gistfile1.java

Foobar foobar = new FoobarBuilder()
    .someFooThing(17)
    .aBarField("hello world")
    .build();

String json = mapper.writeValueAsString(foobar);
out.println(json);

gistfile2.json

{
  "some_foo_thing": 17,
  "a_bar_field": "hello world"
}

gistfile3.txt

ObjectMapper mapper = new ObjectMapper()
    .registerModule(new AutoMatterModule(CAMEL_CASE_TO_LOWER_CASE_WITH_UNDERSCORES));

gistfile4.java

@AutoMatter(json = LOWER_CASE_WITH_UNDERSCORES)
public interface Foobar {
  int someFooThing();
  String aBarField();
}