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作者：bettermann

toutiao.com/i6891531055631696395/

老鐵們是不是經(jīng)常為寫一些實(shí)體轉(zhuǎn)換的原始代碼感到頭疼，尤其是實(shí)體字段特別多的時(shí)候。介紹一個(gè)開(kāi)源項(xiàng)目 mapstruct ，可以輕松優(yōu)雅的進(jìn)行轉(zhuǎn)換，簡(jiǎn)化你的代碼。當(dāng)然有的人喜歡寫get set，或者用BeanUtils 進(jìn)行復(fù)制，代碼只是工具，本文只是提供一種思路。

先貼下官網(wǎng)地址吧：https://mapstruct.org/

廢話不多說(shuō)，上代碼：

pom 配置：

<properties>        <project.build.sourceEncoding>UTF-8project.build.sourceEncoding>        <maven.compiler.source>1.8maven.compiler.source>        <maven.compiler.target>1.8maven.compiler.target>        <org.mapstruct.version>1.4.1.Finalorg.mapstruct.version>        <org.projectlombok.version>1.18.12org.projectlombok.version>properties>
<dependencies>        <dependency>            <groupId>org.mapstructgroupId>            <artifactId>mapstructartifactId>            <version>${org.mapstruct.version}version>        dependency>
                <dependency>            <groupId>org.projectlombokgroupId>            <artifactId>lombokartifactId>            <version>${org.projectlombok.version}version>            <scope>providedscope>        dependency>
             <dependency>            <groupId>org.mapstructgroupId>            <artifactId>mapstruct-processorartifactId>            <version>${org.mapstruct.version}version>            <scope>providedscope>        dependency>
dependencies>
<build>        <plugins>            <plugin>                <groupId>org.apache.maven.pluginsgroupId>                <artifactId>maven-compiler-pluginartifactId>                <version>3.8.1version>                <configuration>                    <source>1.8source>                    <target>1.8target>                    <annotationProcessorPaths>                        <path>                            <groupId>org.projectlombokgroupId>                            <artifactId>lombokartifactId>                            <version>${org.projectlombok.version}version>                        path>                        <path>                            <groupId>org.mapstructgroupId>                            <artifactId>mapstruct-processorartifactId>                            <version>${org.mapstruct.version}version>                        path>                    annotationProcessorPaths>                configuration>            plugin>        plugins>    build>

關(guān)于lombok和mapstruct的版本兼容問(wèn)題多說(shuō)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(huì)出現(xiàn)下面的錯(cuò)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(dǎo)致缺少get setter方法造成的。還有就是缺少構(gòu)造函數(shù)也會(huì)拋異常。

@Data@Builder@AllArgsConstructor@NoArgsConstructorpublic 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@NoArgsConstructorpublic class StudentVO {    private String name;    private int age;    private String gender;    private Double height;    private String birthday;}@Mapperpublic 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(shí)體類是開(kāi)發(fā)過(guò)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(gè)Mapper的接口，編譯完成后會(huì)自動(dòng)生成相應(yīng)的實(shí)現(xiàn)類

然后就可以直接用mapper進(jìn)行實(shí)體的轉(zhuǎn)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(shí)際要用的代碼        StudentVO studentVO = StudentMapper.INSTANCE.student2StudentVO(student);        System.out.println(studentVO);
    }
}

mapper可以進(jìn)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(rèn)處理。

可以手動(dòng)指定格式化的方法：

@Mapperpublic 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(jiǎn)單的實(shí)體映射處理，下面介紹一些高級(jí)用法

1.List 轉(zhuǎn)換

屬性映射基于上面的mapping配置

@Mapperpublic 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(duì)象轉(zhuǎn)換到一個(gè)對(duì)象

@Data@Builder@AllArgsConstructor@NoArgsConstructorpublic class Student {
    private String name;    private int age;    private GenderEnum gender;    private Double height;    private Date birthday;
}@Data@AllArgsConstructor@Builder@NoArgsConstructorpublic class Course {
    private String courseName;    private int sortNo;    private long id;
}@Data@Builder@AllArgsConstructor@NoArgsConstructorpublic class StudentVO {    private String name;    private int age;    private String gender;    private Double height;    private String birthday;    private String course;}@Mapperpublic 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(yǔ)文").build();
        StudentVO studentVO = StudentMapper.INSTANCE.studentAndCourse2StudentVO(student, course);        System.out.println(studentVO);    }
}

3.默認(rèn)值

@Mapperpublic 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);
}

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