PageInfo.java

/*
 * JEF - Copyright 2009-2010 Jiyi (mr.jiyi@gmail.com)
 *
 * 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
 *
 *      http://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 jef.tools;

/**
 * 分页计算工具
 * 
 * @author Administrator
 */
public class PageInfo {
	private static final int UNKNOWN = -1;
	private long total = UNKNOWN;// 总条数
	private int rowsPerPage = 10;// 每页面显示的条目数
	private int curPage = 1; // 当前页面
	private int totalPage = UNKNOWN; // 总页数

	private long offset = 0;

	public PageInfo() {
	}

	/**
	 * 设置Offset。即采用偏移模式，即PageInfo的当前页数总是为0。
	 * 
	 * @param offset
	 */
	public void setOffset(int offset) {
		this.offset = offset;
	}

	/**
	 * 根据记录所在的页数来设置页。记录从0开始计数。 例如每页10条时。
	 * 
	 * <pre>
	 * setCurrentPageByOffset(0) == 1
	 * setCurrentPageByOffset(9) == 1
	 * setCurrentPageByOffset(10) == 2
	 * setCurrentPageByOffset(19) == 2
	 * setCurrentPageByOffset(20) == 3
	 * </pre>
	 * 
	 * @param offset
	 * @return 设置后当前的页数
	 */
	public int setCurrentPageByOffset(int offset) {
		if (offset < 0)
			return getCurrentPage();
		long num = offset / rowsPerPage;
		this.curPage = (int) (num + 1);
		this.offset = 0;
		return curPage;
	}

	/**
	 * 设置 curPage 的值 类型 为 int
	 * 
	 * @param curPage
	 *            当面页面从1开始
	 */
	public void setCurPage(int curPage) {
		if (this.curPage < 1) {
			this.curPage = 1;
		} else {
			this.curPage = curPage;
		}
		this.offset = 0;

	}

	/**
	 * 获取 curPage 的信息
	 */
	public int getCurrentPage() {
		if (offset > 0)
			return 0;
		return curPage;
	}

	/**
	 * 构造
	 * 
	 * @param total
	 *            总记录数
	 * @param rowsPerPage
	 *            每页记录数
	 */
	public PageInfo(int total, int rowsPerPage) {
		this.total = total;
		this.rowsPerPage = rowsPerPage;
		sumPage();
	}

	public String toString() {
		StringBuilder sb = new StringBuilder();
		sb.append("Records: " + total);
		sb.append(" \tPage: ").append(getCurrentPage()).append('/').append(totalPage);
		sb.append(" \tCurrentShows: ").append(this.getCurrentRecordRange().toString());
		return sb.toString();
	}

	/**
	 * 获取 总的行数
	 */
	public long getTotal() {
		return total;
	}

	/**
	 * 获取每页行数
	 * 
	 * @return
	 */
	public int getRowsPerPage() {
		return rowsPerPage;
	}

	/**
	 * 设置每页行数
	 */
	public void setRowsPerPage(int pageRow) {
		if (pageRow < 1) {
			throw new IllegalArgumentException("The Page size must greater than zero!, you page size " + pageRow + " is invalid!");
		}
		if (pageRow == this.rowsPerPage)
			return;
		rowsPerPage = pageRow;
		sumPage();
	}

	/**
	 * 设置总行数
	 */
	public void setTotal(long total) {
		if (total == this.total)
			return;
		this.total = (int) total;
		sumPage();
	}

	public boolean hasNext() {
		if (total == UNKNOWN)
			return true;
		return curPage <= totalPage;
	}

	/**
	 * 下一页
	 * 
	 * @return int nextPage
	 */
	public boolean gotoNext() {
		if (totalPage != UNKNOWN && curPage >= totalPage)
			return false;
		curPage++;
		return true;
	}

	/**
	 * 得到上一页
	 * 
	 * @return int prePage
	 */
	public boolean gotoPrev() {
		if (curPage <= 1)
			return false;
		curPage--;
		return true;
	}

	/**
	 * 去第一页
	 * 
	 * @return int firstPage
	 */
	public void gotoFirst() {
		curPage = 1;
	}

	public void gotoLast() {
		curPage = totalPage;
	}

	public int getTotalPage() {
		return totalPage;
	}

	// 返回当前页记录的序号(含头含尾)
	public PageLimit getCurrentRecordRange() {
		long start;
		if (offset > 0) {
			start = offset;
		} else {
			start = rowsPerPage * (curPage - 1);
		}

		if (curPage == totalPage && totalPage != UNKNOWN) {
			long limit=total - start;
			if(limit>Integer.MAX_VALUE){
				throw new IllegalStateException("Rows in page too big:"+ limit);
			}
			return new PageLimit(start, (int)limit);
		} else {
			return new PageLimit(start, rowsPerPage);
		}
	}

	/**
	 * 分页计算
	 */
	private void sumPage() {
		if (total > UNKNOWN) {
			long page = ((total - 1) / rowsPerPage) + 1; // 计算总页面;
			if (page > Integer.MAX_VALUE) {
				throw new IllegalArgumentException("Too many pages:" + page);
			}
			totalPage = (int) page;
		} else {
			totalPage = UNKNOWN;
		}
	}
}