Convert a Flat JSON Object to a Basic Java POJO

From a Flat JSON Object to a Java POJO

The simplest JSON-to-Java conversion takes a flat object — no nesting, no arrays — and produces a class with one private field per key, plus a matching pair of accessor methods.

Example JSON

{
  "id": 42,
  "name": "Alice",
  "email": "alice@example.com",
  "active": true,
  "score": 98.5
}

Generated Java POJO

package com.example.model;

public class User {
    private Integer id;
    private String name;
    private String email;
    private Boolean active;
    private Double score;

    public Integer getId() { return id; }
    public void setId(Integer id) { this.id = id; }

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

    // ... and so on for the remaining fields
}

Type Mapping

JSON value	Java type
string	String
integer	Integer (or Long for values beyond 32-bit range)
decimal	Double
boolean	Boolean
null	Object (cannot infer further)
array	List<T> with recursively inferred T

Why Boxed Types?

The generator emits the boxed wrapper types (Integer, Long, Double, Boolean) rather than the primitives (int, long, double, boolean) because JSON allows null for any field. Boxed types can hold null; primitives cannot. If you know a field is always present, you are free to swap to a primitive after generation.

Usage with Jackson

ObjectMapper mapper = new ObjectMapper();
User user = mapper.readValue(json, User.class);

This pattern is the foundation every other example builds on. Once you have the basic POJO, adding Lombok, switching to a record, or annotating for Jackson are all incremental refinements.