2021/9/6

GraphQL in java

GraphQL 是由 Facebook 在 2012 提出,2015 開源,2018 移交給 GraphQL 基金會。他跟 SQL 不同,並不是隸屬於某一種資料庫的查詢語言,GraphQL 也不是圖形資料庫,他單純是一種簡化 web API 的開發的方法。一般來說在網頁開發時,如果需要使用後端資料庫的資料,就會撰寫 rest 或 web service 的介面,根據資料對應產生許多 rest API,當頁面內的資料來源越多,rest API 就越複雜。GraphQL 透過資料定義,能夠用統一的 rest 介面,提供查詢多樣化資料的功能,也能避免大量冗餘資料傳給網頁。

GraphQL 除了查詢功能,支援了讀取、寫入、資料變更訂閱的功能。

以下根據 Getting started with GraphQL Java and Spring Boot 初步了解 GraphQL

專案目標

根據這個 GraphQL schema 定義

type Query {
  bookById(id: ID): Book 
}

type Book {
  id: ID
  name: String
  pageCount: Int
  author: Author
}

type Author {
  id: ID
  firstName: String
  lastName: String
}

製作一個提供這個 schema 的 GraphQL Server,可透過網頁 API 用以下語法查詢

{
  bookById(id: "book-1"){
    id
    name
    pageCount
    author {
      firstName
      lastName
    }
  }
}

得到的查詢結果為

{ 
  "bookById":
  {
    "id":"book-1",
    "name":"Harry Potter and the Philosopher's Stone",
    "pageCount":223,
    "author": {
      "firstName":"Joanne",
      "lastName":"Rowling"
    }
  }
}

Project

首先產生一個 Java Maven Project,修改 pom.xml

<?xml version="1.0" encoding="UTF-8"?>
<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>

    <groupId>com.graphqljava.tutorial</groupId>
    <artifactId>bookdetails</artifactId>
    <version>1.0.0</version>

    <dependencies>
        <dependency>
            <groupId>com.graphql-java</groupId>
            <artifactId>graphql-java</artifactId>
            <version>11.0</version>
        </dependency>

        <dependency>
            <groupId>com.graphql-java</groupId>
            <artifactId>graphql-java-spring-boot-starter-webmvc</artifactId>
            <version>1.0</version>
        </dependency>

        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>26.0-jre</version>
        </dependency>

        <dependency>
            <groupId>com.graphql-java</groupId>
            <artifactId>graphql-java-spring-boot-starter-webmvc</artifactId>
            <version>1.0</version>
        </dependency>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
            <version>2.1.2.RELEASE</version>
        </dependency>

        <!-- testing facilities -->
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <version>2.1.2.RELEASE</version>
            <scope>test</scope>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.6.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

schema.graphqls

將 GraphQL schema 放在 src/main/resources/schema.graphqls

type Query {
    bookById(id: ID): Book
}

type Book {
    id: ID
    name: String
    pageCount: Int
    author: Author
}

type Author {
    id: ID
    firstName: String
    lastName: String
}

GraphQLProvider.java

利用 schema.graphqls,製作 com.graphqljava.tutorial.bookdetails.GraphQLProvider.java

package com.graphqljava.tutorial.bookdetails;

import com.google.common.base.Charsets;
import com.google.common.io.Resources;
import graphql.GraphQL;
import graphql.schema.GraphQLSchema;
import graphql.schema.idl.RuntimeWiring;
import graphql.schema.idl.SchemaGenerator;
import graphql.schema.idl.SchemaParser;
import graphql.schema.idl.TypeDefinitionRegistry;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.context.annotation.Bean;
import org.springframework.stereotype.Component;

import javax.annotation.PostConstruct;
import java.io.IOException;
import java.net.URL;

import static graphql.schema.idl.TypeRuntimeWiring.newTypeWiring;

@Component
public class GraphQLProvider {


    @Autowired
    GraphQLDataFetchers graphQLDataFetchers;

    private GraphQL graphQL;

    @PostConstruct
    public void init() throws IOException {
        // 以 Resources 讀取 schema.graphqls 產生 GraphQLSchema, GraphQL
        URL url = Resources.getResource("schema.graphqls");
        String sdl = Resources.toString(url, Charsets.UTF_8);
        GraphQLSchema graphQLSchema = buildSchema(sdl);
        this.graphQL = GraphQL.newGraphQL(graphQLSchema).build();
    }

    // 實作 buildSchema 產生 GraphQLSchema
    private GraphQLSchema buildSchema(String sdl) {
        TypeDefinitionRegistry typeRegistry = new SchemaParser().parse(sdl);
        RuntimeWiring runtimeWiring = buildWiring();
        SchemaGenerator schemaGenerator = new SchemaGenerator();
        return schemaGenerator.makeExecutableSchema(typeRegistry, runtimeWiring);
    }

    // 透過 graphQLDataFetchers,註冊兩個 dataFetcher
    private RuntimeWiring buildWiring() {
        return RuntimeWiring.newRuntimeWiring()
                .type(newTypeWiring("Query")
                        .dataFetcher("bookById", graphQLDataFetchers.getBookByIdDataFetcher()))
                .type(newTypeWiring("Book")
                        .dataFetcher("author", graphQLDataFetchers.getAuthorDataFetcher()))
                .build();
    }

    @Bean
    public GraphQL graphQL() {
        return graphQL;
    }

}

以下是 GraphQL 與 GraphQLSchema 的關係圖

GraphQLDataFetchers.java

com.graphqljava.tutorial.bookdetails.GraphQLDataFetchers.java

package com.graphqljava.tutorial.bookdetails;

import com.google.common.collect.ImmutableMap;
import graphql.schema.DataFetcher;
import org.springframework.stereotype.Component;

import java.util.Arrays;
import java.util.List;
import java.util.Map;

@Component
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);
        };
    }
}

BookDetailsApplication.java

製作主程式 com.graphqljava.tutorial.bookdetails.BookDetailsApplication.java

package com.graphqljava.tutorial.bookdetails;

import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;

@SpringBootApplication
public class BookDetailsApplication {

    public static void main(String[] args) {
        SpringApplication.run(BookDetailsApplication.class, args);
    }

}

Postman

在 Postman 的 APIs 可填寫 graphql schema 定義,在進行 API 查詢時,Postman 就能根據 schema 提供語法 hint

在 Request 中,將 Data Type 改為 GraphQL,就能進行 GraphQL 查詢並得到結果

{
  bookById(id: "book-1"){
    id
    name
    pageCount
    author {
      firstName
      lastName
    }
  }
}

References

GraphQL

GraphQL or gRPC in Java

Build and Test a CRUD API using GraphQL, Spring Boot and MongoDB

GraphQL, MongoDB and Java: An introduction

Spring Boot + GraphQL + MongoDB example with Spring Data & graphql-java

GraphQL Java 从Schema文件到GraphQL实例源码解析

GraphQL Java从入门到实践

Netflix DGS framework

An Advanced GraphQL with Spring Boot and Netflix DGS

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