> For clean Markdown content of this page, append .md to this URL. For the complete documentation index, see https://learning.postman.com/llms.txt. # Use Kotlin SDKs generated in Postman This guide provides instructions for using Kotlin SDK generated by the Postman SDK Generator. It covers how to import the SDK into your Kotlin project, run example code, and best practices for using the SDK effectively in your applications. Postman SDK Generator generates Java SDKs that are fully compatible with Kotlin. Since Kotlin runs on the JVM and has seamless Java interoperability, you can use the generated Java SDK directly in your Kotlin projects. The SDK structure, build configuration, and publishing process are identical to the [Java SDK](/docs/sdk-generator/use/java-sdk/). This guide provides Kotlin-specific code examples for all SDK features. ## SDK structure The Java SDK includes the following key files: * `[SdkName].java` — Main SDK client, instantiated with `[SdkName]Config`. * `services/` — Service classes with both sync and async methods. * `models/` — Data models (POJOs with Lombok builders, enums, typed exceptions) with Jackson serialization. * `config/` — Configuration classes for auth, retry, and SDK client settings. * `pom.xml` — Specifies dependencies (OkHttp, Jackson, Lombok). The following is an example of the typical structure of a generated Java SDK: ## Example usage Each generated SDK includes an `examples/` directory with a working project demonstrating SDK usage. The example includes the following features: * SDK initialization with config builder pattern * Synchronous API calls * Working with model builders * Exception handling #### Location `examples/src/main/kotlin/Main.kt` #### Run the example ```bash cd examples ./run.sh ``` Or manually: ```bash cd path/to/your-sdk mvn clean install cd examples gradle run ``` #### Example code structure ```kotlin import com.example.sdk.Sdk import com.example.sdk.config.SdkConfig import com.example.sdk.config.ApiKeyAuthConfig import com.example.sdk.models.User fun main() { // Initialize the SDK val config = SdkConfig.builder() .apiKeyAuthConfig( ApiKeyAuthConfig.builder() .apiKey("your-api-key") .build() ) .build() val sdk = Sdk(config) try { // Call an API endpoint val user = sdk.usersService.getUser("123") println("User: $user") } catch (e: Exception) { System.err.println("Error: ${e.message}") } } ``` ## Import the SDK locally You can import the generated SDK into your Kotlin project using Gradle, Maven, or project file path. Below are instructions for each method. ### Import using Gradle To import the generated SDK using Gradle, first install it to your local Maven repository: ```bash cd path/to/your-sdk mvn clean install ``` Then, add the dependency to your build file: #### Kotlin DSL (build.gradle.kts) ```kotlin repositories { mavenLocal() mavenCentral() } dependencies { implementation("com.example:your-sdk:1.0.0") } ``` #### Groovy DSL (build.gradle) ```gradle dependencies { implementation group: 'com.example', name: 'your-sdk', version: '1.0.0' } ``` Alternatively, if you want to reference the SDK as a JAR file, first build the fat JAR: ```bash cd path/to/your-sdk mvn compile assembly:single ``` Then, add the JAR to your build file: #### Kotlin DSL (build.gradle.kts) ```kotlin dependencies { implementation(files("../path/to/your-sdk/target/your-sdk-1.0.0-jar-with-dependencies.jar")) } ``` #### Groovy DSL (build.gradle) ```gradle dependencies { implementation files('../path/to/your-sdk/target/your-sdk-1.0.0-jar-with-dependencies.jar') } ``` ### Import using a Maven local repository To import the generated SDK using a local Maven repository, do the following: 1. Install SDK to local Maven repository. ```bash cd path/to/your-sdk mvn clean install ``` 2. Add dependency to your project's `pom.xml`. ```xml com.example your-sdk 1.0.0 ``` 3. Use the SDK in your code. ```kotlin import com.example.sdk.Sdk import com.example.sdk.config.SdkConfig val config = SdkConfig.builder().build() val sdk = Sdk(config) ``` ### Import using the project file path To import the generated SDK using the project file path, do the following: 1. Add SDK as a module in your project's `pom.xml`. ```xml ../path/to/your-sdk your-app ``` 2. Reference as dependency. ```xml com.example your-sdk ${project.version} ``` ## Publish To publish your generated Kotlin SDK, see [Publish Kotlin SDKs generated in Postman](/docs/sdk-generator/publish/kotlin-manual/). ## Advanced usage You can further customize the SDK by modifying the generated code, adding new features, or integrating it with your existing codebase. Here are some advanced topics to explore. ### Authentication The SDK supports various authentication methods. You can configure authentication when initializing the SDK client. The SDK includes authentication support based on the security schemes defined in your API specification. The following examples show the possible authentication methods. #### API Key ```kotlin val config = SdkConfig.builder() .apiKeyAuthConfig( ApiKeyAuthConfig.builder() .apiKey("your-api-key") .build() ) .build() val sdk = Sdk(config) ``` #### Bearer Token ```kotlin val config = SdkConfig.builder() .accessToken("your-bearer-token") .build() val sdk = Sdk(config) ``` #### Basic Auth ```kotlin val config = SdkConfig.builder() .basicAuthConfig( BasicAuthConfig.builder() .username("your-username") .password("your-password") .build() ) .build() val