如何在不实例化的情况下从对象填充项目列表

Question

我有一个填充的对象列表，我需要从一个对象中填充更多属性。

考虑使用mapperstruct，我无法从目标列表中修改Object的先前属性。

// type for obj in list target
public class ObjectExampleA {

    private String id;
    private String firstAttr;
    private String secondAttr;
    private String thirdAttr;
}

// target list
// List<ObjectExampleA> listTarget;

// at this point considering an elements in list like this...
// {"id":1, "firstAttr":"blue", "secondAttr":"black", "thirdAttr": null}
// {"id":2, "firstAttr":"gray", "secondAttr":"red", "thirdAttr": null}

// source obj 
public class ObjectExampleB {

    private String thirdAttr;
}

// I need to populate all thirdAttr atribute of all elements in listTarget from ObjectExampleB.thirdAttr value


@Mapper(componentModel = "spring")
public interface ExampleMapper {

    void populateThirdAttrInList(@MappingTarget List<ObjectExampleA> listTarget, ObjectExampleB objectExampleB);
}

Answer 1

执行集合元素的更新并不总是那么简单。但是，可以通过更新ObjectExampleA来以简单的方式解决您的案件。

例如

@Mapper(componentModel = "spring")
public interface ExampleMapper {

    default void populateThirdAttrInList(@MappingTarget List<ObjectExampleA> listTarget, ObjectExampleB objectExampleB) {
        for(ObjectExampleA exampleA: listTarget) {
            populateThirdAttr(exampleA, objectExampleB);
        }
    }

    void populateThirdAttr(@MappingTarget ObjectExampleA exampleA, ObjectExampleB exampleB);
}