java - Gson Serialize field only if not null or not empty

Question

I have requirement where I need to convert java object to json.

I am using Gson for that but i need the converter to only serialize the non null or not empty values.

For example:

//my java object looks like
class TestObject{
    String test1;
    String test2;
    OtherObject otherObject = new OtherObject();
}

now my Gson instance to convert this object to json looks like

Gson gson = new Gson();
TestObject obj = new TestObject();
obj.test1 = "test1";
obj.test2 = "";

String jsonStr = gson.toJson(obj);
println jsonStr;

In the above print, the result is

{"test1":"test1", "test2":"", "otherObject":{}}

Here i just wanted the result to be

{"test1":"test1"}

Since the test2 is empty and otherObject is empty, i don't want them to be serialized to json data.

Btw, I am using Groovy/Grails so if there is any plugin for this that would be good, if not any suggestion to customize the gson serialization class would be good.

Answer 1

Create your own TypeAdapter

public class MyTypeAdapter extends TypeAdapter<TestObject>() {

    @Override
    public void write(JsonWriter out, TestObject value) throws IOException {
        out.beginObject();
        if (!Strings.isNullOrEmpty(value.test1)) {
            out.name("test1");
            out.value(value.test1);
        }

        if (!Strings.isNullOrEmpty(value.test2)) {
            out.name("test2");
            out.value(value.test1);
        }
        /* similar check for otherObject */         
        out.endObject();    
    }

    @Override
    public TestObject read(JsonReader in) throws IOException {
        // do something similar, but the other way around
    }
}

You can then register it with Gson.

Gson gson = new GsonBuilder().registerTypeAdapter(TestObject.class, new MyTypeAdapter()).create();
TestObject obj = new TestObject();
obj.test1 = "test1";
obj.test2 = "";
System.out.println(gson.toJson(obj));

produces

 {"test1":"test1"}

The GsonBuilder class has a bunch of methods to create your own serialization/deserialization strategies, register type adapters, and set other parameters.

Strings is a Guava class. You can do your own check if you don't want that dependency.