GraphQL入門總體創(chuàng)建教程

更新時(shí)間：2022年08月03日 15:29:15 作者：王者之峰

這篇文章主要為大家介紹了GraphQL入門總體創(chuàng)建教程示例詳解，有需要的朋友可以借鑒參考下，希望能夠有所幫助，祝大家多多進(jìn)步，早日升職加薪

簡(jiǎn)介

因?yàn)槟壳白龅捻?xiàng)目查詢提供的接口都使用GraphQL替代典型的REST API，所以有必要去對(duì)它進(jìn)行了解和源碼的閱讀。本篇主要大致了解下GraphQL。

一種用于API的查詢語(yǔ)言，讓你的請(qǐng)求數(shù)據(jù)不多不少。前端按需獲取，后端動(dòng)態(tài)返回（不需要的數(shù)據(jù)不會(huì)返回甚至不會(huì)查庫(kù)），對(duì)比起典型的REST API將更加靈活，后端代碼提供可選能力。如果增加新的字段應(yīng)用不想處理這部分?jǐn)?shù)據(jù)可以不用區(qū)分版本。

后端確定哪些接口行為是被允許的，前端按需獲取數(shù)據(jù)，讓你的請(qǐng)求數(shù)據(jù)不多不少。

詳細(xì)的介紹可以參考官方首頁(yè)配合動(dòng)圖更加清晰。

簡(jiǎn)單示例

最好使用Spring Initializr去創(chuàng)建一個(gè)新的項(xiàng)目，不會(huì)產(chǎn)生一些沖突。

maven依賴

<?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 https://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>2.1.6.RELEASE</version>
        <relativePath/> <!-- lookup parent from repository -->
    </parent>
    <groupId>com.graphql-java.tutorial</groupId>
    <artifactId>book-details</artifactId>
    <version>0.0.1-SNAPSHOT</version>
    <name>book-details</name>
    <description>Demo project for Spring Boot</description>
    <properties>
        <java.version>1.8</java.version>
    </properties>
    <dependencies>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter</artifactId>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-test</artifactId>
            <scope>test</scope>
        </dependency>
        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.graphql-java/graphql-java -->
        <dependency>
            <groupId>com.graphql-java</groupId>
            <artifactId>graphql-java</artifactId>
            <version>11.0</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.graphql-java/graphql-java-spring-boot-starter-webmvc -->
        <dependency>
            <groupId>com.graphql-java</groupId>
            <artifactId>graphql-java-spring-boot-starter-webmvc</artifactId>
            <version>1.0</version>
        </dependency>
        <!-- https://mvnrepository.com/artifact/com.google.guava/guava -->
        <dependency>
            <groupId>com.google.guava</groupId>
            <artifactId>guava</artifactId>
            <version>26.0-jre</version>
        </dependency>
    </dependencies>
    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>
    <repositories>
        <repository>
            <id>central</id>
            <name>aliyun maven</name>
            <url>http://maven.aliyun.com/nexus/content/groups/public/</url>
            <layout>default</layout>
            <!-- 是否開啟發(fā)布版構(gòu)件下載 -->
            <releases>
                <enabled>true</enabled>
            </releases>
            <!-- 是否開啟快照版構(gòu)件下載 -->
            <snapshots>
                <enabled>false</enabled>
            </snapshots>
        </repository>
    </repositories>
</project>

Schema

在src/main/resources中創(chuàng)建schema.graphqls文件：

type Query {
    bookById(id: ID): Book
}
type Book {
    id: ID
    name: String
    pageCount: Int
    author: Author
}
type Author {
    id: ID
    firstName: String
    lastName: String
}

可以看到定義了一個(gè)bookById查詢，用于根據(jù)id查詢書籍，書籍中包含id、name、pageCount、author屬性，其中author是一個(gè)復(fù)合類型所以定義了type Author。

上面顯示的用于描述schema的特定于域的語(yǔ)言稱為schema定義語(yǔ)言或SDL。更多細(xì)節(jié)可以在這里找到。

解析schema并關(guān)聯(lián)對(duì)應(yīng)的fetchers

一旦我們有了這個(gè)文件，我們需要通過(guò)讀取文件并解析它并且添加代碼來(lái)為它獲取數(shù)據(jù)使它“栩栩如生”。

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 {
    private GraphQL graphQL;
    /**
     * 注入GraphQL實(shí)例，GraphQL Java Spring適配器將使用GraphQL實(shí)例使我們的schema可用，通過(guò)Http-使用默認(rèn)的"/graphql"url路徑
     *
     * @return
     */
    @Bean
    public GraphQL graphQL() {
        return graphQL;
    }
    @PostConstruct
    public void init() throws IOException {
        //使用Resources讀取graphqls文件
        URL url = Resources.getResource("schema.graphqls");
        //拿到graphqls文件內(nèi)容
        String sdl = Resources.toString(url, Charsets.UTF_8);
        GraphQLSchema graphQLSchema = buildSchema(sdl);
        this.graphQL = GraphQL.newGraphQL(graphQLSchema).build();
    }
    @Autowired
    GraphQLDataFetchers graphQLDataFetchers;
    /**
     * 創(chuàng)建GraphQLSchema實(shí)例：解析schema并關(guān)聯(lián)fetcher
     *
     * @param sdl
     * @return
     */
    private GraphQLSchema buildSchema(String sdl) {
        TypeDefinitionRegistry typeRegistry = new SchemaParser().parse(sdl);
        RuntimeWiring runtimeWiring = buildWiring();
        SchemaGenerator schemaGenerator = new SchemaGenerator();
        return schemaGenerator.makeExecutableSchema(typeRegistry, runtimeWiring);
    }
    /**
     * 根據(jù)層級(jí)去關(guān)聯(lián)fetcher構(gòu)建RuntimeWiring。最外層為Query可以提供bookById所需參數(shù)。第二層為Book-經(jīng)過(guò)第一層獲得的，可以為author提供所需參數(shù)。
     *
     * @return
     */
    private RuntimeWiring buildWiring() {
        return RuntimeWiring.newRuntimeWiring()
                .type(newTypeWiring("Query")
                        .dataFetcher("bookById", graphQLDataFetchers.getBookByIdDataFetcher()))
                .type(newTypeWiring("Book")
                        .dataFetcher("author", graphQLDataFetchers.getAuthorDataFetcher()))
                .build();
    }
}

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 {
    /**
     * books靜態(tài)數(shù)據(jù)
     */
    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")
    );
    /**
     * autors靜態(tài)數(shù)據(jù)
     */
    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")
    );
    /**
     * bookById的fetcher，這里只是簡(jiǎn)單的通過(guò)靜態(tài)數(shù)據(jù)進(jìn)行篩選，具體生產(chǎn)使用sql進(jìn)行查詢
     *
     * @return
     */
    public DataFetcher getBookByIdDataFetcher() {
        return dataFetchingEnvironment -> {
            // 獲得查詢篩選參數(shù)
            String bookId = dataFetchingEnvironment.getArgument("id");
            return books
                    .stream()
                    .filter(book -> book.get("id").equals(bookId))
                    .findFirst()
                    .orElse(null);
        };
    }
    /**
     * 第二層author fetcher
     *
     * @return
     */
    public DataFetcher getAuthorDataFetcher() {
        return dataFetchingEnvironment -> {
            //獲得上級(jí)對(duì)象
            Map<String, String> book = dataFetchingEnvironment.getSource();
            //根據(jù)上級(jí)對(duì)象找到關(guān)聯(lián)id（相當(dāng)于外鍵）
            String authorId = book.get("authorId");
            return authors
                    .stream()
                    .filter(author -> author.get("id").equals(authorId))
                    .findFirst()
                    .orElse(null);
        };
    }
}

DataFetchers

對(duì)于GraphQL Java服務(wù)器來(lái)說(shuō)，最重要的概念可能是DataFetcher：DataFetcher在執(zhí)行查詢時(shí)獲取一個(gè)字段的數(shù)據(jù)。

GraphQL Java在執(zhí)行查詢時(shí)，會(huì)為查詢中遇到的每個(gè)字段調(diào)用相應(yīng)的DataFetcher。DataFetcher是函數(shù)接口，函數(shù)具有一個(gè)參數(shù)為DataFetchingEnvironment類型。

public interface DataFetcher<T> {
T get(DataFetchingEnvironment dataFetchingEnvironment) throws Exception;
}

Default DataFetchers

如上我們實(shí)現(xiàn)了兩個(gè)DataFetchers。如上所述，如果你不指定一個(gè)，PropertyDataFetcher則是被默認(rèn)使用。比如上面的例子中Book.id，Book.name，Book.pageCount,Author.id，Author.firstName和Author.lastName都有一個(gè)PropertyDataFetcher與之關(guān)聯(lián)。

PropertyDataFetcher嘗試以多種方式查找Java對(duì)象的屬性。如果是java.util.Map，簡(jiǎn)單的通過(guò)key查找。這對(duì)我們來(lái)說(shuō)非常好，因?yàn)閎ook和author Maps的keys與schema中指定的字段相同。