web工程login时提示空指针异常，怎么解决

异常信息：严重: Servlet.service() for servlet jsp threw exception
java.lang.NullPointerException
at org.apache.jsp.check_jsp._jspService(check_jsp.java:72)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:388)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:293)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:859)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:602)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:619)
2012-4-29 10:59:08 org.apache.catalina.core.StandardWrapperValve invoke
下面的是源码：
<%@ page language="java" contentType="text/html; charset=UTF-8" 
    pageEncoding="UTF-8"%>
<!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=UTF-8">
<title>验证页面</title>
</head>
<body>
  <%
   String name=(String)request.getParameter("username");
   String password=(String)request.getParameter("password");
   String repassword=(String)request.getParameter("repassword");
   String sex=(String)request.getParameter("sex");
   String work=(String)request.getParameter("work");
   String[] love=(String[])request.getParameterValues("love");
   String show=(String)request.getParameter("show"); 
   /*将复选框得到的数组的值取出*/
   String strLove= "";
   for(int i=0;i<love.length;i++)
   {
     if(strLove.trim().equals(""))
     {
       strLove=strLove+"'"+love[i].toString()+"'";
     }
     else
     {
     strLove=strLove+","+love[i].toString()+"'";
     }
   }
   if(strLove.trim().substring(0,strLove.trim().length()).equals(","))
   {
    strLove=strLove.trim().substring(0,strLove.trim().length()-1);
   }
   %>
   <!-- 使用font标签控制字体的大小和颜色 -->
   <font size="4" color="blue">您的注册信息是</font><br>
   <!-- 将得到的相关信息显示在网页上 -->
   用户名：<%=name %><br>
   密码：<%=password %><br>
   确认密码：<%=repassword %><br>
   性别：<%=sex %><br>
   职业：<%=work %><br>
   个人爱好：<%=strLove %>
</body>
</html>

解决方案 »

  1.   

    下面的是login的代码，谁帮忙看一下：<%@ page language="java" contentType="text/html; charset=UTF-8"
        pageEncoding="UTF-8"%>
    <!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=UTF-8">
    <title>用户注册</title>
    </head>
    <body>
      <!-- center标签的作用是使他之内的内容全部居中 -->
      <center>
        <!-- 使用form表单提交注册信息 -->
          <form action="check.jsp" method="post">
            <!-- 使用一个八行两列的表格控制显示 -->
              <table>
               <!-- 注册用户信息 -->
               
                <tr>
                  <td align="right">
                                                  用户名 ：
                  </td>
                  <td align="left">
                    <!-- 输入文本框 -->
                    <input type="text" name="username" value="wang"/>
                   </td>
                 </tr>
                   
                   <!-- 注册密码信息 -->
                    <tr>
                        <td align="right">
                                                     密码  ：
                         </td>
                       <td align="left">   
                         <!-- 密码框 -->
                           <input type="password" name="password" value="123"/>
                         </td>
                     </tr>
                    
                    <!-- 注册确认密码信息 -->
                     <tr>
                      <td align="right">
                                                      确认密码：   
                       </td>
                       <td align="left">
                       <input type="password" name=repassword value="123"/>
                       </td>
                       </tr> 
                       
                       <!-- 注册性别信息 -->
                       <tr>
                        <td align="right">
                                                      性别 ：
                         </td>
                         <td align="left">
                           <!-- 单选按钮 -->
                           <input type="radio" name="sex" value="male" checked/>男
                           <input type="radio" name="sex" value="female" />女
                           </td>
                           </tr>   
                      <!-- 注册职业信息 -->
                     <tr>
                       <td align="right">
                       职业：
                       </td>
                       <td align="left">
                        <!-- 下拉列表 -->
                         <select size="1" name="work">
                             <option selected="selected" value="student">学生</option>
                             <option>职员</option>
                             <option>经理</option>
                             <option>军人</option>
                             <option>自由人</option>
                         </select>                  
                         </td>
                         </tr>
                         
                        <!-- 注册个人爱好信息 -->
                        <tr>
                          <td align="right">
                           个人爱好：
                           </td>
                           <td align="left">
                            <!-- 复选框 -->
                  <input type="checkbox" name="love1" value=""/>电脑网络
                  <input type="checkbox" name="love2" value=""/>影视娱乐
                  <input type="checkbox" name="love3" value=""/>棋牌娱乐<br/>
                  <input type="checkbox" name="love4" value=""/>读书读报
                  <input type="checkbox" name="love5" value=""/>美酒佳肴
                  <input type="checkbox" name="love6" value=""/>绘画书法
                  </td>
                  </tr>
              <!-- 注册个人信息说明 -->
              <tr>
               <td align="right">
                                         个人说明：
                      </td>
                       <td align="left">
                       <!-- 输入文本域 -->
                       <textarea name="show" rows="15" cols="30"></textarea>    
                       </td>
                       </tr>
                       <!-- 定义提交重置按钮 -->
                      <tr>
                      <td align="right">   
                      <input type="submit" value="提交">   
                      </td>
                      <td align="left">  
                      <input type="reset" value="重置">
                      </td>
                      </tr>                                                                                     
              </table>
          </form>
      </center>
    </body>
    </html>
      

  2.   

    String[] love=(String[])request.getParameterValues("love");页面没名字为 love 的属性值
      

  3.   

    去tomcat的work目录下搜check_jsp.java文件，打开看看第72行是什么代码
      

  4.   

    楼主，用request.getParameter方法返回的是String类型，没必要再强转String，这样还有可能报错
      

  5.   

    谢谢各位了，问题已经解决了。我把checkbox里的name属性都改成了love，然后就成功了。虽然最后编码出了点问题。嗯，继续学习。