如何在jsp页面中，显示一个表中所有信息。下面代码有什么问题呢？

<%@ page language="java" contentType="text/html; charset=gbk"
    pageEncoding="gbk" import="com.alaska.bo.UserManager" 
    import="com.alaska.bo.UserManagerImpl"
    import="com.alaska.domain.User"
    import=" java.util.List"
    import=" java.util.ArrayList"
    import=" java.util.Iterator"
    import="java.io.PrintWriter"%>
<!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=ISO-8859-1">
<title>显示所有用户的情况</title>
</head>
<body>
<% 
User user = new User();
UserManager um = new UserManagerImpl();
//um.getAllUsers(user);//一个集合。
List<User> li = new ArrayList<User>();
li=um.getAllUsers(user);
Iterator<User> it = li.iterator();
//PrintWriter pw = response.getWriter();
%>
<table>
<%
while(it.hasNext()){%>
<% User u1 = it.next();%>
<tr><td><%=u1 %></td></tr>
<% }%></table>
</body>
</html>

解决方案 »

  1.   

    HTTP Status 500 - --------------------------------------------------------------------------------type Exception reportmessage description The server encountered an internal error () that prevented it from fulfilling this request.exception org.apache.jasper.JasperException
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:358)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
    root cause java.lang.NullPointerException
    com.alaska.dao.UserDAOJDBCImpl.getAllUsers(UserDAOJDBCImpl.java:175)
    com.alaska.bo.UserManagerImpl.getAllUsers(UserManagerImpl.java:46)
    org.apache.jsp.user.showmessage_jsp._jspService(showmessage_jsp.java:60)
    org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:133)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
    org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:311)
    org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:301)
    org.apache.jasper.servlet.JspServlet.service(JspServlet.java:248)
    javax.servlet.http.HttpServlet.service(HttpServlet.java:856)
    note The full stack trace of the root cause is available in the Tomcat logs.
    --------------------------------------------------------------------------------Apache Tomcat/5.0.18
      

  2.   

    空指针异常在UserDAOJDBCImpl.java，175行
      

  3.   

    com.alaska.bo.UserManagerImpl.getAllUsers(UserManagerImpl.java:46)li=um.getAllUsers(user); 把断点设在这里调一下。
    我感觉User user = new User(); 
    没有对user处理就
    li=um.getAllUsers(user); 
    肯定有问题的