From 6c68d4658b6faacdf222257f90f3362b2922d432 Mon Sep 17 00:00:00 2001
From: Looly <loolly@gmail.com>
Date: Mon, 10 Jan 2022 08:28:38 +0800
Subject: [PATCH] add hash

---
 CHANGELOG.md                                  |  1 +
 .../cn/hutool/core/lang/hash/KetamaHash.java  | 51 +++++++++++++++++++
 2 files changed, 52 insertions(+)
 create mode 100755 hutool-core/src/main/java/cn/hutool/core/lang/hash/KetamaHash.java

diff --git a/CHANGELOG.md b/CHANGELOG.md
index 2dab59eda..947c1d987 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -7,6 +7,7 @@
 
 ### 🐣新特性
 * 【core   】     增加对null值友好的groupingBy操作的Collector实现，可指定map类型（pr#498@Gitee）
+* 【core   】     增加KetamaHash（issue#2084@Github）
 * 
 ### 🐞Bug修复
 * 【core   】     修复setter重载导致匹配错误（issue#2082@Github）
diff --git a/hutool-core/src/main/java/cn/hutool/core/lang/hash/KetamaHash.java b/hutool-core/src/main/java/cn/hutool/core/lang/hash/KetamaHash.java
new file mode 100755
index 000000000..bc2f3cbf2
--- /dev/null
+++ b/hutool-core/src/main/java/cn/hutool/core/lang/hash/KetamaHash.java
@@ -0,0 +1,51 @@
+package cn.hutool.core.lang.hash;
+
+import cn.hutool.core.exceptions.UtilException;
+import cn.hutool.core.util.StrUtil;
+
+import java.security.MessageDigest;
+import java.security.NoSuchAlgorithmException;
+
+/**
+ * Ketama算法，用于在一致性Hash中快速定位服务器位置
+ *
+ * @author looly
+ * @since 5.7.20
+ */
+public class KetamaHash implements Hash64<String>, Hash32<String> {
+
+	@Override
+	public long hash64(String key) {
+		byte[] bKey = md5(key);
+		return ((long) (bKey[3] & 0xFF) << 24)
+				| ((long) (bKey[2] & 0xFF) << 16)
+				| ((long) (bKey[1] & 0xFF) << 8)
+				| (bKey[0] & 0xFF);
+	}
+
+	@Override
+	public int hash32(String key) {
+		return (int) (hash64(key) & 0xffffffffL);
+	}
+
+	@Override
+	public Number hash(String key) {
+		return hash64(key);
+	}
+
+	/**
+	 * 计算MD5值，使用UTF-8编码
+	 *
+	 * @param key 被计算的键
+	 * @return MD5值
+	 */
+	private static byte[] md5(String key) {
+		final MessageDigest md5;
+		try {
+			md5 = MessageDigest.getInstance("MD5");
+		} catch (NoSuchAlgorithmException e) {
+			throw new UtilException("MD5 algorithm not suooport!", e);
+		}
+		return md5.digest(StrUtil.utf8Bytes(key));
+	}
+}