使用 jackson 库解析 json 时将 NaN 值转换为 null

Question

What is the best way to parse a json string in to a JsonNode object, and convert all the NaN value in to null? The following code will convert the Nan to DoubleNode NaN. I try to register a custom deserializer but it didn't pick up the Nan node.

JsonMapper mapper =  JsonMapper.builder()
            .enable(JsonReadFeature.ALLOW_NON_NUMERIC_NUMBERS).build();

final String testJson =  "{\"key\":NaN}";
JsonNode node = mapper.readTree(testJson)

Answer 1

One way it could be done is like below

1. Create some POJO class with @JsonSetter on setter method.

    public class KeyPojo {
    
        private Double key;
    
        @JsonSetter
        public void setKey(Double key) {
            if (Double.isNaN(key)) {
                this.key = null;
            } else {
                this.key = key;
            }
        }
    }

2. And parse json text like below.

    KeyPojo keyObj = mapper.readValue(testJson, KeyPojo.class);

now, keyObj.key contains NULL value.