Java 8 Stream String Null Or Empty Filter

Question

I\'ve got Google Guava inside Stream:

this.map.entrySet().stream()
.filter(entity -> !Strings.isNullOrEmpty(entity.getValue()))
.map(obj -> String.form         


        

Answer 1

In java 11 there is a new method Predicate::not.

So you can filter out empty string :

list.stream()
  .filter(Objects::nonNull)
  .filter(Predicate.not(String::isEmpty))

Answer 2

If you prefer to use commons-lang3, StringUtils has

• isEmpty()
• isNotEmpty()
• isBlank()
• isNotBlank()

These methods can be used in filters as method references:

this.stringList.stream().filter(StringUtils::isNotBlank);

or as lambdas:

this.stringList.stream().filter(s -> StringUtils.isNotBlank(s));

Answer 3

You can write your own predicate:

final Predicate<Map.Entry<?, String>> valueNotNullOrEmpty
    = e -> e.getValue() != null && !e.getValue().isEmpty();

Then just use valueNotNullOrEmpty as your filter argument.

Answer 4

It works for me: list.stream().filter(el-> el != null && !el.toString().trim().isEmpty()).collect(Collectors.toList());

Answer 5

You can create your own Strings class with your own predicate:

public class Strings {
  public static boolean isNotNullOrEmpty (String str) {
    return str != null && !str.isEmpty();
  }
}

Then in your code:

.filter(Strings::isNotNullOrEmpty)

But as @fge mentionned, you can't use that on a Map.Entry<?,?>...

Answer 6

You can break down the filter into two steps:

this.map.entrySet().stream()
    .filter(entity -> entity.getValue() != null)
    .filter(entity -> !entity.getValue().isEmpty())
    .map(obj -> String.format("%s=%s", obj.getKey(), obj.getValue()))
    .collect(Collectors.joining(","))

On a side note, most Map.Entry.toString() implementations do exactly what you're doing in map(), so you could theoretically just do map(Map.Entry::toString). But I wouldn't rely on that unless you're producing a toString() or something that doesn't require documented or deterministic behavior.

Also, I know you want to abandon Guava, but here's a solution that might make you reconsider:

Joiner.on(',').withKeyValueSeparator("=")
      .join(Maps.filterValues(map, Predicates.not(Strings::isNullOrEmpty)));