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Generate Java data classes from JSON schemas

Generate Java data classes from JSON Schema (.json) files for use in Apache Kafka® applications. Use the jsonschema2pojo CLI tool to generate Java classes that match your schema structure.

Prerequisites​

Generate the Java classes​

Generate Java classes from your JSON schema file using the jsonschema2pojo CLI:

jsonschema2pojo --source src/main/resources/schema.json --target src/main/java/
  • Replace schema.json with your schema file.
  • Replace src/main/java/ with your preferred output directory.
note

Use the --package option to specify the Java package during code generation. Kafka serialization depends on the fully qualified class name.

For example:

jsonschema2pojo \
  --source src/main/resources/users.json \
  --target src/main/java/io/aiven/example \
  --package io.aiven.example

Example schema​

{
  "type": "object",
  "title": "User",
  "javaType": "io.aiven.example.User",
  "properties": {
    "id": { "type": "integer" },
    "email": { "type": "string" }
  },
  "required": ["id", "email"]
}

This schema generates the following Java file:

src/main/java/io/aiven/example/User.java

Optional: Add Confluent schema annotation​

To enable additional features in Confluent’s deserializers (which are compatible with schema registries like Karapace), you can add this annotation to your JSON Schema:

"@io.confluent.kafka.schemaregistry.annotations.Schema": {
  "value": "{...your schema as a string...}",
  "refs": []
}

This annotation makes runtime methods such as schema() and refs() available in the generated Java classes.

Use this only for advanced use cases that require schema introspection at runtime.

Add Maven dependencies​

Add these dependencies to your pom.xml to compile and use the generated classes for JSON Schema serialization and deserialization in Kafka producers and consumers.

<dependencies>
  <!-- Apache Kafka client dependency -->
  <dependency>
    <groupId>org.apache.kafka</groupId>
    <artifactId>kafka-clients</artifactId>
    <version>3.8.1</version>
  </dependency>

  <!-- Confluent dependency for JSON Schema serialization -->
  <dependency>
    <groupId>io.confluent</groupId>
    <artifactId>kafka-json-schema-serializer</artifactId>
    <version>8.0.0</version>
  </dependency>

  <!-- Core Jackson library for JSON binding -->
  <dependency>
    <groupId>com.fasterxml.jackson.core</groupId>
    <artifactId>jackson-databind</artifactId>
    <version>2.19.2</version>
  </dependency>
</dependencies>

Optional dependencies​

Depending on your schema complexity or tooling, you might also need these:

<!-- Jackson support for Java 8 types -->
<dependency>
  <groupId>com.fasterxml.jackson.datatype</groupId>
  <artifactId>jackson-datatype-jdk8</artifactId>
  <version>2.19.2</version>
</dependency>

<!-- Jackson support for Java time (JSR-310) -->
<dependency>
  <groupId>com.fasterxml.jackson.datatype</groupId>
  <artifactId>jackson-datatype-jsr310</artifactId>
  <version>2.19.2</version>
</dependency>

<!-- JSON Schema validation -->
<dependency>
  <groupId>com.github.erosb</groupId>
  <artifactId>everit-json-schema</artifactId>
  <version>1.14.6</version>
</dependency>

These optional dependencies support features like Java 8 types, JSR-310 date/time classes, and schema validation. Add them only if your schema or generated class uses these features.

Related pages

jsonschema2pojo CLI reference