Jackson JsonNode 和 Java Streams 返回 Optional Empty

Question

So I have a json input, something like this:

{
    "a":"something",
    "b":"something2"
}

This input can come in 2 other forms:

{
    "a":"something",
    "b":""
}

And

{
    "a":"something"
}

I have a input class like this that I store it in:

public class Foo {
    private String a;
    private Optional<String> b;
}

In the latter 2 cases I want to store b as Optional.empty(). I have figured out how to do that in the 3rd case with this line of code:

Optional.ofNullable(inputNode.get("b")).map(node -> node.asText())

This works well for the 3rd case. It returns Optional.empty. But not so much for the 2nd case because b ends up just being an empty string. I tried to use .reduce before and after the .map but for some reason it won't let me use that anywhere.

And idea how to achieve what I want?

Answer 1

You can filter the Optional to check that the value is not the empty String:

Optional<String> b = Optional.ofNullable(inputNode.get("b"))
        .map(JsonNode::asText)
        .filter(s -> !s.isEmpty());

Answer 2

此代码还有助于：

Optional.ofNullable(jsonNode.findValue("XYZ")).map(JsonNode::asText).orElse(null);