GraphQL Java Generator

What is it?

The GraphQL Java Generator makes it easy to work in Java with graphQL in a schema first approach.

This project is an accelerator to develop GraphQL clients and GraphQL servers in java.

That is: graphql-java-generator generates the boilerplate code, and lets you concentrate on what’s specific to your use case. Then, the running code doesn’t depend on any dependencies from graphql-java-generator. So you can get rid of graphql-java-generator at any time: just put the generated code in your SCM, and that’s it.

  • In client mode : graphql-java-generator generates a class for each query, mutation type and/or subscription type. These classes contain the methods to call the queries, mutations and subscriptions. That is, to call the GraphQL server, you just call one of this method.
    • graphql-java-generator also generates the POJOs from the GraphQL schema. The GraphQL response is stored in these POJOs, for easy and standard use in Java.
  • In server mode : graphql-java-generator generates the whole heart of the GraphQL server. The developer has only to develop request to the data. That is :
    • graphql-java-generator generates the main method (in a jar project) or the main servler (in a war project), and all the Spring wiring, based on graphql-java-spring, itself being build on top of graphql-java.
    • graphql-java-generator generates the POJOs. An option allows to annotate them with the standard JPA annotations, to make it easy to link with a database. But of course, you can also implement your GraphQL server based on REST resources, or any other kind of data storage.
    • graphql-java-generator also generates interfaces, named DataFetchersDelegate. It expects a Spring Bean to be defined.
    • The developer just has to implement each DataFetchersDelegate, and the GraphQL server is ready to go!

Please, take a look at the projects that are within the graphql-maven-plugin-samples: they show various ways to implement a GraphQL server, based on the graphql-java library.

The interesting part is that graphql-java-generator is just an accelerator: you don’t depend on any library from graphql-java-generator. So, it just helps you to build application based on graphql-java . If the generated code doesn’t fully suit your needs, you can take what’s generated as a full sample for graphql-java usage, based on your use case. You can then update the generated code, where it’s not compliant for you. And that’s it. The only thing, there, is that we would like to know what was not correct for your use case, so that we can embed it into next versions. Or perhaps, if it’s just a matter of documentation, to better explain how to use it…

Availibility: Maven and Gradle

The generator is currently available both as a Maven plugin and as a Gradle plugin: * The Maven plugin is available in the project (graphql-maven-plugin-project) * A Gradle plugin is available in the project graphql-gradle-plugin-project. It offers exactly the same functionalities.

Documentation

This README

This README gives you a quick overview of what this plugin offers

The tutorials

Two tutorials are available for the Maven plugin: * The Client tutorial describes how to use this plugin, when building a GraphQL client. It’s in the GraphQL-Forum-Maven-Tutorial-client project. * The Server tutorial describes how to build a GraphQL server in the GraphQL-Forum-Maven-Tutorial-server project.

The same two tutorials exist for the Gradle plugin: * The Client tutorial describes how to use this plugin, when building a GraphQL client. It’s in the GraphQL-Forum-Gradle-Tutorial-client git repository. * The Server tutorial describes how to build a GraphQL server in the GraphQL-Forum-Gradle-Tutorial-server.

The plugin’s goals

This plugin contains these goals (Maven) / tasks (Gradle): * graphql is the main goal, that generates the code from the Graphql schema file(s) * The plugin parameters for this goal/task are described here * merge allows to generate a GraphQL schema file, based on the source GraphQL schemas. It can be used to merge several GraphQL schema files into one file, or to reformat the schema files. * The plugin parameters for this goal/task are described here

The full project documentation

The Full documentation is available here , for both the Gradle and the Maven plugin.

Aim of this project

The aim of this project is to:

  • Hide all the GraphQL technical stuff and boilerplate code
  • Let the developer concentrate on his/her specific use case
  • Make it very easy to create a GaphQL client, based on the generated POJOs. The calls to the GraphQL server are hidden. The client code just call a generated Java method, with Java parameters.
  • Make it easy to create a GraphQL server. The plugin generated the server boilerplate code and the POJOs. But it’s still up to the developer to map the GraphQL schema to the database schema. See the provided samples for different ways to do this. The generated POJOs integrate the JPA schema, making the database access easy, thanks to the Spring Data Repositories.
  • Let the generated code work as a standalone code. That is: your project, when it runs, doesn’t depend on any dependency from graphql-java-generator.

How to use it?

Full project documentation

You’ll find below a quick presentation of the plugin.

For all the available information, please go to the project website

Plugin documentation

The plugin documentation, generated by maven, is available on this page

Samples

You’ll find the following samples in the project. For all of these samples, there are two projects: the client and the server.

  • allGraphQLCases
    • This project is a compilation of GraphQL capabilities … that are managed by this plugin. Its main objective is for integration testing.
    • The server is packaged as a Spring Boot application
    • The GraphQL server exposes http
  • Forum
    • The server is packaged as a Spring Boot application
    • The GraphQL server exposes http
    • The server uses the schema personalization, to override the default code generation
    • The GraphQL model maps to the database model
    • The Forum client project shows implementation of the same queries in the XxxQueries classes.
    • This sample contains a subscription, on both the client and the server side
  • StarWars (only in the Maven plugin project)
    • The server is packaged as a war
    • The GraphQL server exposes https
    • The GraphQL interfaces in this model (character, and friends relation) makes it difficult to map to native RDBMS data model. This project uses JPA native queries to overcome this.
    • The StarWars client project shows implementation of the same queries in the XxxQueries classes.
    • This sample contains a subscription, on both the client and the server side
  • CustomTemplates (only in the Maven plugin project)
    • An example related on how to customize code templates
      • graphql-maven-plugin-samples-CustomTemplates-resttemplate project offers a customize template for Query/Mutation/Subscriptino client class and offer a Spring-base RestTemplate implementation for QueryExecutor template
      • graphql-maven-plugin-samples-CustomTemplates-resttemplate proyect defines a client project that generates code with customized template defined in previous project

Note: The client projects for these samples contain integration tests. They are part of the global build. These integration tests check the graphql-maven-plugin behaviour for both the client and the server for these samples.

