JSON -> Immutable custom Java object. Insufficient data in JSON

Question

I use Jackson to deserialize JSON to an immutable custom Java object. Here is the class:

final class DataPoint {
  private final int count;
  private final double mean;

  @JsonCreator
  DataPoint(
      @JsonProperty("count") int count,
      @JsonProperty("mean") double mean) {
    if (count <= 0) {
      throw new IllegalArgumentException("...");
    }
    this.count = count;
    this.mean = mean;
  }

  // getters...
}

Here is the JSON I deserialize:

{
  "count": 1,
  "mean": 2
}

It works fine. Now I break the JSON, i.e. remove one proprerty:

{
  "count": 1
}

The deserialization code is:

String json = "..."; // the second JSON
ObjectMapper mapper = new ObjectMapper();
DataPoint data  = mapper.readValue(json, DataPoint.class);

Now I get count == 1, and mean == 0.0. Instead, I would like the Jackson to throw an exception, sine one of the required field is missing in the JSON. How can I archive that?

Thank you a lot, guys!

What if you change to @JsonProperty("mean") Double mean and check whether it is null or not? — StanislavL
– StanislavL, Commented May 5, 2017 at 8:04
@StanislavL: Well, it's a kind of a solution. Than you a lot! Am I right there is no means in Jackson letting me to get what I want witout boxing? — danissimo
– danissimo, Commented May 5, 2017 at 8:12
@StanislavL You won't be able to tell if it's missing, or present but set to null. — shmosel
– shmosel, Commented May 5, 2017 at 8:15
@shmosel it fails on null anyway. It's not possible to convert null to double but your answer is better +1. I suggested just a workaround. — StanislavL
– StanislavL, Commented May 5, 2017 at 8:17
@StanislavL It's possible that the implicit conversion from null to 0 is acceptable, as long as the property is defined. Your solution would throw an exception in either case. Of course, only OP can say if that's a problem. — shmosel
– shmosel, Commented May 5, 2017 at 8:22

shmosel · Accepted Answer · 2017-05-05 08:11:30Z

3

Since you're using a constructor, you can enable DeserializationFeature.FAIL_ON_MISSING_CREATOR_PROPERTIES to throw an exception on missing properties:

String json = "..."; // the second JSON
ObjectMapper mapper = new ObjectMapper()
        .enable(DeserializationFeature.FAIL_ON_MISSING_CREATOR_PROPERTIES);
DataPoint data  = mapper.readValue(json, DataPoint.class);

answered May 5, 2017 at 8:11

shmosel

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1 Comment

danissimo Over a year ago

Thank you a lot! You suggestion just works fine. I jsut needed to increate the version of the Jersey BOM. Thankx again, dude!

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