ModelMapper：如何映射作为通用传递的 List<String>？

Question

我有一个摘要class:

public abstract class AbstractBeanDTO<T> extends AbstractBigDTO {
protected T value;

//getter setter 
}

扩展 class 具有通用类型 List

public class ItemsBeanDTO extends AbstractBeanDTO<List<String>> {
}

我正在尝试将模型 class 映射到也具有相同结构的 DTO。

AbstractBeanDTO<?> dto =  (AbstractBeanDTO<?>) modelMapper.map(modelBean, ItemsBeanDTO.class);

我的 modelMapper 配置为严格匹配。它能够转换其他泛型类型，如 Long、Integer、String 但不能转换 List。

我收到以下错误：

org.modelmapper.MappingException: ModelMapper mapping errors:

1) Failed to instantiate instance of destination java.util.List. Ensure that java.util.List has a non-private no-argument constructor.
Caused by: java.lang.NoSuchMethodException: java.util.List.<init>()
    at java.lang.Class.getConstructor0(Unknown Source)
    at java.lang.Class.getDeclaredConstructor(Unknown Source)
    at org.modelmapper.internal.MappingEngineImpl.instantiate(MappingEngineImpl.java:333)
    at org.modelmapper.internal.MappingEngineImpl.createDestination(MappingEngineImpl.java:348)
    at org.modelmapper.internal.MappingEngineImpl.typeMap(MappingEngineImpl.java:141)
    at org.modelmapper.internal.MappingEngineImpl.map(MappingEngineImpl.java:115)
    at org.modelmapper.internal.converter.MergingCollectionConverter.convert(MergingCollectionConverter.java:59)
    at org.modelmapper.internal.converter.MergingCollectionConverter.convert(MergingCollectionConverter.java:31)
    at org.modelmapper.internal.MappingEngineImpl.convert(MappingEngineImpl.java:303)
    at org.modelmapper.internal.MappingEngineImpl.map(MappingEngineImpl.java:110)
    at org.modelmapper.internal.MappingEngineImpl.setDestinationValue(MappingEngineImpl.java:242)
    at org.modelmapper.internal.MappingEngineImpl.propertyMap(MappingEngineImpl.java:188)
    at org.modelmapper.internal.MappingEngineImpl.typeMap(MappingEngineImpl.java:152)
    at org.modelmapper.internal.MappingEngineImpl.map(MappingEngineImpl.java:115)
    at org.modelmapper.internal.MappingEngineImpl.map(MappingEngineImpl.java:72)
    at org.modelmapper.ModelMapper.mapInternal(ModelMapper.java:573)
    at org.modelmapper.ModelMapper.map(ModelMapper.java:406)

我尝试使用 TypeMap 显式映射它，但它是一样的。

modelMapper.createTypeMap(ItemsBean.class, ItemsBeanDTO.class).addMappings(mapper -> {
            mapper.map(src -> src.getValue(), (dest, value) -> dest.setValue((List<String>) value));
        });

唯一有效的方法是将变量显式声明为 List。（但我不想这样做）

我正在使用 2.3.5 版的 ModelMapper 和 Java8。谁能帮我看看这是怎么回事？

我尝试如下使用 typeMap 和 typeToken，

Type listType = new TypeToken<ItemsBeanDTO>() {
        }.getType();

modelMapper.createTypeMap(ItemsBean.class, ItemsBeanDTO.class).addMappings(mapper -> {
        mapper.map(src -> src.getValue(), (dest, value) -> dest.setValue(modelMapper.map(value, listType)));
});

