Spring自动装配报空指针异常
这几天在学Spring的自动装配，自己动手做一个小项目，但是被一个空指针异常卡住了。
启动的时候弹出index.jsp,这是一个登陆页面：
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<title>消费管理系统--首页title>
<style type="text/css">
#surebtn{
align:center;
}
style>
<script type="text/javascript">
script>
head>
<body>
<h1>用户登录h1>
<div>
<form action="UserServlet">
用户名：<input id="username" type="text" name="nickname"/><br/>
密码：<input id="password" type="password" name="password"><br/>
<input type="hidden" name="action" value="login">
<input id="surebtn" type="submit" value="登录"><button onclick="#" id="regbtn">注册button>
form>
div>
body>
html>跳转到UserServlet:
package com.ffy.servlet;
import java.io.IOException;
import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Component;
import org.springframework.web.context.WebApplicationContext;
import org.springframework.web.context.support.WebApplicationContextUtils;
import com.ffy.bean.User;
import com.ffy.service.UserService;
public class UserServlet extends HttpServlet{
@Autowired
private UserService userService;
private static WebApplicationContext context;
private String action=null;
@Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
context=WebApplicationContextUtils.getRequiredWebApplicationContext(getServletContext());
userService=context.getBean(UserService.class);
if(req.getParameter("action")!=null){
action=req.getParameter("action");
if("login".equals(action)){
if(login(req,resp)!=null){
User user=login(req,resp);
req.getRequestDispatcher("/list.jsp?userId="+user.getId()).forward(req, resp);
}else{
req.getRequestDispatcher("loginError.jsp").forward(req, resp);
}
}
}
}
@Override
protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
doGet(req, resp);
}
private User login(HttpServletRequest req,HttpServletResponse resp){
User user=new User();
user.setNickName(req.getParameter("nickname"));
user.setPassword(req.getParameter("password"));
User returnu=userService.login(user);
if(returnu!=null){
return returnu;
}
return null;
}
}若用户名和密码都正确，跳转到list.jsp,一个账单列表：
<%@page import="org.springframework.web.context.support.WebApplicationContextUtils"%>
<%@page import="org.springframework.context.ApplicationContext"%>
<%@page import="javax.enterprise.context.spi.Context"%>
<%@page import="org.springframework.beans.factory.annotation.Autowired"%>
<%@page import="com.ffy.bean.Record"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<%@ page import="java.util.List" %>
<%@ page import="com.ffy.service.UserService" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<%
**UserService service=new UserService();**
list=service.listRecordByUserId(Integer.parseInt(request.getParameter("userId")));
%>
<title>账单title>
head>
<body>
<h1>账单h1>
<hr>
<table>
<tr>
<td>编号td>
<td>金额td>
<td>类型td>
<td>日期td>
<td>描述td>
tr>
<%
for(Record r:list){
%>
<tr>
<td><%=r.getId() %>td>
<td><%=r.getPrice() %>td>
<td><%=r.getType().getName() %>td>
<td><%=r.getDate() %>td>
<td><%=r.getDescription() %>td>
tr>
<%
}
%>
table>
body>
html>注意加粗的那句话，这个list.jsp会调用UserService的listRecordByUserId(int userId)方法，具体如下：
package com.ffy.service;
import java.util.List;
import org.hibernate.Session;
import org.hibernate.query.Query;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.transaction.annotation.Transactional;
import com.ffy.bean.Record;
import com.ffy.bean.User;
@Service
@Transactional
public class UserService {
@Autowired
private HibernateManage hibernateManage;
public HibernateManage getHibernateManage() {
return hibernateManage;
}
public void setHibernateManage(HibernateManage hibernateManage) {
this.hibernateManage = hibernateManage;
}
public User login(User user){
System.out.println("login........");
Session session=hibernateManage.getSession();
Queryquery=session.createQuery("from User where nickname=:nickname and password=:password",User.class);
query.setParameter("nickname",user.getNickName());
query.setParameter("password", user.getPassword());
if(query.getResultList().size()>0){
return query.getResultList().get(0);
}
return null;
}
public List listRecordByUserId(int userId){
if(hibernateManage==null){
System.out.println("null-----------------------");
}
**Session session=hibernateManage.getSession();**
Query q=session.createQuery("from Record r,User u where r.id=r.user.id",Record.class);
List list=q.getResultList();
return list;
}
}
这个时候加粗的那句话就报空指针了，这是因为我在list.jsp直接new了一个UserService,直接new的话那这个UserService的实例service就不归spring管了，spring是不会自动装配UserService里面hibernateManage，所以报了空指针异常。只要将list.jsp里的UserService service=new UserService();改成ApplicationContext context=WebApplicationContextUtils.getWebApplicationContext(request.getSession().getServletContext());
UserService service=context.getBean(UserService.class);就可以了。
<%@page import="org.springframework.web.context.support.WebApplicationContextUtils"%>
<%@page import="org.springframework.context.ApplicationContext"%>
<%@page import="javax.enterprise.context.spi.Context"%>
<%@page import="org.springframework.beans.factory.annotation.Autowired"%>
<%@page import="com.ffy.bean.Record"%>
<%@ page language="java" contentType="text/html; charset=utf-8"
pageEncoding="utf-8"%>
<%@ page import="java.util.List" %>
<%@ page import="com.ffy.service.UserService" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<%
ApplicationContext context=WebApplicationContextUtils.getWebApplicationContext(request.getSession().getServletContext());
UserService service=context.getBean(UserService.class);
List list=service.listRecordByUserId(Integer.parseInt(request.getParameter("userId")));
%>
<title>账单title>
head>
<body>
<h1>账单h1>
<hr>
<table>
<tr>
<td>编号td>
<td>金额td>
<td>类型td>
<td>日期td>
<td>描述td>
tr>
<%
for(Record r:list){
%>
<tr>
<td><%=r.getId() %>td>
<td><%=r.getPrice() %>td>
<td><%=r.getType().getName() %>td>
<td><%=r.getDate() %>td>
<td><%=r.getDescription() %>td>
tr>
<%
}
%>
table>
body>
html>唉，因为这个查了好久，对于大牛来说这种问题太low了，但是对于我这种还没毕业的小白来说实在是一个挺难的问题了，在这里记录一下。