ssh2-ssh中遇到java.lang.NumberFormatException

ssh中遇到java.lang.NumberFormatException

想做一個歌曲的分頁顯示 出現java.lang.NumberFormatException: For input string: "null"
java.lang.NumberFormatException.forInputString(NumberFormatException.java:48)

//按songname查找歌曲
public String getSbn(){

      songlist=service.getSongByName(this.songname);
      currentpage=1;

      //總結果數
      totalresults=songlist.size();

      if(totalresults%pagesize!=0){
      pagenumber=(totalresults/pagesize)+1;
      }
      else{pagenumber=totalresults/pagesize;
      }
       start=(currentpage-1)*pagesize;
       end=(currentpage)*pagesize-1;
       request.getSession().setAttribute("songlist",songlist);
       request.getSession().setAttribute("currentpage",currentpage);
       request.getSession().setAttribute("pagenumber",pagenumber);
      return "searchresult";


}

//下一頁
public String nextPage(){
        songlist=(List<Song>) session.getAttribute("songlist");
        totalresults=songlist.size();
        //將object轉化成int
        //此處"currentpage"為空
        currentpage= Integer.parseInt(String.valueOf(request.getSession().getAttribute("currentpage")));
        currentpage++;
        request.getSession().setAttribute("currentpage",currentpage);
        if(totalresults%pagesize!=0){
            pagenumber=(totalresults/pagesize)+1;
            }
            else{pagenumber=totalresults/pagesize;
            }
             start=(currentpage-1)*pagesize;
             end=(currentpage)*pagesize-1;
            return"addsongok";
    }

jsp上調用nextpage()的部分
 <% if((session.getAttribute("currentpage")!=null)&&(session.getAttribute("pagenumber")!=null)){
if(Integer.parseInt(String.valueOf(request.getSession().getAttribute("currentpage")))==Integer.parseInt(String.valueOf(request.getSession().getAttribute("pagenumber"))))
{ %><% } else { %>
<a href="SongManage_nextPage?">下一頁</a> 

<% }} %>

    currentpage= Integer.parseInt(String.valueOf(request.getSession().getAttribute("currentpage")));這裡取回的currentpage為空。請問是為什麼？

最佳回答：

既用 session.getAttribute("songlist");
又用 request.getSession().getAttribute("currentpage")
控制台輸出一下session的id吧 可能不是同一個session了 自然就取不到值了