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Version: 3.x.x

Client Customization

Ktor HTTP Client Customization#

GraphQLClient 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 GraphQLClient can be used to power 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 GraphQLClient 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 = GraphQLClient(
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#

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")

Custom GraphQL client#

GraphQLClient is an open class which means you can also extend it to provide custom execute logic.

class CustomGraphQLClient(url: URL) : GraphQLClient<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

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: String): UUID = UUID.fromString(rawValue)
override fun toJson(value: UUID): String = 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"
converters.put("UUID", ScalarConverterMapping("java.util.UUID", "com.example.UUIDScalarConverter"))

See Gradle and Maven plugin documentation for additional details.

Last updated on by jgorman-exp