Automate POJO Generation in Spring Boot 3 with jsonschema2pojo

1. Introduction

In backend development, writing POJO classes that mirror JSON structures is repetitive and error‑prone. Developers must define each field and match data types, which consumes time and often leads to bugs during API integration.

2. What is jsonschema2pojo?

jsonschema2pojo is a library that automatically converts JSON Schema or raw JSON data into Java POJOs that follow standard conventions, removing the need for manual coding and reducing the risk of omissions or type mismatches.

3. What is JSON Schema?

JSON Schema is a specification for describing and validating the structure of JSON data. It defines field names, data types, constraints, and required properties, enabling reliable data exchange and interface standardisation.

2.1 Prepare the Environment

Add the following Maven dependencies to your Spring Boot 3.5.0 project:

<dependency>
  <groupId>org.jsonschema2pojo</groupId>
  <artifactId>jsonschema2pojo-core</artifactId>
  <version>1.3.3</version>
</dependency>
<dependency>
  <groupId>org.glassfish.jaxb</groupId>
  <artifactId>codemodel</artifactId>
  <version>4.0.6</version>
</dependency>
<dependency>
  <groupId>org.apache.commons</groupId>
  <artifactId>commons-lang3</artifactId>
  <version>3.20.0</version>
</dependency>

2.2 Generate Java Classes from a JSON Schema

Define a JSON Schema for a Product object:

{
  "$schema": "https://json-schema.org/draft/2020-12/schema",
  "$id": "http://pack.com/product.schema.json",
  "title": "Product",
  "description": "商品信息",
  "type": "object",
  "properties": {
    "productId": {"description": "唯一标识", "type": "integer"},
    "productName": {"description": "商品名称", "type": "string"},
    "price": {"description": "商品价格", "type": "number", "exclusiveMinimum": 0},
    "tags": {"description": "商品标签", "type": "array", "items": {"type": "string"}, "minItems": 1, "uniqueItems": true}
  },
  "required": ["productId", "productName", "price"]
}

Use the following Java code to generate the POJO:

String schema = """
    ...
    """;
JCodeModel codeModel = new JCodeModel();
GenerationConfig config = new DefaultGenerationConfig() {
    @Override public boolean isGenerateBuilders() { return true; }
    @Override public boolean isIncludeAdditionalProperties() { return false; }
    @Override public boolean isIncludeGeneratedAnnotation() { return false; }
    @Override public boolean isUseLongIntegers() { return true; }
    @Override public boolean isUseBigDecimals() { return true; }
};
SchemaMapper mapper = new SchemaMapper(new RuleFactory(config, new Jackson2Annotator(config), new SchemaStore()), new SchemaGenerator());
mapper.generate(codeModel, "Product", "com.pack", schema);
codeModel.build(new File("F://genclass"));

The generated class includes builder methods, proper type handling, and optional annotations. Note that the default @Generated annotation may contain an incorrect package name that must be corrected manually.

2.3 Generate Java Classes Directly from JSON Data

Define a JSON document representing a book:

{
  "name": "Spring Boot 3实战案例锦集",
  "price": 70,
  "author": "Pack_xg",
  "tags": ["Java", "Spring", "Spring Boot", "Spring Cloud"],
  "Profile": {"city": "乌鲁木齐", "country": "中国"}
}

Generate the corresponding POJOs with this code (notice the SourceType.JSON override):

String json = """
    ...
    """;
JCodeModel jcodeModel = new JCodeModel();
GenerationConfig config = new DefaultGenerationConfig() {
    @Override public boolean isGenerateBuilders() { return true; }
    @Override public SourceType getSourceType() { return SourceType.JSON; }
};
SchemaMapper mapper = new SchemaMapper(new RuleFactory(config, new Jackson2Annotator(config), new SchemaStore()), new SchemaGenerator());
mapper.generate(jcodeModel, "Book", "com.pack", json);
jcodeModel.build(outputJavaClassDirectory);

The process creates two classes: Book and Profile, as shown in the screenshots below.

2.4 Automate Generation with the Maven Plugin

Add the following plugin configuration to your pom.xml to generate POJOs during the build:

<plugin>
  <groupId>org.jsonschema2pojo</groupId>
  <artifactId>jsonschema2pojo-maven-plugin</artifactId>
  <version>1.3.3</version>
  <configuration>
    <sourceDirectory>${basedir}/src/main/resources/schema</sourceDirectory>
    <targetPackage>com.pack.json_gen_class</targetPackage>
  </configuration>
  <executions>
    <execution>
      <goals>
        <goal>generate</goal>
      </goals>
    </execution>
  </executions>
</plugin>

The schema files placed under src/main/resources/schema are processed, and the generated classes appear as illustrated in the following screenshots.

3. Important Note

The generated classes contain a @Generated annotation whose package name may be incorrect; you need to edit it manually.

For a complete list of supported options, visit the official site: https://www.jsonschema2pojo.org/