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一种灵活的API设计模式：在Spring Boot中支持GraphQL

导读：GraphQL是一种基于api的查询语言，它提供了一种更高效、强大和灵活的数据提供方式。它是由Facebook开发和开源，目前由来自世界各地的大公司和个人维护。本文作者先介绍了GraphQL，随后通过示例详细说明了GraphQL的开发流程是如何使用。

你可能已经听说过GraphQL以及Facebook如何在其移动应用中使用GraphQL。在此本文中，我将向你展示如何在Spring Boot中组合GraphQL，看看GraphQL到底提供了什么样的功能。

为什么使用GraphQL?

GraphQL是REST API的查询语言。 GraphQL不受任何特定数据库或存储引擎的约束。你现有的技术架构通常都支持GraphQL。

GraphQL的主要优势：

与REST不同，GraphQL无需在应用程序中创建多个API（应用程序编程接口）endpoint，在REST中，我们公开了多个endpoint以检索此类数据。

https://localhost:8080/person 
https://localhost:8080/person/{id}

使用GraphQL，我们可以按需获取数据。 这与REST不同，在REST实现中，即使只需要一些属性的值，我们也会获取完整的数据响应。 例如，当我们查询REST API时，即使仅需要id和name，我们也会获得如下所示的完整数据。

{“id”: “100”,”name”: “Vijay”,”age”:34"city”: “Faridabad”,”gender”: “Male”}

通过REST API可以将前端（例如移动应用程序）与GraphQL集成在一起，并且响应非常迅速。

本文将介绍如何构建一个Spring Boot应用程序来存储和书查询籍信息。

创建应用

访问Spring Initializr或使用IntelliJ IDEA Ultimate生成具有Web，HSQLDB，Spring Boot 2.1.4等依赖项的Spring Boot应用程序。

生成的POM如下。

<modelVersion>4.0.0</modelVersion>
 <parent>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-parent</artifactId>
 <version>2.1.4.RELEASE</version>
 <relativePath/>
 </parent>
<artifactId>springboot.graphql.app</artifactId>
 <name>springboot-graphql-app</name>
 <description>Demo project for Spring Boot with Graph QL</description>
<properties>
 <java.version>1.8</java.version>
 </properties>
<dependencies>
 <dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-data-jpa</artifactId>
 </dependency>
 <dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-web</artifactId>
 </dependency>
 <dependency>
 <groupId>org.hsqldb</groupId>
 <artifactId>hsqldb</artifactId>
 <scope>runtime</scope>
 </dependency>
 <dependency>
 <groupId>org.springframework.boot</groupId>
 <artifactId>spring-boot-starter-test</artifactId>
 <scope>test</scope>
 </dependency>
 <dependency>
 <groupId>com.graphql-java</groupId>
 <artifactId>graphql-spring-boot-starter</artifactId>
 <version>3.6.0</version>
 </dependency>
 <dependency>
 <groupId>com.graphql-java</groupId>
 <artifactId>graphql-java-tools</artifactId>
 <version>3.2.0</version>
 </dependency>
 </dependencies>

添加EndPoint

让我们从BookController开始，如下所示。

package graphqlapp.controller;
import graphqlapp.service.GraphQLService;
import graphql.ExecutionResult;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.HttpStatus;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.PostMapping;
import org.springframework.web.bind.annotation.RequestBody;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
@RequestMapping(“/rest/books”)
@RestController
public class BookController {
 private static Logger logger = LoggerFactory.getLogger(BookController.class);
private GraphQLService graphQLService;
@Autowired
 public BookController(GraphQLService graphQLService) {
 this.graphQLService=graphQLService;
 }
@PostMapping
 public ResponseEntity<Object> getAllBooks(@RequestBody String query){
 logger.info(“Entering getAllBooks@BookController”);
 ExecutionResult execute = graphQLService.getGraphQL().execute(query);
 return new ResponseEntity<>(execute, HttpStatus.OK);
 }
}

