Get list of JSON objects with Spring RestTemplate

Navigating the JSON Jungle

The complicated JSON structure can often feel like a labyrinth. Follow these breadcrumbs to map your way out:

1. Internal Object Mapping: Mirror the JSON's nested structures using individual classes.
2. Handle Unexpected Turns: Prevent errors induced by unknown JSON fields with @JsonIgnoreProperties(ignoreUnknown = true).
3. Know Your Path: Reflect on the JSON's hierarchy and data types for precise mapping to Java objects.

Deciphering Server Responses

When you use restTemplate.exchange, the responses are wrapped up snugly in a ResponseEntity<List<T>>. It's a package full of goodies, like response status codes and headers:

ResponseEntity<List<MyObject>> responseEntity = restTemplate.exchange(
  "http://api.url/endpoint", 
  HttpMethod.GET,
  null, 
  new ParameterizedTypeReference<List<MyObject>>() {}
);
HttpStatus statusCode = responseEntity.getStatusCode();  // status code, or "I wonder what happened with my request"


• Server-Side Detective: Use HttpStatus for off-the-books investigation of server responses.
• Knowing the Package Content: Use MediaType to ensure you've got the right stuff.

From Arrays to the List Life

Arrays are like the college dorm rooms of data storage: crammed and inflexible. Upgrade to a roomier List apartment with a simple line:

MyObject[] array = restTemplate.getForObject("http://api.url/endpoint", MyObject[].class);
List<MyObject> list = Arrays.asList(array);  // "Freedom, sweet freedom!"


Generic Deals: A Reflection

Generics are like supermarket items in an opaque bag. You know it's food; you just don't know what type, thanks to type erasure. Here's how to peek inside the bag:

• Use ParameterizedTypeReference in fetching lists with generics to keep your type's info intact.
• For flexibility in REST endpoints, use ResponseEntity<?> as a return type within @Controller methods. It's like having a multi-cuisine restaurant!

Combine Kotlin and Spring for Less Code

In case you fancy a side of Kotlin with your Spring, here's how to cut down on verbosity when dealing with JSON:

restTemplate.exchange<List<MyObject>>(
  "http://api.url/endpoint",
  HttpMethod.GET,
  null,
  object : ParameterizedTypeReference<List<MyObject>>() {}
)?.body


In Kotlin, type inference can come to your rescue and keep your ParameterizedTypeReference in sight but out of your hair. It's like having your cake and eating it too!