Lookup enum value in a map to initialise list

Question

Given I have the following

Map

and call to

writeMetadata(...)

:

Map<Report, TransferStatus> transferStatusMap = sftpService.transfer(reportDeliverables);



dbMetadataWriter.writeMetadata(successReports);

ENUM

as:

public enum TransferStatus {

    SUCCESS,

    FAILURE

}

Firstly, how can I create the

successReport

list with all

Report

with status

TransferStatus.SUCCESS

with Java 8?

Secondly, before call to

dbMetadataWriter.writeMetadata(successReports);

there should be a check to see if any values with success exist.

and finally, in general how should failed transfers be handled? Practically, what is best practice?

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Answer 1

 List<Report> successReports = transferStatusMap.entrySet()
          .stream()
          .filter(e -> e.getValue() == TransferStatus.SUCCESS)
          .map(Entry::getKey)
          .collect(Collectors.toList());

 if(!reports.isEmpty()){
     dbMetadataWriter.writeMetadata(successReports);
 }

Or you could collect them both to a Map:

Map<TransferStatus, List<Report>> map = 
     transferStatusMap.entrySet()
                      .stream()
                      .collect(Collectors.groupingBy(
                            Entry::getValue,
                            Collectors.mapping(Entry::getKey, Collectors.toList()));

Lookup enum value in a map to initialise list

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