Collectives™ on Stack Overflow
Find centralized, trusted content and collaborate around the technologies you use most.
Learn more about Collectives
Teams
Q&A for work
Connect and share knowledge within a single location that is structured and easy to search.
Learn more about Teams
How to map a list of JSON objects using Spring RestTemplate.
How to map nested JSON objects.
I am trying to consume
https://bitpay.com/api/rates
, by following the tutorial from
http://spring.io/guides/gs/consuming-rest/
.
–
First define an object to hold the entity coming back in the array.. e.g.
@JsonIgnoreProperties(ignoreUnknown = true)
public class Rate {
private String name;
private String code;
private Double rate;
// add getters and setters
Then you can consume the service and get a strongly typed list via:
ResponseEntity<List<Rate>> rateResponse =
restTemplate.exchange("https://bitpay.com/api/rates",
HttpMethod.GET, null, new ParameterizedTypeReference<List<Rate>>() {
List<Rate> rates = rateResponse.getBody();
The other solutions above will also work, but I like getting a strongly typed list back instead of an Object[].
–
–
–
Maybe this way...
ResponseEntity<Object[]> responseEntity = restTemplate.getForEntity(urlGETList, Object[].class);
Object[] objects = responseEntity.getBody();
MediaType contentType = responseEntity.getHeaders().getContentType();
HttpStatus statusCode = responseEntity.getStatusCode();
Controller code for the RequestMapping
@RequestMapping(value="/Object/getList/", method=RequestMethod.GET)
public @ResponseBody List<Object> findAllObjects() {
List<Object> objects = new ArrayList<Object>();
return objects;
ResponseEntity is an extension of HttpEntity that adds a HttpStatus status code. Used in RestTemplate as well @Controller methods.
In RestTemplate this class is returned by getForEntity() and exchange().
–
–
–
–
Object[] forNow = template.getForObject("URL", Object[].class);
searchList= Arrays.asList(forNow);
Where Object is the class you want
–
–
–
then using ParameterizedTypeReference of List of BitPay you can use as:
RestTemplate restTemplate = new RestTemplate();
ResponseEntity<List<Employee>> response = restTemplate.exchange(
"https://bitpay.com/api/rates",
HttpMethod.GET,
null,
new ParameterizedTypeReference<List<BitPay>>(){});
List<Employee> employees = response.getBody();
If you would prefer a List of POJOs, one way to do it is like this:
class SomeObject {
private int id;
private String name;
public <T> List<T> getApi(final String path, final HttpMethod method) {
final RestTemplate restTemplate = new RestTemplate();
final ResponseEntity<List<T>> response = restTemplate.exchange(
path,
method,
null,
new ParameterizedTypeReference<List<T>>(){});
List<T> list = response.getBody();
return list;
And use it like so:
List<SomeObject> list = someService.getApi("http://localhost:8080/some/api",HttpMethod.GET);
Explanation for the above can be found here (https://www.baeldung.com/spring-rest-template-list) and is paraphrased below.
There are a couple of things happening in the code above. First, we use ResponseEntity as our return type, using it to wrap the list of objects we really want. Second, we are calling RestTemplate.exchange() instead of getForObject().
This is the most generic way to use RestTemplate. It requires us to specify the HTTP method, optional request body, and a response type. In this case, we use an anonymous subclass of ParameterizedTypeReference for the response type.
This last part is what allows us to convert the JSON response into a list of objects that are the appropriate type. When we create an anonymous subclass of ParameterizedTypeReference, it uses reflection to capture information about the class type we want to convert our response to.
It holds on to this information using Java’s Type object, and we no longer have to worry about type erasure.
–
After multiple tests, this is the best way I found :)
Set<User> test = httpService.get(url).toResponseSet(User[].class);
All you need there
public <T> Set<T> toResponseSet(Class<T[]> setType) {
HttpEntity<?> body = new HttpEntity<>(objectBody, headers);
ResponseEntity<T[]> response = template.exchange(url, method, body, setType);
return Sets.newHashSet(response.getBody());
3 alternative ways have mentioned here to retrieve list of objects. All of these will work flawlessly
@RequestMapping(value = "/emp2", produces = "application/json")
public List<Employee> getEmp2()
HttpHeaders headers = new HttpHeaders();
headers.setAccept(Arrays.asList(MediaType.APPLICATION_JSON));
HttpEntity<String> entity = new HttpEntity<String>(headers);
ResponseEntity<List<Employee>> response = restTemplate.exchange(
"http://hello-server/rest/employees", HttpMethod.GET,entity,
new ParameterizedTypeReference<List<Employee>>() {});
return response.getBody();
@RequestMapping(value = "/emp3", produces = "application/json")
public List<Employee> getEmp3()
Employee[] empArray = restTemplate.getForObject("http://hello-server/rest/employees", Employee[].class);
List<Employee> emp= Arrays.asList(empArray);
return emp;
@RequestMapping(value = "/emp4", produces = "application/json")
public Employee[] getEmp4()
ResponseEntity<Employee[]> responseEntity = restTemplate.getForEntity("http://hello-server/rest/employees", Employee[].class);
Employee[] empList = responseEntity.getBody();
//MediaType contentType = responseEntity.getHeaders().getContentType();
//HttpStatus statusCode = responseEntity.getStatusCode();
return empList;
Employee.class
public class Employee {
private Integer id;
private String name;
private String Designation;
private String company;
//getter setters and toString()
i actually deveopped something functional for one of my projects before and here is the code :
* @param url is the URI address of the WebService
* @param parameterObject the object where all parameters are passed.
