如何在Java中只删除字符串的尾随空格并保留前导空格？

Question

trim()函数删除了尾部和前导空格，但是，如果我只想删除字符串的尾随空格，我该怎么办？

Answer 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); ie, 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

Answer 2

另一种选择是使用Apache Commons StringUtils ，特别是StringUtils.stripEnd

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

Answer 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

Answer 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| 

Answer 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 ' '.

Answer 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.

Answer 7

从JDK11您可以使用stripTrailing ：

String result = str.stripTrailing();

Answer 8

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

trimTrailingWhitespace

Answer 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);
}

Answer 10

String value= "Welcome to java ";

So we can use

value = value.trim();