GraphQL Annotations for Java

GraphQL-Java is a great library, but its syntax is a little bit verbose. This library offers an annotations-based syntax for GraphQL schema definition.

Getting Started

(Gradle syntax)

dependencies {
  compile "io.github.graphql-java:graphql-java-annotations:5.0.7"
}

Defining Objects

Any regular Java class can be converted to a GraphQL object type. Fields can be defined with a @GraphQLField (see more on fields below) annotation:

public class SomeObject {
  @GraphQLField
  public String field;
}

// ...
GraphQLObjectType object = GraphQLAnnotations.object(SomeObject.class);

Defining Interfaces

This is very similar to defining objects:

public interface SomeInterface {
  @GraphQLField
  String field();
}

// ...
GraphQLInterfaceType object = GraphQLAnnotations.iface(SomeInterface.class);

Fields

In addition to specifying a field over a Java class field, a field can be defined over a method:

public class SomeObject {
  @GraphQLField
  public String field() {
    return "field";
  }
}

Or a method with arguments:

public class SomeObject {
  @GraphQLField
  public String field(String value) {
    return value;
  }
}

Note: You need to use -parameters javac option to compile, which makes argument name as the default GraphQL name. Otherwise, you will need to add the @GraphQLName("value") annotation to specify one.

You can also inject DataFetchingEnvironment as an argument, at any position:

public class SomeObject {
  @GraphQLField
  public String field(DataFetchingEnvironment env, String value) {
    return value;
  }
}

Additionally, @GraphQLName can be used to override field name. You can use @GraphQLDescription to set a description.

These can also be used for field parameters:

public String field(@GraphQLName("val") String value) {
  return value;
}

In addition, @GraphQLDefaultValue can be used to set a default value to a parameter. Due to limitations of annotations, the default value has to be provided by a class that implements Supplier<Object>:

public static class DefaultValue implements Supplier<Object> {
  @Override
  public Object get() {
    return "default";
  }
}

@GraphQLField
public String field(@GraphQLDefaultValue(DefaultValue.class) String value) {
  return value;
}

@GraphQLDeprecate and Java's @Deprecated can be used to specify a deprecated field.

You can specify a custom data fetcher for a field with @GraphQLDataFetcher

Type extensions

Having one single class declaring all fields in a graphQL object type is not always possible, or can lead to huge classes. Modularizing the schema by defining fields in different classes allows you to split it in smaller chunks of codes. In IDL, this is usually written by using the extend keyword on top of a type definition. So you have a type defined like this :

type Human {
    id: ID!
    name: String!
}

It would be possible to extend it later on by using the following syntax :

extend type Human {
    homePlanet: String
}

Defining extensions in annotations

This is possible when using annotations by registering "extensions" classes, corresponding to extend clauses, before creating the objects with the GraphQLAnnotationsProcessor. Extension classes are simple classes, using the same annotations, with an additional @GraphQLTypeExtension on the class itself. The annotation value is required and will be the class that it actually extends.

So the previous schema could be defined by the following classes :

@GraphQLName("Human")
public class Human {
    @GraphQLField
    public String name() { }
}

@GraphQLTypeExtension(Human.class)
public class HumanExtension {
    @GraphQLField
    public String homePlanet() { }
}

Classes marked as "extensions" will actually not define a new type, but rather set new fields on the class it extends when it will be created. All GraphQL annotations can be used on extension classes.

Extensions are registered in GraqhQLAnnotationProcessor by using registerTypeExtension. Note that extensions must be registered before the type itself is requested with getObject() :

GraphQLAnnotationsProcessor processor = GraphQLAnnotations.getInstance(); 

// Register extensions
processor.registerTypeExtension(HumanExtension.class);

// Create type
GraphQLObjectType type = processor.getObject(Human.class);

Data fetching with extensions

As opposed to standard annotated classes mapped to GraphQL types, no instance of the extensions are created by default. In DataFetcher, the source object will still be an instance of the extended class. It is however possible to provide a constructor taking the extended class as parameter. This constructor will be used to create an instance of the extension class when a field with the default DataFetcher (without @DataFetcher) will be queried. If no such constructor is provided, the field must either be declared as static or marked as @GraphQLInvokeDetached. Original source object can be found in the DataFetchingEnvironment.

@GraphQLTypeExtension(Human.class)
public class HumanExtension {
    
    public HumanExtension(Human human) {
        this.human = human;   
    }
    
    @GraphQLField
    public String homePlanet() { 
        // get value somehow from human object
    }
}

Type Inference

By default, standard GraphQL types (String, Integer, Long, Float, Boolean, Enum, List) will be inferred from Java types. Also, it will respect @javax.validation.constraints.NotNull annotation with respect to value's nullability, as well as @GraphQLNonNull

Stream type is also supported and treated as a list.

If you want to register an additional type (for example, UUID), you have to create a new class implementing TypeFunction for it:

public class UUIDTypeFunction implements TypeFunction {
    ...
}

And register it with GraphQLAnnotations:

GraphQLAnnotations.register(new UUIDTypeFunction())

// or if not using a static version of GraphQLAnnotations:
// new GraphQLAnnotations().registerType(new UUIDTypeFunction())

You can also specify custom type function for any field with @GraphQLType annotation.

Relay support

Mutations

You can use @GraphQLRelayMutation annotation to make mutation adhere to Relay specification for mutations

Connection

You can use @GraphQLConnection annotation to make a field iterable in adherence to Relay Connection specification.
If a field is annotated with the annotation, the associated dataFetcher must return an instance of PaginatedData.
The PaginatedData class holds the result of the connection:

1. The data of the page
2. Whether or not there is a next page and a previous page
3. A method that returns for each entity the encoded cursor of the entity (it returns string)

For you convenience, there is AbstractPaginatedData that can be extended.

If you want to use you own implementation of connection, that's fine, just give a value to connection().
Please note that if you do so, you also have to specify your own connection validator that implements ConnectionValidator
(and should throw @GraphQLConnectionException if something is wrong)

NOTE: because PropertyDataFetcher and FieldDataFetcher can't handle connection, this annotation cant be used on a field that doesn't have a dataFetcher

Customizing Relay schema

By default, GraphQLAnnotations will use the graphql.relay.Relay class to create the Relay specific schema types (Mutations, Connections, Edges, PageInfo, ...). It is possible to set a custom implementation of the Relay class with GraphQLAnnotations.setRelay method. The class should inherit from graphql.relay.Relay and can redefine methods that create Relay types.