RestTemplate postForEntity get List of DTOs - json

Question

I has the same issue as mentioned in here. So I implemented my code as follows.
String url = "http://localhost:8080/admin/user/find/all/email"+"?email={email}";
ResponseEntity<List<LdapUserDto>> responseEntity = restTemplate.exchange(
url,
HttpMethod.POST,
null,
new ParameterizedTypeReference<List<LdapUserDto>>() {},
email);
Here is the DTO I used.
#Getter
#Setter
#NoArgsConstructor
#AllArgsConstructor
public class LdapUserDto {
#JsonProperty("id")
private String id;
#JsonProperty("email")
private String email;
#JsonProperty("fullName")
private String fullName;
}
The response expected from the API is as follows.
[
{
"id": "7264a0e5",
"email": "Admin#telecom.mu",
"fullName": "Administrator"
},
{
"id": "0eccd314",
"email": "ABC.John#telecom.mu",
"fullName": "ABC John"
}
]
Once I test the API, it gives me following error which I cannot understand the reason for it.
2022-08-16 01:06:48.407 DEBUG [admin,917e5c4b9e42604c,917e5c4b9e42604c] 15716 --- [nio-8080-exec-1] o.s.web.servlet.DispatcherServlet : Failed to complete request: org.springframework.web.client.RestClientException: Error while extracting response for type [java.util.List<com.cloudportal.admin.dto.response.user.LdapUserDto>] and content type [application/json;charset=UTF-8]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize value of type `java.util.ArrayList<com.cloudportal.admin.dto.response.user.LdapUserDto>` from Object value (token `JsonToken.START_OBJECT`); nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.ArrayList<com.cloudportal.admin.dto.response.user.LdapUserDto>` from Object value (token `JsonToken.START_OBJECT`)
at [Source: (org.springframework.util.StreamUtils$NonClosingInputStream); line: 1, column: 1]
2022-08-16 01:06:48.415 ERROR [admin,917e5c4b9e42604c,917e5c4b9e42604c] 15716 --- [nio-8080-exec-1] o.a.c.c.C.[.[.[/].[dispatcherServlet] : Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.web.client.RestClientException: Error while extracting response for type [java.util.List<com.cloudportal.admin.dto.response.user.LdapUserDto>] and content type [application/json;charset=UTF-8]; nested exception is org.springframework.http.converter.HttpMessageNotReadableException: JSON parse error: Cannot deserialize value of type `java.util.ArrayList<com.cloudportal.admin.dto.response.user.LdapUserDto>` from Object value (token `JsonToken.START_OBJECT`); nested exception is com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.ArrayList<com.cloudportal.admin.dto.response.user.LdapUserDto>` from Object value (token `JsonToken.START_OBJECT`)
at [Source: (org.springframework.util.StreamUtils$NonClosingInputStream); line: 1, column: 1]] with root cause
com.fasterxml.jackson.databind.exc.MismatchedInputException: Cannot deserialize value of type `java.util.ArrayList<com.cloudportal.admin.dto.response.user.LdapUserDto>` from Object value (token `JsonToken.START_OBJECT`)
at [Source: (org.springframework.util.StreamUtils$NonClosingInputStream); line: 1, column: 1]
Can anyone help me to fix this issue?

Answer 1

I reproduced the above problem. I noticed 2 things.
i) If the response is a list of objects in your case List there is no issue .
ii) If the response is a single object then you will get the above error.
I suggest you look into how you are sending the object in this API:
http://localhost:8080/admin/user/find/all/email"+"?email={email}
P.S I wouldve added this as a comment but I am short on RP.