Similar to this question, I want to exchange information between two microservices. However the difference is, that my generics is an abstract class and by this I'm having trouble.
My class looks like that:
public <T extends Account> Page<T> getAllAccounts() { // not working
ParameterizedTypeReference<Page<T>> responseType = new ParameterizedTypeReference<Page<T>>() { };
ResponseEntity<Page<T>> result = restTemplate.exchange("http://localhost:8080/api/v1/accounts/", HttpMethod.GET, null, responseType);
Page<T> accounts = result.getBody();
return accounts;
}
The function behind the API-call has the return type public <T extends Account> Page<T> getAccounts...) {..}. T can be everything that extends Account, because there are several "Accounts" possible.
The given method also works for non-abstract classes (e.g. Page<CustomerAccount>), however with abstract classes it doesn't.
If I try to call the function, I get the following error message:
This application has no explicit mapping for /error, so you are seeing this as a fallback.
Fri Dec 18 14:55:33 CET 2020
There was an unexpected error (type=Internal Server Error, status=500).
Type definition error: [simple type, class org.springframework.data.domain.Page]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `org.springframework.data.domain.Page` (no Creators, like default constructor, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information at [Source: (PushbackInputStream); line: 1, column: 1]
org.springframework.http.converter.HttpMessageConversionException: Type definition error: [simple type, class org.springframework.data.domain.Page]; nested exception is com.fasterxml.jackson.databind.exc.InvalidDefinitionException: Cannot construct instance of `org.springframework.data.domain.Page` (no Creators, like default constructor, exist): abstract types either need to be mapped to concrete types, have custom deserializer, or contain additional type information
at [Source: (PushbackInputStream); line: 1, column: 1]
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.readJavaType(AbstractJackson2HttpMessageConverter.java:282)
at org.springframework.http.converter.json.AbstractJackson2HttpMessageConverter.read(AbstractJackson2HttpMessageConverter.java:243)
at org.springframework.web.client.HttpMessageConverterExtractor.extractData(HttpMessageConverterExtractor.java:105)
at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:1034)
at org.springframework.web.client.RestTemplate$ResponseEntityResponseExtractor.extractData(RestTemplate.java:1017)
at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:777)
at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:710)
at org.springframework.web.client.RestTemplate.exchange(RestTemplate.java:630)
at de.rwth.swc.lab.ws2021.daifu.businesslogic.services.AccountService.getAllAccounts(AccountService.java:50)
at de.rwth.swc.lab.ws2021.daifu.businesslogic.api.AccountController.getAllAccounts(AccountController.java:47)
... (rest shortend for better readability)
Question
How can I communicate from Port 8081 with the MS running on port 8080 with "abstract generics" (I think you call them different, but idk atm :D)