通用分页的概念

通用分页简而言之就是通用，可以多次使用，是为了提高代码的复用性的。

实现效果

这个效果和之前有一点不一样，追加了部分bootstrap样式，分页条也改变了，这个分页条展示的当前页码加前四页和后五页的页码，嘿嘿嘿比之前的高端了不少吧！

通用分页后台代码的思维

通用分页的后台代码主要就是BaseDao方法，它取代了我们之前做分页的查询办法，做成了一个通用的查询方法，像下面：

然后前台展示和后台查询结果的衔接主要是靠pageBean和servlet中的代码，pageBean负责存储页面的属性和请求，servlet负责是控制，初始化pageBean和利用pageBean来查询数据。

需要的工具

工具类：连接数据库类、字符编码过滤类、做通用分页的类、判断字符串工具类、连接数据库的配置文件
jar包：

代码解读

后台做通用的dao方法，可以看到赋值那块利用了反射来获取属性然后循环逐个赋值，这小小的几条代码可是很节省代码的勒，因为我们以前赋值的时候需要一个一个读取出来然后赋值，反射这个小技巧就很棒博主就很爱！

package com.zengjing.dao;import java.lang.reflect.Field;
import java.sql.Connection;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.util.ArrayList;
import java.util.List;import com.zengjing.entity.Book;
import com.zengjing.util.DBAccess;
import com.zengjing.util.PageBean;
import com.zengjing.util.StringUtils;public class BaseDao<K> {public List<K> executeQuery(String sql, Class clz,PageBean pagebean) throws Exception{List<K> ls=new ArrayList<K>();Connection con = DBAccess.getConnection();PreparedStatement ps = con.prepareStatement(sql);ResultSet rs=null;if(pagebean!=null && pagebean.isPagination()) {//想分页String countSql=getCountSql(sql);ps = con.prepareStatement(countSql);rs=ps.executeQuery();if(rs.next()) {pagebean.setTotal(rs.getObject(1).toString());}//展示想要看到的数据 比如说第三条的数据String pageSql=getPageSql(sql,pagebean);ps = con.prepareStatement(pageSql);rs=ps.executeQuery();}else {//不想分页ps = con.prepareStatement(sql);rs=ps.executeQuery();}while(rs.next()) {//ls.add(new Book(rs.getInt("bid"), rs.getString("bname"), rs.getString("price")));K k=(K)clz.newInstance();//Field[] fields = clz.getDeclaredFields();for (Field f : clz.getDeclaredFields()) {f.setAccessible(true);f.set(k, rs.getObject(f.getName()));}ls.add(k);}DBAccess.close(con, ps, rs);return ls;}private String getCountSql(String sql) {// TODO Auto-generated method stubreturn "select count(1) from ("+sql+") t";}private String getPageSql(String sql, PageBean pagebean) {// TODO Auto-generated method stubreturn sql+" limit "+pagebean.getStartIndex()+","+pagebean.getRows();}}

pageBean类嘛，就主要是关于页面的一些属性：页码（page）、页的行数（rows），总记录数（total），baseDao中传一个pagebean也是为了传递这些页码的属性：

package com.zengjing.util;import java.util.HashMap;
import java.util.Map;import javax.servlet.http.HttpServletRequest;/*** 分页工具类**/
public class PageBean {private int page = 1;// 页码private int rows = 10;// 页大小private int total = 0;// 总记录数private boolean pagination = true;// 是否分页//上一次查询所携带的查询条件private Map<String, String[]> parameterMap=new HashMap<String, String[]>();//上一次查询的urlprivate String url;public void setRequest(HttpServletRequest req) {//初始化jsp页面传递过来的当前页this.setPage(req.getParameter("page"));//初始化jsp页面传递过来的页大小this.setRows(req.getParameter("rows"));//初始化jsp页面传递过来的是否分页this.setPagination(req.getParameter("pagination"));//保留上一次的查询请求this.setUrl(req.getRequestURI().toString());//保留上一次的查询条件this.setParameterMap(req.getParameterMap());}private void setPagination(String parameter) {//只有填写了false才代表不分页this.setPagination(!"false".equals(parameter));}private void setRows(String parameter) {if(StringUtils.isNotBlank(parameter))this.rows=(Integer.valueOf(parameter));}private void setPage(String parameter) {if(StringUtils.isNotBlank(parameter))this.page=(Integer.valueOf(parameter));}public Map<String, String[]> getParameterMap() {return parameterMap;}public void setParameterMap(Map<String, String[]> parameterMap) {this.parameterMap = parameterMap;}public String getUrl() {return url;}public void setUrl(String url) {this.url = url;}public PageBean() {super();}public int getPage() {return page;}public void setPage(int page) {this.page = page;}public int getRows() {return rows;}public void setRows(int rows) {this.rows = rows;}public int getTotal() {return total;}public void setTotal(int total) {this.total = total;}public void setTotal(String total) {this.total = Integer.parseInt(total);}public boolean isPagination() {return pagination;}public void setPagination(boolean pagination) {this.pagination = pagination;}/*** 获得起始记录的下标* * @return*/public int getStartIndex() {return (this.page - 1) * this.rows;}@Overridepublic String toString() {return "PageBean [page=" + page + ", rows=" + rows + ", total=" + total + ", pagination=" + pagination + "]";}//上一页public int getPrevPage() {return this.page>1?this.page-1:this.page;}//下一页public int getNextPage() {return this.page < this.getMaxPage()? this.page+1:this.page;}//最大页public int getMaxPage() {return this.total % this.rows == 0 ? this.total/this.rows : (this.total/this.rows)+1;}
}