sdk = Sdk(config) ``` #### OAuth 2.0 ```kotlin val config = SdkConfig.builder() .clientId("your-client-id") .clientSecret("your-client-secret") .build() val sdk = Sdk(config) // SDK automatically handles token refresh val user = sdk.usersService.getUser("123") ``` To update the credentials after initialization, run one of the following. The `setApiKey`, `setAccessToken`, and `setBasicAuthCredentials` methods are each only generated when the corresponding auth type is in the specification. ```kotlin sdk.setApiKey("new-api-key") sdk.setAccessToken("new-token") sdk.setBasicAuthCredentials("new-username", "new-password") ``` ### Synchronous and asynchronous calls Every service method has a sync variant (`methodName`) and an async variant (`methodNameAsync`). Sync methods return the type directly (for example, `Pet`), while async methods return `CompletableFuture` (for example, `CompletableFuture`). For void methods, async returns `CompletableFuture`. ```kotlin import java.util.concurrent.CompletableFuture // Synchronous — blocks until the response is returned val pet = sdk.petService.getPetById(123) println("Pet: ${pet.name}") // Asynchronous — returns a CompletableFuture val futurePet: CompletableFuture = sdk.petService.getPetByIdAsync(123) // Option 1: Non-blocking with callbacks futurePet .thenAccept { p -> println("Pet: ${p.name}") } .exceptionally { e -> System.err.println("Error: ${e.message}") null } // Option 2: Blocking wait when needed val result = futurePet.get() ``` If you use Kotlin coroutines, you can convert `CompletableFuture` to a suspending call with the `kotlinx-coroutines-jdk8` library: ```kotlin import kotlinx.coroutines.future.await suspend fun fetchPet() { val pet = sdk.petService.getPetByIdAsync(123).await() println("Pet: ${pet.name}") } ``` ### Environment management The SDK supports multiple environments (for example, production, staging) with different base URLs. ```kotlin // Use environment enum sdk.setEnvironment(Environment.PRODUCTION) // Or set custom base URL sdk.setBaseUrl("https://custom.api.example.com") ``` ### Hierarchical configuration Java supports all four levels of configuration: SDK (through `SdkConfig` or `sdk.setEnvironment()/sdk.setBaseUrl()`), and service, method, and request levels (through `RequestConfig`). Each level overrides the previous, with request being most specific. ```kotlin import com.example.sdk.Sdk import com.example.sdk.config.SdkConfig import com.example.sdk.config.RequestConfig import com.example.sdk.http.Environment // 1. SDK level — default for everything val config = SdkConfig.builder() .baseUrl("https://api.example.com") .timeout(10000) .build() val sdk = Sdk(config) // 2. Service level — override for all methods in usersService sdk.usersService.setConfig( RequestConfig.builder() .timeout(15000L) .build() ) // 3. Method level — override for getUser only sdk.usersService.setGetUserConfig( RequestConfig.builder() .baseUrl("https://legacy-api.example.com") .build() ) // 4. Request level — override for this single call val user = sdk.usersService.getUser( "123", RequestConfig.builder() .timeout(30000L) .build() ) ``` ### Error handling The SDK raises custom exceptions for API errors, which include details about the error message, status code, and response body. You can catch these exceptions to handle errors gracefully in your application. To handle errors, do the following: ```kotlin import com.example.sdk.exceptions.ApiError try { val user = sdk.usersService.getUser("123") println(user) } catch (e: ApiError) { System.err.println("API error: ${e.message}") System.err.println("Status code: ${e.status}") System.err.println("Response: ${e.response}") } catch (e: Exception) { System.err.println("Unexpected error: ${e.message}") } ``` To handle specific error codes, do the following: ```kotlin try { sdk.usersService.deleteUser("123") } catch (e: ApiError) { when (e.status) { 404 -> println("User not found") 403 -> println("Permission denied") else -> println("API error: ${e.message}") } } ``` When the API specification defines error response models, the SDK generates typed exception classes (for example, `NotFoundErrorException`) that extend `ApiError` and include the deserialized error model. The exception's `getMessage()` and `getStatus()` work directly, but to access specification-defined error fields, use `getError()`. ```kotlin import com.example.sdk.models.NotFoundErrorException try { sdk.usersService.getUser("123") } catch (e: NotFoundErrorException) { // message and status available directly from ApiError println("Status: ${e.status}") println("Message: ${e.message}") // spec-defined error model fields require getError() val error = e.error println("Detail: ${error.detail}") println("Request ID: ${error.requestId}") } catch (e: ApiError) { // fallback for unmapped error responses println("API error: ${e.status} ${e.message}") } ``` ### Timeouts and retries To set a global timeout, do the following: ```kotlin val config = SdkConfig.builder() .timeout(10000) // 10 seconds in milliseconds (default: 10000) .build() val sdk = Sdk(config) ``` To pass the retry configuration through `SdkConfig`, do the following: ```kotlin val retryConfig = RetryConfig.builder() .maxRetries(3) .initialDelay(150) // milliseconds between retries (default: 150) .maxDelay(5000) // max delay cap in milliseconds (default: 5000) .backoffFactor(2.0) // exponential