如何为可选流中的列表映射索引0处的值

Question

我有下面的方法，这是有效的。我试图完成所有的事情，并获得可选流中的值，而不必执行额外的if检查。是否可以映射并在索引0处获取结果对象？请指教，谢谢。

public String getData(HttpEntity<Request> request, String endPoint){
    ResponseEntity<Reponse> response = 
        template.exchange(endPoint, HttpMethod.POST, request, Reponse.class);

    List<Result> results = Optional.ofNullable(response)
        .map(ResponseEntity::getBody)
        .map(Response::getQueryResult)
        .map(QueryResult::getResults)
        // getResults is an ArrayList of Result Objects. Could I get the Result Object at index 0 here? 
        // following that I plan to go .map(Result::getValue) here. 
        .orElse(null);
    if(CollectionUtils.isNotEmpty(results)){
        return results.get(0).getValue();
    }
    return null;
}

Answer 1

return Optional.ofNullable(response)
               .map(ResponseEntity::getBody)
               .map(Response::getQueryResult)
               .map(QueryResult::getResults)
               .filter(CollectionUtils::isNotEmpty)
               .map(list -> list.get(0)) // hate this part :)
               .map(Result::getValue)
               .orElse(null);

如果您是方法引用的粉丝，并且发现lambdas很无聊

return Optional.ofNullable(response)
               .map(ResponseEntity::getBody)
               .map(Response::getQueryResult)
               .map(QueryResult::getResults)
               .filter(CollectionUtils::isNotEmpty)
               .map(List::iterator)
               .map(Iterator::next)
               .map(Result::getValue)
               .orElse(null);

我展示它是出于教育原因，尽管我喜欢它，但我不提倡它。