java - 将泛型类型从一个类传递到另一个类？

Question

这更多的是泛型以及如何扩展子类以使用定义的类型的问题。

我有一个 APIResponse 类，我定义了通过泛型传递的数据类型，该类还存储其他详细信息，例如我想要传递给调用 REST 服务的 UI 的消息、错误。

当我尝试创建具有指定类型的 APIResponseEntity 实例时，出现错误。我在这里可能没有正确使用泛型，请您告诉我如何将返回的数据类型传递到 APIResponseEntity 中，最终可以在 APIResponse 中使用。

public class APIResponseEntity<T> extends ResponseEntity<APIResponse<T>> {


public APIResponseEntity(HttpStatus pStatusCode) {
    super(pStatusCode);
}

public APIResponseEntity(HttpStatus pStatusCode, MultiValueMap<String, String> pHeaders) {
    super(pHeaders, pStatusCode);
}

public APIResponseEntity(HttpStatus pStatusCode, APIResponse<T> pBody) {
    super(pBody, pStatusCode);
}

public APIResponseEntity(HttpStatus pStatusCode, APIResponse<T> pBody, MultiValueMap<String, String> pHeaders) {
    super(pBody, pHeaders, pStatusCode);
}

}

@JsonPropertyOrder({ "status", "error", "data", "messages" })
public final class APIResponse<T> {


private APIResponseStatus _status;

private T _data;

private APIError _error;

private List<APIMessage> _messages;


public APIResponse() {
    super();
    _messages = new ArrayList<>();
}

public APIResponse(T pData) {
    this();
    _status = APIResponseStatus.OK;
    _data = pData;
}

public APIResponse(APIError pError) {
    this();
    _status = APIResponseStatus.ERROR;
    _error = pError;
}


public APIResponseStatus getStatus() {
    return _status;
}

public void setStatus(APIResponseStatus pStatus) {
    _status = pStatus;
}

public Object getData() {
    return _data;
}

public void setData(T pData) {
    _data = pData;
}

public APIError getError() {
    return _error;
}

public void setError(APIError pError) {
    _error = pError;
}

public List<APIMessage> getMessages() {
    return _messages;
}

public void setMessages(List<APIMessage> pMessages) {
    _messages = pMessages;
}

private void addMessage(APIMessageStatus pMessageStatus, String pMessage) {
    _messages.add(new APIMessage(pMessageStatus, pMessage));
}

public void addMessageInfo(String pMessage) {
    addMessage(APIMessageStatus.INFO, pMessage);
}

public void addMessageWarning(String pMessage) {
    addMessage(APIMessageStatus.WARNING, pMessage);
}

public void addMessageError(String pMessage) {
    addMessage(APIMessageStatus.ERROR, pMessage);
}

当我尝试使用泛型创建 APIResponseEntity 对象时出现编译错误

@RequestMapping(value = "/banks", method = RequestMethod.GET)
public APIResponseEntity<List<Bank>> getBanks(WebRequest pWebRequest) {

    IUser user = getUser(pWebRequest);
    BankCriteria criteria = new BankCriteria();
    List<Bank> banks= _bankService.getBanks(user, criteria);
    APIResponse<List<Bank>> response = new APIResponse<>(banks);
    APIResponseEntity<List<Bank>> entity =  new APIResponseEntity<>(HttpStatus.OK, banks); // errror , cannot infer type arguments for APIResponseEntity
    return entity;

}

Answer 1

你为什么使用new APIResponseEntity<>(HttpStatus.OK, banks)而不是new APIResponseEntity<>(HttpStatus.OK, response) ？您没有APIResponseEntity构造函数采用 List<>作为定义的第二个参数。

将代码更改为:

@RequestMapping(value = "/banks", method = RequestMethod.GET)
public APIResponseEntity<List<Bank>> getBanks(WebRequest pWebRequest) {

    IUser user = getUser(pWebRequest);
    BankCriteria criteria = new BankCriteria();
    List<Bank> banks= _bankService.getBanks(user, criteria);
    APIResponse<List<Bank>> response = new APIResponse<>(banks);
    APIResponseEntity<List<Bank>> entity =  new APIResponseEntity<List<Bank>>(HttpStatus.OK, response); // errror , cannot infer type arguments for APIResponseEntity
    return entity;
}