Gson serialization depending on field value

Question

I have a POJO that is similar to:

public class MyGsonPojo {

    @Expose
    @SerializedName("value1")
    private String valueOne;

    @Expose
    @SerializedName("value2")
    private boolean valueTwo;

    @Expose
    @SerializedName("value3")
    private int valueThree;

    // Getters and other stuff here
}

The issue is that this object has to be serialized into a json body for a call to the server. Some fields are optional for the request and if I even send it with default and null values, the API responds differently (Unfortunately changing the api is not an option).

So basically I need to exclude fields from serialization if any of them is set to a default value. For example if the field valueOne is null the resulting json should be:

{
    "value2" : true,
    "value3" : 2
}

Any idea how to make this a painless effort? I wouldn't want to build the json body manually.

Any help would be great. Thank you in advice.

Answer 1

Steps to follow:

• Convert the JSON String into Map<String,Object> using Gson#fromJson()
• Iterate the map and remove the entry from the map which are null
• Form the JSON String back from the final map using Gson#toJson() .

I have already posted the sample code in the same context here:

• Remove empty collections from a JSON with Gson

Answer 2

Option 1) Use a TypeAdapter, see accepted answer here :

Option 2) If using Jackson instead of gson is a possibility, you can annotate/serialize on getters instead of on fields, and put your logic for returning whatever you need for "default values" in your getters.

//won't get serialized because it's private 
private String valueOne;
...
@JsonSerialize
String getValueOne(){
   if (valueOne == null) return "true"
   else...
}

You could also use a single @JsonInclude(Include.NON_NULL) or @JsonInclude(Include.NON_EMPTY) annotation at the top of your class to prevent any null or empty fields from being serialized.