隨著微服務(wù)和分布式應(yīng)用的廣泛采用，出于服務(wù)的獨(dú)立性和數(shù)據(jù)的安全性方面的考慮，每個(gè)服務(wù)都會(huì)按照自己的需要定義業(yè)務(wù)數(shù)據(jù)對(duì)象，這樣當(dāng)服務(wù)相互調(diào)用時(shí)就要經(jīng)常進(jìn)行數(shù)據(jù)對(duì)象之間的映射。目前，有很多實(shí)現(xiàn)數(shù)據(jù)對(duì)象映射的庫(kù)，本文介紹一種高性能的映射庫(kù)MapStruct。

https://mapstruct.org/documentation/stable/reference/html/

Java數(shù)據(jù)對(duì)象映射庫(kù)MapStruct介紹（2）

MapStruct簡(jiǎn)介

MapStruct是在編譯時(shí)根據(jù)定義（接口）生成映射類(lèi)（實(shí)現(xiàn)），自動(dòng)生成需要手工編寫(xiě)數(shù)據(jù)映射代碼，通過(guò)直接調(diào)用復(fù)制數(shù)據(jù)，不需要通過(guò)反射，因此速度非常快。

本文將介紹一些MapStruct的基礎(chǔ)功能，包括：

Maven安裝
字段映射：自動(dòng)映射，指定映射關(guān)系，從多個(gè)源對(duì)象映射，映射子對(duì)象；
類(lèi)型轉(zhuǎn)換：基本類(lèi)型轉(zhuǎn)換，枚舉類(lèi)型轉(zhuǎn)換；
設(shè)置對(duì)象值：使用默認(rèn)值，使用Java表達(dá)式

通過(guò)Maven安裝

在pom.xml中安裝MapStruct。

指定MapStruct的版本。

<properties>
    <org.mapstruct.version>1.4.2.Final</org.mapstruct.version>
</properties>

<dependencies>
    <dependency>
        <groupId>org.mapstruct</groupId>
        <artifactId>mapstruct</artifactId>
        <version>${org.mapstruct.version}</version>
    </dependency>
</dependencies>

MapStruct作用于編譯階段，需要在build中添加插件。

<build>
  <plugins>
    <plugin>
      <groupId>org.apache.maven.plugins</groupId>
      <artifactId>maven-compiler-plugin</artifactId>
      <version>3.8.1</version>
      <configuration>
        <source>${java.version}</source>
        <target>${java.version}</target>
        <annotationProcessorPaths>
          <path>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
            <version>${org.projectlombok.version}</version>
          </path>
          <path>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct-processor</artifactId>
            <version>${org.mapstruct.version}</version>
          </path>
        </annotationProcessorPaths>
      </configuration>
    </plugin>
    <plugin>
      <groupId>org.springframework.boot</groupId>
      <artifactId>spring-boot-maven-plugin</artifactId>
      <configuration>
        <excludes>
          <exclude>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
          </exclude>
        </excludes>
      </configuration>
    </plugin>
  </plugins>
</build>

定義字段映射關(guān)系

基本定義

假設(shè)我們有兩個(gè)數(shù)據(jù)對(duì)象Doctor和DoctorDto，它們有相同的字段。注意：兩個(gè)數(shù)據(jù)對(duì)象都添加了@Data注解（lombok），用于自動(dòng)生成getter/setter方法，否則無(wú)法實(shí)現(xiàn)映射。

@Data
public class Doctor {
    private int id;
    private String name;
}

@Data
public class DoctorDto {
    private int id;
    private String name;
}

現(xiàn)在我們用MapStruct的注解@Mapper定義兩個(gè)數(shù)據(jù)類(lèi)的映射關(guān)系。

@Mapper(componentModel = "spring")
public interface DoctorMapper {
    DoctorDto toDto(Doctor doctor);
}

