About JSON to Java Online
Paste a JSON object and instantly get Java POJO class definitions compatible with Java 8 and later. Each class has private fields, a no-args constructor, an all-args constructor, and typed getters/setters following JavaBeans conventions. Nested objects generate their own classes. Arrays map to List<T> with boxed types.
Frequently Asked Questions
What is JSON to Java class generation?
JSON to Java class generation analyses a JSON sample and produces Java class definitions with Jackson @JsonProperty annotations. Each key becomes a field with getter and setter, making the class immediately usable with ObjectMapper.readValue() for JSON deserialisation.
Should I use Jackson or Gson annotations on my generated POJO?
Jackson is the more widely adopted library and is the default in Spring Boot. The generated classes use Jackson @JsonProperty annotations. For Gson compatibility, replace @JsonProperty with @SerializedName. Both libraries handle nested objects and arrays similarly; choose based on which dependency is already in your project.
When should I use Java records instead of a POJO class?
Java records (Java 16+) are ideal for immutable data transfer objects: they automatically generate constructors, accessors, equals, hashCode, and toString. Jackson supports records with no extra configuration in Jackson 2.12+. Use records for simple read-only JSON models; use regular POJOs when you need inheritance or mutable state.
How do I handle unknown JSON fields in a Jackson POJO?
By default Jackson throws an error on unknown fields. Add @JsonIgnoreProperties(ignoreUnknown = true) at the class level to silently skip unknown keys — essential for API clients consuming a third-party API that may add fields. Alternatively, add a @JsonAnyGetter / @JsonAnySetter pair to capture unknown fields in a Map.
Can I add Lombok annotations to reduce boilerplate in generated classes?
Yes. After copying the generated classes, add @Data (generates getters, setters, equals, hashCode, toString) or @Value (immutable version). Combine with @NoArgsConstructor and @AllArgsConstructor as needed. Lombok and Jackson are fully compatible — Jackson's @JsonProperty annotations coexist with Lombok-generated accessor methods.
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