diff --git a/src/main/java/xyz/zhouxy/plusone/commons/util/IdGenerator.java b/src/main/java/xyz/zhouxy/plusone/commons/util/IdGenerator.java
index e40a988..76f73f7 100644
--- a/src/main/java/xyz/zhouxy/plusone/commons/util/IdGenerator.java
+++ b/src/main/java/xyz/zhouxy/plusone/commons/util/IdGenerator.java
@@ -49,7 +49,8 @@ public class IdGenerator {
     public static SnowflakeIdGenerator getSnowflakeIdGenerator(long workerId, long datacenterId) {
         SnowflakeIdGenerator generator = snowflakePool.get(workerId, datacenterId);
         if (generator == null) {
-            synchronized (IdGenerator.class) {
+            // 其它地方需注意，对 snowflakePool 的操作，也都锁 snowflakePool 对象。
+            synchronized (snowflakePool) {
                 generator = snowflakePool.get(workerId, datacenterId);
                 if (generator == null) {
                     generator = new SnowflakeIdGenerator(workerId, datacenterId);
diff --git a/src/main/java/xyz/zhouxy/plusone/commons/util/PagingParams.java b/src/main/java/xyz/zhouxy/plusone/commons/util/PagingParams.java
new file mode 100644
index 0000000..a636ad1
--- /dev/null
+++ b/src/main/java/xyz/zhouxy/plusone/commons/util/PagingParams.java
@@ -0,0 +1,68 @@
+/*
+ * Copyright 2022-2023 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      https://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package xyz.zhouxy.plusone.commons.util;
+
+import javax.annotation.Nullable;
+
+import xyz.zhouxy.plusone.commons.annotation.StaticFactoryMethod;
+
+/**
+ * PageInfo
+ * 
+ * <p>
+ * 推荐的实现是，请求处理方法用两个 RequestParam 分别接收请求中的 pageNumber 和 size，
+ * 应用服务使用 {@link PagingParams#of(Long pageNumber, Integer size)} 构建 PagingParams 对象,
+ * 用于查询数据库。
+ * </p>
+ * 
+ * @author <a href="https://gitee.com/zhouxy108">ZhouXY</a>
+ */
+public class PagingParams {
+    private final long pageNumber;
+    private final int size;
+    private final long offset;
+
+    private PagingParams(long pageNumber, int size) {
+        this.pageNumber = pageNumber;
+        this.size = size;
+        this.offset = (pageNumber - 1) * size;
+    }
+
+    @StaticFactoryMethod(PagingParams.class)
+    public static PagingParams of(@Nullable Long pageNumber, @Nullable Integer size) {
+        pageNumber = pageNumber == null ? 1 : pageNumber;
+        size = size == null ? 15 : size;
+        return new PagingParams(pageNumber, size);
+    }
+
+    public long getPageNumber() {
+        return pageNumber;
+    }
+
+    public int getSize() {
+        return size;
+    }
+
+    public long getOffset() {
+        return offset;
+    }
+
+    @Override
+    public String toString() {
+        return "PageInfo [pageNumber=" + pageNumber + ", size=" + size + "]";
+    }
+}
diff --git a/src/main/java/xyz/zhouxy/plusone/commons/util/RandomUtil.java b/src/main/java/xyz/zhouxy/plusone/commons/util/RandomUtil.java
new file mode 100644
index 0000000..9375728
--- /dev/null
+++ b/src/main/java/xyz/zhouxy/plusone/commons/util/RandomUtil.java
@@ -0,0 +1,18 @@
+package xyz.zhouxy.plusone.commons.util;
+
+import java.security.SecureRandom;
+
+public final class RandomUtil {
+    private RandomUtil() {
+        throw new IllegalStateException("Utility class");
+    }
+
+    public static String secureRandomStr(char[] sourceCharacters, int length) {
+        SecureRandom random = new SecureRandom();
+        char[] result = new char[length];
+        for (int i = 0; i < length; i++) {
+            result[i] = sourceCharacters[random.nextInt(sourceCharacters.length)];
+        }
+        return String.valueOf(result);
+    }
+}