接口中定義了數(shù)據(jù)映射方法toDto()，接收一個(gè)Doctor實(shí)例，返回一個(gè)DoctorDto實(shí)例。@Mapper(componentModel = "spring")將會(huì)給生成的實(shí)現(xiàn)添加@Component注解，用于支持Spring的依賴(lài)注入。注意：這里只指定了類(lèi)型，并不需要指定字段的映射關(guān)系。

執(zhí)行mvn compile生成DoctorMapperImpl.class。

@Component
public class DoctorMapperImpl implements DoctorMapper {
  public DoctorDto toDto(Doctor doctor) {
    if (doctor == null)
      return null; 
    DoctorDto doctorDto = new DoctorDto();
    doctorDto.setId(doctor.getId());
    doctorDto.setName(doctor.getName());
    return doctorDto;
  }
}

從生成的實(shí)現(xiàn)類(lèi)可以看到自動(dòng)生成的代碼和我們手工賦值的代碼沒(méi)有什么區(qū)別。代碼中已經(jīng)添加@Component，在Spring中可以通過(guò)依賴(lài)注入的方式使用映射類(lèi)實(shí)例。

映射字段名

如果映射的數(shù)據(jù)對(duì)象字段名不一致，用@Mapping指定映射關(guān)系。

@Data
public class Doctor {
    private int id;
    private String name;
    private String specialty; // 不一致的字段名
}

@Data
public class DoctorDto {
    private int id;
    private String name;
    private String specialization; // 不一致的字段名
}

@Mapper(componentModel = "spring")
public interface DoctorMapper {
  @Mapping(source = "doctor.specialty", target = "specialization") // 指定映射關(guān)系
  DoctorDto toDto(Doctor doctor);
}

@Component
public class DoctorMapperImpl implements DoctorMapper {
  public DoctorDto toDto(Doctor doctor) {
    if (doctor == null)
      return null; 
    DoctorDto doctorDto = new DoctorDto();
    doctorDto.setSpecialization(doctor.getSpecialty()); // 按照指定的關(guān)系映射
    doctorDto.setId(doctor.getId());
    doctorDto.setName(doctor.getName());
    return doctorDto;
  }
}

從多個(gè)源對(duì)象映射

有時(shí)候需要從多個(gè)數(shù)據(jù)對(duì)象映射到一個(gè)數(shù)據(jù)對(duì)象，這時(shí)需要在定義的映射函數(shù)toDto()中指定所有源數(shù)據(jù)對(duì)象。如果多個(gè)源數(shù)據(jù)對(duì)象有同樣的字段，例如：id，那么必須通過(guò)@Mapping指定用哪個(gè)源中的字段。

@Data
public class Education {
    private String degreeName;
    private String institute;
    private Integer yearOfPassing;
}

@Data
public class DoctorDto {
  private int id;
  private String name;
  private String degree;
  private String specialization;
}

@Mapper(componentModel = "spring")
public interface DoctorMapper {
  @Mapping(source = "doctor.specialty", target = "specialization")
  @Mapping(source = "education.degreeName", target = "degree")
  DoctorDto toDto(Doctor doctor, Education education); // 從多個(gè)對(duì)象映射
}

@Component
public class DoctorMapperImpl implements DoctorMapper {
  public DoctorDto toDto(Doctor doctor, Education education) {
    if (doctor == null && education == null)
      return null; 
    DoctorDto doctorDto = new DoctorDto();
    if (doctor != null) {
      doctorDto.setSpecialization(doctor.getSpecialty());
      doctorDto.setId(doctor.getId());
      doctorDto.setName(doctor.getName());
    } 
    if (education != null)
      doctorDto.setDegree(education.getDegreeName()); 
    return doctorDto;
  }
}

映射子對(duì)象

@Data
public class Patient {
  private int id;
  private String name;
}

@Data
public class Doctor {
  private int id;
  private String name;
  private String specialty;
  private List<Patient> patientList; // 增加了子對(duì)象的列表
}

@Data
public class PatientDto {
  private int id;
  private String name;
}

@Data
public class DoctorDto {
  private int id;
  private String name;
  private String degree;
  private String specialization;
  private List<PatientDto> patientDtoList; // 子對(duì)象的映射對(duì)象列表
}

