jsp页面显示新闻.公告之类的上一篇下一篇

http://hi.baidu.com/a393060727/blog/item/19dc08d5f2408acd51da4b3b.html

 

 

jsp页面显示新闻.公告之类的上一篇下一篇(转载)

2009-07-14 23:23

此方法有二种： 1　在JSP前台页面判断并输出，（适合初学，易理解） 2　在SERVLET里判断并输出（符合MVC架构） 我们先说第一种方法： 先说dao层，主要是取比当前ID小的只一条，取比当前ID大的只一条，注意排序！下面是在查询时的最基本语句，这是最基本的：     //String max="select max(id) from news where id< "+id+" order by id desc limit 0,1;";     //String min="select min(id) from news where id> "+id+" order by id asc limit 0,1;";    public News max(Long id)throws Exception{    /**    * 取下一条    */    News maxnews=null;    try {     conn=Dbinit.getConn();     //String max="select max(id) from news where id< "+id+" order by id desc limit 0,1;";     //String min="select min(id) from news where id> "+id+" order by id asc limit 0,1;";     pstmt=conn.prepareStatement("select * from news where id>? order by id asc limit 0,1 ;");     pstmt.setLong(1, id);     rs=pstmt.executeQuery();     if(rs!=null && rs.next()){      maxnews=new News();      maxnews.setId(rs.getLong("id"));      maxnews.setTitle(rs.getString("title"));      maxnews.setZuozhe(rs.getString("zuozhe"));      maxnews.setLaiyuan(rs.getString("laiyuan"));      maxnews.setContent(rs.getString("content"));      maxnews.setFabutime(rs.getString("fabutime"));     }        } catch (RuntimeException e) {     // TODO Auto-generated catch block     e.printStackTrace();     return null;    }finally{     Dbinit.close(rs, pstmt, conn);    }    return maxnews; } public News min(Long id)throws Exception{    /**    * 取上一条    */    News minnews=null;    try {     conn=Dbinit.getConn();     //String max="select max(id) from news where id< "+id+" order by id desc limit 0,1;";     //String min="select min(id) from news where id> "+id+" order by id asc limit 0,1;";     pstmt=conn.prepareStatement("select * from news where id    pstmt.setLong(1, id);     rs=pstmt.executeQuery();     if(rs!=null && rs.next()){        minnews=new News();      minnews.setId(rs.getLong("id"));      minnews.setTitle(rs.getString("title"));      minnews.setZuozhe(rs.getString("zuozhe"));      minnews.setLaiyuan(rs.getString("laiyuan"));      minnews.setContent(rs.getString("content"));      minnews.setFabutime(rs.getString("fabutime"));     }        } catch (RuntimeException e) {     // TODO Auto-generated catch block     e.printStackTrace();     return null;    }finally{     Dbinit.close(rs, pstmt, conn);    }    return minnews; } 　二　再说servlet层 在我们显示详细新闻的页面show.jsp所用的servlet方法show()中调用上面两个DAO方法 public void maxMin(HttpServletRequest request,HttpServletResponse response)throws Exception{     /**     * 专用来供前台show.jsp调用的方法（先经show()调用）     */     NewsDao newsdao = new NewsDao();     News maxNews=null;     News minNews =null;     //StringBuffer out=new StringBuffer();     //Long maxId=0L;     //Long minId=0L;     Long currentId=Long.parseLong(request.getParameter("id"));     maxNews=newsdao.max(currentId);     minNews=newsdao.min(currentId);     request.setAttribute("currentid",currentId);     request.setAttribute("maxnews", maxNews);     request.setAttribute("minnews", minNews);               //return out.toString();    } public void show(HttpServletRequest request,HttpServletResponse response)throws Exception{     /**     * 后台查看新闻详细信息     */     NewsDao newsdao = new NewsDao();     Long id= Long.parseLong(request.getParameter("id"));    News news = null;    if (id!= 0) {     try {      news = newsdao.show(id);     } catch (Exception e) {      // TODO Auto-generated catch block      e.printStackTrace();     }    this.maxMin(request, response);//调用     request.setAttribute("viewnews", news);     request.getRequestDispatcher("showNews.jsp").forward(request,response);    }     } 第三：前台show.jsp页面 <%@ page language="java" import="java.util.*,bean.*" pageEncoding="UTF-8"%> <% String path = request.getContextPath(); String basePath = request.getScheme()+"://"+request.getServerName()+":"+request.getServerPort()+path+"/"; %>                          新闻详细信息          ${viewnews.title }       新闻来源：${viewnews.laiyuan }   编辑：${viewnews.zuozhe }   发布时间：${viewnews.fabutime}       ${viewnews.content }       [关闭本页面]               <%        News maxNews=null;     News minNews=null;        Long maxId=0L;     Long minId=0L;     Long currentid=(Long)request.getAttribute("currentid");     maxNews=(News)request.getAttribute("maxnews");     minNews=(News)request.getAttribute("minnews");         if(maxNews!=null && minNews!=null){        maxId=maxNews.getId();        minId=minNews.getId();        if(currentid<=minId){        %>               上一篇: 没有上一篇        下一篇: ${maxnews.title }               <%        }           if(minId       %>     　　        上一篇: ${minnews.title }        下一篇: ${maxnews.title }            <%        }           if(currentid>=maxId){     %>     　　        上一篇: ${minnews.title }        下一篇: 没有下一篇     <%        }         }     if(maxNews==null && minNews!