如何防止创建空对象

Question

我试图将每个列表都位于嵌套对象内的webservice模型映射到更简单的对象。

1. 模型1

public class Parent {
   private Children children;
}

public class Children {
   private List<Child> children;
}

public class Child {
}

public class Parent2 {
   private List<Child2> children;
}

public class Child {
}

映射非常简单：

@Mappings({@Mapping(source = "entity.children.children", target = "children")})
Parent2 parentToParent2(Parent entity);
@InheritInverseConfiguration
Parent parent2ToParent(Parent2 entity);

映射工作正常，除了一个问题。当我将带有null子级的父母映射到父母2并返回父母时，儿童对象是用空列表创建的。有什么方法可以防止这种情况吗？

Answer 1

您可以使用映射器装饰器或AfterMapping钩子来实现这一点。

装饰：

public abstract class MapperDecorator implements Mapper {

    private final Mapper delegate;

    public MapperDecorator(Mapper delegate) {
        this.delegate = delegate;
    }

    @Override
    public Parent parent2ToParent(Parent2 entity) {
        Parent parent = delegate.parent2ToParent(entity);

        if (entity.getChildren() == null) {
            parent.setChildren(null);
        }

        return parent;
    }
}

映射器：

@org.mapstruct.Mapper
@DecoratedWith(MapperDecorator.class)
public interface Mapper {
    @Mapping(source = "entity.children.children", target = "children")
    Parent2 parentToParent2(Parent entity);

    @InheritInverseConfiguration
    Parent parent2ToParent(Parent2 entity);

    Child2 childToChild2(Child entity);

    Child child2ToChild(Child2 entity);
}

映射器：

@org.mapstruct.Mapper
public abstract class Mapper {
    @Mapping(source = "entity.children.children", target = "children")
    public abstract Parent2 parentToParent2(Parent entity);

    @InheritInverseConfiguration
    public abstract Parent parent2ToParent(Parent2 entity);

    public abstract Child2 childToChild2(Child entity);

    public abstract Child child2ToChild(Child2 entity);

    @AfterMapping
    public void afterParent2ToParent(Parent2 source,
                                     @MappingTarget Parent target) {
        if (source.getChildren() == null) {
            target.setChildren(null);
        }
    }
}