我的分页程序出现java.lang.NullPointerException该怎么办？

Question

那就把你的
if else代码贴出来吧！

Answer 1

.................
<%while(listBean.isAvailable()){%>//isAvailable()是bean里的一个方法跟next()的意思差不多； 
  .....
  <%=listBean.getData("id")%>
   .....
 
   <%if(admin.equals("1")){%>
    <!--这里显示admin是1时的内容-->
   <%}else{%>
     <!--这里显示admin是0时的内容-->
   <%}%><%}%>
.......
<!--这里是分页程序的代码-->
<table cellspacing="0" cellpadding="0" border="0">
<tr>
    <td><img src="images/trans.gif" width="58" height="2" border="0" /></td>
    <%if(listBean.getCurrentPage()<=1){%>
<td><img src="images/n_first_off.gif" width="30" height="5" alt="" border="0"></td>
    <td><img src="images/trans.gif" width="8" height="2" border="0" /></td>
    <td><img src="images/n_prev_off.gif" width="26" height="5" alt="" border="0"></td>
        <td><img src="images/trans.gif" width="8" height="2" border="0" /></td>
<%}else {%>
<td><a href="addressList.jsp?pageNo=1"><img src="images/n_first_on.gif" width="30" height="5" alt="" border="0"></a></td>
    <td><img src="images/trans.gif" width="8" height="2" border="0" /></td>
    <td><a href="addressList.jsp?pageNo=<%=listBean.getCurrentPage()-1%>"><img src="images/n_prev_on.gif" width="26" height="5" alt="" border="0"></a></td>
        <td><img src="images/trans.gif" width="8" height="2" border="0" /></td>
<%} if((listBean.getCurrentPage()!=listBean.getLastPage())&&(listBean.getLastPage()!=-1)){%>
    <td><a href="addressList.jsp?pageNo=<%=listBean.getCurrentPage()+1%>"><img src="images/n_next_on.gif" width="26" height="5" alt="" border="0"></a></td>
    <td><img src="images/trans.gif" width="8" height="2" border="0" /></td>
    <td><a href="addressList.jsp?pageNo=<%=listBean.getLastPage()%>"><img src="images/n_last_on.gif" width="27" height="5" alt="" border="0"></a></td>
    <td><img src="images/trans.gif" width="8" height="2" border="0" /></td>
<%}else{%>
<td><img src="images/n_next_off.gif" width="26" height="5" alt="" border="0"></td>
    <td><img src="images/trans.gif" width="8" height="2" border="0" /></td>
    <td><img src="images/n_last_off.gif" width="27" height="5" alt="" border="0"></td>
    <td><img src="images/trans.gif" width="8" height="2" border="0" /></td>
<%}%>
</tr>
</table>

Answer 2

admin是从上一页传来的判断是否administrator的参数

Answer 3

既然while(listBean.isAvailable())与while(rs.next())类似，那你经过这么一个循环后，指针不就移到最末了吗？
如果只是判断记录是否为空，用if(listBean.isAvailable())，如果要循环显示，请注意while的结束位置（显示语句应该在while里）

Answer 4

你怎么没把最重要的贴出来！
if else中的代码！

Answer 5

这是while ,if ..else 语句的内容:
--------------------------------------
<%while(listBean.isAvailable()){%>
<tr>
    <td align="center" class="name"><a href="#" onclick="javascript:popup('showList.jsp?id=<%=listBean.getData("id")%>');"><%=listBean.getData("name")%></a></td>
    <td><img src="images/trans.gif" width="15" height="2" border="0" /></td>
    <td align="center" class="registerDate"><%=listBean.getData("registerDate")%></td>
    <td><img src="images/trans.gif" width="20" height="2" border="0" /></td>
    <td align="center">
<table cellspacing="0" cellpadding="0" border="0">
<tr>
<%if(admin.equals("1")){%>
    <td><img src="images/trans.gif" width="13" height="2" border="0" /></td>
    <td><a href="editAddress.jsp?id=<%=listBean.getData("id")%>" target="_blank"><img src="images/im_edit.gif" width="14" height="9" alt="edit" border="0"></a></td>
    <td><img src="images/trans.gif" width="7" height="2" border="0" /></td>
    <td><a href="#" onclick="checkDel(<%=listBean.getData("id")%>);"><img src="images/im_delete.gif" width="14" height="9" alt="delete" border="0"></a></td>
    <td><img src="images/trans.gif" width="13" height="2" border="0" /></td>
<%}else{%>
    <td><img src="images/trans.gif" width="13" height="2" border="0" /></td>
    <td><img src="images/im_edit_off.gif" width="14" height="9" alt="edit" border="0"></td>
    <td><img src="images/trans.gif" width="7" height="2" border="0" /></td>
    <td><img src="images/im_delete_off.gif" width="14" height="9" alt="delete" border="0"></td>
    <td><img src="images/trans.gif" width="13" height="2" border="0" /></td>
<%}%>
</tr>

Answer 6

还有一个问题就是如果我把if(admin.equals("1"))换成if(admin=="1")的话，就不会有NullPointer错误出现，但是，这样就达不到验证是否是administrator

Answer 7

to: zxhong(红) 
是这样：加上if..else语句的话，点击“下一页”按钮，就会出现NullPointer错误。去掉，点击“下一页”正常

Answer 8

把admin这个参数加到分页的url里
如：
><a href="addressList.jsp?pageNo=<%=listBean.getCurrentPage()+1%>&admin=<%=admin%>"><img src="images/n_next_on.gif" width="26" height="5" alt="" border="0"></a>

Answer 9

对了
URL里的admin参数名admin要与你的(request.getParameter("admin"))一致！
good luck!

Answer 10

说明你的admin是null,如 zxhong(红) 所说，你应首先检查一下你的各参数、变量名是否一致
然后在判断时可进一步限制：
if(admin!=null&&admin.equals("1"))

Answer 11

两位说的极是。我加上了这句if(admin!=null&&admin.equals("1"))， 没有提示错误，但是第一页正常，第二页就不行了。按理说每一页都应该是打印出if后面大括号内的内容，可到第二页打出的却是else{}里的内容。应该debug中
<%if(admin!=null&&admin.equals("1")){%>
    <td><img src="images/trans.gif" width="13" height="2" border="0" /></td>
    <td><a href="editAddress.jsp?id=<%=listBean.getData("id")%>" target="_blank"><img src="images/im_edit.gif" width="14" height="9" alt="edit" border="0"></a></td>
    <td><img src="images/trans.gif" width="7" height="2" border="0" /></td>
    <td><a href="#" onclick="checkDel(<%=listBean.getData("id")%>);"><img src="images/im_delete.gif" width="14" height="9" alt="delete" border="0"></a></td>
    <td><img src="images/trans.gif" width="13" height="2" border="0" /></td>
<%}else{%>
    <td><img src="images/trans.gif" width="13" height="2" border="0" /></td>
    <td><img src="images/im_edit_off.gif" width="14" height="9" alt="edit" border="0"></td>
    <td><img src="images/trans.gif" width="7" height="2" border="0" /></td>
    <td><img src="images/im_delete_off.gif" width="14" height="9" alt="delete" border="0"></td>
    <td><img src="images/trans.gif" width="13" height="2" border="0" /></td>
<%}%>