GraphQLJavaToolsDataLoader.kt

class ParentType(val id: Long)
class ChildType
class ChildTypeBatchApi {
    fun load(keys: List<Long>): List<ChildType> = mutableListOf()
}
val childTypeBatchApi = ChildTypeBatchApi()

// Example BatchLoader
var batchLoader: BatchLoader<Long, ChildType> = BatchLoader { keys ->
    CompletableFuture.supplyAsync<List<ChildType>> { childTypeBatchApi.load(keys) }
}

// How to register all the dataloaders zo graphql-java-tools can use them for injection ?
var childDataLoader = DataLoader<Long, ChildType>(batchLoader)

@Component
class ChildResolver() : GraphQLResolver<ParentType> {

    // Optionally, could inject the DataLoader bean, but more clear adding it as a parameter in the resolver function
    // val childDataLoader: DataLoader<Long, ChildType>
    
    // Inject the DataLoader for this specific type (using reflection)
    fun childField(parentItem: ParentType, childDataLoader: DataLoader<Long, ChildType>): CompletableFuture<ChildType> {
      // Should return the CompletableFuture for the DataLoader to do its work
      return childDataLoader.load(parentItem.id)
                .thenApply { it }
                .exceptionally { e ->
                    throw Exception(e.message, e)
                }
    }
}

// Need to invoke dispatchAndJoin after processing this level in the graph
childDataLoader.dispatchAndJoin();