Java Language Joining a stream to a single String


Example

A use case that comes across frequently, is creating a String from a stream, where the stream-items are separated by a certain character. The Collectors.joining() method can be used for this, like in the following example:

Stream<String> fruitStream = Stream.of("apple", "banana", "pear", "kiwi", "orange");

String result = fruitStream.filter(s -> s.contains("a"))
           .map(String::toUpperCase)
           .sorted()
           .collect(Collectors.joining(", "));
           
System.out.println(result);

Output:

APPLE, BANANA, ORANGE, PEAR

The Collectors.joining() method can also cater for pre- and postfixes:

String result = fruitStream.filter(s -> s.contains("e"))
           .map(String::toUpperCase)
           .sorted()
           .collect(Collectors.joining(", ", "Fruits: ", "."));
           
System.out.println(result);

Output:

Fruits: APPLE, ORANGE, PEAR.

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