添加model

接下来，我们将添加一个model类来代表书。我们将其命名为Book。 model类的代码如下。

package graphqlapp.model;
import javax.persistence.Entity;
import javax.persistence.Id;
import javax.persistence.Table;
@Table
@Entity
public class Book {
@Id
 private String isn;
 private String title;
 private String publisher;
 private String publishedDate;
 private String[] author;
public Book() {
 }
public Book(String isn, String title, String publisher, String publishedDate, String[] author) {
 this.isn = isn;
 this.title = title;
 this.publisher = publisher;
 this.publishedDate = publishedDate;
 this.author = author;
 }
public String getIsn() {
 return isn;
 }
public void setIsn(String isn) {
 this.isn = isn;
 }
public String getTitle() {
 return title;
 }
public void setTitle(String title) {
 this.title = title;
 }
public String getPublisher() {
 return publisher;
 }
public void setPublisher(String publisher) {
 this.publisher = publisher;
 }
public String getPublishedDate() {
 return publishedDate;
 }
public void setPublishedDate(String publishedDate) {
 this.publishedDate = publishedDate;
 }
public String[] getAuthor() {
 return author;
 }
public void setAuthor(String[] author) {
 this.author = author;
 }
}

创建BookRepository

BookRepository扩展了JpaRepository，如下所示。

package graphqlapp.repository;
import graphqlapp.model.Book;
import org.springframework.data.jpa.repository.JpaRepository;
public interface BookRepository extends JpaRepository<Book, String> {
}

添加GraphQL模式（schema）

接下来，我们将在资源文件夹中编写一个GraphQL模式，名为books.graphql。

schema{
 query:Query
}type Query{
 allBooks: [Book]
 book(id: String): Book
}type Book{
 isn:String
 title:String
 publisher:String
 author:[String]
 publishedDate:String
}

该文件是使用GraphQL的关键。在这里，我们定义了模式，你可以将其与查询相关联。我们还定义了查询类型。

在此示例中，我们定义了两种类型：

当用户查询所有书籍（通过使用allBooks）时，应用程序将返回一个Book数组。
当用户通过传递ID查询特定书籍时，应用程序将返回Book对象。

添加GraphQL服务

接下来，我们需要添加GraphQL服务。让我们将其命名为GraphQLService。

package graphqlapp.service;
import graphqlapp.model.Book;
import graphqlapp.repository.BookRepository;
import graphqlapp.service.datafetcher.AllBooksDataFetcher;
import graphqlapp.service.datafetcher.BookDataFetcher;
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.slf4j.Logger;
import org.slf4j.LoggerFactory;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.beans.factory.annotation.Value;
import org.springframework.core.io.Resource;
import org.springframework.stereotype.Service;
import javax.annotation.PostConstruct;
import java.io.File;
import java.io.IOException;
import java.util.stream.Stream;
@Service
public class GraphQLService {
 private static Logger logger = LoggerFactory.getLogger(GraphQLService.class);
private BookRepository bookRepository;
private AllBooksDataFetcher allBooksDataFetcher;
private BookDataFetcher bookDataFetcher;
@Value(“classpath:books.graphql”)
 Resource resource;
private GraphQL graphQL;
@Autowired
 public GraphQLService(BookRepository bookRepository, AllBooksDataFetcher allBooksDataFetcher,
 BookDataFetcher bookDataFetcher) {
 this.bookRepository=bookRepository;
 this.allBooksDataFetcher=allBooksDataFetcher;
 this.bookDataFetcher=bookDataFetcher;
 }
@PostConstruct
 private void loadSchema() throws IOException {
 logger.info(“Entering loadSchema@GraphQLService”);
 loadDataIntoHSQL();
//Get the graphql file
 File file = resource.getFile();
//Parse SchemaF
 TypeDefinitionRegistry typeDefinitionRegistry = new SchemaParser().parse(file);
 RuntimeWiring runtimeWiring = buildRuntimeWiring();
 GraphQLSchema graphQLSchema = new SchemaGenerator().makeExecutableSchema(typeDefinitionRegistry, runtimeWiring);
 graphQL = GraphQL.newGraphQL(graphQLSchema).build();
 }
private void loadDataIntoHSQL() {
 Stream.of(
 new Book(“1001”, “The C Programming Language”, “PHI Learning”, “1978”,
 new String[] {
 “Brian W. Kernighan (Contributor)”,
 “Dennis M. Ritchie”
 }),
 new Book(“1002”,”Your Guide To Scrivener”, “MakeUseOf.com”, “ April 21st 2013”,
 new String[] {
 “Nicole Dionisio (Goodreads Author)”
 }),
 new Book(“1003”,”Beyond the Inbox: The Power User Guide to Gmail”, “ Kindle Edition”, “November 19th 2012”,
 new String[] {
 “Shay Shaked”
 , “Justin Pot”
 , “Angela Randall (Goodreads Author)”
 }),
 new Book(“1004”,”Scratch 2.0 Programming”, “Smashwords Edition”, “February 5th 2015”,
 new String[] {
 “Denis Golikov (Goodreads Author)”
 }),
 new Book(“1005”,”Pro Git”, “by Apress (first published 2009)”, “2014”,
 new String[] {
 “Scott Chacon”
 })
).forEach(book -> {
 bookRepository.save(book);
 });
 }
private RuntimeWiring buildRuntimeWiring() {
 return RuntimeWiring.newRuntimeWiring()
 .type(“Query”, typeWiring -> typeWiring
 .dataFetcher(“allBooks”, allBooksDataFetcher)
 .dataFetcher(“book”, bookDataFetcher))
 build();
 }
public GraphQL getGraphQL(){
 return graphQL;
 }
}

