GraphQL is a modern query language for retrieving data from a server. There is a large amount of documentation on building APIs for a whole bunch of platforms, but unfortunately the official documentation for Java contains only one example, which involves building an application based on the Spring Framework . The example hides some implementation details, forcing the user to read the source. In this article, we will fix this and create an analogue on a combination of Google Guice and Spark . Before proceeding, I recommend that you familiarize yourself with the original tutorial , because I will not delve into the architecture of the library and the description of the Java GraphQL entities
1. Creating a Guice application
Gradle. , gradle init
:
Select type of project to generate: application
Select implementation language: Java
Select build script DSL: Kotlin
Select test framework: JUnit Jupiter
Project name: guice-spark-graphql
Source package: guice.spark.graphql
Java src/main/java/guice/spark/graphql/App.java
build.gradle.kts
dependencies {
// This dependency is used by the application.
implementation("com.google.guava:guava:29.0-jre")
//Guice
implementation("com.google.inject:guice:5.0.1") //NEW
//Spark
implementation("com.sparkjava:spark-core:2.9.3") //NEW
implementation("com.sparkjava:spark-template-velocity:2.7.1") ////NEW spark template engine
implementation("org.slf4j:slf4j-simple:1.7.21") //NEW fix Spark SLF4J: Failed to load class "org.slf4j.impl.StaticLoggerBinder".
implementation("com.fasterxml.jackson.core:jackson-databind:2.12.3") //NEW
//graphql
implementation("com.graphql-java:graphql-java:16.2") //NEW
// Use JUnit Jupiter API for testing.
testImplementation("org.junit.jupiter:junit-jupiter-api:5.6.2")
// Use JUnit Jupiter Engine for testing.
testRuntimeOnly("org.junit.jupiter:junit-jupiter-engine:5.6.2")
}
Guice, GraphQL Spark Slf4j, Jackson Velocity Template. Guava , -
2. GraphQL
GraphQL , API. schema.graphqls
src/main/resources
type Query { bookById(id: ID): Book } type Book { id: ID name: String pageCount: Int author: Author } type Author { id: ID firstName: String lastName: String }
3. Guice
Guice DI src/main/java/guice/spark/graphql/App.java
public class App {
@Inject
private GraphQLService service;
public static void main(String[] args) {
App app = new App();
Injector injector = Guice.createInjector(new GraphQLModule());
injector.injectMembers(app);
app.service.initialize();
}
}
Guice Injector, GraphQLModule . injector.injectMembers(app)
service GraphQLService
, ,
4. GraphQLModule
Guice . src/main/java/guice/spark/graphql/GraphQLModule.java
public class GraphQLModule extends AbstractModule {
protected void configure() {
bind(GraphQLService.class).asEagerSingleton();
bind(GraphQL.class).toProvider(GraphQlProvider.class).asEagerSingleton();
bind(ObjectMapper.class).asEagerSingleton();
}
}
configure
:
GraphQLService
Spark c Spark, GraphQL
GraphQL
ObjectMapper
JSON
5. GraphQlProvider
, GraphQL
, Provider
Guice, . GraphQlProvider
public class GraphQlProvider implements Provider<GraphQL> {
private GraphQLDataFetchers graphQLDataFetchers;
@Inject
public GraphQlProvider(GraphQLDataFetchers graphQLDataFetchers) {
this.graphQLDataFetchers = graphQLDataFetchers;
}
@Override
public GraphQL get() {
URL url = Resources.getResource("schema.graphqls");
String sdl = null;
try {
sdl = Resources.toString(url, Charsets.UTF_8);
} catch (IOException e) {
e.printStackTrace();
}
GraphQLSchema graphQLSchema = buildSchema(sdl);
return GraphQL.newGraphQL(graphQLSchema).build();
}
private GraphQLSchema buildSchema(String sdl) {
TypeDefinitionRegistry typeRegistry = new SchemaParser().parse(sdl);
RuntimeWiring runtimeWiring = buildWiring();
SchemaGenerator schemaGenerator = new SchemaGenerator();
return schemaGenerator.makeExecutableSchema(typeRegistry, runtimeWiring);
}
private RuntimeWiring buildWiring() {
return RuntimeWiring.newRuntimeWiring()
.type(newTypeWiring("Query")
.dataFetcher("bookById", graphQLDataFetchers.getBookByIdDataFetcher()))
.type(newTypeWiring("Book")
.dataFetcher("author", graphQLDataFetchers.getAuthorDataFetcher()))
.build();
}
}
get() , GraphQL . ,
6. GraphQLDataFetchers
DataFetcher
GraphQL Java. DataFetcher - .
