映射函数空参数检查

Question

我正在结合Lombok和构建器模式使用MapSTRt。我有一个问题，即MapSTRt正在对生成的映射器函数中的所有参数进行显式空检查，并在所有参数为空的情况下提前退出，例如：

// Object A
@Value
@Builder(builderClassName = "Builder")
public class SourceA{
    private int a;
}

// Object B
@Value
@Builder(builderClassName = "Builder")
public class SourceB{
    private int a;
}

// Object C
@Value
@Builder(builderClassName = "Builder")
public class SourceC{
    private int a;
}

// Object Target
@Value
@Builder(builderClassName = "Builder")
public class Target{
    private int a;
    private int b;
    private int c;
}

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

    @Mappings({
            @Mapping(target = "a", source = "sourceA.a"),
            @Mapping(target = "b", source = "sourceB.a"),
            @Mapping(target = "c", source = "sourceC.a")
    })
    Target toTarget(SourceA sourceA, SourceB sourceB, SourceC sourceC);
};

// mapstruct impl
// Auto Generated by MapStruct!
public class MapperImpl implements Mapper {
    public Target toTarget(SourceA sourceA, SourceB sourceB, SourceC sourceC){
        // Problamatic line
        if (sourceA == null && sourceB == null && sourceC == null) {
            return null;
        } else {
            Target.Builder builder = Target.builder();
            // map objects
            return builder.builder();
        }
    }
}

我想实现MapStruct不实现完整的空检查。即使所有参数都为null，它也应该设置整个生成器，并在生成器进行null检查（如果有）时调用build。

Answer 1

为了实现所需的目标，请始终使用NullValueMappingStrategy创建目标对象的默认实例。

在mapper上，您可以执行@mapper（nullValueMappingStrategy=nullValueMappingStrategy.RETURN_DEFAULT）当您执行此操作时，生成的代码应该如下所示：

public class MapperImpl implements Mapper {
    public Target toTarget(SourceA sourceA, SourceB sourceB, SourceC sourceC){

        Target.Builder builder = Target.builder();
        // map objects
        return builder.builder();
    }
}