写在最前面

使用场景，复杂的对象之间进行转换。
比如电商业务中，经常会出现一些订单之间转换的场景。
或者是使用它来做一些业务处理。

官网：https://mapstruct.org/
参考1：https://blog.csdn.net/mobiusstrip/article/details/105674343
参考2：https://blog.csdn.net/u013217730/article/details/107212201

1 开发环境

这里列的是我的使用环境：
java11，springboot，安装好lombok（高版本idea不用安装，直接引入依赖即可）
idea中设置：
在这里插入图片描述

1.1 pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.5.7</version>
        <relativePath/>
    </parent>

    <groupId>com.example</groupId>
    <artifactId>boot-demo</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>boot-demo</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>11</java.version>
        <maven.compiler.source>11</maven.compiler.source>
        <maven.compiler.target>11</maven.compiler.target>

        <org.mapstruct.version>1.4.2.Final</org.mapstruct.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <!--map struct-->
        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct</artifactId>
            <version>${org.mapstruct.version}</version>
        </dependency>
        <dependency>
            <groupId>org.mapstruct</groupId>
            <artifactId>mapstruct-processor</artifactId>
            <version>${org.mapstruct.version}</version>
        </dependency>

        <dependency>
            <groupId>org.projectlombok</groupId>
            <artifactId>lombok</artifactId>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>${maven-compiler-plugin.version}</version>
                <inherited>true</inherited>
                <configuration>
                    <source>11</source>
                    <target>11</target>
                    <parameters>true</parameters>

                    <annotationProcessorPaths>
                        <path>
                            <groupId>org.mapstruct</groupId>
                            <artifactId>mapstruct-processor</artifactId>
                            <version>${org.mapstruct.version}</version>
                        </path>
                        <!-- 整合mapstruct-lombok-->
                        <path>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok-mapstruct-binding</artifactId>
                            <version>0.2.0</version>
                        </path>
                        <path>
                            <groupId>org.projectlombok</groupId>
                            <artifactId>lombok</artifactId>
                            <version>${lombok.version}</version>
                        </path>
                        <!-- other annotation processors -->
                    </annotationProcessorPaths>
                    <showWarnings>true</showWarnings>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

2 文件结构介绍

在这里插入图片描述
以上，是源java文件，在编译之后：增加了一个UserConvertImpl的类。

2.1 各个java文件的内容

2.1.1 Score

package com.example.mapstruct;

import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

import java.math.BigDecimal;
import java.math.RoundingMode;

@Data
@NoArgsConstructor
@ToString
public class Score {
    private BigDecimal mathScore;
    private BigDecimal englishScore;
    private BigDecimal chineseScore;

    public BigDecimal getSum(){
        return mathScore.add(englishScore).add(chineseScore).setScale(2, RoundingMode.HALF_UP);
    }

    public BigDecimal getAvg(){
        return (mathScore.add(englishScore).add(chineseScore)).divide(new BigDecimal("3"), RoundingMode.HALF_UP).setScale(2, RoundingMode.HALF_UP);
    }
}

2.1.2 StudentDTO

package com.example.mapstruct;

import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;

import java.math.BigDecimal;
import java.time.LocalDateTime;

@Data
@NoArgsConstructor
@ToString
public class StudentDTO {
    private String id;
    private String studentName;
    private LocalDateTime createTime;
    private LocalDateTime updateTime;

    private BigDecimal sumScore;
    private BigDecimal avgScore;
}

2.1.3 UserConvert

这个接口是mapstruct的主要使用的位置，其实也可以定义为一个抽象类和抽象方法。这里导入了UserConvertUtil类。

package com.example.mapstruct;

import org.mapstruct.Mapper;
import org.mapstruct.Mapping;
import org.mapstruct.Mappings;

