How to remove only trailing spaces of a string in Java and keep leading spaces?

问题

The trim() function removes both the trailing and leading space, however, if I only want to remove the trailing space of a string, how can I do it?

回答1:

Since JDK 11

If you are on JDK 11 or higher you should probably be using stripTrailing().

---

Earlier JDK versions

Using the regular expression \s++$, you can replace all trailing space characters (includes space and tab characters) with the empty string ("").

final String text = "  foo   ";
System.out.println(text.replaceFirst("\\s++$", ""));

Output

  foo

Online demo.

Here's a breakdown of the regex:

• \s – any whitespace character,
• ++ – match one or more of the previous token (possessively); i.e., match one or more whitespace character. The + pattern is used in its possessive form ++, which takes less time to detect the case when the pattern does not match.
• $ – the end of the string.

Thus, the regular expression will match as much whitespace as it can that is followed directly by the end of the string: in other words, the trailing whitespace.

The investment into learning regular expressions will become more valuable, if you need to extend your requirements later on.

References

• Java regular expression syntax

回答2:

Another option is to use Apache Commons StringUtils, specifically StringUtils.stripEnd

String stripped = StringUtils.stripEnd("   my lousy string    "," ");

回答3:

I modified the original java.lang.String.trim() method a bit and it should work:

  public String trim(String str) {
        int len = str.length();
        int st = 0;

        char[] val = str.toCharArray();

        while ((st < len) && (val[len - 1] <= ' ')) {
            len--;
        }
        return str.substring(st, len);
    }

Test:

  Test test = new Test();
  String sample = "            Hello World               "; // A String with trailing and leading spaces
  System.out.println(test.trim(sample) + " // No trailing spaces left");

Output:

        Hello World // No trailing spaces left

回答4:

The most practical answer is @Micha's, Ahmad's is reverse of what you wanted so but here's what I came up with in case you'd prefer not to use unfamiliar tools or to see a concrete approach.

public String trimEnd( String myString ) {

    for ( int i = myString.length() - 1; i >= 0; --i ) {
        if ( myString.charAt(i) == ' ' ) {
            continue;
        } else {
            myString = myString.substring( 0, ( i + 1 ) );
            break;
        }
    }
    return myString;
}

Used like:

public static void main( String[] args ) {

    String s = "    Some text here   ";
    System.out.println( s + "|" );
    s = trimEnd( s );
    System.out.println( s + "|" );
}

Output:

Some text here   |
Some text here|

回答5:

The best way in my opinion:

public static String trimEnd(String source) {
    int pos = source.length() - 1;
    while ((pos >= 0) && Character.isWhitespace(source.charAt(pos))) {
        pos--;
    }
    pos++;
    return (pos < source.length()) ? source.substring(0, pos) : source;
}

This does not allocate any temporary object to do the job and is faster than using a regular expression. Also it removes all whitespaces, not just ' '.

回答6:

Here's a very short, efficient and easy-to-read version:

public static String trimTrailing(String str) {
    if (str != null) {
        for (int i = str.length() - 1; i >= 0; --i) {
            if (str.charAt(i) != ' ') {
                return str.substring(0, i + 1);
            }
        }
    }
    return str;
}

As an alternative to str.charAt(i) != ' ' you can also use !Character.isWhitespace(str.charAt(i) if you want to use a broader definition of whitespace.

回答7:

As of JDK11 you can use stripTrailing:

String result = str.stripTrailing();

回答8:

Spring framework gives a useful org.springframework.util.StringUtils.

trimTrailingWhitespace

回答9:

This code is intended to be read a easily as possible by using descriptive names (and avoiding regular expressions).

It does use Java 8's Optional so is not appropriate for everyone.

public static String removeTrailingWhitspace(String string) {
    while (hasWhitespaceLastCharacter(string)) {
        string = removeLastCharacter(string);
    }
    return string;
}

private static boolean hasWhitespaceLastCharacter(String string) {
    return getLastCharacter(string)
            .map(Character::isWhitespace)
            .orElse(false);
}

private static Optional<Character> getLastCharacter(String string) {
    if (string.isEmpty()) {
        return Optional.empty();
    }
    return Optional.of(string.charAt(string.length() - 1));
}

private static String removeLastCharacter(String string) {
    if (string.isEmpty()) {
        throw new IllegalArgumentException("String must not be empty");
    }
    return string.substring(0, string.length() - 1);
}

回答10:

String value= "Welcome to java ";

So we can use

value = value.trim();

来源：https://stackoverflow.com/questions/16974267/how-to-remove-only-trailing-spaces-of-a-string-in-java-and-keep-leading-spaces