@Mapper(componentModel = "spring")
public interface DoctorMapper {
  @Mapping(source = "doctor.specialty", target = "specialization")
  @Mapping(source = "doctor.patientList", target = "patientDtoList") // 子對(duì)象列表的映射關(guān)系
  @Mapping(source = "education.degreeName", target = "degree")
  DoctorDto toDto(Doctor doctor, Education education);
}

@Component
public class DoctorMapperImpl implements DoctorMapper {
  public DoctorDto toDto(Doctor doctor, Education education) {
    if (doctor == null && education == null)
      return null; 
    DoctorDto doctorDto = new DoctorDto();
    if (doctor != null) {
      doctorDto.setSpecialization(doctor.getSpecialty());
      doctorDto.setPatientDtoList(patientListToPatientDtoList(doctor.getPatientList()));
      doctorDto.setId(doctor.getId());
      doctorDto.setName(doctor.getName());
    } 
    if (education != null)
      doctorDto.setDegree(education.getDegreeName()); 
    return doctorDto;
  }
  
  protected PatientDto patientToPatientDto(Patient patient) {
    if (patient == null)
      return null; 
    PatientDto patientDto = new PatientDto();
    patientDto.setId(patient.getId());
    patientDto.setName(patient.getName());
    return patientDto;
  }
  
  protected List<PatientDto> patientListToPatientDtoList(List<Patient> list) {
    if (list == null)
      return null; 
    List<PatientDto> list1 = new ArrayList<>(list.size());
    for (Patient patient : list)
      list1.add(patientToPatientDto(patient)); 
    return list1;
  }
}

類(lèi)型轉(zhuǎn)換

基本類(lèi)型轉(zhuǎn)換

MapStruct支持基本類(lèi)型的自動(dòng)類(lèi)型轉(zhuǎn)換，包括：

原始類(lèi)型和相應(yīng)的包裹類(lèi)型間的轉(zhuǎn)換，例如：int和Integer，float和Float，long和Long，boolean和Boolean。
原始類(lèi)型和包裹類(lèi)型間的相互轉(zhuǎn)換，例如：int和long，byte和Integer等。
原始類(lèi)型和包裹類(lèi)型與String類(lèi)型之間的轉(zhuǎn)換，boolean和String，Integer和String，float和String等。

@Data
public class PatientDto {
  private int id;
  private String name;
  private LocalDate dateOfBirth;
}

@Data
public class Patient {
  private int id;
  private String name;
  private String dateOfBirth;
}

@Mapper(componentModel = "spring")
public interface PatientMapper {
  @Mapping(source = "dateOfBirth", target = "dateOfBirth", dateFormat = "dd/MMM/yyyy")
  PatientDto toDto(Patient patient);
}

@Component
public class PatientMapperImpl implements PatientMapper {
  public PatientDto toDto(Patient patient) {
    if (patient == null)
      return null; 
    PatientDto patientDto = new PatientDto();
    if (patient.getDateOfBirth() != null)
      patientDto.setDateOfBirth(LocalDate.parse(patient.getDateOfBirth(), DateTimeFormatter.ofPattern("dd/MMM/yyyy")));  // 自動(dòng)生成了時(shí)間類(lèi)型轉(zhuǎn)換代碼
    patientDto.setId(patient.getId());
    patientDto.setName(patient.getName());
    return patientDto;
  }
}

枚舉類(lèi)型轉(zhuǎn)換

MapStruct支持枚舉類(lèi)型之間的轉(zhuǎn)換，如果枚舉名是相同的自動(dòng)完成映射，如果名稱(chēng)不一致，通過(guò)@ValueMapping進(jìn)行映射。

public enum PaymentType {
  CASH, CHEQUE, CARD_VISA, CARD_MASTER, CARD_CREDIT
}

public enum PaymentTypeView {
  CASH, CHEQUE, CARD
}

@Mapper(componentModel = "spring")
public interface PaymentTypeMapper {
  @ValueMappings({ @ValueMapping(source = "CARD_VISA", target = "CARD"),
      @ValueMapping(source = "CARD_MASTER", target = "CARD"), @ValueMapping(source = "CARD_CREDIT", target = "CARD") })
  PaymentTypeView paymentTypeToPaymentTypeView(PaymentType paymentType);
}