backoff multiplier .jitter(50) // random jitter in milliseconds (default: 50) .build() val config = SdkConfig.builder() .retryConfig(retryConfig) .build() val sdk = Sdk(config) ``` ### Validation The SDK generates validators that enforce OpenAPI constraints at runtime. These include `minLength`, `maxLength`, `pattern`, `min`, `max`, `uniqueItems`, and more. Validation happens automatically when making API calls. The SDK validates parameters before sending the request. If validation fails, a `ValidationException` is thrown with a list of `Violation` objects describing what went wrong. You don't need to call validators manually. They're built into the service methods. ```kotlin import com.example.sdk.validation.exceptions.ValidationException try { // If the spec defines constraints (e.g. minLength: 3 for username), // the SDK validates before sending the request sdk.usersService.createUser(user) } catch (e: ValidationException) { // e.message returns a formatted summary of all violations System.err.println(e.message) // Output: "Validation failed with the following violations: // username: must be at least 3 characters long // age: must be greater than or equal to 0" // Access individual violations for programmatic handling for (violation in e.violations) { System.err.println("${violation.path}: ${violation.message}") } } catch (e: ApiError) { System.err.println("API error: ${e.message}") } ``` The list of supported constraints can also be grouped by type like this: * String — `minLength`, `maxLength`, `pattern` (regex) * Numeric — `min`, `max` (inclusive or exclusive) * List/array — `minItems`, `maxItems`, `uniqueItems` * Required fields — Validated automatically, based on the specification. ### Optional and nullable field handling The SDK uses `JsonNullable` wrappers for optional fields, providing clear distinction between undefined, null, and present values. This is important for users building request models. Omitting an optional field versus explicitly setting it to null produces different JSON payloads. ```kotlin // Example 1: Creating an object with all field types val model = ModelWithOptionalNullableDefaultValues.builder() .requiredString("requiredString") // Required Non-Nullable .requiredInteger(8L) // Required Non-Nullable .requiredNullableString("not null") // Required Nullable .requiredNullableInteger(null) // Required Nullable (can be null) .optionalString("optionalString") // Optional Non-Nullable .optionalInteger(9L) // Optional Non-Nullable .optionalNullableString("optional") // Optional Nullable .optionalNullableInteger(null) // Optional Nullable (can be null) .build() // Example 2: Optional fields omitted entirely val minimalModel = ModelWithOptionalNullableDefaultValues.builder() .requiredString("requiredString") .requiredInteger(8L) .requiredNullableString(null) // Still required, but can be null .requiredNullableInteger(null) // Still required, but can be null // Optional fields omitted - they will be omitted from JSON when serialized and sent to API .build() // Example 3: Optional fields with mixed values val mixedModel = ModelWithOptionalNullableDefaultValues.builder() .requiredString("requiredString") .requiredInteger(8L) .requiredNullableString("not null") .requiredNullableInteger(null) .optionalString("present") // Optional non-nullable with value .optionalNullableString(null) // Optional nullable set to null // optionalInteger and optionalNullableInteger omitted .build() // What the server receives for Example 1 (all fields set): // { // "requiredString": "requiredString", // "requiredInteger": 8, // "requiredNullableString": "not null", // "requiredNullableInteger": null, // "optionalString": "optionalString", // "optionalInteger": 9, // "optionalNullableString": "optional", // "optionalNullableInteger": null // } // What the server receives for Example 2 (minimal model): // { // "requiredString": "requiredString", // "requiredInteger": 8, // "requiredNullableString": null, // "requiredNullableInteger": null // // Note: optional fields are completely omitted from JSON // } // What the server receives for Example 3 (mixed model): // { // "requiredString": "requiredString", // "requiredInteger": 8, // "requiredNullableString": "not null", // "requiredNullableInteger": null, // "optionalString": "present", // "optionalNullableString": null // // Note: optionalInteger and optionalNullableInteger are omitted // } ``` ## Additional resources Consider the following resources for using and customizing your Java SDK from Kotlin: * SDK documentation — Check the `documentation/` directory in your SDK. * Javadoc — Generate with `mvn javadoc:javadoc`. * Example usage — Refer to the `examples/` directory for a working code sample demonstrating basic SDK usage. * Kotlin-Java interop — Refer to the [Kotlin documentation on calling Java from Kotlin](https://kotlinlang.org/docs/java-interop.html) for details on how Kotlin interacts with Java libraries. * Coroutines integration — Use [kotlinx-coroutines-jdk8](https://kotlinlang.org/api/kotlinx.coroutines/kotlinx-coroutines-jdk8/) to convert `CompletableFuture` to Kotlin coroutines with `.await()`. * Dependencies — The SDK uses the following dependencies: * OkHttp: An HTTP client. * Jackson: JSON serialization and `jackson-databind-nullable`, a dependency used for optional nullable field handling. * Lombok: Reduce boilerplate code.