MapStruct：将数据从一个bean传输到另一个bean

将数据从一种形式转换为另一种形式在IT行业中是一种被高度利用的概念。 MapStruct通过在编译时生成映射器实现，允许基于注释的Bean转换。这样可以确保在运行时没有性能开销。

什么是MapStruct？

MapStruct是一个代码生成器，它基于约定优于配置的方法大大简化了Java Bean类型之间的映射的实现。

生成的映射代码使用简单的方法调用，因此速度快，类型安全且易于理解。

为什么选择MapStruct？

多层应用程序通常需要在不同的对象模型（例如实体和DTO）之间进行映射。编写此类映射代码是一项繁琐且容易出错的任务。 MapStruct旨在通过使其尽可能自动化来简化这项工作。

与其他映射框架相比，MapStruct在编译时生成Bean映射，以确保高性能，允许快速的开发人员反馈和彻底的错误检查。

实作

pom.xml

在web.xml中，添加“ maven-compiler-plugin ”，并使用组ID“ org.apache.maven.plugins ”。您可以添加特定的jdk源/目标版本，并从以下位置获取最新版本
MapStruct网站。

<plugin><groupId>org.apache.maven.plugins</groupId><artifactId>maven-compiler-plugin</artifactId><version>3.5.1</version><configuration><source>1.6</source> <!-- or higher, depending on your project --><target>1.6</target> <!-- or higher, depending on your project --><annotationProcessorPaths><path><groupId>org.mapstruct</groupId><artifactId>mapstruct-processor</artifactId><version>1.1.0.Beta1</version></path></annotationProcessorPaths></configuration>
</plugin>

现在添加mapstruct jar作为依赖项。

<dependency><groupId>org.mapstruct</groupId><artifactId>mapstruct</artifactId><version>1.1.0.Beta1</version>
</dependency>

问题陈述与解决方案

假设我们有两个表示个人和业务联系的pojo，如下所述，并且我们都在特定的jsps上使用这两个pojo。现在，对于两个联系人都相同的功能，我们需要将数据从一种pojo传输到另一种。

PrimaryContact.java

public class PrimaryContact {private String name;private String phone;private String email;public PrimaryContact() {super();}public PrimaryContact(String name, String phone, String email) {super();this.name = name;this.phone = phone;this.email = email;}public String getName() {return name;}public void setName(String name) {this.name = name;}public String getPhone() {return phone;}public void setPhone(String phone) {this.phone = phone;}public String getEmail() {return email;}public void setEmail(String email) {this.email = email;}@Overridepublic String toString() {return "PrimaryContact [name=" + name + ", phone=" + phone + ", email=" + email + "]";}}

BusinessContact.java

public class BusinessContact {private String firstName;private String lastName;private String businessPhone;private String businessEmail;private String businessCountry;public BusinessContact() {super();}public BusinessContact(String firstName, String lastName, String businessPhone, String businessEmail,String businessCountry) {super();this.firstName = firstName;this.lastName = lastName;this.businessPhone = businessPhone;this.businessEmail = businessEmail;this.businessCountry = businessCountry;}public String getFirstName() {return firstName;}public void setFirstName(String firstName) {this.firstName = firstName;}public String getLastName() {return lastName;}public void setLastName(String lastName) {this.lastName = lastName;}public String getBusinessPhone() {return businessPhone;}public void setBusinessPhone(String businessPhone) {this.businessPhone = businessPhone;}public String getBusinessEmail() {return businessEmail;}public void setBusinessEmail(String businessEmail) {this.businessEmail = businessEmail;}public String getBusinessCountry() {return businessCountry;}public void setBusinessCountry(String businessCountry) {this.businessCountry = businessCountry;}@Overridepublic String toString() {return "BusinessContact [firstName=" + firstName + ", lastName=" + lastName + ", businessPhone=" + businessPhone+ ", businessEmail=" + businessEmail + ", businessCountry=" + businessCountry + "]";}}

我们编写一个Mapper来传输数据，如下所示。注释@Mappings定义了将源pojo中的哪些属性转移到目标pojo中的特定属性。批注定义@InheritInverseConfiguration反向映射要完成。

ContactMapper.java

/*** @author javareferencegv*/
@Mapper
@DecoratedWith(ContactMapperDecorator.class)
public interface ContactMapper {ContactMapper INSTANCE = Mappers.getMapper(ContactMapper.class);/*** We define only those mappings which doesn't have same signature in source and target*/   @Mappings({ @Mapping(source = "phone", target = "businessPhone"),@Mapping(source = "email", target = "businessEmail"),@Mapping(target = "businessCountry", constant="USA")})BusinessContact primaryToBusinessContact(PrimaryContact primary);@InheritInverseConfigurationPrimaryContact businessToPrimaryContact(BusinessContact business);}

在某些情况下，映射不是直接的，我们需要在将一个属性映射到另一个属性之前使用自定义逻辑。这里的一个例子是主要联系人有全名，而业务联系人有名和姓。在这种情况下，我们使用装饰器添加自定义实现。这是在映射器中添加定义的注释@DecoratedWith。装饰器的实现如下：

ContactMapperDecorator.java

public abstract class ContactMapperDecorator implements ContactMapper{private final ContactMapper delegate;public ContactMapperDecorator(ContactMapper delegate) {this.delegate = delegate;}@Overridepublic BusinessContact primaryToBusinessContact(PrimaryContact primary){BusinessContact business = delegate.primaryToBusinessContact(primary); //Executes the mapperString[] names = primary.getName().split(" ");business.setFirstName(names[0]);business.setLastName(names[1]);return business;}@Overridepublic PrimaryContact businessToPrimaryContact(BusinessContact business){PrimaryContact primary = delegate.businessToPrimaryContact(business); //Executes the mapperprimary.setName(business.getFirstName() + " " + business.getLastName());return primary;}}

执行方式：

一旦我们构建了一个实现类文件，它将由mapstruct生成。我们都准备运行映射器。

public class ContactConvertor {public static void main(String[] args) {PrimaryContact primary = new PrimaryContact("Jack Sparrow","9999999999","test@javareferencegv.com");BusinessContact business = ContactMapper.INSTANCE.primaryToBusinessContact(primary);System.out.println(business);PrimaryContact primaryConverted = ContactMapper.INSTANCE.businessToPrimaryContact(business);System.out.println(primaryConverted);}}

输出：

BusinessContact [firstName=Jack, lastName=Sparrow, businessPhone=9999999999, businessEmail=test@javareferencegv.com, businessCountry=USA]
PrimaryContact [name=Jack Sparrow, phone=9999999999, email=test@javareferencegv.com]