ModelMapper:如何映射作为泛型传递的List<String>？
ModelMapper:如何映射作为泛型传递的List<String>？
提问于 2020-12-22 08:09:58
我有一节抽象的课：
public abstract class AbstractBeanDTO<T> extends AbstractBigDTO {
protected T value;
//getter setter
}扩展类具有泛型类型列表。
public class ItemsBeanDTO extends AbstractBeanDTO<List<String>> {
}我试图将模型类映射到DTO，DTO也具有相同的结构。
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。
我得到以下错误：
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)我试着用TypeMap解释地映射它，但是它是一样的。
modelMapper.createTypeMap(ItemsBean.class, ItemsBeanDTO.class).addMappings(mapper -> {
mapper.map(src -> src.getValue(), (dest, value) -> dest.setValue((List<String>) value));
});唯一起作用的是，当您明确声明变量为List时。(但我不想这么做)
我使用的是2.3.5版本的ModelMapper和Java8。有人能帮我一下吗？
我尝试使用typeMap和typeToken，如下所示，
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，我得到了以下错误：
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$22(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$20(BeanModelMapperFactory.java:117)
at org.modelmapper.internal.TypeMapImpl.addMappings(TypeMapImpl.java:266)回答 3
Stack Overflow用户
回答已采纳
发布于 2020-12-23 09:55:07
最后，我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手动设置列表。
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;
});Stack Overflow用户
发布于 2020-12-22 08:26:43
List是一个接口，没有构造函数。ModelMapper需要一个混凝土级，因此您需要选择List的实现，包括ArrayList或LinkedList等。
Stack Overflow用户
发布于 2021-01-05 03:58:51
您可以使用我的库豆刀代替。它是一个注释处理器。这意味着它动态地生成DTO类。您可以检查生成的类的来源，不再有魔力。转换器方法嵌入到生成的类中。它们并不复杂，但它们很麻烦，因此自动化是必要的。您可以筛选从原始类继承的属性，甚至可以更改或向生成的类添加新属性。库提供了一种通过注释实现属性转换的方法。例如，如果Integer为null，则将其转换为零。您还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;
}会产生
// 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 ...
}下面是更多的示例
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原文链接：
https://stackoverflow.com/questions/65405156
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