Java Optional Null Json Field

Question

I am using the JsonNode objects from the Jackson library to hold json responses. I could potentially have a json like so:

{
    "a": "test",
    "b": true
}

However, at times the b field could be missing. So it could come back like this:

{
    "a": "test"
}

In that case I want to return Optional.isEmpty() when I'm trying to retrieve its value. Essentially this is the java code for that:

if(json.path("b").isMissingNode()) {
    return Optional.empty();
} else {
    return Optional.of(json.get("b").asBoolean());
}

However, I want to condense this into 1 line using .filter and .ofNullable but I'm not exactly sure how to do this. I found this post that shows an example of how to use the filter but I understand what the s is....

Basically I want to find the field labeled b, if it's not there then return empty. If it is there then return the boolean value of it's field.

Edit: This is not a duplicate because I am not serializing the entire json into an object. I don't have any need for the JsonIgnore annotations. I only want to extract 1 value. Which is like above.

Possible duplicate of [How to tell Jackson to ignore a field during serialization if its value is null?](http://stackoverflow.com/questions/11757487/how-to-tell-jackson-to-ignore-a-field-during-serialization-if-its-value-is-null) — ΦXocę 웃 Пepeúpa ツ, Mar 14 '16 at 20:27
This isn't a duplicate because I'm not serializing into an object. I'm just extracting 1 value — Richard, Mar 14 '16 at 20:31

score 1 · Accepted Answer · answered Mar 14 '16 at 20:48

You can use code like so:

Optional<Boolean> b = Optional.ofNullable(json.get("b"))
                              .map(node -> node.asBoolean());

A couple of points worth noting:

You don't need to use filter. ofNullable is going to return an empty nullable. According to Jackson documentation, null is returned if node value is not present.
Closely related to your question about s in referenced question, map is a function that is run only when the Optional is present (e.g. JSON has b value). It takes a lambda expression which is an equivalent of using an anonymous class. node is a parameter for the Function interface that has only one method (apply). You can take a look at the examples here.

Java Optional Null Json Field

1 Answers1