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 。
org.apache.maven.plugins
maven-compiler-plugin
3.5.1
1.6
1.6
org.mapstruct
mapstruct-processor
1.1.0.Beta1
现在添加mapstruct jar作为依赖项。
org.mapstruct
mapstruct
1.1.0.Beta1
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;
}
@Override
public 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;
}
@Override
public 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);
@InheritInverseConfiguration
PrimaryContact 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;
}
@Override
public BusinessContact primaryToBusinessContact(PrimaryContact primary){
BusinessContact business = delegate.primaryToBusinessContact(primary); //Executes the mapper
String[] names = primary.getName().split(" ");
business.setFirstName(names[0]);
business.setLastName(names[1]);
return business;
}
@Override
public PrimaryContact businessToPrimaryContact(BusinessContact business){
PrimaryContact primary = delegate.businessToPrimaryContact(business); //Executes the mapper
primary.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","[email protected]");
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, [email protected], businessCountry=USA]
PrimaryContact [name=Jack Sparrow, phone=9999999999, [email protected]]翻译自: https://www.javacodegeeks.com/2016/12/mapstruct-transferring-data-one-bean-another.html