How to Deserialize JSON object with dynamic variable names to a Java POJO?

Question

I am trying to parse the following nested JSON object using RestTemplate's getForObject method:

  "rates":{
    "USD":1.075489,
    "AUD":1.818178,
    "CAD":1.530576,
    "PLN":4.536389,
    "MXN":25.720674
  }

The number of currency rates varies depending on user input (it can be one or more).

How can I map such list of objects or a HashMap to a Java POJO class?

I tried with composition in the rates object:

public class Rates implements Serializable {

    private List<ExternalApiQuoteCurrencyRate> list;

     // getter and no-args constructor
}

public class ExternalApiQuoteCurrencyRate implements Serializable {

    private String currency;
    private BigDecimal rate;

    // getters and no-args constructor
}

But the rates object gets deserialized as null.

Could somebody please help? Thanks a lot in advance!

I tried it, Rates still arrives as null - I added the following variable in Rates: private Map<String, BigDecimal> rates; — Petar Bivolarski
– Petar Bivolarski, Commented Mar 20, 2020 at 16:17
Your JSON structure suggests fields called 'USD', 'AUD' etc. You won't be able to deserialize that into a POJO. How about returning a Map<String, Serializable> from the RestTemplate? (that's possibly what @bhspencer meant) — Simon
– Simon, Commented Mar 20, 2020 at 16:23

Petar Bivolarski · Accepted Answer · 2020-03-20 21:38:38Z

1

Thanks to @Simon and @bhspencer I solved the issue by exporting the JSON object to a HashMap using JsonNode.

Here is the solution:

  ResponseEntity<JsonNode> e = restTemplate.getForEntity(API_URL, JsonNode.class);
  JsonNode map = e.getBody(); // this is a key-value list of all properties for this object
  // but I wish to convert only the "rates" property into a HashMap, which I do below:
  ObjectMapper mapper = new ObjectMapper();
  Map<String, BigDecimal> exchangeRates = mapper.convertValue(map.get("rates"), new TypeReference<Map<String, BigDecimal>>() {});

edited Mar 20, 2020 at 21:38

answered Mar 20, 2020 at 17:33

Petar Bivolarski

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