Client mode

When in client mode, you can query the server with just one line of code.

For instance :

String id = [an id];

Human human = queryType.human("{id name appearsIn homePlanet friends{name}}", id);

You can use input types:

HumanInput input = new HumanInput();
... [some initialization of input content]

Human human = mutationType.createHuman("{id name appearsIn friends {id name}}", input);

In this mode, the plugin generates:

  • One java class for the Query object
  • One java class for the Mutation object (if any)
  • One POJO for each standard object of the GraphQL object
  • All the necessary runtime is actually attached as source code into your project: the generated code is stand-alone. So, your project, when it runs, doesn’t depend on any external dependency from graphql-java-generator.

You’ll find more information on the client page.

Server mode

When in server mode, the plugin generates:

  • The main class:
    • When in a jar maven project, the main class to start a Spring Boot application
    • When in a war maven project, the servlet configuration to be embedded in a war package. It can then be deployed in any standard application server
  • The declaration of all the graphql-java stuff
  • The DataFetchersDelegate interface declarations for all the Data Fetchers, which is the graphql-java word for GraphQL resolvers.
    • The DataFetchersDelegate groups the Data Fetchers into one class per GraphQL object (including the Query and the Mutation)
    • It contains the proper declarations to use the DataLoader out of the box
  • The POJOs to manipulate the GraphQL objects defined in the GraphQL schema.
    • These POJOs are annotated with JPA annotations. This allows you to link them to almost any database
    • You can customize these annotations, with the Schema Personalization file (see below for details)
  • All the necessary runtime is actually attached as source code into your project: the generated code is stand-alone. So, your project, when it runs, doesn’t depend on any external dependency from graphql-java-generator.

Once all this is generated, your only work is to implement the DataFetchersDelegate interfaces. They are the link between the GraphQL schema and your data storage. As such, they are specific to your use case. A DataFetchersDelegate implementation looks like this:

package com.graphql_java_generator.samples.forum.server.specific_code;

[imports]

@Component
public class DataFetchersDelegateTopicImpl implements DataFetchersDelegateTopic {

	@Resource
	MemberRepository memberRepository;
	@Resource
	PostRepository postRepository;
	@Resource
	TopicRepository topicRepository;

	@Resource
	GraphQLUtil graphQLUtil;

	@Override
	public CompletableFuture<Member> author(DataFetchingEnvironment dataFetchingEnvironment,
			DataLoader<UUID, Member> dataLoader, Topic source) {
		return dataLoader.load(source.getAuthorId());
	}

	@Override
	public List<Post> posts(DataFetchingEnvironment dataFetchingEnvironment, Topic source, String since) {
		if (since == null)
			return graphQLUtil.iterableToList(postRepository.findByTopicId(source.getId()));
		else
			return graphQLUtil.iterableToList(postRepository.findByTopicIdAndSince(source.getId(), since));
	}

	@Override
	public List<Topic> batchLoader(List<UUID> keys) {
		return topicRepository.findByIds(keys);
	}
}

You’ll find all the info on the server page.

Custom code templates

Customizing the templates allows you to modify the generated code, in the way you want.

So, if for any reason you may need to customize the generated code, you can replace the default templates by your own, by using the plugin parameter templates: the templates plugin parameter is a map where the key is the ID of the template to customize and the value is a classpath entry to the resources containing the customized template.

Customize templates shall be provided in a dependency configured in the plugin.

Both client and server templates can be customized.

All the documentation, and the list of available templates is available in the Customizing code templates page.

Compatibility with GraphQL

This plugin respects quite all the GraphQL specification: - queries, mutations and subscriptions - introspection - custom scalars - input types - interfaces and unions (that are both implemented in Java interfaces into the generated code) - directives - fragments (global and inline) - input parameters (for fields and directives) - Use of Bind Parameters to map Java variables with input parameters - easy execution of just a query/mutation/subscription (one field of the query, mutation or subscription type) as a standard method call - execution of a full GraphQL request, which allows to execute several queries or several mutations at once

You’ll find below the main changes, that are planned in the near future: - Comments coming from the graphQL schema should be reported in the generated code, especially the POJOs and the queries, mutations and subscriptions

Change log

The Change Log is available here

Note for contributors

All the plugin logic is stored in the graphql-maven-plugin-project project.

The Maven plugin and the Gradle plugin are just wrapper for the plugin logic, available in the graphql-maven-plugin-logic module of the maven project.

If you want to compile the maven project, you’ll have to add the lombok.jar file in your IDE. Please see the relevant section, in the Install menu of the https://projectlombok.org/ home page. This very nice tools generates all java boiler plate code, like setters, getters, constructors from fields…

If you use eclipse, please use the code formatter given with the project (file graphql-java-generator (eclipse code formatter).xml at the root of the project). This allows to have the sample code formatting: the code is then homogeneous, and the comparison between versions is simpler. To do this, go to the eclipse preferences, select Java/Code Style/Formatter, and import this file. Then, in the Java/Editor/Save Actions, check the “Perform the selected action on save”, “Format source code”, “Format all lines”, “Organize imports” and “Additional actions” which its default content

Full project documentation

For all the available information, please go to the project website

License

graphql-java-generator is licensed under the MIT License. See LICENSE for details.