@Component
public class PaymentTypeMapperImpl implements PaymentTypeMapper {
  public PaymentTypeView paymentTypeToPaymentTypeView(PaymentType paymentType) {
    PaymentTypeView paymentTypeView;
    if (paymentType == null)
      return null; 
    switch (paymentType) {
      case CARD_VISA:
        paymentTypeView = PaymentTypeView.CARD;
        return paymentTypeView;
      case CARD_MASTER:
        paymentTypeView = PaymentTypeView.CARD;
        return paymentTypeView;
      case null:
        paymentTypeView = PaymentTypeView.CARD;
        return paymentTypeView;
      case CASH:
        paymentTypeView = PaymentTypeView.CASH;
        return paymentTypeView;
      case CHEQUE:
        paymentTypeView = PaymentTypeView.CHEQUE;
        return paymentTypeView;
    } 
    throw new IllegalArgumentException("Unexpected enum constant: " + paymentType);
  }
}

設(shè)置字段值

設(shè)置默認(rèn)值

MapStruct提供兩種方式設(shè)置目標(biāo)數(shù)據(jù)對(duì)象字段默認(rèn)值，constant和default，constant是不論源數(shù)據(jù)對(duì)象字段是什么值都將目標(biāo)數(shù)據(jù)對(duì)象字段設(shè)置為對(duì)應(yīng)的值，default是源數(shù)據(jù)對(duì)象字段的值如果為null就使用指定的值。

@Mapper(componentModel = "spring")
public interface DoctorMapper {
  @Mapping(target = "id", constant = "-1") // 使用固定的值
  @Mapping(source = "doctor.specialty", target = "specialization", defaultValue = "沒(méi)有指定") // 如果源數(shù)據(jù)對(duì)象的值為null，使用指定的值
  @Mapping(source = "doctor.patientList", target = "patientDtoList")
  @Mapping(source = "education.degreeName", target = "degree")
  DoctorDto toDto(Doctor doctor, Education education);
}

@Component
public class DoctorMapperImpl implements DoctorMapper {
  public DoctorDto toDto(Doctor doctor, Education education) {
    if (doctor == null && education == null)
      return null; 
    DoctorDto doctorDto = new DoctorDto();
    if (doctor != null) {
      if (doctor.getSpecialty() != null) {
        doctorDto.setSpecialization(doctor.getSpecialty());
      } else {
        doctorDto.setSpecialization("沒(méi)有指定"); // 用default指定的值
      } 
      doctorDto.setPatientDtoList(patientListToPatientDtoList(doctor.getPatientList()));
      doctorDto.setName(doctor.getName());
    } 
    if (education != null)
      doctorDto.setDegree(education.getDegreeName()); 
    doctorDto.setId(-1); // 用constant指定的值
    return doctorDto;
  }
}

使用Java表達(dá)式

除了使用constant和default設(shè)置目標(biāo)值，還可以用expression和defaultExpression，expression是忽略源數(shù)據(jù)對(duì)象的值進(jìn)行設(shè)置，defaultExpression是源對(duì)象的值如果為null時(shí)進(jìn)行設(shè)置。

@Data
public class Doctor {
  private int id;
  private String name;
  private String externalId; // 新添字段
  private String specialty;
  private LocalDateTime availability; // 新添字段
  private List<Patient> patientList;
}

@Data
public class DoctorDto {
  private int id;
  private String name;
  private String externalId; // 新添字段
  private String degree;
  private String specialization;
  private LocalDateTime availability; // 新添字段
  private List<PatientDto> patientDtoList;
}

