&linkCode=as2&tag=javadesignpat-20&linkId=014237a67c9d46f384b35e10151956bd)

data-transfer-object-enum-impl/etc/data-transfer-object-enum-impl.urm.puml

+@startuml
+package com.iluwatar.datatransferenum {
+  class App {
+    - LOGGER : Logger {static}
+    + App()
+    + main(args : String[]) {static}
+  }
+  class Product {
+    - cost : Double
+    - id : Long
+    - name : String
+    - price : Double
+    - supplier : String
+    + Product()
+    + getCost() : Double
+    + getId() : Long
+    + getName() : String
+    + getPrice() : Double
+    + getSupplier() : String
+    + setCost(cost : Double) : Product
+    + setId(id : Long) : Product
+    + setName(name : String) : Product
+    + setPrice(price : Double) : Product
+    + setSupplier(supplier : String) : Product
+    + toString() : String
+  }
+  enum ProductDTO {
+    + valueOf(name : String) : ProductDTO {static}
+    + values() : ProductDTO[] {static}
+  }
+  -interface Cost {
+    + getCost() : Double {abstract}
+  }
+  -interface Id {
+    + getId() : Long {abstract}
+  }
+  -interface Name {
+    + getName() : String {abstract}
+  }
+  -interface Price {
+    + getPrice() : Double {abstract}
+  }
+  enum Request {
+    + valueOf(name : String) : Request {static}
+    + values() : Request[] {static}
+  }
+  class Create {
+    - cost : Double
+    - name : String
+    - price : Double
+    - supplier : String
+    + Create()
+    + getCost() : Double
+    + getName() : String
+    + getPrice() : Double
+    + getSupplier() : String
+    + setCost(cost : Double) : Create
+    + setName(name : String) : Create
+    + setPrice(price : Double) : Create
+    + setSupplier(supplier : String) : Create
+  }
+  enum Response {
+    + valueOf(name : String) : Response {static}
+    + values() : Response[] {static}
+  }
+  class Private {
+    - cost : Double
+    - id : Long
+    - name : String
+    - price : Double
+    + Private()
+    + getCost() : Double
+    + getId() : Long
+    + getName() : String
+    + getPrice() : Double
+    + setCost(cost : Double) : Private
+    + setId(id : Long) : Private
+    + setName(name : String) : Private
+    + setPrice(price : Double) : Private
+    + toString() : String
+  }
+  class Public {
+    - id : Long
+    - name : String
+    - price : Double
+    + Public()
+    + getId() : Long
+    + getName() : String
+    + getPrice() : Double
+    + setId(id : Long) : Public
+    + setName(name : String) : Public
+    + setPrice(price : Double) : Public
+    + toString() : String
+  }
+  -interface Supplier {
+    + getSupplier() : String {abstract}
+  }
+  class ProductResource {
+    - products : List<Product>
+    + ProductResource(products : List<Product>)
+    + getAllProductsForAdmin() : List<Private>
+    + getAllProductsForCustomer() : List<Public>
+    + getProducts() : List<Product>
+    + save(createProductDTO : Create)
+  }
+}
+Create ..+ Request
+Request ..+ ProductDTO
+Private ..+ Response
+Supplier ..+ ProductDTO
+Name ..+ ProductDTO
+ProductResource -->  "-products" Product
+Public ..+ Response
+Id ..+ ProductDTO
+Price ..+ ProductDTO
+Response ..+ ProductDTO
+Cost ..+ ProductDTO
+Create ..|> Name 
+Create ..|> Price 
+Create ..|> Cost 
+Create ..|> Supplier 
+Private ..|> Id 
+Private ..|> Name 
+Private ..|> Price 
+Private ..|> Cost 
+Public ..|> Id 
+Public ..|> Name 
+Public ..|> Price 
+@enduml

