Make the Jackson fail on converting double to int during deserialization
deserialization, jackson, java, json
Solution
There is the option `ACCEPT_FLOAT_AS_INT` for that purpose. E.g. :
ObjectMapper mapper = new ObjectMapper();
mapper.disable(DeserializationFeature.ACCEPT_FLOAT_AS_INT);
And for `"0.1"` you will get:
Exception in thread "main" com.fasterxml.jackson.databind.JsonMappingException: Can not coerce a floating-point value ('0.1') into Integer; enable `DeserializationFeature.ACCEPT_FLOAT_AS_INT` to allow
You can see pertinent docs here
Note that this is available since Jackson 2.6
Problem
I use Jackson to deserialize a JSON to an immutable custom Java object. Here is the class: ``` final class DataPoint { private final int count; private final int median; @JsonCreator DataPoint( @JsonProperty("count") int count, @JsonProperty("median") int median) { if (count <= 0) { throw new IllegalArgumentException("..."); } this.count = count; this.median = median; } // getters... } ``` Here is the JSON I deserialize: ``` { "count": 1, "median": 2 } ``` It works fine. Now, I break the JSON, i.e. replace the integer `median` with the decimal: ``` { "count": 1, "median": 0.1 } ``` Now, I get `count == 1`, and `median == 0`. Instead, I would like the Jackson to fail deserilizing, since the data type of the JSON property `median` and the formal `median` parameter type (an `int`) are different, and the conversion looses the data actually. Here is the deserializing code: ``` String json = "..."; // the second JSON ObjectMapper mapper = new ObjectMapper() .enable(DeserializationFeature.FAIL_ON_MISSING_CREATOR_PROPERTIES) .enable(DeserializationFeature.FAIL_ON_NULL_FOR_PRIMITIVES) .enable(DeserializationFeature.FAIL_ON_INVALID_SUBTYPE); DataPoint data = mapper.readValue(json, DataPoint.class); ``` Can I make Jackson fail when deserializing a decimal to an integer?