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Client Customization

Ktor HTTP Client Customization

GraphQLKtorClient is a thin wrapper on top of Ktor HTTP Client and supports fully asynchronous non-blocking communication. It is highly customizable and can be configured with any supported Ktor HTTP engine and features.

GraphQLKtorClient uses the Ktor HTTP Client to execute the underlying queries. Clients can be customized with different engines (defaults to Coroutine-based IO) and HTTP client features. Custom configurations can be applied through Ktor DSL style builders.

See Ktor HTTP Client documentation for additional details.

Global Client Customization

A single instance of GraphQLKtorClient can be used to handle many GraphQL operations. You can specify a target engine factory and configure it through the corresponding HttpClientConfig. Ktor also provides a number of standard HTTP features and allows you to easily create custom ones that can be configured globally.

The below example configures a new GraphQLKtorClient to use the OkHttp engine with custom timeouts, adds a default X-MY-API-KEY header to all requests, and enables basic logging of the requests.

val client = GraphQLKtorClient(
        url = URL("http://localhost:8080/graphql"),
        engineFactory = OkHttp
) {
    engine {
        config {
            connectTimeout(10, TimeUnit.SECONDS)
            readTimeout(60, TimeUnit.SECONDS)
            writeTimeout(60, TimeUnit.SECONDS)
        }
    }
    defaultRequest {
        header("X-MY-API-KEY", "someSecretApiKey")
    }
    install(Logging) {
        logger = Logger.DEFAULT
        level = LogLevel.INFO
    }
}

Per Request Customization

In order to be able to customize individual GraphQL requests you need to configure GraphQL Kotlin plugin to generate Ktor specific client code. See Gradle and Maven plugin documentation for additional details.

Individual GraphQL requests can be customized through HttpRequestBuilder. You can use this mechanism to specify custom headers, update target url to include custom query parameters, configure attributes that can be accessed from the pipeline features as well specify timeouts per request.

val helloWorldQuery = HelloWorldQuery(client)
val result = helloWorldQuery.execute(variables = HelloWorldQuery.Variables(name = null)) {
    header("X-B3-TraceId", "0123456789abcdef")
}

Spring WebClient Customization

GraphQLWebClient is a thin wrapper on top of Spring WebClient that relies on Reactor Netty for fully asynchronous non-blocking communications. If you want to use Jetty instead you will need to exclude provided io.projectreactor.netty:reactor-netty dependency and instead add org.eclipse.jetty:jetty-reactive-httpclient dependency.

Global Client Customization

A single instance of GraphQLWebClient can be used to handle many GraphQL operations and you can customize it by providing a custom instance of WebClient.Builder. See Spring documentation for additional details.

Example below configures GraphQLWebClient with custom timeouts and adds a default X-MY-API-KEY header to all requests.

val httpClient: HttpClient = HttpClient.create()
    .option(ChannelOption.CONNECT_TIMEOUT_MILLIS, 10_000)
    .responseTimeout(Duration.ofMillis(10_000))
val connector: ClientHttpConnector = ReactorClientHttpConnector(httpClient.wiretap(true))
val webClientBuilder = WebClient.builder()
    .clientConnector(connector)
    .defaultHeader("X-MY-API-KEY", "someSecretApiKey")

val client = GraphQLWebClient(
    url = "http://localhost:8080/graphql",
    builder = webClientBuilder
)

Per Request Customization

In order to be able to customize individual GraphQL requests you need to configure GraphQL Kotlin plugin to generate Spring WebClient specific client code. See Gradle and Maven plugin documentation for additional details.

Individual GraphQL requests can be customized by providing WebClient.RequestBodyUriSpec lambda. You can use this mechanism to specify custom headers or include custom attributes or query parameters.

val helloWorldQuery = HelloWorldQuery(client)
val result = helloWorldQuery.execute(variables = HelloWorldQuery.Variables(name = null)) {
    header("X-B3-TraceId", "0123456789abcdef")
}

Custom GraphQL Client

GraphQL Kotlin libraries provide generic a GraphQLClient interface as well as Ktor HTTP Client and Spring WebClient based reference implementations. Both GraphQLKtorClient and GraphQLWebClient are open classes which means you can also extend them to provide some custom execute logic.

class CustomGraphQLClient(url: URL) : GraphQLKtorClient<CIOEngineConfig>(url = url, engineFactory = CIO) {

    override suspend fun <T> execute(query: String, operationName: String?, variables: Any?, resultType: Class<T>, requestBuilder: HttpRequestBuilder.() -> Unit): GraphQLResponse<T> {
        // custom init logic
        val result = super.execute(query, operationName, variables, resultType, requestBuilder)
        // custom finalize logic
        return result
    }
}

NOTE: When implementing custom GraphQLClient make sure to select proper client type when generating your client code. By default, generated client code is targeting generic interface which allows you to use any client implementations. If you are using Ktor or Spring WebClient based implementations make sure to select corresponding type as that will provide customization options.

Jackson Customization

GraphQLClient relies on Jackson to handle polymorphic types and default enum values. You can specify your own custom object mapper configured with some additional serialization/deserialization features but due to the necessary logic to handle the above, currently we don't support other JSON libraries.

val customObjectMapper = jacksonObjectMapper()
val client = GraphQLClient(url = URL("http://localhost:8080/graphql"), mapper = customObjectMapper)

Deprecated Field Usage

Build plugins will automatically fail generation of a client if any of the specified query files are referencing deprecated fields. This ensures that your clients have to explicitly opt-in into deprecated usage by specifying allowDeprecatedFields configuration option.

Custom GraphQL Scalars

By default, custom GraphQL scalars are serialized and type-aliased to a String. GraphQL Kotlin plugins also support custom serialization based on provided configuration.

In order to automatically convert between custom GraphQL UUID scalar type and java.util.UUID, we first need to create our custom ScalarConverter.

package com.example.client

import com.expediagroup.graphql.client.converter.ScalarConverter
import java.util.UUID

class UUIDScalarConverter : ScalarConverter<UUID> {
    override fun toScalar(rawValue: Any): UUID = UUID.fromString(rawValue.toString())
    override fun toJson(value: UUID): Any = value.toString()
}

And then configure build plugin by specifying

  • Custom GraphQL scalar name
  • Target class name
  • Converter that provides logic to map between GraphQL and Kotlin type
graphql {
    packageName = "com.example.generated"
    endpoint = "http://localhost:8080/graphql"
    customScalars = listOf(GraphQLScalar("UUID", "java.util.UUID", "com.example.UUIDScalarConverter"))
}

See Gradle and Maven plugin documentation for additional details.