当Spring Boot应用程序运行时，Spring框架将调用@PostConstruct方法。 @PostConstruct方法中的代码会将书籍信息写入HQL数据库中。

在此服务类的buildRuntimeWiring()方法中，我们将两个数据获取程序进行运行时绑定： allBook和book。此处定义的名称allBookand book必须与我们已经创建的GraphQL文件中定义的类型匹配。

创建数据访问层

GraphQL模式中的每种类型都有一个对应的数据提取器（data fetcher）。

我们需要为在架构中定义的allBooks和Book类型编写两个单独的数据获取器。

allBooks类型的数据获取程器是这个。

package graphqlapp.service.datafetcher;
import graphql.schema.DataFetcher;
import graphql.schema.DataFetchingEnvironment;
import graphqlapp.model.Book;
import graphqlapp.repository.BookRepository;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import java.util.List;
@Component
public class AllBooksDataFetcher implements DataFetcher<List<Book>> {
private BookRepository bookRepository;
@Autowired
 public AllBooksDataFetcher(BookRepository bookRepository) {
 this.bookRepository=bookRepository;
 }
@Override
 public List<Book> get(DataFetchingEnvironment dataFetchingEnvironment) {
 return bookRepository.findAll();
 }
}

Book类型的数据获取器是这个。

package graphqlapp.service.datafetcher;
import graphql.schema.DataFetcher;
import graphqlapp.model.Book;
import graphqlapp.repository.BookRepository;
import graphql.schema.DataFetchingEnvironment;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
@Component
public class BookDataFetcher implements DataFetcher<Book> {
private BookRepository bookRepository;
@Autowired
 public BookDataFetcher(BookRepository bookRepository){
 this.bookRepository = bookRepository;
 }
@Override
 public Book get(DataFetchingEnvironment dataFetchingEnvironment) {
 String isn = dataFetchingEnvironment.getArgument(“id”);
 return bookRepository.findById(isn).orElse(null);
 }
}

