What is a good alternative of LTRIM and RTRIM in Java?

What is a good alternative of JavaScript ltrim() and rtrim() functions in Java?

With a regex you could write:

String s = ...
String ltrim = s.replaceAll("^\\s+","");
String rtrim = s.replaceAll("\\s+$","");

If you have to do it often, you can create and compile a pattern for better performance:

private final static Pattern LTRIM = Pattern.compile("^\\s+");

public static String ltrim(String s) {
    return LTRIM.matcher(s).replaceAll("");
}

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From a performance perspective, a quick micro benchmark shows (post JIT compilation) that the regex approach is about 5 times slower than the loop (0.49s vs. 0.11s for 1 million ltrim).

I personally find the regex approach more readable and less error prone but if performance is an issue you should use the loop solution.

Using regex may be nice, but it's quite a lot slower than a simple trimming functions:

public static String ltrim(String s) {
    int i = 0;
    while (i < s.length() && Character.isWhitespace(s.charAt(i))) {
        i++;
    }
    return s.substring(i);
}

public static String rtrim(String s) {
    int i = s.length()-1;
    while (i >= 0 && Character.isWhitespace(s.charAt(i))) {
        i--;
    }
    return s.substring(0,i+1);
}

Source: http://www.fromdev.com/2009/07/playing-with-java-string-trim-basics.html

Also, there are some libraries providing such functions. For example, Spring StringUtils. Apache Commons StringUtils provides similar functions too: strip, stripStart, stripEnd

StringUtils.stripEnd("abc  ", null)    = "abc"

import org.apache.commons.lang3.StringUtils;

private String rTrim(String str) {
    return StringUtils.stripEnd(str, /*stripChars*/" ");
}

private String lTrim(String str) {
    return StringUtils.stripStart(str, /*stripChars*/" ");
}

You can simply try the following

String s = "  Hello world  "

String ltrim = s.stripLeading();

String rtrim = s.stripTrailing();

Guava has CharMatcher trimLeadingFrom and trimTrailingFrom

e.g. CharMatcher.whitespace.trimTrailingFrom(s)

Based on the answer of @bezmax I had a look at the Spring StringUtils, but it couldn't justify the overload for me of switching to the Spring framework. Therfore I decided to create a Characters class to easily left / right trim strings for any given character(-class). The class is available on GitHub.

Characters.valueOf('x').trim( ... )
Characters.valueOf('x').leftTrim( ... )
Characters.valueOf('x').rightTrim( ... )

If you would like to trim for whitespaces, there is a predefined character-class available:

Characters.WHITESPACE.trim( ... )
Characters.WHITESPACE.leftTrim( ... )
Characters.WHITESPACE.rightTrim( ... )

The class does feature also other kinds of character operations, such condense, replace or split.

Might be a bit cheap, but you might also use these without any other library:

final var string = "   Hello World   ";

final var rtrimmed = ("." + string).trim().substring(1);
// => "   Hello World"

var ltrimmed = (string + ".").trim();
ltrimmed = ltrimmed.substring(0, ltrimmed.length - 1);
// => "Hello World   "

I admit, that the ltrimmed is not that pretty, but it will do the trick.