一款 PO VO DTO 转换神器

「爱情、让人受尽委屈。」 2022-08-28 06:50 187阅读 0赞

### 老铁们是不是经常为写一些实体转换的原始代码感到头疼，尤其是实体字段特别多的时候。介绍一个开源项目 mapstruct ，可以轻松优雅的进行转换，简化你的代码。    ###

当然有的人喜欢写get set，或者用BeanUtils 进行复制，代码只是工具，本文只是提供一种思路。

先贴下官网地址吧：https://mapstruct.org/

废话不多说，上代码：

pom 配置：

<properties>
            <project.build.sourceEncoding>UTF-8</project.build.sourceEncoding>
            <maven.compiler.source>1.8</maven.compiler.source>
            <maven.compiler.target>1.8</maven.compiler.target>
            <org.mapstruct.version>1.4.1.Final</org.mapstruct.version>
            <org.projectlombok.version>1.18.12</org.projectlombok.version>
    </properties>
    
    <dependencies>
            <dependency>
                <groupId>org.mapstruct</groupId>
                <artifactId>mapstruct</artifactId>
                <version>${org.mapstruct.version}</version>
            </dependency>
    
            
            <dependency>
                <groupId>org.projectlombok</groupId>
                <artifactId>lombok</artifactId>
                <version>${org.projectlombok.version}</version>
                <scope>provided</scope>
            </dependency>
    
            
         <dependency>
                <groupId>org.mapstruct</groupId>
                <artifactId>mapstruct-processor</artifactId>
                <version>${org.mapstruct.version}</version>
                <scope>provided</scope>
            </dependency>
    
    </dependencies>
    
    <build>
            <plugins>
                <plugin>
                    <groupId>org.apache.maven.plugins</groupId>
                    <artifactId>maven-compiler-plugin</artifactId>
                    <version>3.8.1</version>
                    <configuration>
                        <source>1.8</source>
                        <target>1.8</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>
            </plugins>
        </build>

关于lombok和mapstruct的版本兼容问题多说几句，maven插件要使用3.6.0版本以上、lombok使用1.16.16版本以上，另外编译的lombok mapstruct的插件不要忘了加上。否则会出现下面的错误：

`No property named "aaa" exists in source parameter(s). Did you mean "null"?`

这种异常就是lombok编译异常导致缺少get setter方法造成的。还有就是缺少构造函数也会抛异常。

@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);
    
    }

实体类是开发过程少不了的，就算是用工具生成肯定也是要有的，需要手写的部分就是这个Mapper的接口，编译完成后会自动生成相应的实现类

![7c55fcc34f21faa2c63ce0ed22169613.png][]

然后就可以直接用mapper进行实体的转换了

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);
            //这行代码便是实际要用的代码
            StudentVO studentVO = StudentMapper.INSTANCE.student2StudentVO(student);
            System.out.println(studentVO);
    
        }
    
    }

![f7a2dc47b2a994537c86103913f9a7e8.png][]

mapper可以进行字段映射，改变字段类型，指定格式化的方式，包括一些日期的默认处理。

可以手动指定格式化的方法：

@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();
        }
    
    }

上面只是最简单的实体映射处理，下面介绍一些高级用法

1. List 转换

属性映射基于上面的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<StudentVO> students2StudentVOs(List<Student> 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<Student> list = new ArrayList<>();
        list.add(student);
        List<StudentVO> result = StudentMapper.INSTANCE.students2StudentVOs(list);
        System.out.println(result);
    }

![89c2235b515a904c2c973b7a8f5240c7.png][]

### 2.多对象转换到一个对象 ###

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

![107ba90da6ad93cecb48404ae04c86bb.png][]

### 3.默认值 ###

@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 = "张三")
        StudentVO studentAndCourse2StudentVO(Student student, Course course);
    
    }

![503aecc94be93967655906fdc8ed684c.png][]

### 来源：toutiao.com/i6891531055631696395 ###