=null){        %>     　        上一篇: ${minnews.title }        下一篇: 没有下一篇     <%     }     if(maxNews!=null && minNews==null){        %>     　        上一篇: 没有上一篇        下一篇: ${maxnews.title }     <%     }     %>         ============================================================= ============================================================== 下面开始说第二种方法：2　在SERVLET里判断并输出（符合MVC架构） 先说dao层，和上面的方法中一模一样： 主要是取比当前ID小的只一条，取比当前ID大的只一条，注意排序！下面是在查询时的最基本语句，这是最基本的：     //String max="select max(id) from news where id< "+id+" order by id desc limit 0,1;";     //String min="select min(id) from news where id> "+id+" order by id asc limit 0,1;";    public News max(Long id)throws Exception{    /**    * 取下一条    */    News maxnews=null;    try {     conn=Dbinit.getConn();     //String max="select max(id) from news where id< "+id+" order by id desc limit 0,1;";     //String min="select min(id) from news where id> "+id+" order by id asc limit 0,1;";     pstmt=conn.prepareStatement("select * from news where id>? order by id asc limit 0,1 ;");     pstmt.setLong(1, id);     rs=pstmt.executeQuery();     if(rs!=null && rs.next()){      maxnews=new News();      maxnews.setId(rs.getLong("id"));      maxnews.setTitle(rs.getString("title"));      maxnews.setZuozhe(rs.getString("zuozhe"));      maxnews.setLaiyuan(rs.getString("laiyuan"));      maxnews.setContent(rs.getString("content"));      maxnews.setFabutime(rs.getString("fabutime"));     }        } catch (RuntimeException e) {     // TODO Auto-generated catch block     e.printStackTrace();     return null;    }finally{     Dbinit.close(rs, pstmt, conn);    }    return maxnews; } public News min(Long id)throws Exception{    /**    * 取上一条    */    News minnews=null;    try {     conn=Dbinit.getConn();     //String max="select max(id) from news where id< "+id+" order by id desc limit 0,1;";     //String min="select min(id) from news where id> "+id+" order by id asc limit 0,1;";     pstmt=conn.prepareStatement("select * from news where id    pstmt.setLong(1, id);     rs=pstmt.executeQuery();     if(rs!=null && rs.next()){        minnews=new News();      minnews.setId(rs.getLong("id"));      minnews.setTitle(rs.getString("title"));      minnews.setZuozhe(rs.getString("zuozhe"));      minnews.setLaiyuan(rs.getString("laiyuan"));      minnews.setContent(rs.getString("content"));      minnews.setFabutime(rs.getString("fabutime"));     }        } catch (RuntimeException e) {     // TODO Auto-generated catch block     e.printStackTrace();     return null;    }finally{     Dbinit.close(rs, pstmt, conn);    }    return minnews; } 再说servlet层 public String updown(HttpServletRequest request,HttpServletResponse response)throws Exception{     NewsDao newsdao = new NewsDao();     News maxNews=null;     News minNews=null;     StringBuffer out=new StringBuffer();     Long maxId=0L;     Long minId=0L;     Long currentId=Long.parseLong(request.getParameter("id"));     maxNews=newsdao.max(currentId);     minNews=newsdao.min(currentId);     if (maxNews != null && minNews != null) {         maxId = maxNews.getId();         minId = minNews.getId();         String maxstr = "admin/news.do?method=show&id=" + maxId;         String minstr = "admin/news.do?method=show&id=" + minId;        out.append(" ");       if (minId < currentId && currentId < maxId) {      out.append("上一篇:"+ minNews.getTitle() + "");      out.append("下一篇:"+ maxNews.getTitle() + "");     }       }     if(maxNews != null && minNews == null){      maxId = maxNews.getId();      String maxstr = "admin/news.do?method=show&id=" + maxId;     out.append("上一篇:没有上一篇");     out.append("下一篇:"+ maxNews.getTitle() + "");      }     if(maxNews == null && minNews != null){         minId = minNews.getId();         System.out.println(minId+"@@@@@@@@@@@@@@@");         String minstr = "admin/news.do?method=show&id=" + minId;        out.append("上一篇:"+ minNews.getTitle() + "");     out.append("下一篇:没有下一篇");     }     out.append(" ");     return out.toString(); }     public void show(HttpServletRequest request,HttpServletResponse response)throws Exception{     /**     * 后台查看新闻详细信息     */     NewsDao newsdao = new NewsDao();     Long id= Long.parseLong(request.getParameter("id"));    News news = null;    if (id!= 0) {     try {      news = newsdao.show(id);     } catch (Exception e) {      // TODO Auto-generated catch block      e.printStackTrace();     }     String updown=this.updown(request, response);     request.setAttribute("updown", updown);     request.setAttribute("viewnews", news);     request.getRequestDispatcher("showNews.jsp").forward(request,response);    }     } 最后，在前台调用就方便多了 一句话：${updown}