java 无法获得通用 ResponseEntity<T>，其中 T 是通用类“SomeClass<SomeGenericType>”
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Unable to get a generic ResponseEntity<T> where T is a generic class "SomeClass<SomeGenericType>"
提问by IgorA
Please help me to get a ResponseEntity<T>where Tis itself a generic type. As I see it of now, this is not supported nowdays by spring RestTemplate. I'm using Spring MVC version 3.1.2
请帮我得到一个ResponseEntity<T>whereT本身就是一个泛型类型。正如我现在所见，现在 Spring RestTemplate 不支持此功能。我使用的是 Spring MVC 3.1.2 版
Here is my code, that I want to use: Code:
这是我要使用的代码：代码：
ResponseEntity<CisResponse<CisResponseEntity>> res =
this.restTemplate.postForEntity(
this.rootURL, myRequestObj, CisResponse.class);
I'm getting this error:
我收到此错误：
Type mismatch: cannot convert from ResponseEntity<CisResponse> to
ResponseEntity<CisResponse<CisResponseEntity>>
It's obvious error, but how I can workaround it today?
这是明显的错误，但我今天如何解决它？
Than I do want to get my generic response type:
比我想得到我的通用响应类型：
CisResponse<CisResponseEntity> myResponse= res.getBody();
CisResponseEntity entity = myResponse.getEntityFromResponse();
For now, I use this solution, with postForObject()and not postForEntity():
现在，我使用这个解决方案，postForObject()而不是postForEntity()：
CisResponse<CisResponseEntity> response =
this.restTemplate.postForObject(
this.rootURL,myRequestObj, CisResponse.class);
回答by Raffaele
This was a known issue. Now it's fixed with the introduction of ParameterizedTypeReference, which is a parameterized type that you explicitely inheritto supply type information at runtime. This is called a super-type token, and works around type erasure because subclasses (anoniymous in this case) keep the type arguments of the generic supertypeat runtime.
这是一个已知问题。现在它通过引入来修复ParameterizedTypeReference，它是一个参数化类型，您显式继承它以在运行时提供类型信息。这称为超类型标记，并且可以解决类型擦除问题，因为子类（在这种情况下是匿名的）在运行时保留泛型超类型的类型参数。
However you can't use postForObject, because the API only supports exchange():
但是您不能使用postForObject，因为该 API 仅支持exchange()：
ResponseEntity<CisResponse<CisResponseEntity>> res = template.exchange(
rootUrl,
HttpMethod.POST,
null,
new ParameterizedTypeReference<CisResponse<CisResponseEntity>>() {});
Note that the last line demonstrates the idea of super type tokens: you don't supply the literal CisResponse.class, but an anonymous instantiation of the parameterized type ParameterizedTypeReference<T>, which at runtime can be expected to extract subtype information. You can think of super type tokens as hacksfor achieving Foo<Bar<Baz>>.class
请注意，最后一行演示了超类型标记的想法：您不提供文字CisResponse.class，而是提供参数化类型的匿名实例化ParameterizedTypeReference<T>，它可以在运行时提取子类型信息。你能想到的超类型令牌作为黑客实现Foo<Bar<Baz>>.class
BTW, in Java you don't need to prefix access to instance variable with this: if your object defines a urland templatemembers, just access them with their simple name, and not by prefixing like you do this.urland this.template
顺便说一句，在 Java 中，您不需要使用前缀访问实例变量this：如果您的对象定义了 aurl和template成员，只需使用它们的简单名称访问它们，而不是像您那样通过前缀访问this.url和this.template
