來源：toutiao.com/i6891531055631696395

老鐵們是不是經常為寫一些實體轉換的原始代碼感到頭疼，尤其是實體字段特別多的時候。介紹一個開源項目 mapstruct ，可以輕松優雅的進行轉換，簡化你的代碼。

當然有的人喜歡寫get set，或者用BeanUtils 進行復制，代碼只是工具，本文只是提供一種思路。

先貼下官網地址吧：https://mapstruct.org/

廢話不多說，上代碼：

pom 配置：


UTF-8project.build.sourceEncoding>
1.8maven.compiler.source>
1.8maven.compiler.target>
1.4.1.Finalorg.mapstruct.version>
1.18.12org.projectlombok.version>
properties>


org.mapstructgroupId>
mapstructartifactId>
${org.mapstruct.version}version>
dependency>


org.projectlombokgroupId>
lombokartifactId>
${org.projectlombok.version}version>
providedscope>
dependency>


org.mapstructgroupId>
mapstruct-processorartifactId>
${org.mapstruct.version}version>
providedscope>
dependency>

dependencies>

關于lombok和mapstruct的版本兼容問題多說幾句，maven插件要使用3.6.0版本以上、lombok使用1.16.16版本以上，另外編譯的lombok mapstruct的插件不要忘了加上。否則會出現下面的錯誤：No property named "aaa" exists in source parameter(s). Did you mean "null"?

這種異常就是lombok編譯異常導致缺少get setter方法造成的。還有就是缺少構造函數也會拋異常。

@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class Student {

private String name;
private int age;
private GenderEnum gender;
private Double height;
private Date birthday;

}
public enum GenderEnum {
Male("1", "男"),
Female("0", "女");

private String code;
private String name;

public String getCode() {
return this.code;
}

public String getName() {
return this.name;
}

GenderEnum(String code, String name) {
this.code = code;
this.name = name;
}
}
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class StudentVO {
private String name;
private int age;
private String gender;
private Double height;
private String birthday;
}
@Mapper
public interface StudentMapper {

StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class);

@Mapping(source = "gender.name", target = "gender")
@Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
StudentVO student2StudentVO(Student student);

}


實體類是開發過程少不了的，就算是用工具生成肯定也是要有的，需要手寫的部分就是這個Mapper的接口，編譯完成后會自動生成相應的實現類

然后就可以直接用mapper進行實體的轉換了

public class Test {

public static void main(String[] args) {

Student student = Student.builder().name("小明").age(6).gender(GenderEnum.Male).height(121.1).birthday(new Date()).build();
System.out.println(student);
//這行代碼便是實際要用的代碼
StudentVO studentVO = StudentMapper.INSTANCE.student2StudentVO(student);
System.out.println(studentVO);

}

}


mapper可以進行字段映射，改變字段類型，指定格式化的方式，包括一些日期的默認處理。

可以手動指定格式化的方法：

@Mapper
public interface StudentMapper {

StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class);

@Mapping(source = "gender", target = "gender")
@Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
StudentVO student2StudentVO(Student student);

default String getGenderName(GenderEnum gender) {
return gender.getName();
}

}


上面只是最簡單的實體映射處理，下面介紹一些高級用法

1.List 轉換

屬性映射基于上面的mapping配置

@Mapper
public interface StudentMapper {

StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class);

@Mapping(source = "gender.name", target = "gender")
@Mapping(source = "birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
StudentVO student2StudentVO(Student student);

List students2StudentVOs(List studentList);

}
public static void main(String[] args) {

Student student = Student.builder().name("小明").age(6).gender(GenderEnum.Male).height(121.1).birthday(new Date()).build();

List list = new ArrayList<>();
list.add(student);
List result = StudentMapper.INSTANCE.students2StudentVOs(list);
System.out.println(result);
}
2.多對象轉換到一個對象 @Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class Student {

private String name;
private int age;
private GenderEnum gender;
private Double height;
private Date birthday;

}
@Data
@AllArgsConstructor
@Builder
@NoArgsConstructor
public class Course {

private String courseName;
private int sortNo;
private long id;

}
@Data
@Builder
@AllArgsConstructor
@NoArgsConstructor
public class StudentVO {
private String name;
private int age;
private String gender;
private Double height;
private String birthday;
private String course;
}
@Mapper
public interface StudentMapper {

StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class);

@Mapping(source = "student.gender.name", target = "gender")
@Mapping(source = "student.birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
@Mapping(source = "course.courseName", target = "course")
StudentVO studentAndCourse2StudentVO(Student student, Course course);

}
public class Test {

public static void main(String[] args) {

Student student = Student.builder().name("小明").age(6).gender(GenderEnum.Male).height(121.1).birthday(new Date()).build();
Course course = Course.builder().id(1L).courseName("語文").build();

StudentVO studentVO = StudentMapper.INSTANCE.studentAndCourse2StudentVO(student, course);
System.out.println(studentVO);
}

}
3.默認值 @Mapper
public interface StudentMapper {

StudentMapper INSTANCE = Mappers.getMapper(StudentMapper.class);

@Mapping(source = "student.gender.name", target = "gender")
@Mapping(source = "student.birthday", target = "birthday", dateFormat = "yyyy-MM-dd HH:mm:ss")
@Mapping(source = "course.courseName", target = "course")
@Mapping(target = "name", source = "student.name", defaultValue = "張三")
StudentVO studentAndCourse2StudentVO(Student student, Course course);

}


END

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org.apache.maven.pluginsgroupId>
maven-compiler-pluginartifactId>
3.8.1version>
1.8source>
1.8target>
org.projectlombokgroupId>
lombokartifactId>
${org.projectlombok.version}version>
path>
org.mapstructgroupId>
mapstruct-processorartifactId>
${org.mapstruct.version}version>
path>
annotationProcessorPaths>
configuration>
plugin>
plugins>
build>