Java 8 Streams 根据条件过滤列表

Question

我正在尝试根据某些条件在原始列表之上提取过滤列表。我正在使用 Java 8 的反向移植版本，我不太确定如何执行此操作。我从 ccarReport.getCcarReportWorkflowInstances() 调用中获取 Set。我需要根据条件匹配来迭代和过滤这个集合（我将每个对象中的日期属性与传递的请求日期进行比较。下面是代码

  Set<CcarReportWorkflowInstance> ccarReportWorkflowInstanceSet = ccarReport.getCcarReportWorkflowInstances();
  List<CcarReportWorkflowInstance> ccarReportWorkflowInstances = StreamSupport.stream(ccarReportWorkflowInstanceSet).filter(ccarReportWorkflowInstance -> DateUtils.isSameDay(cobDate, ccarReportWorkflowInstance.getCobDate()));

正在做这项工作的例程

  public List<CcarRepWfInstDTO> fetchReportInstances(Long reportId, Date cobDate) {
    List<CcarRepWfInstDTO> ccarRepWfInstDTOs = null;
    CcarReport ccarReport = validateInstanceSearchParams(reportId, cobDate);
    Set<CcarReportWorkflowInstance> ccarReportWorkflowInstanceSet = ccarReport.getCcarReportWorkflowInstances();
    List<CcarReportWorkflowInstance> ccarReportWorkflowInstances = StreamSupport.stream(ccarReportWorkflowInstanceSet).filter(ccarReportWorkflowInstance -> DateUtils.isSameDay(cobDate, ccarReportWorkflowInstance.getCobDate()));
    ccarRepWfInstDTOs = ccarRepWfInstMapper.ccarRepWfInstsToCcarRepWfInstDTOs(ccarReportWorkflowInstances);
    return ccarRepWfInstDTOs;
}

我在尝试使用流时遇到错误。

Answer 1

假设我理解你想要做什么，你可以用一行替换你的方法体：

return 
  validateInstanceSearchParams(reportId, cobDate).getCcarReportWorkflowInstances()
                                                 .stream()
                                                 .filter(c -> DateUtils.isSameDay(cobDate, c.getCobDate()))
                                                 .collect(Collectors.toList());

1. 您可以使用stream() 方法从Set 中获取Stream。不需要StreamSupport.stream()。
2. 过滤 Stream 后，您应该将其 collect 输入到输出 List。
3. 我会使用较短的变量和方法名称。你的代码读起来很痛苦。