title: Firebase Java SDK serialized POJO not using gson annotation
body: <p>Firebase Java SDK underlying use gson to serialize / deserialize pojo. In my class I set the annotation @SerializedName for the serialized json field name. However, after the data was saved to firebase database, the field name is not the value in my SerializedName annotation.</p>
  
  <p>How can I set a customized serializer for forebase java sdk?</p>