One of my favorite things about Jackson was being able to arbitrarily navigate through the document with a rich and fluent API (JsonNode) in jackson.databind, which this JEP at least conceptually borrows from with the JsonValue abstraction. Both of these are better than how some of the other implementations do it, where you are effectively working with glorified Map<String,Object>
String body = ... REST response body, which is a JSON document ... ;
JsonValue json = Json.parse(body);
json.get("properties").get("periods").asList().stream()
.mapToInt(j -> j.get("temperature").asInt())
.average()
.ifPresent(IO::println);
> If the JsonValue instance is of the wrong type, or if the requested member or element does not exist, the access methods throw a JsonValueException.
So if I get an exception, I can't tell whether the value was of the wrong type or the object didn't have the requested key? This looks like a footgun to me.
They just brought pattern matching to Java. Why not move those .get to JsonArray and JsonObject? That would solve this confusions. So we could just use something like `if (json instanceof JsonObject o) o.get("properties")`
I already have one of these (I'm sure I'm not alone). It's about 500 lines.
I found I'm not a huge fan of the JAX-B-ish style serialization of Java objects for JSON. I don't want to really downplay them, they certainly have their uses, they're very popular, I just don't like fighting them. Hand writing JSON marshaling code has not been arduous for me (notably with my utility layer). (I also, philosophically, strive to avoid "magic" in my code as much as practical.)
Of course, I still need a parser, I'm using GSONs parser, which means I'm still dragging in the whole bean level serialization infrastructure. I just don't use it. And while I've done JSON parsers before, I felt it was something better to import than maintain myself. So, in that sense, it's a mixed bag.
But, I do enjoy using it.
This will be a worthwhile JDK capability. Ideally it can replace mine.
This seems to repeat the same mistakes of Go's built in JSON library where the ecosystem is full of workarounds and other libraries that are faster or have better features.
As similar as all the almost-JSON formats are, I still think it's best to keep APIs single-purpose: one for JSON, one for JSON-lines, one for JSONC, and so on. It's a larger code surface, but a less potentially surprising one.
1. An HTTP server library/framework
2. A JSON library
We got a decently-performing and unopionated HTTP server in JDK 18 with "HttpHandlers" and "SimpleFileServer" plus "jwebserver" CLI
It later received Virtual Thread support, which made performance + scalability very competitive.
With a JSON module, you finally won't NEED to rely on external deps to build a basic JVM web service without pain.
Now, we just need a proper CLI framework like picocli, or at least "argparse" from Python stdlib...
A web server using this could only start parsing when it receives the last byte, and could only start responding when it’s done serializing, all while holding non-lazy trees of JsonValue objects in memory.
I'm sure lots of them exist, but for your typical CRUD API, this has not been a phenomena I've run into.
I find it interesting to note that nowhere in this JEP is the word "serialization", which is what most people might associate with JSON libs. Or rather, they are studiously ignoring that feature and just improving the ergonomics of interacting with JSON.
Does anyone know how this behaves when encountering a repeated key in an object? (RFC8259 states that keys SHOULD be unique, which makes that generally allowed and implementations all behave slightly differently).
Surely there could be some way of creating a JsonArray of native Java Strings, Booleans, Doubles, and Integers without requiring clients to explicitly convert each value into a JsonValue. And why am I forced to convert a native List into a JsonArray just so I can make it the value of a JsonObject?
Why can't I write this?
The kotlin stdlib-adjacent json lib does it like this
[1] https://kotlinlang.org/docs/type-safe-builders.htmlThey literally asked why they couldn't write JsonObject.of(Map.of(...))
Indeed, Java JSON libraries typically offer all these conveniences and more, but this package is not intended to replace them - as the JEP clearly states ("It is not a goal to create an API that supplants established external JSON libraries"). It is intended to support only simple JSON tasks without requiring a library. For that goal, feature creep is particularly problematic: the more you offer (which reduces the need for the popular libraries in more situations) the greater the pressure to add even more.
Often, it's best to start with the minimum required, and then, as the API gets used in the field, see what the most valuable convenience methods to add on top.
But for constructing JSON out of strings, numbers, booleans, lists, and maps, there's really not that much scope to creep into.
Specifically, I think it would be perfectly cromulent to have JsonArray.of() be able to support any Iterable of native Strings, Integers, Doubles, or Booleans; that doesn't feel like feature creep to me at all. It would transparently support Sets. (Right now, the API only accepts Lists of JsonValues, which is what makes the API feel so ceremonious.)
First, we've been in this game far too long to know that this isn't the case. Second, this is only incubation. It may well be that the team behind this feature intend to add more convenience methods but wish to do it later once the core is more battle-tested. It's always best to focus on the core first and add ornamentation once you know the core is right.
What type would that method accept? Wouldn't it need to be Object? That seems worse than boilerplate
It does seem like any serious application is going to use another library, and this will be useful for very simple json usage or single-file hello-world type programs (e.g. to go along with Implicitly Defined Classes and the Flexible Launch Protocol).
This would help a lot:
Then, you could at least write: And for JsonObject, a little fluent builder API would probably knock out a lot of ceremony, too. The alternative today looks quite ceremonious:The clean way of doing this is to build a json marshaling mechanism for the type system as it already exists. This is doable in Java, and some json libraries (e.g. gson) are already capable of this.
I must admit I don't fully understand the motivation behind this JEP. Like when would I ever reach for this?
As I understand that section (and I wasn't involved in writing this JEP), good and popular marshalling libraries for JSON already exist, and the JEP clearly states that it is not the goal to replace them or perform their role. The JEP says that this package may be what you'd reach for when a program only wants to do some very simple, small tasks with JSON data and the requirements and code size don't merit pulling in a fully-featured JSON library (e.g. when you're writing a one-file script, or exploring in JShell).