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GraphQL Directive（指令）是GraphQL中的一种特殊类型，它允许开发者在GraphQL schema中添加元数据，以控制查询和解析操作的行为

Directive的详细说明及使用可见GraphQL（五）指令[Directive]详解

本文将介绍通过自定义Directive实现的GraphQL登录态校验，步骤依次为：

1. Schema中定义directive
2. 实现DgsReactiveCustomContextBuilderWithRequest接口，构建请求内全局使用的上下文对象
3. 实现SchemaDirectiveWiring，对Field进行拦截校验
4. Directive注入

Schema Directive定义

"必须要登录"
directive @needLogin on FIELD_DEFINITIONtype Employee {"雇员名称"employees(month: Date : [String] @needLogin
}

LoginContextBuilder

实现DgsReactiveCustomContextBuilderWithRequest接口，可以使用当前的请求信息，例如 HTTP 请求头、请求参数等构建自定义的上下文对象

在查询执行过程中，GraphQL 会将该上下文对象传递给所有的数据解析器（DataFetcher），使得数据解析器能够访问和修改上下文对象中的数据

使用DgsReactiveCustomContextBuilderWithRequest接口可以实现许多有用的功能，例如：

• 存储用户身份验证信息，以便在数据解析器中进行鉴权
• 将请求相关的信息（例如请求参数、请求头等）传递给数据解析器，以便数据解析器根据这些信息返回正确的数据
• 存储请求相关的上下文信息，例如请求开始时间、请求结束时间等，以便进行性能分析和监控

@Component
public class LoginContextBuilder implements DgsReactiveCustomContextBuilderWithRequest<YyContext> {private static final Logger LOGGER = LoggerFactory.getLogger(LoginContextBuilder.class);@Autowiredprivate ReactiveLoginService reactiveLoginService;@Autowiredprivate HttpHeaderAuthorization httpHeaderAuthorization;@NotNull@Overridepublic Mono<LoginContext> build(@Nullable Map<String, ?> map, @Nullable HttpHeaders httpHeaders, @Nullable ServerRequest serverRequest) {boolean interiorAuth = httpHeaderAuthorization.auth(serverRequest);if(interiorAuth){LoginContext loginContext = new LoginContext(true, IpUtil.getClientIpAddress(serverRequest)).setInteriorAuth(true);LOGGER.info("interior request loginContext:{}",loginContext);return Mono.just(loginContext);}else{return reactiveLoginService.getUid(serverRequest).doOnSuccess(user-> LOGGER.info("login user:{}",user)).onErrorResume(e-> Mono.just(LoginUser.NOT_LOGIN_USER)).map(user -> new LoginContext(user, IpUtil.getClientIpAddress(serverRequest)));}}
}

ReactiveLoginService

subscribeOn(Schedulers.boundedElastic())将该Mono订阅到一个boundedElastic调度器的线程中，这样Mono中的操作就会在该线程上执行，而不会阻塞当前的线程

Schedulers.boundedElastic()调度器是一个弹性线程池，它根据需要动态地创建和销毁线程，以适应不同的负载情况

public class ReactiveLoginService {private LoginService loginService;public ReactiveLoginService(LoginService loginService){this.loginService = loginService;}/*** 登录校验* @param httpServerRequest* @return*/public Mono<LoginUser> getUid(ServerRequest httpServerRequest){return Mono.fromCallable(()->{long uid = loginService.login(new WebFluxHttpServletRequest(httpServerRequest),null);return uid > 0 ? new LoginUser(uid) : LoginUser.NOT_LOGIN_USER;}).subscribeOn(Schedulers.boundedElastic());}public void close(){loginService.close();}
}

Directive 实现

@Component
public class NeedLoginDirective implements SchemaDirectiveWiring {private static final Logger LOGGER = LoggerFactory.getLogger(NeedLoginDirective.class);public static final String NEED_LOGIN_DIRECTIVE = "needLogin";public NeedLoginDirective() {}@Overridepublic GraphQLFieldDefinition onField(SchemaDirectiveWiringEnvironment<GraphQLFieldDefinition> environment) {GraphQLFieldDefinition field = environment.getElement();GraphQLFieldsContainer parentType = environment.getFieldsContainer();// 原始DataFetcher，无需修改参数值时，最后需返回原始DataFetcher的值DataFetcher originalDataFetcher = environment.getCodeRegistry().getDataFetcher(parentType, field);if (field.getDirective(NEED_LOGIN_DIRECTIVE) == null) {return field;}LOGGER.info("onField field:{} needLogin.", field);DataFetcher needLoginDataFetcher = dfe -> {LoginContext loginContext = DgsContext.getCustomContext(dfe);if (loginContext.getLoginUser().hasLogin()) {return originalDataFetcher.get(dfe);} else {LOGGER.info("not login return null");throw new NeedLoginRuntimeException();}};environment.getCodeRegistry().dataFetcher(parentType, field, needLoginDataFetcher);return field;}
}

Directive 注入

GraphQLSchemaConfiguration

@Configuration
public class GraphQLSchemaConfiguration {@DgsComponentpublic class SecuredDirectiveRegistration {private NeedLoginDirective needLoginDirective;public SecuredDirectiveRegistration(NeedLoginDirective needLoginDirective) {this.needLoginDirective = needLoginDirective;}@DgsRuntimeWiringpublic RuntimeWiring.Builder addSecuredDirective(RuntimeWiring.Builder builder) {return builder.directive(NeedLoginDirective.NEED_LOGIN_DIRECTIVE,needLoginDirective);}}
}

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参考资料：

1. GraphQL（五）指令[Directive]详解
2. Derectives 原理