添加 PagingParams 类。

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 + "]";
+    }
+}