如何从 Java 应用程序调用 GraphQL 端点

问题描述

我正在尝试调用 GraphQL 端点（外部的，不受我控制），我在互联网上所能找到的只是如何使用 Java Spring Boot 设置后端 GraphQL 端点。如何从 Java 应用程序调用 GraphQL 端点？

解决方法

Netflix DGS 有 springboot 客户端库。

参考：https://netflix.github.io/dgs/advanced/java-client/#http-client-wrapper

和

https://netflix.github.io/dgs/generating-code-from-schema/#generating-client-apis。

private RestTemplate dgsRestTemplate;

private static final String URL = "http://someserver/graphql";

private static final String QUERY = "{\n" +
            "  ticks(first: %d,after:%d){\n" +
            "    edges {\n" +
            "      node {\n" +
            "        route {\n" +
            "          name\n" +
            "          grade\n" +
            "          pitches\n" +
            "          location\n" +
            "        }\n" +
            "        \n" +
            "        userStars\n" +
            "      }\n" +
            "    }\n" +
            "  }\n" +
            "}";

public List<TicksConnection> getData() {
    DefaultGraphQLClient graphQLClient = new DefaultGraphQLClient(URL);
    GraphQLResponse response = graphQLClient.executeQuery(query,new HashMap<>(),(url,headers,body) -> {
        /**
         * The requestHeaders providers headers typically required to call a GraphQL endpoint,including the Accept and Content-Type headers.
         * To use RestTemplate,the requestHeaders need to be transformed into Spring's HttpHeaders.
         */
        HttpHeaders requestHeaders = new HttpHeaders();
        headers.forEach(requestHeaders::put);

        /**
         * Use RestTemplate to call the GraphQL service. 
         * The response type should simply be String,because the parsing will be done by the GraphQLClient.
         */
        ResponseEntity<String> exchange = dgsRestTemplate.exchange(url,HttpMethod.POST,new HttpEntity(body,requestHeaders),String.class);

        /**
         * Return a HttpResponse,which contains the HTTP status code and response body (as a String).
         * The way to get these depend on the HTTP client.
         */
        return new HttpResponse(exchange.getStatusCodeValue(),exchange.getBody());
    }); 

    TicksConnection ticks = graphQLResponse.extractValueAsObject("ticks",TicksConnection.class);
    return ticks;
}