Wednesday, September 20, 2017

Re: elemental.json confusion/error

On Wednesday, September 20, 2017 at 12:49:21 PM UTC+2, wrote:
Hi there

I recently started using elemental.json. But I recently stumbled upon strange (expected?) behaviour. Is there any good documentation? The javadoc is quiet lacking, at least in this regard. So, what am I confused about?

My first and main advice would be: don't use Elemental.
If you need to parse JSON with a known structure, use JsInterop to describe that structure (as @JsType(isNative=true, namespace=JsPackage.GLOBAL, name="*"), or name="Object" if you can't use name="*"), and then either<JavaScriptObject>safeEval() with a cast to your JsInterop interface/class, or JsInterop to call JSON.parse() (as @JsMethod(namespace="JSON", name="parse") static native <T> T parseJson(String json)).
If you don't know the structure upfront, then use jsinterop-base's types instead (JsPropertyMap mostly, and the Js helper class), and the same method for parsing. You might also want to have a look at elemental2-core: (which BTW defines JSONType.parse(…)), but be careful as Elemental2 is entirely generated, and might change in the future as the generator evolves (also, Elemental 2 might require that you use the HEAD-SNAPSHOT of GWT)

If you need something that can be used in a JVM too, you might be able to use GSON or Jackson to parse into similar structures (possibly define a JsPropertyMap implementation that wraps a LinkedHashMap).

First, there is a "getNumber" (and it's equivalents), but those fail with a classcastexception, if you use it on parsed Json. There is no problem if you use it on values that were "put" there. Is that working as intended? 
Second, and I guess this is a bug: If you use get(key).asBoolean() on a recently parsed value, you get the correct value. But if you use it on a value "false" you "put" in, you get true. 

I would be happy if someone could shine some light on this for me :)

These are likely bugs, and they're unlikely to ever be fixed (unless maybe someone provides the patch).

I wrote a small "test" to demonstrate it:


import elemental.json.JsonObject;
import elemental.json.impl.JsonUtil;

The correct way is Json.instance(), one shouldn't ever use any "impl" class.

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