GraphQL server in Java: Part I: Basics

Near Zegrzyńskie Lake

Superficially, there is no reason GraphQL servers are typically written in Node.js. However callbacked-based languages that don’t block waiting for the result turn out to play really well with GraphQL philosophy. Before we dive into details why that’s the case, let us first understand how GraphQL server works underneath and how to implement it correctly. In the second installment we shall split the implementation to lazily load only necessary pieces of information. In the third installment we shall rewrite the server using non-blocking idioms to improve latency and throughput.

What is GraphQL

First things first, what is GraphQL? I’d say it lies somewhere between REST and SOAP (sic!) It’s a fairly lightweight, JSON protocol that works best for browsers and mobile apps. Just like REST. On the other hand it has a schema, describing valid attributes, operations and payloads. However, unlike SOAP, schema is designed to evolve and we have a great control over the scope of data we’d like to receive.

There are plenty of GraphQL tutorials out there, so let me jump straight to the example. Here is a fairly simple schema describing some API:

type Player {
    id: String!
    name: String!