Java Stream wants to return only failure list

Question

I have an object delivery template, which I want to delete based on a name. String array which contains delivery template name is taken as an input parameter. I use Java Stream to iterate the list. Please find the code below.

    public static List<String> deleteDeliveryTemplates(String... deliveryTemplateNames) {
    List<String> failureList = new ArrayList<String>();
    Stream<String>deliveryTemplateNamesStream= Stream.of(deliveryTemplateNames);
     deliveryTemplateNamesStream.forEach(deliveryTemplateName ->{
        try
        {
            deleteDeliveryTemplate(deliveryTemplateName);
        } catch (Exception e)
        {
            failureList.add(deliveryTemplateName);
        }
    });
    return failureList;
}

Is there a better way in JAVA 8 to return the failure list using stream. For example: using map function of Stream

Answer 1

Just because you can do it in streams, that doesn't mean you should. What you really want is the following:

public static List<String> deleteDeliveryTemplates(String... deliveryTemplateNames) {
    List<String> failures = new ArrayList<>();
    for (String templateName : deliveryTemplateNames) {
        try {
            deleteDeliveryTemplate(templateName);
        } catch (Exception e) {
            // LOG THIS EXCEPTION!
            failures.add(templateName);
        }
    }
    return failures;
}

This code is clean, simple, does one thing. Note that I removed the overspecification of generics on the right-hand-side of the failureList declaration and changed the names of your local variables a bit to make use of the surrounding context.

I also slightly reformatted the brace positions in try-blocks to be more in line with the usual Java conventions. As long as you're consistent, there's nothing wrong with your style though.

Answer 2

It is somewhat unfortunate for streaming when you base your program flow on exceptions. If you want to attempt the delivery deletion and branch on success-or-not, it would be much better to encapsulate this in a function, which returns a success indicator, e.g.:

private boolean attemptDeleteDelivery(String deliveryTemplateName) {
    try {
         deleteDeliveryTemplate(deliveryTemplateName);
         return true;
    }
    catch(Exception e) {
         // yes, log this!
         return false;
    }
}

With this semantic, you can stream and filter

List<String> failureList
= Stream.of(deliveryTemplateNames)
   .filter(dt -> !attemptDeleteDelivery(dt))
   .collect(Collectors.toList());