Account
Sign in to you account
Sign In Sign Up

How to Generate A JSON Schema From A Kotlin Class?

12 minutes read

To generate a JSON schema from a Kotlin class, you can use the Jackson library along with the Jackson-module-jsonSchema module. Here are the steps involved in this process:

  1. Add the necessary dependencies in your Gradle or Maven configuration to include the Jackson libraries.
  2. Create a Kotlin class that represents your data structure. Annotate the class and its properties using Jackson annotations such as @JsonRootName, @JsonProperty, etc., to define the JSON structure.
  3. Use the ObjectMapper class from Jackson to create an instance of the mapper.
  4. Configure the mapper to enable the JSON schema generation by registering the JsonSchemaGenerator module using registerModule(JsonSchemaModule()).
  5. Invoke the generateSchema() method of the mapper, passing your Kotlin class and retrieve the generated JSON schema.
  6. Optionally, you can convert the JSON schema to a string or write it to a file.


Here's an example illustrating the steps described above:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18

import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.jsonSchema.JsonSchemaGenerator
import com.fasterxml.jackson.module.kotlin.registerKotlinModule

data class MyDataClass(val name: String, val age: Int)

fun main() {
    val mapper = ObjectMapper().registerKotlinModule()
    mapper.registerModule(JsonSchemaGenerator().module)

    val jsonSchema = mapper.generateSchema(MyDataClass::class.java)
    println(jsonSchema)

    // Optionally, convert and save the schema as a string or write it to a file
    val schemaAsString = mapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonSchema)
    // Write the schema to a file
    // mapper.writerWithDefaultPrettyPrinter().writeValue(File("schema.json"), jsonSchema)
}


By following these steps, you can easily generate a JSON schema from a Kotlin class using the Jackson library.

Best Kotlin Books to Read in 2024

1
Atomic Kotlin

Rating is 5 out of 5

Atomic Kotlin

Get Book Now
2
Kotlin in Action

Rating is 4.9 out of 5

Kotlin in Action

Get Book Now
3
Kotlin Cookbook: A Problem-Focused Approach

Rating is 4.8 out of 5

Kotlin Cookbook: A Problem-Focused Approach

Get Book Now
4
Head First Kotlin: A Brain-Friendly Guide

Rating is 4.7 out of 5

Head First Kotlin: A Brain-Friendly Guide

Get Book Now
5
Kotlin Programming: The Big Nerd Ranch Guide (Big Nerd Ranch Guides)

Rating is 4.6 out of 5

Kotlin Programming: The Big Nerd Ranch Guide (Big Nerd Ranch Guides)

Get Book Now
6
Effective Kotlin: Best Practices (Kotlin for Developers Book 5)

Rating is 4.5 out of 5

Effective Kotlin: Best Practices (Kotlin for Developers Book 5)

Get Book Now
7
Java to Kotlin: A Refactoring Guidebook

Rating is 4.4 out of 5

Java to Kotlin: A Refactoring Guidebook

Get Book Now
8
Learn to Program with Kotlin: From the Basics to Projects with Text and Image Processing

Rating is 4.3 out of 5

Learn to Program with Kotlin: From the Basics to Projects with Text and Image Processing

Get Book Now


What is the recommended way to generate a JSON schema from a Kotlin data class?

There are several third-party libraries available for generating JSON schemas from Kotlin data classes. One popular library is jsonschema2pojo, which supports generating JSON schemas from Java classes.


To generate a JSON schema from a Kotlin data class, you can follow these steps:

  1. Add the jsonschema2pojo library as a dependency in your project's build file. For example, if you are using Gradle, you can add the following dependency in your build.gradle file:
1
2
3

dependencies {
    implementation 'org.jsonschema2pojo:jsonschema2pojo-core:1.1.1'
}


  1. Annotate your Kotlin data class with the appropriate annotations for jsonschema2pojo to generate the schema correctly. The annotations you can use include @JsonProperty, @JsonFormat, @JsonInclude, and others from the com.fasterxml.jackson.annotation package.
1
2
3
4
5
6

import com.fasterxml.jackson.annotation.JsonProperty

data class Person(
    @JsonProperty("name") val name: String,
    @JsonProperty("age") val age: Int
)


  1. Write a utility function that uses jsonschema2pojo to generate the JSON schema from the Kotlin data class. Here is an example using jsonschema2pojo:
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11

import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import org.jsonschema2pojo.SchemaGenerator
import org.jsonschema2pojo.SchemaMapper

fun generateJsonSchema(dataClass: Class<*>): String {
    val objectMapper: ObjectMapper = jacksonObjectMapper()
    val schemaGenerator = SchemaGenerator()
    val schemaMapper = SchemaMapper()
    return schemaMapper.generate(schemaGenerator.generateSchema(dataClass), objectMapper.nodeFactory().objectNode())
}


  1. Use the utility function to generate the JSON schema for your Kotlin data class:
1
2

val personJsonSchema = generateJsonSchema(Person::class.java)
println(personJsonSchema)


This will generate the JSON schema for your Kotlin data class in string format and print it to the console.


Note that the above example assumes you have set up jsonschema2pojo correctly and have imported the required classes. Adjust the versions and packages according to your project's configuration.


