Java Jackson - prevent float to int conversion when deserializing

Question

I have a JSON payload with the following structure ...

{
"age": 12
}

... which is mapped to the following class:

public class Student {

    private Integer age;

    public Integer getAge(){return age;}
    public void setAge(Integer age){this.age = age;}
}

At the moment, if the user submits a float value for the age, the decimals are ignored and the only the integer part is accepted. What I want to do is prevent the user from submitting a payload with a float value for the age (see below) and throw an exception (something like "invalid JSON value for field 'age' at line 8 col 5" - as is the standard message when deserialization fails).

{
"age": 12.7 // will be truncated to 12
}

I was thinking of implementing a custom deserializer for numeric values but was wondering if there is a simpler way to achieve this.

Answer 1

A floating-point value will be truncated to an integer value by default from Jackson 2.6. As indicated in a previous answer, setting ACCEPT_FLOAT_AS_INT to false should fix your problem.

@Test(expected = JsonMappingException.class)
public void shouldFailMarshalling() throws IOException {
    final String student = "{\"age\": 12.5}";
    final ObjectMapper mapper = new ObjectMapper();

    // don't accept float as integer
    mapper.configure(ACCEPT_FLOAT_AS_INT, false);
    mapper.readValue(student, Student.class);
}

Answer 2

Toggle off ACCEPT_FLOAT_AS_INT. You can check more details at https://github.com/FasterXML/jackson-databind/wiki/Deserialization-Features