java8 StringJoiner 과 String.join 활용

http://www.slideshare.net/jpaumard/java-se-8-for-java-ee-developers

자바 8에서 전부터 숙원했던, SpringJoiner 와 더불어 String.join(...)이 구현 되었다.

Comparator 체인 또는 필드 기반의 비교를 가능하게 하는 새로운 방식을 제안하고 있단다.

Spring Pool의 기본값이 25k ~ 50K 까지 확장 되었다고 한다. 

SpringJoiner is used to construct of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix.

Prior to adding something to the StringJoiner , its sj.toString() method will, by default, return prefix + suffix .

However , if the setEmptyValue method is called, the emptyValue supplied will be returned instead.

This can be used, for example, when creating a string using set notation to indicate an empty set,

i.e. "{}", where the prefix is "{", the suffix is "}" and nothing has been added to the StringJoiner.

아래는 예제입니다. 

The String "[George:Sally:Fred]" may be constructed as follows : 

StringJoiner sj = new StringJoiner(":","[","]");

sj.add("George").add("Sally").add("Fred");

String desiredString = sj.toString();

A StringJoiner may be employed to create formatted output from a Stream using Collectors.joining(CharSequence).

List<Integer> numbers = Arrays.asList(1,2,3,4);

String commaSeparatedNumbers = numbers.stream().map(i -> i.toString()).collect(Collectors.joining(", "));

이번에는 String join을 활용해보자.

1) public static String join(CharSequence delimiter , CharSequence ... elements)

String message = String.join("-", "Java" , "is" , "Cool");

//message returned is "Java-is-Cool"

두번째는 

2) public static String join(CharSequence delimiter , Iterator<? extends CharSequence> elements)

List<String> strings = new LinkedList<>();

strings.add("Java");

strings.add("is");

strings.add("Cool");

String message = String.join(" " , strings);

//message returned is "Java is Cool"

Set<String> strings = new LinkedHashSet<>();

strings.add("Java");

strings.add("is");

strings.add("very");

strings.add("cool");

String message = String.join("-",strings);

//message return is : "Java-is-very-cool"

그렇다.