src/main/java/guice/spark/graphql/GraphQLDataFetchers.java
@Singleton
public class GraphQLDataFetchers {
private static List<Map<String, String>> books = Arrays.asList(
ImmutableMap.of("id", "book-1",
"name", "Harry Potter and the Philosopher's Stone",
"pageCount", "223",
"authorId", "author-1"),
ImmutableMap.of("id", "book-2",
"name", "Moby Dick",
"pageCount", "635",
"authorId", "author-2"),
ImmutableMap.of("id", "book-3",
"name", "Interview with the vampire",
"pageCount", "371",
"authorId", "author-3")
);
private static List<Map<String, String>> authors = Arrays.asList(
ImmutableMap.of("id", "author-1",
"firstName", "Joanne",
"lastName", "Rowling"),
ImmutableMap.of("id", "author-2",
"firstName", "Herman",
"lastName", "Melville"),
ImmutableMap.of("id", "author-3",
"firstName", "Anne",
"lastName", "Rice")
);
public DataFetcher getBookByIdDataFetcher() {
return dataFetchingEnvironment -> {
String bookId = dataFetchingEnvironment.getArgument("id");
return books
.stream()
.filter(book -> book.get("id").equals(bookId))
.findFirst()
.orElse(null);
};
}
public DataFetcher getAuthorDataFetcher() {
return dataFetchingEnvironment -> {
Map<String, String> book = dataFetchingEnvironment.getSource();
String authorId = book.get("authorId");
return authors
.stream()
.filter(author -> author.get("id").equals(authorId))
.findFirst()
.orElse(null);
};
}
}
@Singleton
Guice - . configure
GraphQLModule
, -
7. GraphQLService
API web . GraphQLService
src/main/java/guice/spark/graphql/GraphQLService.java
public class GraphQLService {
private final GraphQL graphQL;
private final ObjectMapper mapper;
@Inject
public GraphQLService(GraphQL graphQL, ObjectMapper mapper) {
this.graphQL = graphQL;
this.mapper = mapper;
}
public void initialize() {
post("/graphql", (request, response) -> {
GraphQLRequestBody body = mapper.readValue(request.body(), GraphQLRequestBody.class);
String query = body.getQuery();
if (query == null) {
query = "";
}
ExecutionResult executionResult = graphQL.execute(
ExecutionInput.newExecutionInput()
.query(query)
.operationName(body.getOperationName())
.variables(body.getVariables())
.build()
);
response.type("application/json");
return mapper.writeValueAsString(executionResult.toSpecification());
});
get("/playground", (req, res) -> new VelocityTemplateEngine().render(
new ModelAndView(Collections.emptyMap(), "playground.html"))
);
}
initialize
Jetty web server 4567. :
POST http://localhost:4567/graphql ObjectMapper
GraphQLRequestBody
GraphQL . JSON .
GraphQLRequestBody:
public class GraphQLRequestBody {
private String query;
private String operationName;
private Map<String, Object> variables;
public String getQuery() {
return query;
}
public void setQuery(String query) {
this.query = query;
}
public String getOperationName() {
return operationName;
}
public void setOperationName(String operationName) {
this.operationName = operationName;
}
public Map<String, Object> getVariables() {
return variables;
}
public void setVariables(Map<String, Object> variables) {
this.variables = variables;
}
}
GET http://localhost:4567/playground playground.html , src/main/resources
. API .
. http://localhost:4567/playground
API
. :
query {
bookById(id: "book-1") {
name,
author {
firstName
}
}
}
API:
{
"data": {
"bookById": {
"name": "Harry Potter and the Philosopher's Stone",
"author": {
"firstName": "Joanne"
}
}
}
}