Jackson add non-existen field during serialization

Question

Mapper:

public static ObjectMapper mapper = new ObjectMapper()
            .configure(DeserializationFeature.FAIL_ON_UNKNOWN_PROPERTIES, false)
            .setVisibility(PropertyAccessor.FIELD, JsonAutoDetect.Visibility.ANY)
            .enable(SerializationFeature.INDENT_OUTPUT);

Class to serialize:

@Builder(builderClassName = "GooglePlayGameBuilder", toBuilder = true)
@JsonDeserialize(builder = GooglePlayGame.GooglePlayGameBuilder.class)
public final class GooglePlayGame  {

    @JsonProperty("Title") private final String title;
    @JsonProperty("Genre") private final String genre;
    @JsonProperty("Price") private final String price;
    @JsonProperty("Last updated") private final String lastUpdated;
    @JsonProperty("Current version") private final String currentVersion;
    @JsonProperty("Requirements") private final String requiresAndroid;
    @JsonProperty("IAP") private final String IAP;
    @JsonProperty("Contacts") private final String devEmail;

...

Add object to map and then i want to serialize my map:

public static volatile ConcurrentMap<String, GooglePlayGame> games = new ConcurrentSkipListMap<>(String.CASE_INSENSITIVE_ORDER);

Write to file:

public static void saveLibraryToFile(){
        try {
            mapper.writeValue(new File(LIBRARY_FILENAME), games);
        } catch (IOException e) {
            log.error("[Couldn't write to file] ", e.getMessage());
        }
    }

After this my JSON looks like:

{
  "Never Alone: Ki Edition" : {
    "Title" : "Never Alone: Ki Edition",
    "Genre" : "Adventures",
    "Price" : "4,99 €",
    "Last updated" : "September 15, 2016",
    "Current version" : "1.0.0",
    "Requirements" : "2.3+",
    "IAP" : "nope",
    "Contacts" : "[email protected]"
  },
...

If i will annotate my class with lombok @Getter strange field will appear:

{
  "Never Alone: Ki Edition" : {
    "iap" : "nope"
    "Title" : "Never Alone: Ki Edition",
    "Genre" : "Adventures",
    "Price" : "4,99 €",
    "Last updated" : "September 15, 2016",
    "Current version" : "1.0.0",
    "Requirements" : "2.3+",
    "IAP" : "nope",
    "Contacts" : "[email protected]"
  },

I dont understand this field:

"iap" : "nope"

From where Jackson found it? I checked my local map with logs and all fine, this field doesnt exist, but during serialization it appears.

I don't know if you have any constraint... But I recommand you use camelCase for your variable name. I believe your problem is caused by the getter generated by Lombok. — user2447161
Great, I'm happy it is solved. I'm adding this as answer so you can mark it as solved. — user2447161

Andreas Andreas · Accepted Answer · 2020-03-26T21:27:42

Lombok will create a getter method for field IAP named getIap(). Jackson will then auto-detect that as a property named iap. Since property names are case-sensitive, that is a distinct property from the IAP property defined by the @JsonProperty("IAP") annotation.

You have 2 choices:

Rename the field to iap, keep the annotation unchanged.
Recommended, since that follows the Java naming standard.
Add the following annotation to the class:
```
@JsonAutoDetect(getterVisibility = Visibility.NONE, isGetterVisibility = Visibility.NONE)
```
This stops Jackson from auto-detecting properties from getter methods, i.e. only getter methods annotated with @JsonProperty would define a property. Since none of the Lombok-created getters would have that annotation, the effect would be that only annotated fields would define properties.

Jackson add non-existen field during serialization

3 Answers