# Getting Started with GraphQl:Java ## 1. Add maven dependency ```xml com.graphql-java graphql-java 16.2 ``` ## 2. Create GraphQL ObjectType and DataFetchers 1. Define GraphQLObjectType for User, for this I'm creating a class that will help to build different types and being used by SchemaBuilderHelper. ```java import graphql.Scalars; import graphql.schema.GraphQLObjectType; import org.springframework.stereotype.Component; @Component public class MyGraphQLObjectTypes { public GraphQLObjectType getUserType() { return new GraphQLObjectType.Builder() .name("User") .field(builder -> builder .name("name") .type(Scalars.GraphQLString) ) .field(builder -> builder .name("email") .type(Scalars.GraphQLString) ).build(); } // define your own data type for your Model classes } ``` getUserType method will return GraphQLObjectType which is equivalent to below user class ```java import lombok.Data; @Data public class User { private String name; private String email; } ``` 2. Now we will create a user field in root query of type User, which we just created in above step ```java import graphql.Scalars; import graphql.schema.*; import lombok.RequiredArgsConstructor; import org.springframework.stereotype.Component; import java.util.HashMap; @RequiredArgsConstructor @Component public class SchemaBuilderHelper { private final MyGraphQLObjectTypes myGraphQLObjectTypes; public void buildQuery(GraphQLObjectType.Builder queryBuilder, GraphQLCodeRegistry.Builder codeRegistry) { queryBuilder.name("Query"); buildUserQuery(queryBuilder, codeRegistry); } private void buildUserQuery(GraphQLObjectType.Builder queryBuilder, GraphQLCodeRegistry.Builder codeRegistry) { GraphQLObjectType userType = myGraphQLObjectTypes.getUserType(); codeRegistry.dataFetcher(FieldCoordinates.coordinates("Query", "user"), (DataFetcher>) dataFetchingEnvironment -> { HashMap res = new HashMap<>(); res.put("name", "Ram"); res.put("email", "Ram@gmail.com"); return res; }); queryBuilder.field(builder -> builder .name("user") .type(userType)); } } ``` For now, I have created a static dataFetcher for user(type User) but it can be replaced with a dynamic data source. ## 3. Create another class GraphQLConfig This class will be going to use SchemaBuilderHelper to build GraphQLSchema and creating spring bean for it and also for GraphQL which is used for executing graphQL query. ```java import com.example.graphqljava.graphql.SchemaBuilderHelper; import graphql.GraphQL; import graphql.schema.GraphQLCodeRegistry; import graphql.schema.GraphQLObjectType; import graphql.schema.GraphQLSchema; import graphql.schema.idl.SchemaPrinter; import org.springframework.context.annotation.Bean; import org.springframework.context.annotation.Configuration; @Configuration public class GraphQLConfig { @Bean public SchemaPrinter getSchemaPrinter() { return new SchemaPrinter(); } @Bean public GraphQLSchema getGraphQLSchema(SchemaBuilderHelper schemaBuilderHelper) { GraphQLCodeRegistry.Builder codeRegistry = GraphQLCodeRegistry.newCodeRegistry(); GraphQLObjectType.Builder queryBuilder = GraphQLObjectType.newObject(); //build query type schemaBuilderHelper.buildQuery(queryBuilder, codeRegistry); return GraphQLSchema.newSchema() .query(queryBuilder.build()) .codeRegistry(codeRegistry.build()) .build(); } @Bean public GraphQL getGraphQl(GraphQLSchema graphQLSchema) { return GraphQL.newGraphQL(graphQLSchema).build(); } } ``` ## 4. Create model class GraphQLRequest This will represent the graphQl request sent by client. ```java import lombok.Data; @Data public class GraphQLRequest { private String query; private String operationName; private Map variables; } ``` ## 5. Let's create a controller class for handling GraphQL request(GraphQLController) ### This GraphQLController will contain basically two endpoints * POST endpoint : for accepting GraphQL request and return data * GET endpoint : for returning GraphQL schema ```java @RestController @RequiredArgsConstructor @RequestMapping("/api/graphql") public class GraphQLController { private final GraphQL graphQL; private final GraphQLSchema schema; private final SchemaPrinter schemaPrinter; @GetMapping(produces = MediaType.TEXT_PLAIN_VALUE) public String schema() { return schemaPrinter.print(schema); } @PostMapping public Object execute(@RequestBody GraphQLRequest graphQLRequest) { Map variables = Optional.ofNullable(graphQLRequest.getVariables()) .orElse(new HashMap<>()); ExecutionInput input = new ExecutionInput .Builder() .query(graphQLRequest.getQuery()) .operationName(graphQLRequest.getOperationName()) .variables(variables).build(); ExecutionResult execute = graphQL.execute(input); Map result = new HashMap<>(); result.put("data", execute.getData()); //set error if any if (!execute.getErrors().isEmpty()) { result.put("error", execute.getErrors()); } return result; } } ``` # Now we have build simple Spring app with graphQL ![Image description](https://dev-to-uploads.s3.amazonaws.com/uploads/articles/p84pssquzk06qrhau067.png) Here is the github repo for this demo https://github.com/vijaypatidar/graph-ql-java

vijaypatidar

Getting Start With GraphQL in Java

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