另类的缓存分页并读取过程先读取缓存数据

package com.zly.app.common.page; import java.util.List; import com.zly.app.common.dto.DTO; import com.zly.app.common.page.policy.CachePolicy; @SuppressWarnings({ "hiding", "unchecked" }) public abstract class PageImpl<DTO> implements Page { /** * 默认每页条数 */ private static final int DEFAULT_PAGE_CAPACITY = 20; /** * 默认缓存页数 */ private static final int DEFAULT_CACHE_PAGE_NUM = 10; /** * 缓存策略 */ private CachePolicy policy; /** * 总记录数 */ private long total; /** * 最大页码 */ private int maxPageIndex; /** * 当前页码 */ private int curr; /** * 缓存集 */ private List<DTO> cache; /** * 页数 */ private int pageCapacity; /** * 总共缓存页数 */ private int cachePageNum; /** * 缓存启始页 */ private int cachePageStartIndex; /** * 缓存结果页 */ private int cachePageEndIndex; /** * 获取接口对象 */ public Page getPageInstance() { return this; } /** * 初始化 */ public void init() { if (pageCapacity == 0) { pageCapacity = DEFAULT_PAGE_CAPACITY; } if (cachePageNum == 0) { cachePageNum = DEFAULT_CACHE_PAGE_NUM; } total = getTotal(); maxPageIndex = (int)(Math.round(Math.ceil(total*1.0/pageCapacity))-1); rebuildCache(0); curr = -1; } /** * 获取总记录，数据来源数据库. * @return */ public abstract int getTotal(); /** * 获取区间数据，数据来源数据库<或FILE与XML> * @param startOffset * @param endOffset * @return */ public abstract List<DTO> getRecord(int startOffset, int endOffset); /** * 获取当前页数据 * @return 当前数据集 */ public List<DTO> getCurrentPage() { return getPage(curr); } /** * 获取当前页编号 * @return 当前编号 */ public int getCurrentPageIndex() { return curr; } /** * 获取下一页数据集 * @return 下一页数据集 */ public List<DTO> getNextPage() { if (curr+1 <= maxPageIndex) { return getPage(curr+1); } return getPage(curr); } /** * 获取上一页数据集 * @return 上一页数据集 */ public List<DTO> getPerviousPage() { if (curr-1 >= 0) { return getPage(curr-1); } return getPage(curr); } /** * 是否有下一页 * @return 返回true有下一页，则false没有下一页. */ public boolean hasNextPage() { return curr < maxPageIndex; } /** * 是否有下上页 * @return 返回true有下上页，则false没有下上页. */ public boolean hasPerviousPage() { return curr > 0; } @Override public int moveToPage(int pageIndex) { if (pageIndex > maxPageIndex) { curr = maxPageIndex; } else if (pageIndex < 0) { curr = 0; } else { curr = pageIndex; } return curr; } /** * 设置页数 */ public int getPageCapacity() { return pageCapacity; } public void setPageCapacity(int pageCapacity) { this.pageCapacity = pageCapacity; } /** * 设置总共缓存页数 */ public int getCachePageNum() { return cachePageNum; } public void setCachePageNum(int cachePageNum) { this.cachePageNum = cachePageNum; } /** * 设置缓存策略 */ public CachePolicy getPolicy() { return policy; } public void setPolicy(CachePolicy policy) { this.policy = policy; } /** * 设置最大页码 */ public int getMaxPageIndex() { return maxPageIndex; } public void setMaxPageIndex(int maxPageIndex) { this.maxPageIndex = maxPageIndex; } private List<DTO> getPage(int pageIndex) { int index = policy.getRebuildIndex( total, cachePageStartIndex, cachePageEndIndex, cachePageNum, pageCapacity, pageIndex); if (index != -1) { rebuildCache(index); } int tmpStartIndex; int tmpEndIndex; tmpStartIndex = (pageIndex-cachePageStartIndex) * pageCapacity; tmpEndIndex = tmpStartIndex + pageCapacity; if (tmpEndIndex > cache.size()) { tmpEndIndex = cache.size(); } List<DTO> tmpList = cache.subList( tmpStartIndex, tmpEndIndex ); curr = pageIndex; return tmpList; } private void rebuildCache(int pageIndex) { int tmpStartIndex; int tmpEndIndex; tmpStartIndex = pageIndex * pageCapacity; tmpEndIndex = (pageIndex + cachePageNum) * pageCapacity; cache = getRecord(tmpStartIndex, tmpEndIndex); cachePageStartIndex = pageIndex; cachePageEndIndex = pageIndex + (int)Math.round(Math.ceil(cache.size()*1.0 / pageCapacity))-1; } }