How would you use streams or lambda instead of for loop in this example?

Question

I would like to rewrite this function using streams if possible.

public void onTransfer(TransferEvent event) {

    StringBuilder builder = new StringBuilder();
    for (Object item : event.getItems()) {
        Permission perm = Permission.valueOf((String) item);

        try {
            if (event.isAdd()) {
                currentRole.add(perm);
            } else {
                currentRole.remove(perm);
            }
        } catch (Exception e) {
            addErrorMessage("", e.getLocalizedMessage());
            LOGGER.error(e.getMessage(), e);
        }
        builder.append(perm.name()).append(";");
    }

    addMessage("", "Transfered permissions " + builder.toString() + " from/to role :" + currentRole.getName());
}

Thank you in advance!

Why? This task is not really suitable for streams, having side effects. — RealSkeptic, Nov 03 '20 at 12:31
It's an excercise for me given by my employer. I should either use streams or lambda — user5918, Nov 03 '20 at 13:12
Whilst fully agreeing that this method has side effects and therefore not really suited to the use of streams, I would see if me IDE would perhaps offer a refactor of the `for` loop to a `stream.forEach`. It would meet youre employers criteria I believe and depending on your taste it might be considered more readable. Though you might also want to extract the logic inside the loop to a private method. — Gavin, Nov 03 '20 at 13:19

MDK · Accepted Answer · 2020-11-03T15:14:42.187

0

Rewriting this to stream-functions would look like this:

event.getItems().stream()
    .map(item -> Permission.valueOf((String) item))
    .forEach(perm -> {try-clause})
addMessage(event.getItems().stream()
    .map(item -> Permission.valueOf((String) item).name())
    .collect(Collectors.joining(";", "Transfered permissions ", " from/to role :" + currentRole.getName()));

edited Nov 03 '20 at 15:14

answered Nov 03 '20 at 14:19

MDK

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3
14

Note this could not get properly tested without all the other classes. – MDK Nov 03 '20 at 14:19
Thank you! Is there a way doing it without peek or is this the only way? – user5918 Nov 03 '20 at 14:46
Thanks for pointing that out @RealSkeptic, I forgot about that issue. I now corrected it to a better approach. Reference: https://stackoverflow.com/questions/33635717/in-java-streams-is-peek-really-only-for-debugging – MDK Nov 03 '20 at 15:16
There is someting missing, after transfered permission there also needs to be included the + builder.toString() + like above inside collectors joining. I fixed it myself thanks for the rest :) – user5918 Nov 04 '20 at 11:44
The collect operation should correctly replace your stringbuilder though, concatenating all names seperated by ;. If I made a mistake please edit the answer so future readers get the correct solution. – MDK Nov 04 '20 at 11:49

How would you use streams or lambda instead of for loop in this example?

1 Answers1