Trung | Added StringUtils::resizeConsecutiveChars() and related Unit Tests to enrich the StringUtils methods.

Signed-off-by: trungpnt-byte <metopsecret9999@gmail.com>

spring-core/src/main/java/org/springframework/util/StringUtils.java

@@ -1416,4 +1416,63 @@ public abstract class StringUtils {
 		return charSequence.toString();
 	}
 
+	/**
+	 * Resize consecutive characters to repeat a given number of times.
+	 * <p>For example, the string "aaabbbcc" with a appointedChar of 'a' and
+	 * repeatedCount of 2 will return "aabbcc".
+	 * <p>Note that the appointedChar is not removed from the string.
+	 * <p>Note that the repeatedCount is not checked for negative values.
+	 * @param str the string to resize
+	 * @param appointedChar the character to resize
+	 * @param repeatedCount the number of times to repeat the character, default is 1
+	 * @param isRemovedTrailing if true, the trailing characters will be removed
+	 * @param isRemovedLeading if true, the leading characters will be removed
+	 * @return the resized string, or the original string if no changes were made
+	 */
+
+	public static String resizeConsecutiveChars(String str, char appointedChar, @Nullable Integer repeatedCount, boolean isRemovedTrailing, boolean isRemovedLeading) {
+		if (str == null || str.isEmpty()) {
+			return str;
+		}
+		int xTimes = repeatedCount != null ? repeatedCount : 1;
+		char[] collector = new char[str.length()];
+		int collectorIdx = 0;
+		char[] statefulSeparator = new char[1];
+		for (int i = 0; i < str.length(); i++) {
+			char current = str.charAt(i);
+			if (current == appointedChar) {
+				if (statefulSeparator[0] == '\u0000') {
+					statefulSeparator[0] = appointedChar;
+				}
+			} else {
+				if (statefulSeparator[0] == appointedChar) {
+					if (collectorIdx > 0 || !isRemovedLeading) {
+						int repetition = xTimes;
+						while (repetition-- > 0) {
+							collector[collectorIdx++] = appointedChar;
+						}
+						statefulSeparator[0] = '\u0000';
+					}
+				}
+				collector[collectorIdx++] = current;
+			}
+		}
+		if (!isRemovedTrailing && statefulSeparator[0] == appointedChar) {
+			int repetition = xTimes;
+			while (repetition-- > 0) {
+				collector[collectorIdx++] = appointedChar;
+			}
+		}
+		return new String(collector, 0, collectorIdx);
+	}
+
+	/**
+	 * Makes use of resizeConsecutiveChars() sanitize the string to have only one whitespace between words.
+	 * @param str
+	 * @param isTrimmed
+	 * @return the sanitized string
+	 */
+	public static String resizeToOneWhitespace(String str, boolean isTrimmed) {
+		return resizeConsecutiveChars(str, ' ', 1, isTrimmed, isTrimmed);
+	}
 }

spring-core/src/test/java/org/springframework/util/StringUtilsTests.java

@@ -18,7 +18,9 @@ package org.springframework.util;
 
 import java.util.Arrays;
 import java.util.Collections;
+import java.util.LinkedHashMap;
 import java.util.Locale;
+import java.util.Map;
 import java.util.Properties;
 
 import org.junit.jupiter.api.Test;
@@ -817,4 +819,36 @@ class StringUtilsTests {
 		assertThat(StringUtils.truncate(text, 10)).isEqualTo(truncated);
 	}
 
+	@Test
+	void resizeConsecutiveChars() {
+
+		assertThat(StringUtils.resizeConsecutiveChars("11111 111111 111111    111111", '1', 1, false, false)).isEqualTo("1 1 1    1");
+
+		assertThat(StringUtils.resizeConsecutiveChars("aaabbbcc", 'a', 2, false, false)).isEqualTo("aabbbcc");
+
+		assertThat(StringUtils.resizeConsecutiveChars("111111", '1', null, false, false)).isEqualTo("1");
+
+		assertThat(StringUtils.resizeConsecutiveChars(".....$$$42....1424.1.....2.5.12..$!@..$!@%$...", '.', 1, false, false)).isEqualTo(".$$$42.1424.1.2.5.12.$!@.$!@%$.");
+
+		assertThat(StringUtils.resizeConsecutiveChars("1ewjaoij1 a11w11111e11o11iw11 12113121 1", '1', 1, false, false)).isEqualTo("1ewjaoij1 a1w1e1o1iw1 1213121 1");
+
+
+		// resizes whitespaces
+		Map<String, String> cases = new LinkedHashMap<>();
+		cases.put(null, null);
+		cases.put("", "");
+		cases.put("   ", "");
+		cases.put("Hello", "Hello");
+		cases.put("Hello, World!", "Hello, World!");
+		cases.put("Hello,   World!", "Hello, World!");
+		cases.put("a  a       ", "a a");
+		cases.put("  a   c b  ncw   a  c j j j j      j", "a c b ncw a c j j j j j");
+
+		for (Map.Entry<String, String> entry : cases.entrySet()) {
+			String input = entry.getKey();
+			String expected = entry.getValue();
+			assertThat(StringUtils.resizeToOneWhitespace(input, true)).as("actual ").isEqualTo(expected);
+		}
+	}
+
 }