data-transfer-object-enum-impl/pom.xml

+<?xml version="1.0" encoding="UTF-8"?>
+<!--
+
+    The MIT License
+    Copyright © 2014-2019 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: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" xmlns="http://maven.apache.org/POM/4.0.0">
+    <modelVersion>4.0.0</modelVersion>
+    <parent>
+        <groupId>com.iluwatar</groupId>
+        <artifactId>java-design-patterns</artifactId>
+        <version>1.24.0-SNAPSHOT</version>
+    </parent>
+    <artifactId>data-transfer-object-enum-impl</artifactId>
+    <dependencies>
+        <dependency>
+            <groupId>org.junit.jupiter</groupId>
+            <artifactId>junit-jupiter-engine</artifactId>
+            <scope>test</scope>
+        </dependency>
+    </dependencies>
+    <build>
+        <plugins>
+            <plugin>
+                <groupId>org.apache.maven.plugins</groupId>
+                <artifactId>maven-assembly-plugin</artifactId>
+                <executions>
+                    <execution>
+                        <configuration>
+                            <archive>
+                                <manifest>
+                                    <mainClass>com.iluwatar.datatransferenum.App</mainClass>
+                                </manifest>
+                            </archive>
+                        </configuration>
+                    </execution>
+                </executions>
+            </plugin>
+        </plugins>
+    </build>
+</project>

data-transfer-object-enum-impl/src/main/java/com/iluwatar/datatransferenum/App.java

+package com.iluwatar.datatransferenum;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.List;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * The Data Transfer Object pattern is a design pattern in which an data transfer object is used to
+ * serve related information together to avoid multiple call for each piece of information.
+ *
+ * <p>In this example, ({@link App}) as as product details consumer i.e. client to
+ * request for product details to server.
+ *
+ * <p>productResource ({@link ProductResource}) act as server to serve product information. And
+ * The productDto ({@link ProductDto} is data transfer object to share product information.
+ */
+public class App {
+
+  private static final Logger LOGGER = LoggerFactory.getLogger(App.class);
+
+  /**
+   * Method as act client and request to server for details.
+   *
+   * @param args program argument.
+   */
+  public static void main(String[] args) {
+    Product tv =
+        new Product().setId(1L).setName("TV").setSupplier("Sony").setPrice(1000D).setCost(1090D);
+    Product microwave =
+        new Product().setId(2L).setName("microwave").setSupplier("Delonghi").setPrice(1000D)
+            .setCost(1090D);
+    Product refrigerator =
+        new Product().setId(3L).setName("refrigerator").setSupplier("Botsch").setPrice(1000D)
+            .setCost(1090D);
+    Product airConditioner =
+        new Product().setId(4L).setName("airConditioner").setSupplier("LG").setPrice(1000D)
+            .setCost(1090D);
+    List<Product> products =
+        new ArrayList<>(Arrays.asList(tv, microwave, refrigerator, airConditioner));
+    ProductResource productResource = new ProductResource(products);
+
+    LOGGER.info("####### List of products including sensitive data just for admins: \n {}",
+        Arrays.toString(productResource.getAllProductsForAdmin().toArray()));
+    LOGGER.info("####### List of products for customers: \n {}",
+        Arrays.toString(productResource.getAllProductsForCustomer().toArray()));
+
+    LOGGER.info("####### Going to save Sony PS5 ...");
+    ProductDto.Request.Create createProductRequestDto = new ProductDto.Request.Create()
+        .setName("PS5")
+        .setCost(1000D)
+        .setPrice(1220D)
+        .setSupplier("Sony");
+    productResource.save(createProductRequestDto);
+    LOGGER.info("####### List of products after adding PS5: {}",
+        Arrays.toString(productResource.getProducts().toArray()));
+  }
+}

data-transfer-object-enum-impl/src/main/java/com/iluwatar/datatransferenum/Product.java

+package com.iluwatar.datatransferenum;
+
+/**
+ * {@link Product} is a entity class for product entity. This class act as entity in the demo.
+ */
+public final class Product {
+  private Long id;
+  private String name;
+  private Double price;
+  private Double cost;
+  private String supplier;
+
+  /**
+   * Constructor.
+   *
+   * @param id       product id
+   * @param name     product name
+   * @param price    product price
+   * @param cost     product cost
+   * @param supplier product supplier
+   */
+  public Product(Long id, String name, Double price, Double cost, String supplier) {
+    this.id = id;
+    this.name = name;
+    this.price = price;
+    this.cost = cost;
+    this.supplier = supplier;
+  }
+
+  /**
+   * Constructor.
+   */
+  public Product() {
+  }
+
+  public Long getId() {
+    return id;
+  }
+
+  public Product setId(Long id) {
+    this.id = id;
+    return this;
+  }
+
+  public String getName() {
+    return name;
+  }
+
+  public Product setName(String name) {
+    this.name = name;
+    return this;
+  }
+
+  public Double getPrice() {
+    return price;
+  }
+
+  public Product setPrice(Double price) {
+    this.price = price;
+    return this;
+  }
+
+  public Double getCost() {
+    return cost;
+  }
+
+  public Product setCost(Double cost) {
+    this.cost = cost;
+    return this;
+  }
+
+  public String getSupplier() {
+    return supplier;
+  }
+
+  public Product setSupplier(String supplier) {
+    this.supplier = supplier;
+    return this;
+  }
+
+  @Override
+  public String toString() {
+    return "Product{"
+        + "id=" + id
+        + ", name='" + name + '\''
+        + ", price=" + price
+        + ", cost=" + cost
+        + ", supplier='" + supplier + '\''
+        + '}';
+  }
+}

