杰克逊反序列化“”作为一个空列表 [英] Jackson deserialize "" as an empty list

问题描述

我有一个JSON字符串，将空列表标记为而不是 [] 。例如，如果我有一个没有子节点的对象，我会收到一个这样的字符串：

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":""}

我想将它反序列化为Parent类，将孩子正确设置为空子列表。

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;
    }
}

对于上面的JSON字符串，我想要一个将 id 设置为 13 的对象，以及 children 设置为新的ArrayList< Child>（）

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>()

我知道如何为整个班级使用注释

I would know how to use an annotation for the entire class

@JsonDeserialize(using = ParentDeserializer.class)
public class Parent { 
    ...
}

然后

public class ParentDeserializer extends JsonDeserializer<Parent> {
    public Parent deserialize(JsonParser parser, DeserializationContext context) {
        ...    
    }
}

但是，我想解决从字符串中正确实例化列表的一般问题：

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;
    }
}

我能得到类似的东西吗？

Can I get something like that?

推荐答案

多种选择;首先，您要启用`ACCEPT_EMPTY_STRING_AS_NULL_OBJECT'：

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

mapper.enable(DeserializationFeature.ACCEPT_EMPTY_STRING_AS_NULL_OBJECT);

以便空字符串变为空。如果你想让它转换为实际的空列表，覆盖setter：

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;
    }
}

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