@Mapper(componentModel = "spring", imports = {UserConvertUtil.class})
public interface UserConvert {
    @Mappings({
            @Mapping(target = "studentName", source = "userDTO.name"),
            @Mapping(target = "id", expression = "java(String.valueOf(userDTO.getId()))"),
            @Mapping(target = "createTime", source = "userDTO.createTime"),
            @Mapping(target = "updateTime", source = "userDTO.updateTime"),
            @Mapping(target = "sumScore", expression = "java(UserConvertUtil.getStudentSumScore(score))"),
            @Mapping(target = "avgScore", expression = "java(score.getAvg())")
    })
    StudentDTO toStudent(UserDTO userDTO, Score score);
}

2.1.4 UserConvertUtil

这里特意使用了向转换类中引入其他类的方式。展示了另外的写法。

package com.example.mapstruct;

import java.math.BigDecimal;

public class UserConvertUtil {

    public static BigDecimal getStudentSumScore(Score score){
        return score.getSum();
    }
}

2.1.5 UserDTO

package com.example.mapstruct;

import lombok.Data;
import lombok.NoArgsConstructor;
import lombok.ToString;
import java.time.LocalDateTime;

@Data
@NoArgsConstructor
@ToString
public class UserDTO {
    private Integer id;
    private String name;
    private LocalDateTime createTime;
    private LocalDateTime updateTime;

}

2.1.6 TestService

package com.example.service;

public interface TestService {
    String test();
}

2.1.7 TestServiceImpl

package com.example.service;

import com.example.mapstruct.Score;
import com.example.mapstruct.StudentDTO;
import com.example.mapstruct.UserConvert;
import com.example.mapstruct.UserDTO;
import org.springframework.stereotype.Service;

import javax.annotation.Resource;
import java.math.BigDecimal;
import java.time.LocalDateTime;

@Service
public class TestServiceImpl implements TestService{

    @Resource
    private UserConvert userConvert;

    @Override
    public String test() {
        UserDTO userDTO = new UserDTO();
        Score score = new Score();

        userDTO.setId(1001);
        userDTO.setCreateTime(LocalDateTime.now());
        userDTO.setUpdateTime(LocalDateTime.now());
        userDTO.setName("小刘");

        score.setChineseScore(new BigDecimal("99.9"));
        score.setMathScore(new BigDecimal("67.2"));
        score.setEnglishScore(new BigDecimal("89.9"));
        StudentDTO studentDTO = userConvert.toStudent(userDTO, score);

        return studentDTO.toString();
    }
}

2.1.8 TestController

package com.example.controller;

import com.example.service.TestService;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.RestController;

import javax.annotation.Resource;

@RestController
public class TestController {

    @Resource
    private TestService testService;

    @GetMapping("/test")
    public String test(){
        return testService.test();
    }
}

2.1.9 BootDemoApplication 启动类

package com.example;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class BootDemoApplication {
    public static void main(String[] args) {
        SpringApplication.run(BootDemoApplication.class, args);
    }
}

2.2 运行结果

2.2.1 编译

当编译时，会自动生成一个 UserConvert 的实现类：

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by FernFlower decompiler)
//

package com.example.mapstruct;

import org.springframework.stereotype.Component;

@Component
public class UserConvertImpl implements UserConvert {
    public UserConvertImpl() {
    }

    public StudentDTO toStudent(UserDTO userDTO, Score score) {
        if (userDTO == null && score == null) {
            return null;
        } else {
            StudentDTO studentDTO = new StudentDTO();
            if (userDTO != null) {
                studentDTO.setStudentName(userDTO.getName());
                studentDTO.setCreateTime(userDTO.getCreateTime());
                studentDTO.setUpdateTime(userDTO.getUpdateTime());
            }

            studentDTO.setId(String.valueOf(userDTO.getId()));
            studentDTO.setSumScore(UserConvertUtil.getStudentSumScore(score));
            studentDTO.setAvgScore(score.getAvg());
            return studentDTO;
        }
    }
}

2.2.2 启动项目运行

访问：http://localhost:8080/test
得到的是：

StudentDTO{id=‘1001’, studentName=‘小刘’, createTime=2022-03-03T20:06:12.707174, updateTime=2022-03-03T20:06:12.707174, sumScore=257.00, avgScore=85.70}