Java ObjectMapper.readValue将泛型类型转换为LinkedHashMap &

Question

@Service
public class PokemonManager implements PokemonService {
private HttpResponse<String> getStringHttpResponseByUrl(final String url) {
HttpClient httpClient = HttpClient.newHttpClient();
HttpRequest request = HttpRequest.newBuilder()
.GET().header("accept", "application/json")
.uri(URI.create(url)).build();
HttpResponse<String> httpResponse = null;
try {
httpResponse = httpClient.send(request, HttpResponse.BodyHandlers.ofString());
} catch (IOException | InterruptedException e) {
e.printStackTrace();
}
return httpResponse;
}
private <T> T getObjectResponse(T t, String url) {
ObjectMapper objectMapper = new ObjectMapper();
try {
t = objectMapper.readValue(getStringHttpResponseByUrl(url).body(), new TypeReference<>() {
});
} catch (JsonProcessingException e) {
e.printStackTrace();
}
return t;
}
private List<Pokemon> getAllPokemonsAsList() {
final String POSTS_API_URL = "https://pokeapi.co/api/v2/pokemon?limit=10000";
PokeApiResponse pokeApiResponse = new PokeApiResponse();
pokeApiResponse = getObjectResponse(pokeApiResponse, POSTS_API_URL);
System.out.println(pokeApiResponse);
return pokeApiResponse.results;
}
@Override
public List<Pokemon> getAll() {
return getAllPokemonsAsList();
}

我有上面的代码。如果我不使用泛型的"getObjectResponse"方法，代码可以正常工作。然而，当我使用泛型时，& & &;成为"LinkedHashMap"而不是PokeApiResponse"代码就崩溃了。我该如何解决这个问题?

Answer 1

一般使用:

objectMapper.readValue("yourJSONHere", PokeApiResponse.class);

如果你想要一个通用的T响应，也许这将工作

private <T> T getGeneric(Class<T> clazz, String json) throws IOException {
return  new ObjectMapper().readValue(json, clazz);
}

的例子:

Pokemon charmander = getGeneric(Pokemon.class, "{n" +
"  "name": "charmander"n" +
"}");

Answer 2

您没有传递足够的信息让ObjectMapper以这种方式解析JSON。也不需要传递响应的实例，您可以使用Class代替。我还将提取json解析逻辑以分离方法:

public static <T> T jsonToModel(String document, Class<T> type) throws IOException {
return new ObjectMapper().readValue(document, type);
}
private List<Pokemon> getAllPokemonsAsList() {
final String postsApiUrl = "https://pokeapi.co/api/v2/pokemon?limit=10000";
final HttpResponse<String> httpResponse = getStringHttpResponseByUrl(postsApiUrl);
final PokeApiResponse pokeApiResponse = jsonToModel(pokeApiResponse, PokeApiResponse.class);
System.out.println(pokeApiResponse);
return pokeApiResponse.results;
}