From d821c410c6de49055c38695671c2055797f045c4 Mon Sep 17 00:00:00 2001
From: TouyamaRie <yangshuo2077@foxmail.com>
Date: Fri, 28 Nov 2025 16:04:46 +0800
Subject: [PATCH] Fix issue 4167

---
 .../java/cn/hutool/core/util/HexUtil.java     | 15 +++++++--
 .../java/cn/hutool/core/util/HexUtilTest.java | 31 +++++++++++++++++++
 2 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/hutool-core/src/main/java/cn/hutool/core/util/HexUtil.java b/hutool-core/src/main/java/cn/hutool/core/util/HexUtil.java
index 0f209c483..1083e2897 100755
--- a/hutool-core/src/main/java/cn/hutool/core/util/HexUtil.java
+++ b/hutool-core/src/main/java/cn/hutool/core/util/HexUtil.java
@@ -379,15 +379,24 @@ public class HexUtil {
 	 * @return 格式化后的字符串
 	 */
 	public static String format(final String hexStr, String prefix) {
+		if (StrUtil.isEmpty(hexStr)) {
+			return StrUtil.EMPTY;
+		}
 		if (null == prefix) {
 			prefix = StrUtil.EMPTY;
 		}
 
 		final int length = hexStr.length();
 		final StringBuilder builder = StrUtil.builder(length + length / 2 + (length / 2 * prefix.length()));
-		builder.append(prefix).append(hexStr.charAt(0)).append(hexStr.charAt(1));
-		for (int i = 2; i < length - 1; i += 2) {
-			builder.append(CharUtil.SPACE).append(prefix).append(hexStr.charAt(i)).append(hexStr.charAt(i + 1));
+
+		for (int i = 0; i < length; i++) {
+			if (i % 2 == 0) {
+				if (i != 0) {
+					builder.append(CharUtil.SPACE);
+				}
+				builder.append(prefix);
+			}
+			builder.append(hexStr.charAt(i));
 		}
 		return builder.toString();
 	}
diff --git a/hutool-core/src/test/java/cn/hutool/core/util/HexUtilTest.java b/hutool-core/src/test/java/cn/hutool/core/util/HexUtilTest.java
index b37f4b3ff..f8e7a0745 100755
--- a/hutool-core/src/test/java/cn/hutool/core/util/HexUtilTest.java
+++ b/hutool-core/src/test/java/cn/hutool/core/util/HexUtilTest.java
@@ -116,4 +116,35 @@ public class HexUtilTest {
 		final String hex3 = "#FF";
 		assertEquals(new BigInteger("FF", 16), HexUtil.toBigInteger(hex3));
 	}
+
+	@Test
+	public void testFormatEmpty() {
+		String result = HexUtil.format("");
+		assertEquals("", result);
+	}
+
+	@Test
+	public void testFormatSingleChar() {
+		String result = HexUtil.format("1");
+		assertEquals("1", result);
+	}
+
+	@Test
+	public void testFormatOddLength() {
+		String result = HexUtil.format("123");
+		assertEquals("12 3", result);
+	}
+
+	@Test
+	public void testFormatWithPrefixSingleChar() {
+		String result = HexUtil.format("1", "0x");
+		assertEquals("0x1", result);
+	}
+
+	@Test
+	public void testFormatWithPrefixOddLength() {
+		String result = HexUtil.format("123", "0x");
+		assertEquals("0x12 0x3", result);
+	}
+
 }