JSON to Java class generator

Paste a JSON response and get Java types for it in one file. Choose classic classes with private fields, getters and setters, or compact records (Java 16+). Keys that are not valid camelCase names get Jackson's @JsonProperty, so the mapping stays exact.

JSON sample

GenerateClasses (POJO)Records

Jackson @JsonProperty for renamed keys

Java code

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

public class Root {
    @JsonProperty("order_id")
    private long orderId;
    private Customer customer;
    private List<Item> items;
    private boolean paid;

    public long getOrderId() { return orderId; }
    public void setOrderId(long orderId) { this.orderId = orderId; }

    public Customer getCustomer() { return customer; }
    public void setCustomer(Customer customer) { this.customer = customer; }

    public List<Item> getItems() { return items; }
    public void setItems(List<Item> items) { this.items = items; }

    public boolean isPaid() { return paid; }
    public void setPaid(boolean paid) { this.paid = paid; }

    public static class Customer {
        private String name;
        private Object email;

        public String getName() { return name; }
        public void setName(String name) { this.name = name; }

        public Object getEmail() { return email; }
        public void setEmail(Object email) { this.email = email; }
    }

    public static class Item {
        private String sku;
        private long qty;
        private double price;
        @JsonProperty("gift_note")
        private String giftNote;

        public String getSku() { return sku; }
        public void setSku(String sku) { this.sku = sku; }

        public long getQty() { return qty; }
        public void setQty(long qty) { this.qty = qty; }

        public double getPrice() { return price; }
        public void setPrice(double price) { this.price = price; }

        public String getGiftNote() { return giftNote; }
        public void setGiftNote(String giftNote) { this.giftNote = giftNote; }
    }
}

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How to use it

Paste a JSON sample. Arrays with several objects give the best result: keys missing from some items are detected.
Choose classes (fields, getters and setters) or records, and whether to add Jackson annotations.
Save the output as Root.java and rename the classes to fit your project.

How it works

The sample is read into a shape: each key with every type seen at that place. All objects of one array are merged into one class.

Field names are camelCase: order_id → orderId, gift_note → giftNote. Getters follow JavaBeans: getOrderId(), and isPaid() for a primitive boolean.
Class names come from keys: items holds a List, customer becomes Customer.
Imports include only what is used: java.util.List and com.fasterxml.jackson.annotation.JsonProperty.
With a top-level array, a comment names the type to read it into, such as List.

Worked example

{"items":[{"sku":"A","note":null,"qty":1},{"sku":"B","note":"x"}]} as records gives:

import java.util.List;

public record Root(
    List<Item> items
) {
    public record Item(
        String sku,
        String note,
        Long qty
    ) {}
}

qty is missing from the second item, so it is a boxed Long that can be null.

Tips

Read it with Jackson: new ObjectMapper().readValue(json, Root.class).
Add @JsonIgnoreProperties(ignoreUnknown = true) if the real data may carry keys the sample did not have.
Check numeric types: a price that was always whole in the sample comes out as long.

Frequently asked questions

How are JSON types mapped to Java?

Strings become String, true and false boolean, whole numbers long and other numbers double (a mix of both becomes double). Arrays become List<T>, objects become their own classes, and a place holding different kinds of values becomes Object.

When does it use Long instead of long?

A primitive cannot hold null. When the sample has null for a number or boolean, or the key is missing from some objects of an array, the boxed type is used: Long, Double, Boolean. Inside List<...> the boxed type is always used, as Java generics require.

Why are the other classes nested inside Root?

Java allows one public top-level class per file. Putting the others inside Root as public static classes (or nested records) makes the output one file, Root.java, that compiles as it is. Refer to them as Root.Item, or move them to their own files.

What happens to keys like first-name or class?

Field names are camelCase built from the key: first-name becomes firstName, and a Java keyword gets an underscore, class_. With Jackson on, such fields get @JsonProperty("first-name"); with it off, a comment keeps the original key.

Do records work with Jackson?

Yes, Jackson 2.12 and newer deserializes records through their canonical constructor, and @JsonProperty on a record component works the same as on a field.

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All tools in this category: Developer ·Updated November 4, 2026