Keep in mind that jsonschema2pojo primarily targets Java classes, so some limitations or compatibility issues may arise when generating JSON schemas from Kotlin data classes.


How to generate a JSON schema using a Kotlin class with nested properties?

To generate a JSON schema using a Kotlin class with nested properties, you can use the 'kotlinx.serialization' library along with the 'json-schema' generator. Here are the steps you can follow:

  1. Add the kotlinx.serialization and json-schema dependencies to your project's build.gradle file:
1
2
3
4

dependencies {
    implementation "org.jetbrains.kotlinx:kotlinx-serialization-json:1.2.1" // or the latest version
    implementation "com.github.victools.jsonschema-generator:jsonschema-generator:4.25.0" // or the latest version
}


  1. Annotate your Kotlin class and its properties with kotlinx.serialization annotations to define the serialization behavior:
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12

@Serializable
data class MyClass(
    val property1: String,
    val property2: Int,
    val nestedProperty: MyNestedClass
)

@Serializable
data class MyNestedClass(
    val nestedProperty1: Boolean,
    val nestedProperty2: Double
)


  1. Create a JSONSchemaGenerator instance and generate the JSON schema for your class:
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13

import com.fasterxml.jackson.databind.JsonNode
import com.github.victools.jsonschema.generator.SchemaGeneratorConfigBuilder
import com.github.victools.jsonschema.generator.SchemaGeneratorTypeMapper

fun generateJsonSchema(): JsonNode {
    val configBuilder = SchemaGeneratorConfigBuilder(SchemaGeneratorTypeMapper())
        .with(Option.FLATTENED_ENUMS)
        .with(Option.PREFIX_COMPOSITES_SINGLE_TYPE_PROPERTIES)
    val generator = com.github.victools.jsonschema.generator.SchemaGenerator(configBuilder.build())

    val jsonSchemaNode = generator.generateSchema(MyClass::class.java)
    return jsonSchemaNode
}


  1. You can then convert the generated JSON schema to a string for further usage or display:
1
2
3
4
5
6
7

import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper

fun main() {
    val jsonSchemaNode = generateJsonSchema()
    val jsonSchemaString = jacksonObjectMapper().writeValueAsString(jsonSchemaNode)
    println(jsonSchemaString)
}


The 'jsonSchemaString' variable will contain the JSON schema generated from your Kotlin class, including its nested properties.


How to specify the type of each property in a Kotlin class for JSON schema generation?

To specify the type of each property in a Kotlin class for JSON schema generation, you can make use of the @JsonClass and @JsonProperty annotations from the Jackson library. Here's an example:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27

import com.fasterxml.jackson.annotation.JsonClassDescription
import com.fasterxml.jackson.annotation.JsonProperty
import com.fasterxml.jackson.core.JsonProcessingException
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.module.jsonSchema.JsonSchema
import com.fasterxml.jackson.module.jsonSchema.JsonSchemaGenerator

@JsonClass(generateAdapter = true)
data class ExampleClass(
    @JsonProperty("name")
    val name: String,
    
    @JsonProperty("age")
    val age: Int,
    
    @JsonProperty("isStudent")
    val isStudent: Boolean
)

fun main() {
    val objectMapper = ObjectMapper()
    val jsonSchemaGenerator = JsonSchemaGenerator(objectMapper)
    
    val jsonSchema: JsonSchema = jsonSchemaGenerator.generateSchema(ExampleClass::class.java)
    val jsonSchemaAsString: String = objectMapper.writeValueAsString(jsonSchema)
    println(jsonSchemaAsString)
}


In this example, we define a data class called ExampleClass with properties name of type String, age of type Int, and isStudent of type Boolean. We then use the @JsonProperty annotation to specify the property names in the generated JSON schema.


To generate the JSON schema, we use the JsonSchemaGenerator class from Jackson. We pass the ExampleClass::class.java to the generateSchema() method of JsonSchemaGenerator to generate the schema for the class. Finally, we convert the generated JsonSchema object to a JSON string using the ObjectMapper class from Jackson.


By running this code, you'll get a JSON schema as a string that specifies the type of each property in the ExampleClass.


Note: You may need to add the necessary dependencies (Jackson and Jackson Kotlin module) to your project's build.gradle or pom.xml file for successful execution.


How to include the necessary dependencies for JSON schema generation in Kotlin?

To include the necessary dependencies for JSON schema generation in Kotlin, you can follow these steps:


Step 1: Add the required dependencies to your build.gradle file.


For Maven:

1
2
3
4

dependencies {
    implementation 'com.github.victools:jsonschema-generator:4.17.0'
    implementation 'com.fasterxml.jackson.module:jackson-module-kotlin:2.12.2'
}


For Gradle:

1
2
3
4

dependencies {
    implementation("com.github.victools:jsonschema-generator:4.17.0")
    implementation("com.fasterxml.jackson.module:jackson-module-kotlin:2.12.2")
}


Step 2: Sync your project to download the dependencies.


Note: The jsonschema-generator library provides an easy way to generate JSON schemas based on your existing Kotlin classes, and the jackson-module-kotlin library is used for better Kotlin support in JSON serialization and deserialization.


