Java to JSON Converter
Paste a Java POJO, record, or class. Get clean JSON back.
What this tool does
You have a Java record or a classic POJO, and you need a JSON payload that matches it — for a request body, an OpenAPI example, or a test fixture. Paste the class plus a constructor call (or a var order = new Order(...) on Java 10+) and you get back JSON shaped the way Jackson or Gson would serialize it, without you having to instantiate anything.
The tool follows real serializer behaviour, not just string-replace. BigDecimal becomes a JSON number without the BigDecimal(...) wrapper, OffsetDateTime / LocalDateTime / Instant come out as ISO-8601 strings per RFC 8259, UUID is a standard 8-4-4-4-12 hex string, boolean stays boolean, and collections (List, Set, arrays) flatten to JSON arrays. Map<String, V> becomes a JSON object keyed by the map entries.
Jackson annotations are honoured: @JsonProperty("x") renames the key, @JsonIgnore removes the field, and @JsonInclude(Include.NON_NULL) suppresses nulls. Nested classes — the typical Address inside an Order — are expanded in place. Paste a whole file with several classes; each top-level instance ends up as its own entry. For the full annotation reference see the jackson-annotations docs.
How to use it
Three steps. Works whether you paste a one-line record or a whole model file.
Paste your Java (or try the sample)
Drop the class plus a constructor call into the left editor. A POJO with getters/setters, a record, a Lombok @Data class, or multiple classes — all fine. Hit Load Sample if you want a realistic starting point.
You do not need to delete package declarations, imports, or public/private modifiers. Leave the standard Java syntax as-is. Jackson annotations, validation annotations, and Lombok decorations are all accepted.
Hit Convert
Click the green Convert button. The tool reads the class, resolves the constructor arguments, applies any Jackson rename/ignore annotations, and produces indented JSON.
Copy the JSON
The right panel shows JSON ready for a Spring Boot request, a JUnit fixture, or a Swagger example. Copy it wherever you need.
When this actually comes in handy
Spring Boot request samples
Paste a <code>@RequestBody</code> DTO and a constructor call to get a JSON body you can fire at Postman, curl, or HTTPie without booting the app.
JUnit test fixtures
Convert an object you build in a unit test into a standalone JSON file for integration tests, WireMock stubs, or Testcontainers seed data.
OpenAPI / Swagger examples
Use an actual model class to produce the <code>example</code> block for your OpenAPI spec — so the example stays in sync with the real POJO.
Kafka and messaging payloads
Turn a record representing a Kafka message into JSON for producer testing, sample data, or documentation.
Common questions
Does it respect Jackson annotations?
Yes. @JsonProperty renames fields, @JsonIgnore removes them, @JsonInclude(Include.NON_NULL) suppresses nulls, and @JsonFormat controls date formatting. See the jackson-annotations reference for the full list.
How are BigDecimal, LocalDateTime, and UUID handled?
BigDecimal becomes a JSON number. LocalDateTime, OffsetDateTime, and Instant become ISO-8601 strings. UUID is a standard 8-4-4-4-12 hex string. LocalDate is YYYY-MM-DD. These match the defaults of the Jackson JavaTimeModule.
Does it handle records and sealed types?
Yes. Java 14+ record types serialize using their canonical components. Sealed types and their permitted subtypes are flattened to the underlying data shape. See the OpenJDK records JEP for background.
What about Lombok @Data / @Builder classes?
Lombok annotations are recognized — generated getters, setters, and builders are treated as normal accessors. The tool looks at the declared fields plus any constructor call you paste to build the JSON.
Can I paste a whole file with several classes?
Yes. Every top-level class with an instance in the paste ends up as its own entry in the JSON. Inner/nested static classes are expanded inline where they are used.
Is my code stored?
The code is sent to the backend to be converted and is not persisted or logged. As with any online tool, review before pasting anything genuinely sensitive.
Other tools you may need
Java to JSON is one piece of the puzzle. Here are the tools that pair well with it: