graphql-java

GraphQL Java 是一个用于构建数据驱动的应用程序的开源库，它允许客户端以类型安全的方式查询和修改数据。

GraphQL Java 使用指南

GraphQL 是一个用于 API 的查询语言，它允许客户端按照需要请求数据，而不是按照服务器端硬编码的数据结构，这种模式使得客户端可以更灵活地获取所需数据，而服务器端也可以更容易地进行扩展和维护，在 Java 中，我们可以使用 GraphQL Java 库来实现 GraphQL 服务，本文将介绍如何在 Java 项目中使用 GraphQL Java 库。

1、添加依赖

我们需要在项目的 pom.xml 文件中添加 GraphQL Java 库的依赖：

<dependencies>
    <dependency>
        <groupId>com.graphqljava</groupId>
        <artifactId>graphqljava</artifactId>
        <version>17.3</version>
    </dependency>
    <dependency>
        <groupId>com.graphqljava</groupId>
        <artifactId>graphqljavatools</artifactId>
        <version>17.3</version>
    </dependency>
</dependencies>

2、定义 Schema

接下来，我们需要定义一个 GraphQL Schema，用于描述 API 的数据结构和操作，Schema 使用类型系统来定义数据类型和接口，以下是一个简单的示例：

import graphql.schema.GraphQLObjectType;
import graphql.schema.GraphQLSchema;
import graphql.schema.StaticDataFetcher;
import graphql.schema.idl.RuntimeWiring;
import graphql.schema.idl.SchemaGenerator;
import graphql.schema.idl.SchemaParser;
import graphql.schema.idl.TypeDefinitionRegistry;
import graphql.schema.idl.errors.SchemaProblem;
import graphql.schema.idl.language.IdlOperation;
import graphql.schema.idl.language.IdlTypeDefinition;
import graphql.schema.idl.language.impl.DefaultIdlTypeDefinition;
import graphql.schema.idl.language.impl.DefaultIdlOperation;
import graphql.schema.idl.parser.ParserOptions;
import graphql.schema.idl.parser.ParseException;
import graphql.schema.idl.parser.SchemaParserImpl;
import graphql.schema.idl.utils.DependencyTracker;
import graphql.schema.idl.utils.Errors;
import graphql.schema.idl.utils.Utils;
import java.io.*;
import java.util.*;
public class Main {
    public static void main(String[] args) throws Exception {
        // 读取 schema IDL 文件
        File schemaFile = new File("path/to/your/schema/file");
        BufferedReader reader = new BufferedReader(new FileReader(schemaFile));
        String schemaContent = reader.lines().collect(Collectors.joining("
"));
        reader.close();
        // 解析 schema IDL 文件并生成 SchemaGenerator 对象
        ParserOptions options = new ParserOptions();
        List<String> errors = new ArrayList<>();
        SchemaGenerator generator = new SchemaParserImpl().parse(schemaContent, options, errors);
        if (!errors.isEmpty()) {
            throw new IllegalStateException("解析 schema IDL 文件时出错： " + errors);
        }
        // 创建 TypeDefinitionRegistry、RuntimeWiring 和 GraphQLSchema 对象
        TypeDefinitionRegistry typeRegistry = new TypeDefinitionRegistry();
        RuntimeWiring wiring = buildRuntimeWiring(typeRegistry);
        GraphQLSchema schema = builder().build(); // builder() is a method that returns a new instance of the builder class for building the schema object using the provided typeRegistry and wiring objects
    }
}

3、构建 RuntimeWiring 对象

RuntimeWiring 对象用于配置如何将类型映射到实际的数据源，以下是一个简单的示例：

private static RuntimeWiring buildRuntimeWiring(TypeDefinitionRegistry typeRegistry) {
    return RuntimeWiringBuilder() // builder() is a method that returns a new instance of the builder class for building the wiring object using the provided typeRegistry object and default values for other parameters
            .typeRegistry(typeRegistry) // set the typeRegistry to be used by the wiring object
            // add additional configuration as needed, e.g: dataFetcherFactories(), directiveResolvers(), etc...
            // build(); // build() is a method that returns the final wiring object after all configuration has been applied to it using the provided typeRegistry and other parameters (if any) or their default values (if not specified)
}

4、启动 GraphQL Server

我们需要启动一个 HTTP 服务器来处理客户端的请求，以下是一个简单的示例：

import graphql.*; // import the necessary classes from the graphqljava library for handling HTTP requests and responses, e.g: WebHandler, DataFetcherException, etc...
import org.springframework.boot.*; // import the necessary classes from the springboot library for starting an HTTP server, e.g: SpringApplication, SpringBootServletInitializer, etc...
import org.springframework.boot.autoconfigure.*; // import the necessary classes from the springbootautoconfigure library for configuring the application based on its properties, eg: SpringBootApplication, @EnableAutoConfiguration, etc...
import org.springframework.context.*; // import the necessary classes from the springcontext library for managing the application's lifecycle and resources, e