杰克逊通用json到List< T>转换器方法不起作用 [英] Jackson generic json to List<T> converter method does not work
问题描述
public static <T> List<T> convertJSONStringTOListOfT(String jsonString, Class<T> t){
if(jsonString == null){
return null;
}
ObjectMapper mapper = new ObjectMapper();
try
{
List<T> list = mapper.readValue(jsonString, new TypeReference<List<T>>() {});
return list;
} catch (JsonGenerationException e) {
e.printStackTrace();
} catch (JsonMappingException e) {
e.printStackTrace();
} catch (IOException e) {
e.printStackTrace();
}
return null;
}
当我尝试使用以下方法调用它时,我有上述方法:
I have the above method, when I try to invoke it using :
list = convertJSONStringTOListOfT(str, CustomAssessmentQuestionSetItem.class);
返回的列表是列表< LinkedHashMap>
不是列表< CustomAssessmentQuestionSetItem>
虽然如果我不使用泛型,那么下面的代码可以正常工作:
Although if I don't use generics then the below code works fine :
list = mapper.readValue(str, new TypeReference<List<CustomAssessmentQuestionSetItem>>() {});
两次调用对我来说都是一样的。无法理解为什么通用的创建列表< LinkedHashMap>
而不是列表< CustomAssessmentQuestionSetItem>
Both invocations appear the same to me. Unable to understand why the generic one is creating a List<LinkedHashMap>
instead of List<CustomAssessmentQuestionSetItem>
仅供参考:我还尝试将方法签名更改为
FYI : I've also tried changing the method signature to
public static <T> List<T> convertJSONStringTOListOfT(String jsonString, T t)
以及相应的调用
list = convertJSONStringTOListOfT(str,new CustomAssessmentQuestionSetItem());
但它没有用。
推荐答案
由于你有元素类,你可能想要使用你的映射器的 TypeFactory
,如下所示:
Since you have the element class you probably want to use your mapper's TypeFactory
like this:
final TypeFactory factory = mapper.getTypeFactory();
final JavaType listOfT = factory.constructCollectionType(List.class, t);
然后使用 listOfT
作为你的第二个参数 .readValue()
。
Then use listOfT
as your second argument to .readValue()
.
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