The ability of the Jackson ObjectMapper to construct an object and modify a final field post-initialization can be demonstrated by this simple code:
public class jsonNodeApp {
public static void main(String[] args) throws Exception{
ObjectMapper mapper=new ObjectMapper();
Apple apple = mapper.readValue(new File("myapple.json"), Apple.class); //apple.seeds is 10, not -200
System.out.println("Look what you made me do.");
}
}
class Apple {
final int seeds;
Apple(){ //invoked by ObjectMapper
System.out.println("Sole constructor invoked");
seeds = -200;
}
public int getSeeds() { //never called, but existence required by ObjectMapper
System.out.println("Placeholder getter");
return 7676;
}
}
And myapple.json simply contains {"seeds":10}.
I thought ObjectMapper would do something like that suggested here, but a search in the source for Modifier.FINAL was not fruitful.
So how does ObjectMapper do this particular trick?
Disclaimer: The industrial application of this feature is likely limited, and mine is not one of them. I am simply asking out of curiosity.
