Unable to parse json into list of custom Java objects-CodePudding

I am reading JSON from a file, and when trying to unmarshal the file to a java object, I am not getting expected array of custom Java object, however, getting array of LinkedHashMap

Please see below objects

    public class Result<T>{
        private final Map<String, T> data = new LinkedHashMap<>();
    
         public Map<String, T> getAccounts(){
             return accounts;
         }
    }

JSON ->
{
   "data":{
     "account":[
           {
               "accountDetails":{
                      "accountId":"123",
                      "accountType":"Decon"
               }
           },
           {
               "accountDetails":{
                      "accountId":"890",
                      "accountType":"ACX"
               }
           },
           {
               "accountDetails":{
                      "accountId":"123",
                      "accountType":"OOOP"
               }
           }
     ]
   }
}


@Getter
@Setter
@ToString
public class Accounts{
   
   @Getter
   @Setter
   public static class AcountDetails{
      private String accountId;
      private String accountType;
   }
}

I am trying to read this Json as below

 String accounts = Resource.asByteSource(Resources.getResource("account.json")).asCharSource(Charsets.UTF_8).read();
    ObjectMapper mapper = new ObjectMapper();
    Result<List<Accounts> finalResult = mapper.readValue(accounts, Result.class);



 In finalResult variable , 
    
    I am getting a map with key as "account" and value as list
    But, instead of List of "Accounts" object, I am getting list of **LinkedHashMap**

So bascially after parsing, Instead of getting array of Accounts objects, I am getting array of LinkedHashMap

Please find attached screenshot. Please advise

CodePudding user response：

If you are trying to get an Array of objects, your JSON would have to look something like this:

"element": [
{
  "element1": "Value 1",
  "element2": "Value 1"
},
{
  "element1": "Value 1",
  "element2": "Value 1"
}
]

When you are defining another object as you did:

"account":[
       {
           "accountDetails":{
                  "accountId":"123",
                  "accountType":"Decon"
           }
       },

You are creating a List of an Object that contains two more Objects. In Java that's a Map. List<Map<AccountId, AccountType>

Hope it helps

Edit for formatting purposes if "Element1" were another Object:

"element": [
{
  "element1": {
    "element3": "Value",
    "element4": "Value"
  },
  "element2": "Value 1"
},
{
  "element1": "Value 1",
  "element2": "Value 1"
}]

CodePudding user response：

First of all can you confirm what you want to do here:

Map final Map<String, T> accounts = new LinkedHashMap<>(); inside class Result? Because if it is a variable, then remove the leading Map and don't make the variable as final. Also you will need both setters and getters for the variable.

Secondly, your json has 'data' which has a account: [] pair, so first read value from data, then from account and you will get the list.

CodePudding user response：

It worked after changing Result<List finalResult = mapper.readValue(accounts, Result.class);

Result<List> finalResult = mapper.readValue(accounts, new TypeReference<Result<List>>() {});