java - FasterXML Jackson: The JSON @ symbol?

Question

i have the following JSON:

"segmentid": {
    "mot": {
        "@displaytype": "B",
        "@type": "BLT",
        "#text": "Buss"
    },...

The following questions:

• What is the @ notation for?
• If it is used for a specific reason, how can I use it in Jackson?

Answer 1

In this case it seems to be just a normal JSON propety.

You can grab it by using the @JsonProperty annotation in your class:

public YourJacksonClass {
     @JsonProperty("@displayType")
     private String displayType;

     @JsonProperty("@type")
     private String type;

     @JsonProperty("#text")
     private String text;
}

Or, if you are using the readTree method which returns a JsonNode, just access it normally:

JsonNode node = mapper.readTree(...);
String type = node.get("segmentid").get("mot").get("@type");

It is also common to use '@'-prefixed properties when it is necessary to serialize type info together with the object.

@JsonTypeInfo(use=JsonTypeInfo.Id.CLASS, include=JsonTypeInfo.As.PROPERTY, property="@type")

The read type, "BLT" in your case, can then be transformed into an actual type when using a TypeIdResolver in your ObjectMapper.