Iterating on JSON object with Date values

Question

I am trying to locate highest and lowest rate within my API monthly rate call, the object BPI has String values and I am a bit confused how to actually count date as for example a key and rate as a value so the iteration can be done.

I would like to use a Map, but not sure how to proceed correctly:

Answer 1

Looks like you have a JSON document as shown below:

{
  "bpi": {
    "2019-08-18": 9304.6179,
    "2019-08-19": 9860.2835,
    "2019-08-20": 9710.7164,
    "2019-08-21": 9138.8615,
    "2019-08-22": 9126.6978
  }
}

As you seem to be using Java, you could use Jackson to parse the JSON document to an instance of a class such as:

@Data
public class ApiResponse {
    private Map<LocalDate, BigDecimal> bpi;
}

Where the bpi JSON property will be mapped to a Map<LocalDate, BigDecimal> .

For parsing a JSON, you could have:

String json = ...;

ObjectMapper mapper = new ObjectMapper();
mapper.registerModule(new JavaTimeModule());

ApiResponse apiResponse = mapper.readValue(json, ApiResponse.class);;

Then, to find the highest and the lowest values, you can use:

BigDecimal max = Collections.max(apiResponse.getBpi().values());
BigDecimal min = Collections.min(apiResponse.getBpi().values());

In case you need the full map entry, use:

Entry<LocalDate, BigDecimal> max = 
        Collections.max(apiResponse.getBpi().entrySet(), Entry.comparingByValue());

Entry<LocalDate, BigDecimal> min = 
        Collections.min(apiResponse.getBpi().entrySet(), Entry.comparingByValue());

Answer 2

One of possible solutions could be taking advantage of java.util.regex . Following code will parse your json into 2 groups: the date string and the value string. Then I just put those into Map <String, String> (you can convert String 's to whatever type you need):

Map <String, Double> bpiMap = new HashMap();
Pattern.compile("(?m)^\\s*(\\d{4}-\\d{2}-\\d{2})\\s*:\\s*([\\d\\.]+).*");
Matcher matcher = pattern.matcher(json);
while (matcher.find()) {
  bpiMap.put(matcher.group(1), Double.valueOf(matcher.group(2)));
}

Here is the regex decoding for you:
(?m) - multi-line
^ - beginning of the line
(\\d{4}-\\d{2}-\\d{2}) - the first group for the date
\\s - whitespaces
([\\d\\.]+) - the second group for the value

Highest and lowest rates:

Entry<String, Double> hi = Collections.max(bpiMap.entrySet(), Entry.comparingByValue());

Entry<String, Double> lo = Collections.min(bpiMap.entrySet(), Entry.comparingByValue());

Of course this is not the only solution (eg parsing in Jackson objects could also be an option), but it appears to me simpler and doesn't depend on third party libraries (like com.fasterxml.jackson).

Note: this solution works pretty well for the json structure as simple as you have described and may not be as beneficial if the structure is more complex. In that case other options like jackson (well described in @cassiomolin answer) may be considered.