Java Final field Class Json serializable

code :

```java= @Jacksonized @Builder public class BeginEndIdx {

public final int begin;
public final int end;


public static void main(String[] args) {
    BeginEndIdx beginEndIdx = new BeginEndIdx(1, 2);
    String json = JsonUtils.toJson(beginEndIdx);
    System.out.println(json);
    BeginEndIdx beginEndIdx1 = JsonUtils.loadByJson(json, BeginEndIdx.class);
    System.out.println(beginEndIdx1);
}

}

output 
```shell=
{"begin":1,"end":2}
net.bzk.infrastructure.obj.BeginEndIdx@65d6b83b