@Mapper(componentModel = "spring")
public interface DoctorMapper {
  @Mapping(target = "id", constant = "-1")
  @Mapping(target = "externalId", expression = "java(UUID.randomUUID().toString())") // 添加了表達(dá)式
  @Mapping(source = "doctor.availability", target = "availability", defaultExpression = "java(LocalDateTime.now())") // 添加了表達(dá)式
  @Mapping(source = "doctor.specialty", target = "specialization", defaultValue = "沒(méi)有指定")
  @Mapping(source = "doctor.patientList", target = "patientDtoList")
  @Mapping(source = "education.degreeName", target = "degree")
  DoctorDto toDto(Doctor doctor, Education education);
}

@Component
public class DoctorMapperImpl implements DoctorMapper {
  public DoctorDto toDto(Doctor doctor, Education education) {
    if (doctor == null && education == null)
      return null; 
    DoctorDto doctorDto = new DoctorDto();
    if (doctor != null) {
      if (doctor.getAvailability() != null) {
        doctorDto.setAvailability(doctor.getAvailability());
      } else {
        doctorDto.setAvailability(LocalDateTime.now()); // 使用了指定的表達(dá)式
      } 
      if (doctor.getSpecialty() != null) {
        doctorDto.setSpecialization(doctor.getSpecialty());
      } else {
        doctorDto.setSpecialization("沒(méi)有指定");
      } 
      doctorDto.setPatientDtoList(patientListToPatientDtoList(doctor.getPatientList()));
      doctorDto.setName(doctor.getName());
    } 
    if (education != null)
      doctorDto.setDegree(education.getDegreeName()); 
    doctorDto.setId(-1);
    doctorDto.setExternalId(UUID.randomUUID().toString()); // 使用了指定的表達(dá)式
    return doctorDto;
  }
}

總結(jié)

從上面的示例中可以看出MapStruct是一個(gè)功能強(qiáng)大的數(shù)據(jù)對(duì)象映射工具，可以在很大程度上減少手工代碼量，同時(shí)為我們提供了一個(gè)考慮數(shù)據(jù)對(duì)象映射問(wèn)題的基本框架，可以提高代碼質(zhì)量。

本篇文章主要介紹MapStruct的基礎(chǔ)功能，下一篇介紹它的一些高級(jí)功能。

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Java數(shù)據(jù)對(duì)象映射庫(kù)MapStruct介紹（1）

Java數(shù)據(jù)對(duì)象映射庫(kù)MapStruct介紹（1）

MapStruct簡(jiǎn)介

通過(guò)Maven安裝

定義字段映射關(guān)系

基本定義

映射字段名

從多個(gè)源對(duì)象映射

映射子對(duì)象

類(lèi)型轉(zhuǎn)換

基本類(lèi)型轉(zhuǎn)換

枚舉類(lèi)型轉(zhuǎn)換

設(shè)置字段值

設(shè)置默認(rèn)值

使用Java表達(dá)式

總結(jié)

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

色偷偷精品伊人,欧洲久久精品,欧美综合婷婷骚逼,国产AV主播,国产最新探花在线,九色在线视频一区,伊人大交九 欧美,1769亚洲,黄色成人av

Java數(shù)據(jù)對(duì)象映射庫(kù)MapStruct介紹（1）

MapStruct簡(jiǎn)介

通過(guò)Maven安裝

定義字段映射關(guān)系

基本定義

映射字段名

從多個(gè)源對(duì)象映射

映射子對(duì)象

類(lèi)型轉(zhuǎn)換

基本類(lèi)型轉(zhuǎn)換

枚舉類(lèi)型轉(zhuǎn)換

設(shè)置字段值

設(shè)置默認(rèn)值

使用Java表達(dá)式

總結(jié)

相關(guān)閱讀更多精彩內(nèi)容

友情鏈接更多精彩內(nèi)容

色偷偷精品伊人,欧洲久久精品,欧美综合婷婷骚逼,国产AV主播,国产最新探花在线,九色在线视频一区,伊人大交九欧美,1769亚洲,黄色成人av