Java中轉換器設計模式深入講解

更新時間：2019年04月10日 11:14:20 作者：jdon

這篇文章主要給大家介紹了關于Java中轉換器設計模式的相關資料，文中通過示例代碼介紹的非常詳細，對大家學習或者使用Java具有一定的參考學習價值，需要的朋友們下面來一起學習學習吧

前言

在這篇文章中，我們將討論 Java / J2EE項目中最常用的 Converter Design Pattern。由于Java8 功能不僅提供了相應類型之間的通用雙向轉換方式，而且還提供了轉換相同類型對象集合的常用方法，從而將樣板代碼減少到絕對最小值。我們使用Java8 功能編寫了此模式的源代碼。

目的

轉換器設計模式的目的是為相應類型之間的雙向轉換提供一種通用的方式，允許類型無需彼此了解的簡潔的實現(xiàn)。此外，轉換器設計模式引入了雙向收集映射，將樣板代碼減少到最小。

源代碼

轉換器設計模式是一種行為設計模式，允許在相應類型（如DTO和邏輯同構類型的域表示）之間進行雙向轉換。此外，該模式還引入了一種在類型之間轉換對象集合的通用方法。

類圖

讓我們根據(jù)上面的類圖編寫源代碼。

在本例中，我們將把customerd轉換為customer實體，反之亦然，我們還將在類型之間轉換對象集合。

步驟1：讓我們創(chuàng)建一個通用轉換器。

public abstract class Converter < T, C > {

 private final Function < T,
 C > fromDto;
 private final Function < C,
 T > fromEntity;

 /**
  * @param fromDto
  *   Function that converts given dto entity into the domain
  *   entity.
  * @param fromEntity
  *   Function that converts given domain entity into the dto
  *   entity.
  */
 public Converter(final Function < T, C > fromDto, final Function < C, T > fromEntity) {
  this.fromDto = fromDto;
  this.fromEntity = fromEntity;
 }

 /**
  * @param customerDto
  *   DTO entity
  * @return The domain representation - the result of the converting function
  *   application on dto entity.
  */
 public final C convertFromDto(final T customerDto) {
  return fromDto.apply(customerDto);
 }

 /**
  * @param customer
  *   domain entity
  * @return The DTO representation - the result of the converting function
  *   application on domain entity.
  */
 public final T convertFromEntity(final C customer) {
  return fromEntity.apply(customer);
 }

 /**
  * @param dtoCustomers
  *   collection of DTO entities
  * @return List of domain representation of provided entities retrieved by
  *   mapping each of them with the conversion function
  */
 public final List < C > createFromDtos(final Collection < T > dtoCustomers) {
  return dtoCustomers.stream().map(this::convertFromDto).collect(Collectors.toList());
 }

 /**
  * @param customers
  *   collection of domain entities
  * @return List of domain representation of provided entities retrieved by
  *   mapping each of them with the conversion function
  */
 public final List < T > createFromEntities(final Collection < C > customers) {
  return customers.stream().map(this::convertFromEntity).collect(Collectors.toList());
 }
}

步驟2：讓我們創(chuàng)建一個簡單客戶轉換器的實現(xiàn)。

public class CustomerConverter extends Converter<CustomerDto, Customer> {

 public CustomerConverter() {
 super(customerDto -> new Customer(customerDto.getCustomerId(), customerDto.getCustomerName(),
 customerDto.getCustomerLastName(), customerDto.isStatus()),
 customer -> new CustomerDto(customer.getCustomerId(), customer.getCustomerName(),
  customer.getCustomerLastName(), customer.isStatus()));

 }

}

步驟3: 創(chuàng)建customerdto類。

public class CustomerDto {
 private String customerId;
 private String customerName;
 private String customerLastName;
 private boolean status;
 public CustomerDto(String customerId, String customerName, String customerLastName, boolean status) {
  super();
  this.customerId = customerId;
  this.customerName = customerName;
  this.customerLastName = customerLastName;
  this.status = status;
 }
 public String getCustomerId() {
  return customerId;
 }
 public void setCustomerId(String customerId) {
  this.customerId = customerId;
 }
 public String getCustomerName() {
  return customerName;
 }
 public void setCustomerName(String customerName) {
  this.customerName = customerName;
 }
 public String getCustomerLastName() {
  return customerLastName;
 }
 public void setCustomerLastName(String customerLastName) {
  this.customerLastName = customerLastName;
 }
 public boolean isStatus() {
  return status;
 }
 public void setStatus(boolean status) {
  this.status = status;
 }

}

步驟4: 創(chuàng)建Customer實體類。

public class Customer {
 private String customerId;
 private String customerName;
 private String customerLastName;
 private boolean status;
 public Customer(String customerId, String customerName, String customerLastName, boolean status) {
  super();
  this.customerId = customerId;
  this.customerName = customerName;
  this.customerLastName = customerLastName;
  this.status = status;
 }
 public String getCustomerId() {
  return customerId;
 }
 public void setCustomerId(String customerId) {
  this.customerId = customerId;
 }
 public String getCustomerName() {
  return customerName;
 }
 public void setCustomerName(String customerName) {
  this.customerName = customerName;
 }
 public String getCustomerLastName() {
  return customerLastName;
 }
 public void setCustomerLastName(String customerLastName) {
  this.customerLastName = customerLastName;
 }
 public boolean isStatus() {
  return status;
 }
 public void setStatus(boolean status) {
  this.status = status;
 }
}

步驟5: 現(xiàn)在，讓我們通過創(chuàng)建Client類來測試這個模式。

public class Client {
 /**
  * Program entry point
  *
  * @param args command line args
  */
 public static void main(String[] args) {
  Converter < CustomerDto, Customer > CustomerConverter = new CustomerConverter();

  CustomerDto dtoCustomer = new CustomerDto("100", "Ramesh", "Fadatare", true);
  Customer Customer = CustomerConverter.convertFromDto(dtoCustomer);
  System.out.println("Entity converted from DTO:" + Customer);

  List < Customer > customers = new ArrayList < > ();
  customers.add(new Customer("100", "Ramesh1", "Fadatare", true));
  customers.add(new Customer("200", "Ramesh2", "Fadatare", true));
  customers.add(new Customer("300", "Ramesh3", "Fadatare", true));

  customers.forEach(System.out::println);

  customers.forEach((customer) - > System.out.println(customer.getCustomerId()));

  System.out.println("DTO entities converted from domain:");
  List < CustomerDto > dtoEntities = CustomerConverter.createFromEntities(customers);
  dtoEntities.forEach(System.out::println);
  dtoEntities.forEach((customer) - > System.out.println(customer.getCustomerId()));

 }
}

輸出：

Entity converted from DTO:com.ramesh.j2ee.converter.Customer@87aac27
com.ramesh.j2ee.converter.Customer@1b28cdfa
com.ramesh.j2ee.converter.Customer@eed1f14
com.ramesh.j2ee.converter.Customer@7229724f
100
200
300
DTO entities converted from domain:
com.ramesh.j2ee.converter.CustomerDto@4dd8dc3
com.ramesh.j2ee.converter.CustomerDto@6d03e736
com.ramesh.j2ee.converter.CustomerDto@568db2f2
100
200
300

適用性

在以下情況下使用轉換器模式：