example-spark.java

Spark.post("/graphql", (request, response) -> {
    response.type("application/json");

    final String body = request.body();
    final GqlRequestBody gqlRequestBody = gson.fromJson(body, GqlRequestBody.class);

    if (gqlRequestBody.getQuery() != null) {
        ExecutionInput.Builder executionInput = ExecutionInput.newExecutionInput().query(gqlRequestBody.getQuery());
        if (gqlRequestBody.getVariables() != null) {
            executionInput.variables(gqlRequestBody.getVariables());
        }
        if (gqlRequestBody.getOperationName() != null) {
            executionInput.operationName(gqlRequestBody.getOperationName());
        }
        return build.execute(executionInput.build()).toSpecification();
    } else {
        return "";
    }
}, gson::toJson);

GqlRequestBody.java

public static class GqlRequestBody {
        String query;
        Map<String, Object> variables;
        String operationName;

        @Override
        public String toString() {
            return new StringJoiner(", ", GqlRequestBody.class.getSimpleName() + "[", "]")
                    .add("query='" + query + "'")
                    .add("variables=" + variables)
                    .add("operationName='" + operationName + "'")
                    .toString();
        }

        public String getQuery() {
            return query;
        }

        public void setQuery(String query) {
            this.query = query;
        }

        public Map<String, Object> getVariables() {
            return variables;
        }

        public void setVariables(Map<String, Object> variables) {
            this.variables = variables;
        }

        public String getOperationName() {
            return operationName;
        }

        public void setOperationName(String operationName) {
            this.operationName = operationName;
        }
    }