Gson: How to exclude specific fields from Serialization without annotations

Question

I\'m trying to learn Gson and I\'m struggling with field exclusion. Here are my classes

public class Student {    
  private Long                id;
  privat         


        

Answer 1

I came up with a class factory to support this functionality. Pass in any combination of either fields or classes you want to exclude.

public class GsonFactory {

    public static Gson build(final List<String> fieldExclusions, final List<Class<?>> classExclusions) {
        GsonBuilder b = new GsonBuilder();
        b.addSerializationExclusionStrategy(new ExclusionStrategy() {
            @Override
            public boolean shouldSkipField(FieldAttributes f) {
                return fieldExclusions == null ? false : fieldExclusions.contains(f.getName());
            }

            @Override
            public boolean shouldSkipClass(Class<?> clazz) {
                return classExclusions == null ? false : classExclusions.contains(clazz);
            }
        });
        return b.create();

    }
}

To use, create two lists (each is optional), and create your GSON object:

static {
 List<String> fieldExclusions = new ArrayList<String>();
 fieldExclusions.add("id");
 fieldExclusions.add("provider");
 fieldExclusions.add("products");

 List<Class<?>> classExclusions = new ArrayList<Class<?>>();
 classExclusions.add(Product.class);
 GSON = GsonFactory.build(null, classExclusions);
}

private static final Gson GSON;

public String getSomeJson(){
    List<Provider> list = getEntitiesFromDatabase();
    return GSON.toJson(list);
}

Answer 2

I solved this problem with custom annotations. This is my "SkipSerialisation" Annotation class:

@Target (ElementType.FIELD)
public @interface SkipSerialisation {

}

and this is my GsonBuilder:

gsonBuilder.addSerializationExclusionStrategy(new ExclusionStrategy() {

  @Override public boolean shouldSkipField (FieldAttributes f) {

    return f.getAnnotation(SkipSerialisation.class) != null;

  }

  @Override public boolean shouldSkipClass (Class<?> clazz) {

    return false;
  }
});

Example :

public class User implements Serializable {

  public String firstName;

  public String lastName;

  @SkipSerialisation
  public String email;
}

Answer 3

I have Kotlin version

@Retention(AnnotationRetention.RUNTIME)
@Target(AnnotationTarget.FIELD)
internal annotation class JsonSkip

class SkipFieldsStrategy : ExclusionStrategy {

    override fun shouldSkipClass(clazz: Class<*>): Boolean {
        return false
    }

    override fun shouldSkipField(f: FieldAttributes): Boolean {
        return f.getAnnotation(JsonSkip::class.java) != null
    }
}

and how You can add this to Retrofit GSONConverterFactory:

val gson = GsonBuilder()
                .setExclusionStrategies(SkipFieldsStrategy())
                //.serializeNulls()
                //.setDateFormat(DateFormat.LONG)
                //.setFieldNamingPolicy(FieldNamingPolicy.UPPER_CAMEL_CASE)
                //.setPrettyPrinting()
                //.registerTypeAdapter(Id.class, IdTypeAdapter())
                .create()
        return GsonConverterFactory.create(gson)

Answer 4

Any fields you don't want serialized in general you should use the "transient" modifier, and this also applies to json serializers (at least it does to a few that I have used, including gson).

If you don't want name to show up in the serialized json give it a transient keyword, eg:

private transient String name;

More details in the Gson documentation

Answer 5

Kotlin's @Transientannotation also does the trick apparently.

data class Json(
    @field:SerializedName("serialized_field_1") val field1: String,
    @field:SerializedName("serialized_field_2") val field2: String,
    @Transient val field3: String
)

Output:

{"serialized_field_1":"VALUE1","serialized_field_2":"VALUE2"}

Answer 6

I'm working just by putting the @Expose annotation, here my version that I use

compile 'com.squareup.retrofit2:retrofit:2.0.2'
compile 'com.squareup.retrofit2:converter-gson:2.0.2'

In Model class:

@Expose
int number;

public class AdapterRestApi {

In the Adapter class:

public EndPointsApi connectRestApi() {
    OkHttpClient client = new OkHttpClient.Builder()
            .connectTimeout(90000, TimeUnit.SECONDS)
            .readTimeout(90000,TimeUnit.SECONDS).build();

    Retrofit retrofit = new Retrofit.Builder()
            .baseUrl(ConstantRestApi.ROOT_URL)
            .addConverterFactory(GsonConverterFactory.create())
            .client(client)
            .build();

    return retrofit.create  (EndPointsApi.class);
}