Java 8 Streams Filter a list based on a condition

Question

I am trying to extract a filtered list on top of the original list based on some condition. I am using backport version of Java 8 and am not pretty sure how to do this.I get the Set from ccarReport.getCcarReportWorkflowInstances() call. I need to iterate and filter this set based on a condition match( I am comparing the date attribute in each object with the request date being passed. Below is the code

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

The routine which is doing the job

  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;
}

Error I get when I tried to use streams.

Eran · Accepted Answer · 2016-07-19 10:25:26Z

3

Assuming I understood what you are trying to do, you can replace your method body with a single line :

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

You can obtain a Stream from the Set by using the stream() method. No need for StreamSupport.stream().
After filtering the Stream, you should collect it into the output List.
I'd use shorter variable and method names. Your code is painful to read.

answered Jul 19, 2016 at 10:25

Eran

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7 Comments

Balaji Over a year ago

its throwing a compile time error saying it cannot return a custom object but only of Type<T>

Eran Over a year ago

@Balaji On which method call do you get this error?

Balaji Over a year ago

I have attached the image containing the error as part of question.Please have a look

Holger Over a year ago

@Balaji: what’s the problem in simply writing the name of the method? That’s less effort than creating a screenshot.

Holger Over a year ago

@Balaji: Well, that’s exactly the problem. You are mixing two entirely different APIs. Java 8’s standard collector can’t implement your custom collector interface. Of course, it’s unfortunate that both have the same simple name. Look at the beginning of the package names in the error message…

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