jodd-core/src/main/java/jodd/util/StringUtil.java
public static String compressChars(final String s, final char c) {
		int len = s.length();
		StringBuilder sb = new StringBuilder(len);
		boolean wasChar = false;
		for (int i = 0; i < len; i++) {
			char c1 = s.charAt(i);
			if (c1 == c) {
				if (wasChar) {
					continue;
				}
				wasChar = true;
			} else {
				wasChar = false;
			}
			sb.append(c1);
		}
		if (sb.length() == len) {
			return s;
		}
		return sb.toString();
	}
public static String compressChars(final String s, final char c) {
		int len = s.length();
		StringBuilder sb = new StringBuilder(len);
		boolean wasChar = false;
		for (int i = 0; i < len; i++) {
			char c1 = s.charAt(i);
			if (c1 == c) {
				if (wasChar) {
					continue;
				}
				wasChar = true;
			} else {
				wasChar = false;
			}
			sb.append(c1);
		}
		if (sb.length() == len) {
			return s;
		}
		return sb.toString();
	}
Compress multiple occurrences of given char into one appearance.