JEP 540 Proposed to Target JDK 28 with a Simple JSON API

JEP 540 has progressed from Candidate to Proposed to Target for JDK 28, meaning the proposal is now slated for inclusion in the next Java release. If accepted, the API will be packaged in the incubating module jdk.incubator.json, where it can still change incompatibly or be removed based on developer feedback. This status signals that the feature is relatively mature but not yet final, and developers can start experimenting with it now.

The core of the API revolves around a sealed JsonValue hierarchy with six subinterfaces representing objects, arrays, strings, numbers, booleans, and null. All values are immutable and thread-safe, and traversal methods are defined directly on JsonValue, allowing code to navigate JSON structures without repeated casting. The Json class offers static parse methods that return a JsonValue representing the whole document.

Creating JSON values uses factory methods on each subinterface, such as JsonObject.of and JsonString.of, which require wrapping ordinary Java primitives before insertion. This design makes the JSON type of each value explicit but adds ceremony compared with libraries that accept raw Java types. The documentation notes that construction ergonomics are a likely area for feedback during incubation.

The parser operates in a strict mode only: it rejects comments, trailing commas, and any syntax extensions, and it also rejects duplicate object-member names even though the RFC permits them. Errors are reported as an unchecked JsonParseException that includes line and column information but does not expose a structured JSON path. This strictness reduces ambiguity but may require callers to pre-process or validate input more carefully.

Because the API deliberately omits data binding, streaming, and permissive parsing, it is suited for tasks like reading configuration files, inspecting REST responses, or generating small JSON payloads. Engineers adopting it must add the incubating module to their builds, handle unchecked parsing exceptions, and wrap primitive values when constructing JSON. The limited feature set means it will not replace full-featured libraries for complex serialization needs, but it offers a lightweight, JDK-native alternative for simple scenarios.