前台后台的桥梁servlet：

package com.zengjing.web;import java.io.IOException;
import java.util.List;import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;import com.zengjing.dao.BookDao;
import com.zengjing.entity.Book;
import com.zengjing.util.PageBean;
@WebServlet(name="book",urlPatterns="/book.action")
public class BookAction extends HttpServlet{private static final long serialVersionUID = 1L;private BookDao bd=new BookDao();@Overrideprotected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {doPost(req, resp);}@Overrideprotected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {Book b=new Book();b.setBname(req.getParameter("bname"));PageBean pageBean=new PageBean();pageBean.setRequest(req);try {List<Book> list=this.bd.list(b, pageBean);req.setAttribute("bookList", list);req.setAttribute("pageBean", pageBean);req.getRequestDispatcher("/bookList.jsp").forward(req, resp);} catch (Exception e) {// TODO: handle exception}}
}

前台运用到的分页自定义标签，拼接的也是上方效果图中那个分页条：

package com.zengjing.tag;import java.util.Map;
import java.util.Map.Entry;
import java.util.Set;import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.tagext.BodyTagSupport;import com.zengjing.util.PageBean;public class PageTag extends BodyTagSupport{private static final long serialVersionUID = 1L;private PageBean pageBean;public PageBean getPageBean() {return pageBean;}public void setPageBean(PageBean pageBean) {this.pageBean = pageBean;}@Overridepublic int doStartTag() throws JspException {JspWriter out=pageContext.getOut();try {out.print(toHTML());} catch (Exception e) {e.printStackTrace();}return super.doStartTag();}private String toHTML() {StringBuilder sb=new StringBuilder();//将上一次查询的form表单的html拼接sb.append("<form id='pageBeanForm' action='"+pageBean.getUrl()+"' method='post'>");//查询第几页的数据sb.append("<input type='hidden' name='page'>");Map<String, String[]> parameterMap = pageBean.getParameterMap();if(parameterMap.size()>0) {Set<Entry<String,String[]>> entrySet = parameterMap.entrySet();for (Entry<String, String[]> entry : entrySet) {if(!"page".equals(entry.getKey())) {for(String val:entry.getValue()) {sb.append("<input type='hidden' value='"+val+"' name='"+entry.getKey()+"' />");}}}}sb.append("</form>");//默认展示前面4页，当前页，后面5页int page=pageBean.getPage();int max=pageBean.getMaxPage();int before=page>4?4:page-1;int after=10-1-before;after=max-page > after ?after:max-page;//用来控制上一页的点击按钮boolean startFlag = page>1;//用来控制下一页 的点击按钮特效的boolean endFlag = page<max;//      拼接分页条sb.append("<ul class='pagination'>");sb.append("<li class='page-item "+(startFlag ? "disabled" : "")+"'><a class='page-link' href='javascript:gotoPage(1)'>首页</a></li>");sb.append("<li class='page-item "+(startFlag ? "disabled" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.getPrevPage()+")'>&lt;</a></li>");//      代表了当前页的前4页for (int i = before; i > 0 ; i--) {sb.append("<li class='page-item'><a class='page-link' href='javascript:gotoPage("+(page-i)+")'>"+(page-i)+"</a></li>");}sb.append("<li class='page-item active'><a class='page-link' href='javascript:gotoPage("+pageBean.getPage()+")'>"+pageBean.getPage()+"</a></li>");//      代表了当前页的后5页for (int i = 1; i <= after; i++) {sb.append("<li class='page-item'><a class='page-link' href='javascript:gotoPage("+(page+i)+")'>"+(page+i)+"</a></li>");}sb.append("<li class='page-item "+(endFlag ? "disabled" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.getNextPage()+")'>&gt;</a></li>");sb.append("<li class='page-item "+(endFlag ? "disabled" : "")+"'><a class='page-link' href='javascript:gotoPage("+pageBean.getMaxPage()+")'>尾页</a></li>");sb.append("<li class='page-item go-input'><b>到第</b><input class='page-link' type='text' id='skipPage' name='' /><b>页</b></li>");sb.append("<li class='page-item go'><a class='page-link' href='javascript:skipPage()'>确定</a></li>");sb.append("<li class='page-item'><b>共"+pageBean.getTotal()+"条</b></li>");sb.append("</ul>");//      拼接分页的js代码sb.append("<script type='text/javascript'>");sb.append("function gotoPage(page) {");sb.append("document.getElementById('pageBeanForm').page.value = page;");sb.append("document.getElementById('pageBeanForm').submit();");sb.append("}");sb.append("function skipPage() {");sb.append("var page = document.getElementById('skipPage').value;");sb.append("if (!page || isNaN(page) || parseInt(page) < 1 || parseInt(page) > "+max+") {");sb.append("alert('请输入1~N的数字');");sb.append("return;");sb.append("}");sb.append("gotoPage(page);");sb.append("}");sb.append("</script>");return sb.toString();}
}

总结

阿巴阿巴，博主通用分页的分享到此结束啦，有什么问题欢迎留言指教熬！