handle exceptions in stream java 8

Question

I have a string:

"1, 2, 3 , -4"

it is split by ", ". I have a function to convert a number to a enum type which works fine. I want to use java 8 to convert this string to a list of enum objects.

Pattern pattern = Pattern.compile(", ");
List<f> fList = pattern.splitAsStream(str)
  .map(s -> {
    try {
      return this.getEnumObject(Integer.valueOf(s), f.class);
    }
    catch (NoEleException e) {
      e.printStackTrace();
    }
  })
  .collect(Collectors.toList());

This gives me an error:

missing return type.

How could I fix it?

Answer 1

Currently, if an exception occurs no result will be returned hence the compilation error. You'll need to return a value after the catch block .

Answer 2

Basically to ways of managing this:

1. catching the exception and return some value or encapsulate values in Optionals and filter accordingly
2. Throwing a RuntimeException which chains the original one

In the first case we use Optional to put something into the stream on error, and then manage these empty values further in the stream:

pattern.splitAsStream(str)
.map(s -> {
  try {
    return Optional.of(this.getEnumObject(Integer.valueOf(s), f.class));
  }
  catch (NoEleException e) {
    e.printStackTrace();
    return Optional.empty();
  }
 })
.filter(Optional::isPresent) // remove empty optionals
.map(Optional::get) // unwrap them
.collect(Collectors.toList());

In the second case the stream is stopped and you can then try to catch the RuntimeException and unchain the original one:

pattern.splitAsStream(str)
.map(s -> {
  try {
    return Optional.of(this.getEnumObject(Integer.valueOf(s), f.class));
  }
  catch (NoEleException e) {
    e.printStackTrace();
    throw new RuntimeException(e); // stop the stream
  }
 })
.collect(Collectors.toList());