How to Generate Java Records from JSON

Modeling JSON in Java is cleanest with records — concise, immutable carriers that Jackson can bind directly. Generating them from a sample gets the component names, annotations, and types right automatically. Here's how the output is built.

From JSON to records

Each JSON object becomes a record, and nested objects become their own records:

{ "id": 1, "user_name": "Ada" }

import com.fasterxml.jackson.annotation.JsonProperty;

public record Root(
    int id,
    @JsonProperty("user_name") String userName
) {}

Records (Java 16+) give you the constructor, accessors, equals, hashCode, and toString for free, and Jackson binds JSON straight to them.

Component names and @JsonProperty

Java convention is camelCase components. When a JSON key uses another style — user_name, first-name — the component is camel-cased and a Jackson @JsonProperty annotation maps it back to the original key:

@JsonProperty("user_name") String userName

Components that collide with Java keywords get a Value suffix so they stay valid.

Nullable fields and boxed types

A record component that must hold null can't be a primitive, so when you convert an array of objects and a key is missing from some elements, the component uses a boxed type:

Integer views

Required numbers stay primitive (int, long, double, boolean) for efficiency; optional ones become Integer, Long, Double, or Boolean. Arrays map to List<T> with boxed element types, and a null or unknown type falls back to Object.

Related

Generating types for another language? See JSON to Kotlin and JSON to Rust.

Try it

Paste a JSON response and get Java records instantly — everything runs in your browser, nothing uploaded.