Aggregate runtime exceptions in Java 8 streams

Question

Let\'s say I have a method which throws a runtime exception. I\'m using a Stream to call this method on items in a list.

class ABC {

    public voi         


        

Answer 1

There are already some implementations of Try monad for Java. I found better-java8-monads library, for example. Using it, you can write in the following style.

Suppose you want to map your values and track all the exceptions:

public String doStuff(String s) {
    if(s.startsWith("a")) {
        throw new IllegalArgumentException("Incorrect string: "+s);
    }
    return s.trim();
}

Let's have some input:

List input = Arrays.asList("aaa", "b", "abc  ", "  qqq  ");

Now we can map them to successful tries and pass to your method, then collect successfully handled data and failures separately:

Map>> result = input.stream()
        .map(Try::successful).map(t -> t.map(this::doStuff))
        .collect(Collectors.partitioningBy(Try::isSuccess));

After that you can process successful entries:

System.out.println(result.get(true).stream()
    .map(t -> t.orElse(null)).collect(Collectors.joining(",")));

And do something with all the exceptions:

result.get(false).stream().forEach(t -> t.onFailure(System.out::println));

The output is:

b,qqq
java.lang.IllegalArgumentException: Incorrect string: aaa
java.lang.IllegalArgumentException: Incorrect string: abc  

I personally don't like how this library is designed, but probably it will be suitable for you.

Here's a gist with complete example.