Is it possible to extract a set of database rows with RestTemplate? - jpa

Question

I am having difficulties getting multiple datasets out of my database with RestTemplate. I have many routines that extract a single row, with a format like:
IndicatorModel indicatorModel = restTemplate.getForObject(URL + id,
IndicatorModel.class);
and they work fine. However, if I try to extract a set of data, such as:
Map<String, List<S_ServiceCoreTypeModel>> coreTypesMap =
restTemplate.getForObject(URL + id, Map.class);
this returns values in a
Map<String, LinkedHashMap<>>
format. Is there an easy way to return a List<> or Set<> in the desired format?

Answer 1

Fundamentally the issue is that your Java object model does not match the structure of your json document. You are attempting to deserialize a single json element into a java List. Your JSON document looks like:
{
"serviceCoreTypes":[
{
"serviceCoreType":{
"name":"ALL",
"description":"All",
"dateCreated":"2016-06-23 14:46:32.09",
"dateModified":"2016-06-23 14:46:32.09",
"deleted":false,
"id":1
}
},
{
"serviceCoreType":{
"name":"HSI",
"description":"High-speed Internet",
"dateCreated":"2016-06-23 14:47:31.317",
"dateModified":"2016-06-23 14:47:31.317",
"deleted":false,
"id":2
}
}
]
}
But you cannot turn a serviceCoreTypes into a List, you can only turn a Json Array into a List. For instance if you removed the unnecessary wrapper elements from your json and your input document looked like:
[
{
"name": "ALL",
"description": "All",
"dateCreated": "2016-06-23 14:46:32.09",
"dateModified": "2016-06-23 14:46:32.09",
"deleted": false,
"id": 1
},
{
"name": "HSI",
"description": "High-speed Internet",
"dateCreated": "2016-06-23 14:47:31.317",
"dateModified": "2016-06-23 14:47:31.317",
"deleted": false,
"id": 2
}
]
You should be able to then deserialize THAT into a List< S_ServiceCoreTypeModel>. Alternately if you cannot change the json structure, you could create a Java object model that models the json document by creating some wrapper classes. Something like:
class ServiceCoreTypes {
List<ServiceCoreType> serviceCoreTypes;
...
}
class ServiceCoreTypeWrapper {
ServiceCoreType serviceCoreType;
...
}
class ServiceCoreType {
String name;
String description;
...
}

Answer 2

I'm assuming you don't actually mean database, but instead a restful service as you're using RestTemplate
The problem you're facing is that you want to get a Collection back, but the getForObject method can only take in a single type parameter and cannot figure out what the type of the returned collection is.
I'd encourage you to consider using RestTemplate.exchange(...)
which should allow you request for and receive back a collection type.

Answer 3

I have a solution that works, for now at least. I would prefer a solution such as the one proposed by Ben, where I can get the HTTP response body as a list of items in the format I chose, but at least here I can extract each individual item from the JSON node. The code:
S_ServiceCoreTypeModel endModel;
RestTemplate restTemplate = new RestTemplate();
JsonNode node = restTemplate.getForObject(URL, JsonNode.class);
JsonNode allNodes = node.get("serviceCoreTypes");
JsonNode oneNode = allNodes.get(1);
ObjectMapper objectMapper = new ObjectMapper();
endModel = objectMapper.readValue(oneNode.toString(), S_ServiceCoreTypeModel.class);
If anyone has thoughts on how to make Ben's solution work, I would love to hear it.