How to respond with extensions using graphql-java?

Question

My responses from GraphQL have to follow a particular format of

{
    data:{}
    errors:[{}]
    extensions:{}
}

However, I am uncertain how to respond with extensions from my methods. I am using graphql-spring-boot which pulls in graphql-java, graphql-java-tools, and graphql-java-servlet.

I understand that my results from a query/mutation method will be wrapped in the data object, and if any exceptions were thrown they'll be wrapped in errors.

If I have a GraphQL Schema defined as

type Query {
    someQuery(input: String!) : String!
}

and a corresponding Java method

public String someQuery(String input) {
    return "Hello, world!";
}

The GraphQL response will be

{
    data: { "Hello, world!"}
}

I would like to know how I am able to add extensions to my GraphQL response so that the output is as:

{
    data: {"Hello, world!"}
    extensions: { <something>}
}

Answer 1

The best way I've found to return extensions is to implement a subclass of SimpleInstrumentation that overrides instrumentExecutionResult (code stolen partially from graphql-java's TracingInstrumentation):

@Override
public CompletableFuture<ExecutionResult> instrumentExecutionResult(
        ExecutionResult executionResult,
        InstrumentationExecutionParameters parameters) {
    Map<Object, Object> currentExt = executionResult.getExtensions();
    Map<Object, Object> newExtensionMap = new LinkedHashMap<>();
    newExtensionMap.putAll(currentExt == null ? Collections.emptyMap() : currentExt);
    newExtensionMap.put("MyExtensionKey", myExtensionValue);

    return CompletableFuture.completedFuture(
        new ExecutionResultImpl(
            executionResult.getData(), 
            executionResult.getErrors(), 
            newExtensionMap));
}

When setting up the GraphQL instance you then pass an instance of the instrumentation class in:

GraphQL graphQL = GraphQL
        .newGraphQL(schema)
        .instrumentation(new MyInstrumentation())
        .build()

(Not sure entirely how this is handled by graphql-spring-boot but would imagine there is some way to @Autowire or otherwise configure the GraphQL instance? InstrumentationProvider from graphql-java-servlet might be what you'd use to do this)