performance - 使用 java 8 流将键值对转换为按键对象映射分组的最快方法

Question

模型:

public class AgencyMapping {
    private Integer agencyId;
    private String scoreKey;
}

public class AgencyInfo {
    private Integer agencyId;
    private Set<String> scoreKeys;
}

我的代码:

List<AgencyMapping> agencyMappings;
 Map<Integer, AgencyInfo> agencyInfoByAgencyId = agencyMappings.stream()
            .collect(groupingBy(AgencyMapping::getAgencyId,
                    collectingAndThen(toSet(), e -> e.stream().map(AgencyMapping::getScoreKey).collect(toSet()))))
            .entrySet().stream().map(e -> new AgencyInfo(e.getKey(), e.getValue()))
            .collect(Collectors.toMap(AgencyInfo::getAgencyId, identity()));

有没有办法获得相同的结果并使用更简单和更快的代码？

Answer 1

您可以简化对 collectingAndThen(toSet(), e -> e.stream().map(AgencyMapping::getScoreKey).collect(toSet())))) 的调用。调用mapping(AgencyMapping::getScoreKey, toSet()) .

Map<Integer, AgencyInfo> resultSet = agencyMappings.stream()
                .collect(groupingBy(AgencyMapping::getAgencyId,
                        mapping(AgencyMapping::getScoreKey, toSet())))
                .entrySet()
                .stream()
                .map(e -> new AgencyInfo(e.getKey(), e.getValue()))
                .collect(toMap(AgencyInfo::getAgencyId, identity()));

使用 toMap 的另一种查看方式集电极:

Map<Integer, AgencyInfo> resultSet = agencyMappings.stream()
                .collect(toMap(AgencyMapping::getAgencyId, // key extractor
                        e -> new HashSet<>(singleton(e.getScoreKey())), // value extractor
                        (left, right) -> { // a merge function, used to resolve collisions between values associated with the same key
                            left.addAll(right);
                            return left;
                        }))
                .entrySet()
                .stream()
                .map(e -> new AgencyInfo(e.getKey(), e.getValue()))
                .collect(toMap(AgencyInfo::getAgencyId, identity()));

后一个例子可以说比前一个更复杂。尽管如此，您的方法几乎是与使用 mapping 不同的方法。而不是 collectingAndThen正如刚才提到的。

除此之外，我看不到您可以使用显示的代码简化的任何其他内容。

至于更快的代码，如果您建议您当前的方法性能较慢，那么您可能需要阅读答案 here谈到何时应该考虑并行。