Java内存分页工具

代码如下：

import org.springframework.data.domain.Pageable;

import java.util.ArrayList;
import java.util.List;

/**
 * 内存分页工具
 * @author chenb
 */
public class RamPager<T> {
    private static final int DEFAULT_PAGE_SIZE = 20;

    private List<T> data;
    private Pageable pageable;

    public RamPager(List<T> data, Pageable pageable) {
        this.data = data;
        this.pageable = pageable;
    }

    public List<T> page() {
        if (data == null || data.isEmpty()) {
            return new ArrayList<>();
        }
        int pageNum = pageable == null ? 1 : pageable.getPageNumber() + 1;
        int pageSize = pageable == null ? DEFAULT_PAGE_SIZE : pageable.getPageSize();
        if (pageNum < 0) {
            pageNum = 1;
        }
        int from = (pageNum - 1) * pageSize;
        int to = pageNum * pageSize;
        if (to > data.size()) {
            to = data.size();
        }
        if (from >= data.size() || to <= from) {
            return new ArrayList<>();
        }
        return data.subList(from, to);
    }
}

• 各类特殊情况都返回空的List
• pageable接口页码从0开始（与Spring Data JPA相匹配）
• 默认pageSize为20