* @param returnType the return type you are expecting. Exemple : someClass.class
public static <T> T getObject(String url, Object parameterObject, Class<T> returnType) {
try {
ResponseEntity<T> res;
ObjectMapper mapper = new ObjectMapper();
RestTemplate restTemplate = new RestTemplate();
restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
restTemplate.getMessageConverters().add(0, new StringHttpMessageConverter(Charset.forName("UTF-8")));
((SimpleClientHttpRequestFactory) restTemplate.getRequestFactory()).setConnectTimeout(2000);
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);
HttpEntity<T> entity = new HttpEntity<T>((T) parameterObject, headers);
String json = mapper.writeValueAsString(restTemplate.exchange(url, org.springframework.http.HttpMethod.POST, entity, returnType).getBody());
return new Gson().fromJson(json, returnType);
} catch (Exception e) {
e.printStackTrace();
return null;
* @param url is the URI address of the WebService
* @param parameterObject the object where all parameters are passed.
* @param returnType the type of the returned object. Must be an array. Exemple : someClass[].class
public static <T> List<T> getListOfObjects(String url, Object parameterObject, Class<T[]> returnType) {
try {
ObjectMapper mapper = new ObjectMapper();
RestTemplate restTemplate = new RestTemplate();
restTemplate.getMessageConverters().add(new MappingJackson2HttpMessageConverter());
restTemplate.getMessageConverters().add(0, new StringHttpMessageConverter(Charset.forName("UTF-8")));
((SimpleClientHttpRequestFactory) restTemplate.getRequestFactory()).setConnectTimeout(2000);
HttpHeaders headers = new HttpHeaders();
headers.setContentType(MediaType.APPLICATION_JSON);
HttpEntity<T> entity = new HttpEntity<T>((T) parameterObject, headers);
ResponseEntity<Object[]> results = restTemplate.exchange(url, org.springframework.http.HttpMethod.POST, entity, Object[].class);
String json = mapper.writeValueAsString(results.getBody());
T[] arr = new Gson().fromJson(json, returnType);
return Arrays.asList(arr);
} catch (Exception e) {
e.printStackTrace();
return null;
I hope that this will help somebody !
In my case I preferred to extract a String then browse the context using JsonNode interface
var response = restTemplate.exchange("https://my-url", HttpMethod.GET, entity, String.class);
if (response.getStatusCode() == HttpStatus.OK) {
var jsonString = response.getBody();
ObjectMapper mapper = new ObjectMapper();
JsonNode actualObj = mapper.readTree(jsonString);
System.out.println(actualObj);
or quickly
ObjectNode actualObj= restTemplate.getForObject("https://my-url", ObjectNode.class);
then read inner data with path expression i.e.
boolean b = actualObj.at("/0/states/0/no_data").asBoolean();
An Easier Way:
I will show you guys both with Authorization heard and without Authorization header:
Without Authorization:
a. Do Dependency Injection(Constructor Injection):
You can also prefer field injection. I considered constructor injection.
public class RestTemplateService {
private final RestTemplate template;
public RestTemplateService(RestTemplate template) {
this.template = template;
b. Invoke getList() method:
public ResponseEntity<List> getResponseList(String url, HttpMethod type) {
return template.exchange(url, type, new HttpEntity<>(new HttpHeaders()), List.class);
With Authorization: I love small methods. So I segregated the functionalities as such:
public ResponseEntity<List> getResponse(String url, HttpMethod type) {
return template.exchange(url, type, getRequest(getHeaders(USERNAME, PASS)), List.class);
private HttpEntity<String> getRequest(HttpHeaders headers) {
return new HttpEntity<>(headers);
private HttpHeaders getHeaders(String username, String password) {
HttpHeaders headers = new HttpHeaders();
headers.add("Authorization", "Basic " + new String(Base64.encodeBase64((username + ":" + password).getBytes())));
return headers;
Hopefully the problem will be resolved!
I found work around from this post https://jira.spring.io/browse/SPR-8263.
Based on this post you can return a typed list like this:
ResponseEntity<? extends ArrayList<User>> responseEntity = restTemplate.getForEntity(restEndPointUrl, (Class<? extends ArrayList<User>>)ArrayList.class, userId);
–