data-transfer-object-enum-impl/src/main/java/com/iluwatar/datatransferenum/ProductDto.java

+package com.iluwatar.datatransferenum;
+
+/**
+ * {@link ProductDto} is a data transfer object POJO.
+ * Instead of sending individual information to
+ * client We can send related information together in POJO.
+ *
+ * <p>Dto will not have any business logic in it.
+ */
+public enum ProductDto {
+  ;
+
+  /**
+   * This is Request class which consist of Create or any other request DTO's
+   * you might want to use in your API.
+   */
+  public enum Request {
+    ;
+
+    /**
+     * This is Create dto class for requesting create new product.
+     */
+    public static final class Create implements Name, Price, Cost, Supplier {
+      private String name;
+      private Double price;
+      private Double cost;
+      private String supplier;
+
+      @Override
+      public String getName() {
+        return name;
+      }
+
+      public Create setName(String name) {
+        this.name = name;
+        return this;
+      }
+
+      @Override
+      public Double getPrice() {
+        return price;
+      }
+
+      public Create setPrice(Double price) {
+        this.price = price;
+        return this;
+      }
+
+      @Override
+      public Double getCost() {
+        return cost;
+      }
+
+      public Create setCost(Double cost) {
+        this.cost = cost;
+        return this;
+      }
+
+      @Override
+      public String getSupplier() {
+        return supplier;
+      }
+
+      public Create setSupplier(String supplier) {
+        this.supplier = supplier;
+        return this;
+      }
+    }
+  }
+
+  /**
+   * This is Response class which consist of any response DTO's
+   * you might want to provide to your clients.
+   */
+  public enum Response {
+    ;
+
+    /**
+     * This is Public dto class for API response with the lowest data security.
+     */
+    public static final class Public implements Id, Name, Price {
+      private Long id;
+      private String name;
+      private Double price;
+
+      @Override
+      public Long getId() {
+        return id;
+      }
+
+      public Public setId(Long id) {
+        this.id = id;
+        return this;
+      }
+
+      @Override
+      public String getName() {
+        return name;
+      }
+
+      public Public setName(String name) {
+        this.name = name;
+        return this;
+      }
+
+      @Override
+      public Double getPrice() {
+        return price;
+      }
+
+      public Public setPrice(Double price) {
+        this.price = price;
+        return this;
+      }
+
+      @Override
+      public String toString() {
+        return "Public{"
+            + "id="
+            + id
+            + ", name='"
+            + name
+            + '\''
+            + ", price="
+            + price
+            + '}';
+      }
+    }
+
+    /**
+     * This is Private dto class for API response with the highest data security.
+     */
+    public static final class Private implements Id, Name, Price, Cost {
+      private Long id;
+      private String name;
+      private Double price;
+      private Double cost;
+
+      @Override
+      public Long getId() {
+        return id;
+      }
+
+      public Private setId(Long id) {
+        this.id = id;
+        return this;
+      }
+
+      @Override
+      public String getName() {
+        return name;
+      }
+
+      public Private setName(String name) {
+        this.name = name;
+        return this;
+      }
+
+      @Override
+      public Double getPrice() {
+        return price;
+      }
+
+      public Private setPrice(Double price) {
+        this.price = price;
+        return this;
+      }
+
+      @Override
+      public Double getCost() {
+        return cost;
+      }
+
+      public Private setCost(Double cost) {
+        this.cost = cost;
+        return this;
+      }
+
+      @Override
+      public String toString() {
+        return "Private{"
+            +
+            "id="
+            + id
+            +
+            ", name='"
+            + name
+            + '\''
+            +
+            ", price="
+            + price
+            +
+            ", cost="
+            + cost
+            +
+            '}';
+      }
+    }
+  }
+
+  /**
+   * Use this interface whenever you want to provide the product Id in your DTO.
+   */
+  private interface Id {
+    /**
+     * Unique identifier of the product.
+     *
+     * @return : id of the product.
+     */
+    Long getId();
+  }
+
+  /**
+   * Use this interface whenever you want to provide the product Name in your DTO.
+   */
+  private interface Name {
+    /**
+     * The name of the product.
+     *
+     * @return : name of the product.
+     */
+    String getName();
+  }
+
+  /**
+   * Use this interface whenever you want to provide the product Price in your DTO.
+   */
+  private interface Price {
+    /**
+     * The amount we sell a product for.
+     * <b>This data is not confidential</b>
+     *
+     * @return : price of the product.
+     */
+    Double getPrice();
+  }
+
+  /**
+   * Use this interface whenever you want to provide the product Cost in your DTO.
+   */
+  private interface Cost {
+    /**
+     * The amount that it costs us to purchase this product
+     * For the amount we sell a product for, see the {@link Price Price} parameter.
+     * <b>This data is confidential</b>
+     *
+     * @return : cost of the product.
+     */
+    Double getCost();
+  }
+
+  /**
+   * Use this interface whenever you want to provide the product Supplier in your DTO.
+   */
+  private interface Supplier {
+    /**
+     * The name of supplier of the product or its manufacturer.
+     * <b>This data is highly confidential</b>
+     *
+     * @return : supplier of the product.
+     */
+    String getSupplier();
+  }
+}