Step 3: Start using the JSON schema generation in your Kotlin code.


Here's an example of how you can generate a JSON schema for a Kotlin data class using these dependencies:

 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19

import com.fasterxml.jackson.module.kotlin.jacksonObjectMapper
import com.fasterxml.jackson.module.kotlin.readValue
import com.github.victools.jsonschema.generator.SchemaGenerator
import com.github.victools.jsonschema.generator.SchemaGeneratorConfig
import com.github.victools.jsonschema.generator.SchemaVersion

data class Person(val name: String, val age: Int)

fun main() {
    val schemaVersion = SchemaVersion.DRAFT_2019_09
    val objectMapper = jacksonObjectMapper()
    val schemaGeneratorConfig = SchemaGeneratorConfig(objectMapper, schemaVersion)
    val schemaGenerator = SchemaGenerator(schemaGeneratorConfig)
    val schema = schemaGenerator.generateSchema(Person::class.java)
    val jsonSchema = objectMapper.writeValueAsString(schema)
    println(jsonSchema)
    val deserializedSchema = objectMapper.readValue<JsonSchema>(jsonSchema)
    println(deserializedSchema)
}


In this example, we use the com.fasterxml.jackson.module.kotlin package to serialize the schema object to JSON. You can adjust the code based on your requirements.


That's it! You have included the necessary dependencies for JSON schema generation in Kotlin.


What is the purpose of using regular expressions in a JSON schema?

Regular expressions in a JSON schema are used to define patterns and validate the format of string values in JSON data.


The purpose of using regular expressions in a JSON schema is to enforce specific validation rules and constraints on the input data. By specifying a regular expression pattern, the schema can ensure that the expected format of a string value is met before accepting it as valid data.


Common use cases of regular expressions in JSON schemas include:

  1. Validating email addresses: A regular expression can be used to ensure that a string value follows the standard email format, helping to filter out invalid inputs.
  2. Enforcing specific formats: Regular expressions can be used to enforce specific patterns such as phone numbers, URLs, ZIP codes, credit card numbers, etc., thereby maintaining a standardized data format.
  3. Filtering characters: Regular expressions can be used to restrict the type and combination of characters used in a string value, allowing only certain characters and excluding others.


By utilizing regular expressions in a JSON schema, developers can define stricter validation rules, enhance data quality, and ensure consistency in the structure and format of the JSON data they receive.


How to generate a JSON schema with a specific title using Kotlin classes?

To generate a JSON schema with a specific title using Kotlin classes, you can make use of libraries such as "just-json-schema" or "jsonschema-generator". Here's an example using the "jsonschema-generator" library:

  1. Add the necessary dependencies to your project's build.gradle file:
1
2
3
4
5

dependencies {
    implementation 'com.googlecode.jsonschema2pojo:jsonschema2pojo-core:1.1.1'
    implementation 'io.github.json-schema-validator:json-schema-validator:2.2.8'
    ...
}


  1. Create a Kotlin data class representing your JSON structure:
1
2
3
4
5

data class MyJsonObject(
    val name: String,
    val age: Int,
    val address: String
)


  1. Use the "jsonschema-generator" library to generate the JSON schema:
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14

import com.fasterxml.jackson.module.jsonSchema.JsonSchema
import com.fasterxml.jackson.module.jsonSchema.JsonSchemaGenerator
import com.fasterxml.jackson.databind.ObjectMapper
import com.fasterxml.jackson.databind.json.JsonMapper

fun main() {
    val objectMapper: ObjectMapper = JsonMapper()
    val jsonSchemaGenerator: JsonSchemaGenerator = JsonSchemaGenerator(objectMapper)
    
    val jsonSchema: JsonSchema = jsonSchemaGenerator.generateSchema(MyJsonObject::class.java)
    val json: String = objectMapper.writerWithDefaultPrettyPrinter().writeValueAsString(jsonSchema)

    println(json)
}


  1. The generated JSON schema will be printed in the console. To include a specific title, modify the data class as follows:
1
2
3
4
5
6

data class MyJsonObject(
    @JsonProperty("title") val title: String,
    val name: String,
    val age: Int,
    val address: String
)


This will add a title property to your JSON schema with the specified title value.

Twitter LinkedIn Telegram Whatsapp

Related Posts:

How to Parse JSON In Lua?
To parse JSON in Lua, you can use the JSON library. Here are the steps to achieve this:Install the JSON library: Download and include the JSON.lua file in your Lua project. Import the JSON library: Add the following line of code at the beginning of your Lua sc...
How to Serialize And Deserialize JSON In Kotlin?
Serializing and deserializing JSON in Kotlin involves converting JSON data into Kotlin objects and vice versa. Here&#39;s a step-by-step explanation of how to achieve this:Add the JSON serialization and deserialization library: Start by adding the necessary li...
How to Create A Kotlin Class?
To create a Kotlin class, follow these steps:Start by opening your Kotlin project in an integrated development environment (IDE) like IntelliJ IDEA or Android Studio. Create a new Kotlin file by right-clicking on the desired package or directory within your pr...