运行应用

我在端口9002端口上运行此应用程序。因此，我在application.properties文件中如下。

server.port=9002

这样，我们的Spring Boot GraphQL应用程序就准备好了。让我们运行我们的Spring Boot应用程序，并使用Postman工具对其进行测试。

注意这里我们只有一个endpoinst，

http://localhost:9002/rest/books

为此，请打开Postman并在请求正文中添加以下查询。

输入1：我们要查询一本ID为1001的特定书，并且只需要书名即可。

同时，我们正在查询allBooks，并期望响应将包含is，title，author，publisher和publishedDate。

{
 book(id:”1001"){
 title 
 }
 
 allBooks{
 isn
 title
 author
 publisher
 publishedDate
 }
}

输出1：响应如下。

{
 “errors”: [],
 “data”: {
 “book”: {
 “title”: “The C Programming Language”
 },
 “allBooks”: [
 {
 “isn”: “1001”,
 “title”: “The C Programming Language”,
 “author”: [
 “Brian W. Kernighan (Contributor)”,
 “Dennis M. Ritchie”
 ],
 “publisher”: “PHI Learning”,
 “publishedDate”: “1978”
 },
 {
 “isn”: “1002”,
 “title”: “Your Guide To Scrivener”,
 “author”: [
 “Nicole Dionisio (Goodreads Author)”
 ],
 “publisher”: “MakeUseOf.com”,
 “publishedDate”: “ April 21st 2013”
 },
 {
 “isn”: “1003”,
 “title”: “Beyond the Inbox: The Power User Guide to Gmail”,
 “author”: [
 “Shay Shaked”,
 “Justin Pot”,
 “Angela Randall (Goodreads Author)”
 ],
 “publisher”: “ Kindle Edition”,
 “publishedDate”: “November 19th 2012”
 },
 {
 “isn”: “1004”,
 “title”: “Scratch 2.0 Programming”,
 “author”: [
 “Denis Golikov (Goodreads Author)”
 ],
 “publisher”: “Smashwords Edition”,
 “publishedDate”: “February 5th 2015”
 },
 {
 “isn”: “1005”,
 “title”: “Pro Git”,
 “author”: [
 “Scott Chacon”
 ],
 “publisher”: “by Apress (first published 2009)”,
 “publishedDate”: “2014”
 }
 ]
 },
 “extensions”: null
}

输入2：让我们再次通过ID查询特定图书的标题和作者。

{
 book(id:”1001"){
 title
 author
 }
}

输出2：输出是这个。我们获得ID为1001的书的标题和作者。

{
 “errors”: [],
 “data”: {
 “book”: {
 “title”: “The C Programming Language”,
 “author”: [
 “Brian W. Kernighan (Contributor)”,
 “Dennis M. Ritchie”
 ]
 }
 },
 “extensions”: null
}

输入3：让我们查询所有图书的书名，作者，出版日期和出版商详细信息

{
 allBooks{
 isn
 title
 author
 publisher
 publishedDate
 }
}

输出3：输出是这个。

{
 “errors”: [],
 “data”: {
 “allBooks”: [
 {
 “isn”: “1001”,
 “title”: “The C Programming Language”,
 “author”: [
 “Brian W. Kernighan (Contributor)”,
 “Dennis M. Ritchie”
 ],
 “publisher”: “PHI Learning”,
 “publishedDate”: “1978”
 },
 {
 “isn”: “1002”,
 “title”: “Your Guide To Scrivener”,
 “author”: [
 “Nicole Dionisio (Goodreads Author)”
 ],
 “publisher”: “MakeUseOf.com”,
 “publishedDate”: “ April 21st 2013”
 },
 {
 “isn”: “1003”,
 “title”: “Beyond the Inbox: The Power User Guide to Gmail”,
 “author”: [
 “Shay Shaked”,
 “Justin Pot”,
 “Angela Randall (Goodreads Author)”
 ],
 “publisher”: “ Kindle Edition”,
 “publishedDate”: “November 19th 2012”
 },
 {
 “isn”: “1004”,
 “title”: “Scratch 2.0 Programming”,
 “author”: [
 “Denis Golikov (Goodreads Author)”
 ],
 “publisher”: “Smashwords Edition”,
 “publishedDate”: “February 5th 2015”
 },
 {
 “isn”: “1005”,
 “title”: “Pro Git”,
 “author”: [
 “Scott Chacon”
 ],
 “publisher”: “by Apress (first published 2009)”,
 “publishedDate”: “2014”
 }
 ]
 },
 “extensions”: null
}