data-transfer-object-enum-impl/src/main/java/com/iluwatar/datatransferenum/ProductResource.java

+package com.iluwatar.datatransferenum;
+
+import java.util.List;
+import java.util.stream.Collectors;
+
+/**
+ * The resource class which serves product information. This class act as server in the demo. Which
+ * has all product details.
+ */
+public class ProductResource {
+  private final List<Product> products;
+
+  /**
+   * Initialise resource with existing products.
+   *
+   * @param products initialize resource with existing products. Act as database.
+   */
+  public ProductResource(final List<Product> products) {
+    this.products = products;
+  }
+
+  /**
+   * Get all products.
+   *
+   * @return : all products in list but in the scheme of private dto.
+   */
+  public List<ProductDto.Response.Private> getAllProductsForAdmin() {
+    return products
+        .stream()
+        .map(p -> new ProductDto.Response.Private().setId(p.getId()).setName(p.getName())
+            .setCost(p.getCost())
+            .setPrice(p.getPrice()))
+        .collect(Collectors.toList());
+  }
+
+  /**
+   * Get all products.
+   *
+   * @return : all products in list but in the scheme of public dto.
+   */
+  public List<ProductDto.Response.Public> getAllProductsForCustomer() {
+    return products
+        .stream()
+        .map(p -> new ProductDto.Response.Public().setId(p.getId()).setName(p.getName())
+            .setPrice(p.getPrice()))
+        .collect(Collectors.toList());
+  }
+
+  /**
+   * Save new product.
+   *
+   * @param createProductDto save new product to list.
+   */
+  public void save(ProductDto.Request.Create createProductDto) {
+    products.add(new Product()
+        .setId((long) (products.size() + 1))
+        .setName(createProductDto.getName())
+        .setSupplier(createProductDto.getSupplier())
+        .setPrice(createProductDto.getPrice())
+        .setCost(createProductDto.getCost()));
+  }
+
+  /**
+   * List of all products in an entity representation.
+   *
+   * @return : all the products entity that stored in the products list
+   */
+  public List<Product> getProducts() {
+    return products;
+  }
+}

data-transfer-object-enum-impl/src/test/java/com/iluwatar/datatransferenum/AppTest.java

+/*
+ * The MIT License
+ * Copyright © 2014-2019 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.datatransferenum;
+
+import static org.junit.jupiter.api.Assertions.assertDoesNotThrow;
+
+
+import org.junit.jupiter.api.Test;
+
+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#main(String[])}
+   * throws an exception.
+   */
+
+  @Test
+  void shouldExecuteApplicationWithoutException() {
+    assertDoesNotThrow(() -> App.main(new String[] {}));
+  }
+}

pom.xml

@@ -199,6 +199,7 @@
         <module>filterer</module>
         <module>factory</module>
         <module>separated-interface</module>
+        <module>data-transfer-object-enum-impl</module>
     </modules>
 
     <repositories>