java 如何将 Jackson 的 TypeReference 与泛型一起使用？
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How to use Hymanson's TypeReference with generics?
提问by Mark Korzhov
For json mapping I use the following method:
对于 json 映射，我使用以下方法：
public static <T> T mapJsonToObject(String json, T dtoClass) throws Exception {
ObjectMapper mapper = new ObjectMapper();
return mapper.readValue(json, new TypeReference<RestResponse<UserDto>>() {
});
}
And UserDtolooks like this:
而UserDto看起来是这样的：
@JsonIgnoreProperties(ignoreUnknown = true)
public class UserDto {
@JsonProperty("items")
private List<User> userList;
public List<User> getUserList() {
return userList;
}
public void setUserList(List<User> userList) {
this.userList = userList;
}
}
I want to improve this method of mapping without being attached to a UserDtoclass, and replacing it with a generic.
我想在不附加到UserDto类的情况下改进这种映射方法，并将其替换为泛型。
Is it possible? And How?
是否可以？如何？
Thanks.
谢谢。
回答by StaxMan
TypeReferencerequires you to specify parameters statically, not dynamically, so it does not work if you need to further parameterize types.
TypeReference要求您静态地而不是动态地指定参数，因此如果您需要进一步参数化类型，它不起作用。
What I think you need is JavaType: you can build instances dynamically by using TypeFactory. You get an instance of TypeFactoryvia ObjectMapper.getTypeFactory(). You can also construct JavaTypeinstances from simple Classas well as TypeReference.
我认为您需要的是JavaType：您可以使用TypeFactory. 你得到一个TypeFactoryvia的实例ObjectMapper.getTypeFactory()。您还可以JavaType从 simpleClass和TypeReference.
回答by Marcel Baumann
One approach will be to define a Hymanson JavaTyperepresenting a list of items of type clazz. You still need to have access to the class of the generic parameter at runtime. The usual approach is something like
一种方法是定义一个 Hymanson JavaType，表示clazz类型的项目列表。您仍然需要在运行时访问泛型参数的类。通常的方法是这样的
<T> class XX { XX(Class<T> clazz, ...) ... }
to pass the class of the generic parameter into the generic class at construction.
在构造时将泛型参数的类传递到泛型类中。
Upon access to the Class clazzvariable you can construct a Hymanson JavaType representing, for example, a list of items of class clazzwith the following statement.
在访问 Class clazz变量时，您可以构造一个 Hymanson JavaType 表示，例如，使用以下语句表示类clazz的项目列表。
JavaType itemType = mapper.getTypeFactory().constructCollectionType(List.class, clazz);
I hope it helped. I am using this approach in my own code.
我希望它有所帮助。我在自己的代码中使用这种方法。
