MapStruct @MappingTarget 更新机制详解与问题排查指南

public class Destination {
    private String id; // 移除final修饰符
    private String other; // 移除final修饰符

    // 构造函数可以保留，用于初始化或创建新实例
    public Destination(String id, String other) {
        this.id = id;
        this.other = other;
    }

    public String getId() {
        return id;
    }

    public String getOther() {
        return other;
    }

    // 添加公共的setter方法，这是MapStruct更新的关键
    public void setId(String id) {
        this.id = id;
    }

    public void setOther(String other) {
        this.other = other;
    }
}

public class Source {
    private final String id;
    private final String other;

    public Source(String id, String other) {
        this.id = id;
        this.other = other;
    }

    public String getId() {
        return id;
    }

    public String getOther() {
        return other;
    }
}

public class Destination {
    private String id;
    private String other;

    public Destination(String id, String other) {
        this.id = id;
        this.other = other;
    }

    public String getId() {
        return id;
    }

    public String getOther() {
        return other;
    }

    public void setId(String id) {
        this.id = id;
    }

    public void setOther(String other) {
        this.other = other;
    }
}

import org.mapstruct.Mapper;
import org.mapstruct.MappingTarget;
import org.mapstruct.factory.Mappers;

@Mapper // 标记为MapStruct映射器
public interface MyMapper {

    MyMapper INSTANCE = Mappers.getMapper(MyMapper.class); // 获取映射器实例

    // 创建新目标对象的方法
    Destination createDestinationFromSource(Source source);

    // 更新现有目标对象的方法，返回类型为void，通过@MappingTarget修改传入的destination实例
    void updateDestinationFromSource(Source source, @MappingTarget Destination destination);
}

<dependencies>
    <dependency>
        <groupId>org.mapstruct</groupId>
        <artifactId>mapstruct</artifactId>
        <version>1.5.2.Final</version> <!-- 使用您需要的版本 -->
    </dependency>
</dependencies>

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.maven.plugins</groupId>
            <artifactId>maven-compiler-plugin</artifactId>
            <version>3.8.1</version> <!-- 确保使用兼容的编译器版本 -->
            <configuration>
                <source>17</source> <!-- 根据您的Java版本调整 -->
                <target>17</target> <!-- 根据您的Java版本调整 -->
                <annotationProcessorPaths>
                    <path>
                        <groupId>org.mapstruct</groupId>
                        <artifactId>mapstruct-processor</artifactId>
                        <version>1.5.2.Final</version> <!-- 处理器版本应与mapstruct版本一致 -->
                    </path>
                </annotationProcessorPaths>
            </configuration>
        </plugin>
    </plugins>
</build>

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

class MapStructUpdateTest {

    @Test
    void testMapStructCreationAndUpdate() {
        // 1. 创建操作验证
        var source1 = new Source("sourceId1", "sourceOther1");
        var destination1 = MyMapper.INSTANCE.createDestinationFromSource(source1);

        Assertions.assertEquals("sourceId1", destination1.getId());
        Assertions.assertEquals("sourceOther1", destination1.getOther());
        System.out.println("创建成功: " + destination1.getId() + ", " + destination1.getOther());

        // 2. 更新操作验证
        var source2 = new Source("sourceId2", "sourceOther2"); // 新的源数据
        var destinationToUpdate = new Destination("initialDestId", "initialDestOther"); // 待更新的目标对象

        System.out.println("更新前: " + destinationToUpdate.getId() + ", " + destinationToUpdate.getOther());
        MyMapper.INSTANCE.updateDestinationFromSource(source2, destinationToUpdate); // 执行更新

        // 验证更新是否成功
        Assertions.assertEquals("sourceId2", destinationToUpdate.getId());
        Assertions.assertEquals("sourceOther2", destinationToUpdate.getOther());
        System.out.println("更新后: " + destinationToUpdate.getId() + ", " + destinationToUpdate.getOther());
    }
}