Add elements to initialized custom collection

[nli...@gmail.com]

My class contains an initialized custom collection

class MyClass {

    MyList<Integer> myList = MyList.create();

}

where MyList is a j.u.List. When deserializing, I get an exception saying that there is no known deserializer for MyList ("Cannot find a deserializer for non-concrete List type"), which is generally understandable, but I already initialized it, so there's no need for one. Instead, I just want to add the items to the list.

To demonstrate, I can add a private setter inside the class:

private void setMyList(List<Integer> ints) { ints.forEach(MyList::add); }

this works, but I don't think it should be needed. Specifically, Jackson should not create any list. It needs to deserialize the values of the items anyway; then instead of creating a list, add them to the existing one. It's a List, so it should know to call 'add' ('put' for map).

I know there is @JsonMerge, and I thought that that's what I needed, but just adding it to the field doesn't work, I still get the same exception. Am I not understanding @JsonMerge or am I doing something wrong?

Thanks!

[Joo Hyuk Kim]

> Jackson should not create any list.

To be more specific, You do not want to create any list and ur looking for a such feature.

What we can do here  is write a custom deserializer to do such thing and there is already plenty references on the web

2024년 10월 18일 (금) 오전 4:04, nli...@gmail.com <nli...@gmail.com>님이 작성:

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[nli...@gmail.com]

So @JsonMerge is not appropriate here?

[Joo Hyuk Kim]

Your implementation Does not seem too off , But not sure :/

2024년 10월 18일 (금) 오후 4:06, nli...@gmail.com <nli...@gmail.com>님이 작성:

To view this discussion on the web visit https://groups.google.com/d/msgid/jackson-user/4446a07a-f0b8-4bad-8442-3571d0a328d3n%40googlegroups.com.

[nli...@gmail.com]

Perhaps Tatu can have a look?

[Joo Hyuk Kim]

Actually, I think we will get more answers moving the discussion to Github discussions.
WDYT?

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[nli...@gmail.com]

Didn't know they exist. Last time I was told to use the mailing lists.