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:5.2"
}

(Maven syntax)

<dependency>
    <groupId>io.github.graphql-java</groupId>
    <artifactId>graphql-java-annotations</artifactId>
    <version>5.2</version>
</dependency>

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, with the addition of type resolver :

@GraphQLTypeResolver(MyTypeResolver.class)
public interface SomeInterface {
  @GraphQLField
  String field();
}

public class MyTypeResolver implements TypeResolver {
  GraphQLObjectType getType(TypeResolutionEnvironment env) { ... }
}

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

An instance of the type resolver will be created from the specified class. If a getInstance method is present on the class, it will be used instead of the default constructor.

Defining Unions

To have a union, you must annotate an interface with @GraphQLUnion. In the annotation, you must declare all the possible types of the union, and a type resolver. If no type resolver is specified, UnionTypeResolver is used. It follows this algorithm: The resolver assumes the the DB entity's name is the same as the API entity's name. If so, it takes the result from the dataFetcher and decides to which API entity it should be mapped (according to the name). Example: If you have a Pet union type, and the dataFetcher returns Dog, the typeResolver will check for each API entity if its name is equal to Dog, and returns if it finds something

@GraphQLUnion(possibleTypes={Dog.class, Cat.class})
public interface Pet {}

and an example with custom TypeResovler:

@GraphQLUnion(possibleTypes={DogApi.class, Cat.class}, typeResolver = PetTypeResolver.class)
public interface Pet {}


public class PetTypeResolver implements TypeResolver {
    @Override
    GraphQLObjectType getType(TypeResolutionEnvironment env) {
        Object obj = env.getObject();
        if(obj instanceof DogDB) {
            return (GraphQLObjectType) env.getSchema().getType("DogApi");
        }
        else {
            return (GraphQLObjectType) env.getSchema().getType("Cat");
        }
      
    }
}

NOTE: you can have (but not mandatory) a type resolver with constructor that has Class<?>[] as the first parameter and ProcessingElementsContainer as the second. the Class<?>[] parameter contains the possibleTypes class and ProcessingElementsContainer has all sorts of utils (you can check UnionTypeResolver to see how we use it there)

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;
}

The DefaultValue class can define a getInstance method that will be called instead of the default constructor.

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

Custom data fetcher

You can specify a custom data fetcher for a field with @GraphQLDataFetcher. The annotation will reference a class name, which will be used as data fetcher.

An instance of the data fetcher will be created. The args attribute on the annotation can be used to specify a list of String arguments to pass to the constructor, allowing to reuse the same class on different fields, with different parameter. The firstArgIsTargetName attribute can also be set on @GraphQLDataFetcher to pass the field name as a single parameter of the constructor.

Assuming you are using @GraphQLDataFetcher this way:

@GraphQLField
@GraphQLDataFetcher(value = HelloWorldDataFetcher.class, args = { "arg1", "arg2" })
public String getHelloWorld(){
    return null;
}

Then the class that extends from DataFetcher.class will get this args to two supported constructors
Or to a constructor that expecting String array that's way (String[] args or String... args) or for a constructor that expecting the same number of args that you send with in the annotation.
You get to choose which implementation you want.

public class HelloWorldDataFetcher implements DataFetcher<String> {

    public HelloWorldDataFetcher(String[] args){
        // Do something with your args
    }

    // Note that you need to expect the same number of args as you send with in the annotation args
    public HelloWorldDataFetcher(String arg1, String arg2){
        // Do something with your args
    }

    @Override
    public String get(DataFetchingEnvironment environment) {
        return "something";
    }
}

If no argument is needed and a getInstance method is present, this method will be called instead of the constructor.

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 GraphQLAnnotationProcessor 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.

It is also possible to specify for every connection which relay do you want to use, by giving a value to the annotation: @GraphQLConnection(connectionType = customRelay.class). If you do that, please also give values to connectionFetcher and validator.

There is also a support for simple paging, without "Nodes" and "Edges". To use it, annotate you connection like that: @GraphQLConnection(connectionFetcher = SimplePaginatedDataConnectionFetcher.class, connectionType = SimpleRelay.class, validator = SimplePaginatedDataConnectionTypeValidator.class) and the return type must be of type SimplePaginatedData. It has 2 methods:

1. getTotalCount - how many elements are there in total
2. getData - get the data

For you convenience, there are two classes that you can use: AbstractSimplePaginatedData and SimplePaginatedDataImpl For examples, look at the tests