Paste JSON, get Java records: a small IntelliJ plugin for API payloads

#java #intellij #json #productivity

If you write Java against REST APIs, you have typed the same thing many times: copy a JSON response, then hand-write the classes that match it. For years the IntelliJ answer was GsonFormat, which generated old-style POJOs. It stopped working with current IDEs a while ago, and the popular JSON-to-class plugins I checked generate classes, not Java records, which is what you want for an immutable API payload in Java 16+.

So I built a small one: JSON to Java Record, now on the JetBrains Marketplace.

What it does

Copy this JSON:

{
  "order_id": 10452,
  "created_at": "2026-11-08T14:03:00Z",
  "total": 129.95,
  "paid": true,
  "customer": { "id": 88, "full_name": "Ana Ruiz", "email": "ana@example.com" },
  "items": [
    { "sku": "KB-01", "qty": 1, "price": 89.0 },
    { "sku": "MS-02", "qty": 2, "price": 20.475, "gift_wrap": true }
  ]
}

Press Alt+Insert in a Java file, choose Paste JSON as Java Record... (also under Tools), name it Order, and you get this (the plugin's actual output; in the editor it is then reformatted with your own code style):

import java.util.List;

public record Order(
    int orderId,
    String createdAt,
    double total,
    boolean paid,
    Customer customer,
    List<Item> items
) {
    public record Customer(
        int id,
        String fullName,
        String email
    ) {}

    public record Item(
        String sku,
        int qty,
        double price,
        Boolean giftWrap
    ) {}
}

A few details that matter in real payloads:

Nested objects become nested records, and arrays of objects become List<...> of a record.
Arrays are merged. gift_wrap appears in only one of the two items, so it becomes a boxed Boolean (it can be null), while fields present everywhere stay primitive.
Numbers are typed sensibly: int, long for big values, double for decimals; a list mixing 1 and 2.5 becomes List<Double>.
snake_case becomes camelCase, and reserved words are made safe (class becomes class_).

Keep the original JSON names

If your mapper needs the original keys, pick Jackson or Gson in the dialog. Only the fields whose Java name differs get an annotation:

import com.fasterxml.jackson.annotation.JsonProperty;
import java.util.List;

public record Order(
    @JsonProperty("order_id") int orderId,
    @JsonProperty("created_at") String createdAt,
    double total,
    boolean paid,
    Customer customer,
    List<Item> items
) {
    public record Customer(
        int id,
        @JsonProperty("full_name") String fullName,
        String email
    ) {}

    public record Item(
        String sku,
        int qty,
        double price,
        @JsonProperty("gift_wrap") Boolean giftWrap
    ) {}
}

Gson users get @SerializedName instead.

Where it puts the code

In an open Java file, it inserts at the caret (or replaces a selection), adds missing imports at the top and reformats.
From the Project view (right-click a package, New > Paste JSON as Java Record...), it creates Order.java there. It never overwrites an existing file.
Invalid JSON shows an error and changes nothing. It reads your clipboard, works offline and sends no telemetry.

Limits, honestly

IntelliJ IDEA 2025.2 or newer, with Java support. It does not run in PyCharm or WebStorm.
Types are inferred from the sample you paste. A field that is null in your sample becomes Object; paste a fuller sample or fix that one type by hand.
Dates stay String. Mapping them to Instant or LocalDate is your call.

Get it

Marketplace: JSON to Java Record (free)
Source and issues: github.com/datawharf-tools/json-record

It is a first version. If it gets a type wrong on your payload, or you want another output (Lombok, Kotlin data classes, TypeScript), open an issue or tell me in the comments.

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