帮我解决一下,可以吗?

这是空指针异常~~看看你那里对象没有new，就调用属性和方法了。

解决方案 »

  1.   

    这是那个代码,能帮我看看,应该在哪改动吗?
    <%@ page contentType="text/html; charset=gb2312" language="java" import="java.sql.*" errorPage="../error/error.jsp" 
    %>
    <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
    <html >
    <head>
    <meta http-equiv="Content-Type" content="text/html; charset=gb2312">
    <title>主页</title>
    <jsp:useBean id="books" class="BookShop.MyDb" scope="page"/><link rel="stylesheet" type="text/css" href="../css/bs.css"/>
    <script language="javascript" src="../css/bs.js"></script>
    <%! 
    String idbook,bookname;
    %>
    </head>
    <body topmargin="0" > 
    <p>&nbsp;</p>
    <table width="646"  border="1" align="center" cellpadding="-1" cellspacing="0" bordercolor="#FFFFFF" bordercolorlight="#0066ff" bordercolordark="#FFFFFF" > 
      <caption> 
      <div class="two">热点图书</div> 
      <p></p> 
      </caption> 
      <tr>
        <td width="149" height="22" align="center">图书编号</td>
        <td width="404" align="center">图书名称</td>
        <td width="85" align="center">购物车</td>
      </tr> 
    <%
    String sqls="SELECT idbook,bookname FROM books WHERE hotdeal=1";
    Statement stmt=books.getstmtread();
    ResultSet rs=stmt.executeQuery(sqls);
    if(!rs.next()){
    %>
      <tr>
        <td height="40"  colspan="3"  align="center" class="red12">暂无热点图书</td>
      </tr> 
    <%
    books.close();
    }else{
    rs.beforeFirst();
    while(rs.next()){
    idbook=rs.getString(1);
    bookname=rs.getString(2);

    idbook=books.outStr(idbook);
    bookname=books.outStr(bookname);
    %>
    <form action="../shop/trade.jsp" method="post">
      <tr>
        <td height="22" align="center"><%=idbook%></td>
        <td align="center"><a href="bookmsg.jsp?idbook=<%=idbook%>"><%=bookname%></a></td>
        <td align="center">
      <input type="image" src="../image/add.gif" alt="添加购物车" >
    <input type="hidden" name="action" value="add">
    <input type="hidden" name="id" value="<%=idbook%>"> </td>
      </tr> 
    </form>
    <%
      }
    books.close();
    }
    %>
    </table> 
    <table width="472" align="center"  >
      <tr>
        <td height="50" valign="bottom" class="red12"> 
    <%
    String ip="";
    try{
    ip=(String)request.getRemoteAddr();
    }catch(Exception e){
    ip="";
    }
    ip=books.inStr(ip);
    int temp=0,count=0,degree=1;
    String sqls1="SELECT visitip,degree FROM visit WHERE visitip='"+ip+"'";
    stmt=books.getstmtread();
    rs=stmt.executeQuery(sqls1);
    if(rs.next()){
    degree=rs.getInt(2);
    degree++;
    books.close();
    String sqlu="UPDATE visit SET degree="+degree+" WHERE visitip='"+ip+"'";
    Statement stmt1=books.getstmt();
    temp=0;
    temp=stmt1.executeUpdate(sqlu);
    }else{
    books.close();
    String sqli="INSERT INTO visit(visitip) VALUES('"+ip+"')";
    Statement stmt2=books.getstmt();
    temp=0;
    temp=stmt2.executeUpdate(sqli);
    }
    books.close();
    String sqls2="SELECT COUNT(*) FROM visit";
    stmt=books.getstmtread();
    rs=stmt.executeQuery(sqls2);
    if(rs.next()){
    count=rs.getInt(1);
    }
    books.close();
    pageContext.removeAttribute("books");
    out.print("欢迎来自["+ip+"]的朋友"+"<br>");
    out.print("这是您第["+degree+"]次来访"+"<br>");
    out.print("曾有"+count+"位朋友来访");
    %>
    </td>
      </tr>
    </table>
    </body>
    </html>