JSP 分页

Oracle大记录数分页借助rownum
select * from ( select a.*, rownum num from (select * from
guestbook order by name desc) a where rownum <= 20 )
where num >=10;

Mysql大记录数分页借助rownum
select * from (select * from guestbook ) aa limit 0,10

借助Pager标签实现分页功能
<dependency>
<groupId>jsptags</groupId>
<artifactId>pager-taglib</artifactId>
<version>2.0</version>
</dependency>

使用方法：
1.MysqlPagination.java

import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.List;
import java.util.regex.Pattern;

import org.apache.commons.dbutils.ResultSetHandler;
import org.apache.commons.dbutils.handlers.MapListHandler;

public class MysqlPagination implements Pagination {
	private int pageSize = 3;
	private int pageNumber = 1;
	private int maxPages;
	private int maxElements;
	private String sql;
	private MysqlUtil db;

	public MysqlPagination(String sql) {
		this.sql = sql;
		init();
	}

	public MysqlPagination(String sql, int pageSize, int pageNumber) {
		this.sql = sql;
		this.pageSize = pageSize;
		this.pageNumber = pageNumber;
		init();
		this.setPageNumber(pageNumber);
	}

	private void init() {
		db = MysqlUtil.getInstance();
		setMaxElements();
		setMaxPages();
	}

	private void setMaxElements() {
		// select * from xxx order by desc
		// select count(1) from xxx order by desc

		String regex = "select((.)+)from";
		Pattern p = Pattern.compile(regex, Pattern.CASE_INSENSITIVE);
		String[] s = p.split(this.sql);
		String newSql = "select count(1) as total from " + s[1];

		ResultSetHandler handler = new ResultSetHandler() {
			public Object handle(ResultSet rs) throws SQLException {
				if (rs.next()) {
					return new Integer(rs.getInt("total"));
				} else {
					return null;
				}
			}
		};
		this.maxElements = (Integer) db.query(newSql, null, handler);
	}

	private void setMaxPages() {
		if (maxElements != 0 && (maxElements % pageSize == 0)) {
			maxPages = maxElements / pageSize;
		} else {
			maxPages = maxElements / pageSize + 1;
		}
	}

	private String sqlModify(String source,int begin, int size){
		System.out.println(begin+", " + size);
		StringBuffer target = new StringBuffer(200);
		target.append("select * from (");
		target.append(sql);
		target.append(") aa limit ");
		target.append(begin);
		target.append(", ");
		target.append(size);
		return target.toString();		
	}

	private int getEndElement() {
		int endElement = pageNumber * pageSize;
		if (endElement >= maxElements) {
			return maxElements;
		} else {
			return endElement;
		}
	}

	private int getBeginElement() {
		return (pageNumber - 1) * pageSize;
	}

	@Override
	public List<Object> getList() {
		String newSql = this.sqlModify(this.sql, this.getBeginElement(), this.pageSize);
		return (List) db.query(newSql, null, new MapListHandler());
	}

	@Override
	public int getMaxElements() {
		return maxElements;
	}

	@Override
	public int getMaxPages() {
		return maxPages;
	}

	@Override
	public int getNext() {
		if (pageNumber + 1 >= this.getMaxPages()) {
			return getMaxPages();
		}
		return pageNumber + 1;
	}

	@Override
	public int getPageNumber() {
		return pageNumber;
	}

	@Override
	public int getPageSize() {		
		return pageSize;
	}

	@Override
	public int getPrevious() {
		if(pageNumber-1<=1){
			return 1;
		}else{
			return pageNumber-1;
		}
	}

	@Override
	public boolean hasNext() {
		return pageNumber<this.getMaxPages();
	}

	@Override
	public boolean hasPrevious() {
		return pageNumber>1;
	}

	@Override
	public boolean isFirst() {
		return pageNumber==1;
	}

	@Override
	public boolean isLast() {
		return pageNumber>=this.getMaxPages();
	}

	@Override
	public void setPageNumber(int pageNumber) {
		if(pageNumber>maxPages){
			this.pageNumber=maxPages;
		}else if(pageNumber<1){
			this.pageNumber=1;			
		}else{
			this.pageNumber=pageNumber;
		}
	}

	@Override
	public void setPageSize(int pageSize) {
		this.pageSize=pageSize;
	}

	// Pagination p = new OraclePagination(sql,20,3);
	   //List list=p.getList();
}

2. GuestbookDAOJdbc.java

        private static final String SELECT_GUESTBOOKS_SQL="select * from guestbook order by id desc";

	@Override
	public Pagination getGuestbookByPage(int pageSize, int pageNumber) {
		Pagination p = new MysqlPagination(SELECT_GUESTBOOKS_SQL,pageSize,pageNumber);
		return p;
	}

3.GetMessagesServlet.java

public class GetMessagesServlet extends HttpServlet {
	private static final long serialVersionUID = 5964428201228635704L;
	private int pageSize;

	public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
		int pageNumber;
		try {
			pageNumber = Integer.parseInt(request.getParameter("p"));
		} catch (Exception e) {
			pageNumber = 1;
		}
		
		GuestbookDAO dao = new GuestbookDAOJdbc();
		Pagination pager=dao.getGuestbookByPage(pageSize, pageNumber);
		
		request.setAttribute("guestbook.pager", pager);		
		request.getRequestDispatcher("/getMessages.jsp").forward(request, response);
	}
	
	public void init(ServletConfig config)throws ServletException{
		super.init(config);
		try{
			this.pageSize=Integer.parseInt(config.getServletContext().getInitParameter("pageSize"));
		}catch(Exception e){
			this.pageSize=10;
		}
	}
}

4.getMessages.jsp

<%@ taglib uri="http://jsptags.com/tags/navigation/pager" prefix="pg"%>

<pg:pager url="${ctx}/servlet/getMessages"	items="${requestScope['guestbook.pager'].maxElements}"	maxPageItems="${initParam.pageSize}"  maxIndexPages="5">
	<pg:index>
		<pg:first unless="current">
			<a href="${pageUrl}&p=${pageNumber}">首页</a>
		</pg:first>
		<pg:prev>
			<a href="${pageUrl}&p=${pageNumber}">上一页(${pageNumber})</a>
		</pg:prev>
		<pg:pages>
			<a href="${pageUrl}&p=${pageNumber}">${pageNumber}</a>				
		</pg:pages>
		<pg:next>
			<a href="${pageUrl}&p=${pageNumber}">下一页(${pageNumber})</a>
		</pg:next>
		<pg:last unless="current">
			<a href="${pageUrl}&p=${pageNumber}">尾页</a>
		</pg:last>
	</pg:index>
</pg:pager>