Jackson deserialize "" as an empty list

deserialization, jackson, json, spring

Solution

Couple of options; first, you want to enable `ACCEPT_EMPTY_STRING_AS_NULL_OBJECT':

mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);

so that empty String becomes null. And if you want it to get converted to actual empty List, override setter:

public void setChildren(List<Child> c) {
    if (c == null) {
       children = Collections.emptyList();
    } else {
       chidlren = c;
    }
}

Problem

I have a JSON string that marks empty lists as `""` instead of `[]`. So for example, if I have an object with no children, I'll receive a string like this: ``` {"id":13, "children":""} ``` I'd like to deserialize that to a Parent class, with children properly set to an empty list of children. ``` public class Parent { private Long id; private List<Child> children; public Long getId() { return id; } public void setId(Long id) { this.id = id; } public List<Child> getChildren() { return children; } public void setChildren(List<Child> children) { this.children = children; } } ``` For the above JSON string, I'd like an object that will have its `id` set to `13`, and the `children` set to a `new ArrayList<Child>()` ``` Parent id <- 13 children <- new ArrayList<Child>() ``` I would know how to use an annotation for the entire class ``` @JsonDeserialize(using = ParentDeserializer.class) public class Parent { ... } ``` and then ``` public class ParentDeserializer extends JsonDeserializer<Parent> { public Parent deserialize(JsonParser parser, DeserializationContext context) { ... } } ``` However, I'd like to solve a general problem of instantiating Lists properly from `""` strings: ``` public class Parent { ... // Can I get something like this? @JsonDeserialize(using = EmptyArrayDeserializer<Child>.class) public void setChildren(List<Child> children) { this.children = children; } } ``` Can I get something like that?

Original source