FieldMaskedSerializer.java

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package com.google.api.gax.httpjson;

import com.google.gson.Gson;
import com.google.gson.GsonBuilder;
import com.google.gson.JsonElement;
import com.google.gson.JsonNull;
import com.google.gson.JsonObject;
import com.google.gson.JsonSerializationContext;
import com.google.gson.JsonSerializer;
import java.lang.reflect.Type;
import java.util.List;

/** JSON Serializer for messages with a field mask to selectively serialize fields. */
public class FieldMaskedSerializer implements JsonSerializer<ApiMessage> {
  private final List<String> fieldMask;

  public FieldMaskedSerializer(List<String> fieldMask) {
    this.fieldMask = fieldMask;
  }

  @Override
  public JsonElement serialize(
      ApiMessage requestBody, Type typeOfSrc, JsonSerializationContext context) {
    Gson gson = new GsonBuilder().serializeNulls().create();
    if (fieldMask == null) {
      return gson.toJsonTree(requestBody, typeOfSrc);
    }
    JsonObject jsonObject = new JsonObject();
    for (String fieldName : fieldMask) {
      Object fieldValue = requestBody.getFieldValue(fieldName);
      if (fieldValue != null) {
        jsonObject.add(fieldName, gson.toJsonTree(fieldValue, fieldValue.getClass()));
      } else {
        // TODO(andrealin): This doesn't distinguish between the non-existence of a field
        // and a field value being null.
        jsonObject.add(fieldName, JsonNull.INSTANCE);
      }
    }

    return jsonObject;
  }
}