在这种情况下我得到以下错误：

java.lang.IllegalArgumentException: source cannot be null
    at org.modelmapper.internal.util.Assert.notNull(Assert.java:53)
    at org.modelmapper.ModelMapper.map(ModelMapper.java:493)
    at com.lowteq.model.preop.controller.config.BeanModelMapperFactory.lambda(BeanModelMapperFactory.java:117)
    at org.modelmapper.internal.ReferenceMapExpressionImpl.map(ReferenceMapExpressionImpl.java:68)
    at org.modelmapper.internal.ConfigurableConditionExpressionImpl.map(ConfigurableConditionExpressionImpl.java:65)
    at com.lowteq.model.preop.controller.config.BeanModelMapperFactory.lambda(BeanModelMapperFactory.java:117)
    at org.modelmapper.internal.TypeMapImpl.addMappings(TypeMapImpl.java:266)

Answer 1

List 是一个接口，没有构造函数。 ModelMapper 需要 concrete class，因此您需要更喜欢 List 的实现，包括 ArrayList 或 LinkedList 等

Answer 2

我终于找到了解决这个问题的方法。您可以使用 typeMap 跳过 setter 方法设置列表并使用 setProvider 手动设置它。

TypeMap<ItemsBean, ItemsBeanDTO> typeMap = modelMapper.createTypeMap(ItemsBean.class,
                ItemsBeanDTO.class);

        typeMap.addMappings(mapper -> mapper.skip(ItemsBeanDTO::set));

        typeMap.setProvider(request -> {
            ItemsBean source = ItemsBean.class.cast(request.getSource());
            ItemsBeanDTO destination = new ItemsBeanDTO();
            destination.set(source.get());
            return destination;
        });

Answer 3

您可以改用我的图书馆 beanknife。它是一个注解处理器。这意味着它会即时生成 DTO class。您可以检查生成的来源class，不再魔法。转换器方法嵌入到生成的 class 中。它们并不复杂，但很麻烦，因此自动化是必要的。您可以过滤从原始 class 继承的属性，甚至可以更改或添加新的属性到生成的 class。该库提供了一种仅通过注释 convert 和属性的方法。例如，如果 Integer 为 null，则将其转换为零。您也可以编写自己的实现。

例如：

class Pojo1 {
    String a;
    Pojo b;
}

class Pojo2 {
    Pojo1 a;
    List<Pojo1> b;
    Map<List<Pojo1>>[] c;
}

// target Pojo1, and all properties will be included except 'b'
@ViewOf(value = Pojo1.class, includePattern = ".*", excludes={Pojo1Meta.b})
class ConfigureOfPojo2 {}

// target Pojo2, and all properties will be included
@ViewOf(value = Pojo2.class, includePattern = ".*")
class ConfigureOfPojo2 {
    // convert b to dto version. 
    // Pojo1View is the generated dto class of Pojo1.
    // Of course, you can change it. But here use the default name for simpify.
    // If you want change the type or value of a existing property,
    // You should use @OverrideViewProperty.
    // Convert to dto version is internal supported.
    // For more complex case, you may need to use a method to define how the property should be deal with.
    @OverrideViewProperty(Pojo2Meta.b)
    private List<Pojo1View> b;

    // Convert c to dto version
    // BeanKnife support convert list, set, map, array of object to its dto version, only if they has the same shape.
    @OverrideViewProperty(Pojo2Meta.c)
    private Map<List<Pojo1View>>[] c;
}

将生成

// meta class, you can use it to reference the property name in a safe way.
class Pojo1Meta {
    public final String a = "a";
    public final String b = "b";
}

// generated DTO class. The actual one will be more complicate, there are many other method.
class Pojo1View {
    private String a;
    public Pojo1View read(Pojo1 source) { ... }
    ... getters and setters ...
}

class Pojo2Meta {
    public final String a = "a";
    public final String b = "b";
    public final String c = "c";
}

class Pojo2View {
    private String a;
    private List<Pojo1View> b;
    private Map<List<Pojo1View>>[] c;
    public Pojo2View read(Pojo2 source) { ... }
    ... getters and setters ...
}

还有更多examples

ModelMapper：如何映射作为通用传递的 List<String>？

ModelMapper: How to map List<String> which is passed as generic?

java

modelmapper