从Java应用程序向graphql发送HTTP请求

Question

我有一个带有graphql api的nodejs后端。我想从我的Java应用程序向此api发送一个http请求。我发送请求的代码是：

        String query = "query{ login( name: \"" + username + "\", password: \"" + password + "\" ) { token, userId, name }}";


        String postEndpoint = "http://localhost:8000";

        CloseableHttpClient httpClient = HttpClients.createDefault();

        HttpPost httpPost = new HttpPost(postEndpoint);

        httpPost.setHeader("Content-Type", "application/json");

        String inputJson = "{\n" +
                "  \"query\": \"" + query + "\"\n" +
                "}";

        System.out.println(inputJson);

        StringEntity stringEntity = new StringEntity(inputJson);
        httpPost.setEntity(stringEntity);

        HttpResponse response = httpClient.execute(httpPost);

        BufferedReader br = new BufferedReader(
                new InputStreamReader((response.getEntity().getContent()))
        );

        if(response.getStatusLine().getStatusCode() != 200) {
            throw new RuntimeException("Failed : HTTP error code : " +
                    response.getStatusLine().getStatusCode());
        }

        StringBuffer result = new StringBuffer();
        String line = "";
        while((line = br.readLine()) != null) {
            System.out.println("Response : \n"+result.append(line));
        }

在插入变量username的位置，后端总是出现意外的字符错误。这个查询我在做什么错？ 谢谢