Get list of JSON objects with Spring RestTemplate

Question

I have two questions    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

User · Answer

My big issue here was to build the Object structure required to match RestTemplate to a compatible Class  Luckily I found http   www jsonschema2pojo org   get the JSON response in a browser and use it as input  and I can t recommend this enough

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After multiple tests  this is the best way I found     Set lt User gt  test   httpService get url  toResponseSet User   class     All you need there  public  lt T gt  Set lt T gt  toResponseSet Class lt T   gt  setType        HttpEntity lt   gt  body   new HttpEntity lt  gt  objectBody  headers       ResponseEntity lt T   gt  response   template exchange url  method  body  setType       return Sets newHashSet response getBody

User · Answer

For me this worked   Object   forNow   template getForObject  URL   Object   class       searchList  Arrays asList forNow     Where Object is the class you want

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You can create POJO for each entry like   class BitPay  private String code  private String name  private double rate      then using ParameterizedTypeReference of List of BitPay you can use as   RestTemplate restTemplate   new RestTemplate    ResponseEntity lt List lt Employee gt  gt  response   restTemplate exchange     https   bitpay com api rates     HttpMethod GET    null    new ParameterizedTypeReference lt List lt BitPay gt  gt        List lt Employee gt  employees   response getBody

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In my case I preferred to extract a String then browse the context using JsonNode interface     var response    restTemplate exchange  quot https   my-url quot   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  quot https   my-url quot   ObjectNode class    then read inner data with path expression  i e  boolean b   actualObj at  quot  0 states 0 no data quot   asBoolean

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Consider see this answer  specially if you want use generics in List Spring RestTemplate and generic types ParameterizedTypeReference collections like List lt T gt

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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  lt T gt  List lt T gt  getApi final String path  final HttpMethod method             final RestTemplate restTemplate   new RestTemplate        final ResponseEntity lt List lt T gt  gt  response   restTemplate exchange        path        method        null        new ParameterizedTypeReference lt List lt T gt  gt            List lt T gt  list   response getBody        return list     And use it like so   List lt SomeObject gt  list   someService getApi  quot http   localhost 8080 some api quot  HttpMethod GET    Explanation for the above can be found here  https   www baeldung com spring-rest-template-list  and is paraphrased below   quot 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  quot

User · Answer

Maybe this way     ResponseEntity lt Object   gt  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 lt Object gt  findAllObjects          List lt Object gt  objects   new ArrayList lt Object gt         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

User · Answer

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  lt T gt  T getObject String url  Object parameterObject  Class lt T gt  returnType        try           ResponseEntity lt T gt  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 lt T gt  entity   new HttpEntity lt T gt   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  lt T gt  List lt T gt  getListOfObjects String url  Object parameterObject  Class lt T   gt  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 lt T gt  entity   new HttpEntity lt T gt   T  parameterObject  headers           ResponseEntity lt Object   gt  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

User · Answer

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 lt   extends ArrayList lt User gt  gt  responseEntity   restTemplate getForEntity restEndPointUrl   Class lt   extends ArrayList lt User gt  gt  ArrayList class  userId

User · Answer

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 lt List lt Rate gt  gt  rateResponse           restTemplate exchange  https   bitpay com api rates                       HttpMethod GET  null  new ParameterizedTypeReference lt List lt Rate gt  gt                      List lt Rate gt  rates   rateResponse getBody      The other solutions above will also work  but I like getting a strongly typed list back instead of an Object

[java] Get list of JSON objects with Spring RestTemplate

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