JSON guide · 7 min read
How to Generate Java Classes from JSON
Generate Java records or classes from JSON and review nullability, numeric types, nested models and deserialization rules.
Records versus mutable classes
Java records are concise for immutable data carriers. Framework requirements, mutation, inheritance or custom construction may still favor regular classes.
Property names and annotations
JSON names that do not match Java conventions may require annotations such as JsonProperty, depending on the serializer and naming strategy.
Review nullability and collections
A generated reference type can still receive null, and an empty sample array cannot prove its element type. Decide whether fields are required and whether collections should default to empty values.
Choose numeric types from the contract
Do not infer int, long, BigInteger or BigDecimal solely from one observed value. Monetary values and high-precision measurements require special attention.
Common questions
Frequently asked questions
Should generated Java models use records?
Records are suitable for many DTOs, but project conventions and framework requirements should determine the final design.
Why can deserialization still fail?
The real payload may contain missing fields, nulls, unexpected types or names that differ from the generated sample.