Jackson list deserialization. nested Lists
I'm working on creating an API that has nested lists. Jackson seems like a great tool to create objects, but I can't quite figure out how to nest a list, and I'm wondering if its possible.
My object looks like this.
public class Order {
public String name;
public List<Item> items;
}
I'm hoping there is a way to map it to json that looks something like:
{
name : "A name"
items : {
elements : [{
price : 30
}]
}
}
We want to be able to do this so we can add properties to lists.
You can write custom deserializer for List<Item> items
. See below example:
class ItemsJsonDeserializer extends JsonDeserializer<List<Item>> {
@Override
public List<Item> deserialize(JsonParser jp, DeserializationContext ctxt) throws IOException, JsonProcessingException {
InnerItems innerItems = jp.readValueAs(InnerItems.class);
return innerItems.elements;
}
private static class InnerItems {
public List<Item> elements;
}
}
Now, you have to inform Jackson to use it for your property. You can do this in this way:
public class Order {
public String name;
@JsonDeserialize(using = ItemsJsonDeserializer.class)
public List<Item> items;
}
In general it is best to map JSON structure exactly to Java. In your case you could use something like:
public class Order {
public String name;
public ItemList items;
}
public class ItemList {
public List<Item> elements;
// and any properties you might want...
}
alternatively, you could probably also use (relatively) new @JsonFormat
annotation:
public class Order {
public String name;
public ItemList items;
}
// annotation can be used on propery or class
@JsonFormat(shape=Shape.OBJECT) // instead of Shape.ARRAY
public class ItemList extends ArrayList<Item>
{
public Iterator<Item> getElements() { return this.iterator(); }
public String getSomeAttribute() { ... }
}
where you are forcing List
or Collection
to be serialized as if it was POJO, instead of normal special handling. There may be some side-effects, since introspection is used to find possible accessors, but the general approach should work
Your JSON translates to: "the object named items
is of a type that has a property named elements
which is a list of some sort".
So your Item class just needs an elements
property:
class Item {
List<Something> getElements();
}
Note that your Java code doesn't map to your JSON. Your Java classes would map to something like:
{
"name" : "foo",
"items" : [
{ /* encoded version of Item */ }
]
}