我在尝试 getCurrentSession() 时遇到 NullPointerException
java.lang.NullPointerException
servlets.ControlServlet.doPost(ControlServlet.java:46)
javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
我使用Tomcat 5.5 index.jsp页面:
<%@ page language="java" contentType="text/html; charset=ISO-8859-1"pageEncoding="ISO-8859-1"%>
<!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></title>
</head>
<body>
<%@ page import="java.util.List" %>
<%@ page import="data.Singer" %>
<jsp:useBean id="singer" class="data.Singer" scope="session"/>
<jsp:setProperty name="singer" property="*" />
<form action="ControlServlet" method="POST">
<form method=“POST”>
Name:<br />
<input type=“text” name="name" /><br />
Type:<br />
<input type=“text” name="type" /><br />
<input type="submit" name="Add song" value="Add song">
<input type="submit" name="save" value="Save" /><br><br>
<input type ="submit" name="values" value="Get values" >
</form>
</body>
</html>
web.xml
<?xml version="1.0" encoding="UTF-8"?>
<web-app id="WebApp_ID" version="2.4"
xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<display-name>webproject</display-name>
<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/beans.xml, /WEB-INF/conf.xml, /WEB-INF/singers.hbm.xml, /WEB-INF/songs.hbm.xml, /WEB-INF/singerbeans.xml, /WEB-INF/songbeans.xml</param-value>
</context-param>
<servlet>
<servlet-name>context</servlet-name>
<servlet-class>org.springframework.web.context.ContextLoaderServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet>
<servlet-name>test</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<load-on-startup>1</load-on-startup>
</servlet>
<servlet-mapping>
<servlet-name>test</servlet-name>
<url-pattern>*.*</url-pattern>
</servlet-mapping>
<servlet>
<servlet-name>action</servlet-name>
<servlet-class>org.apache.struts.action.ActionServlet</servlet-class>
<init-param>
<param-name>config</param-name>
<param-value>/WEB-INF/beans.xml, /WEB-INF/conf.xml, /WEB-INF/singers.hbm.xml, /WEB-INF/songs.hbm.xml, /WEB-INF/singerbeans.xml, /WEB-INF/songbeans.xml</param-value>
</init-param>
<init-param>
<param-name>debug</param-name>
<param-value>2</param-value>
</init-param>
<init-param>
<param-name>detail</param-name>
<param-value>2</param-value>
</init-param>
<load-on-startup>2</load-on-startup>
</servlet>
<servlet>
<description>
</description>
<display-name>ControlServlet</display-name>
<servlet-name>ControlServlet</servlet-name>
<servlet-class>servlets.ControlServlet</servlet-class>
</servlet>
<servlet-mapping>
<servlet-name>action</servlet-name>
<url-pattern>*.*</url-pattern>
</servlet-mapping>
<servlet-mapping>
<servlet-name>ControlServlet</servlet-name>
<url-pattern>/ControlServlet</url-pattern>
</servlet-mapping>
</web-app>
ControlServlet.java
public class ControlServlet extends HttpServlet {
private static final long serialVersionUID = 1L;
@Autowired
private SingerDao singerdao;
public SingerDao getSingerDao() {
return singerdao;
}
public void setSingerDao(SingerDao singerdao) {
this.singerdao = singerdao;
}
public ControlServlet() {
super();
// TODO Auto-generated constructor stub
}
protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
// TODO Auto-generated method stub
}
protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException {
if (request.getParameter("values") != null) {
response.getWriter().println(singerdao.getDBValues());
}
}
}
和 SingerDao.java
public class SingerDao implements SingerDaoInterface {
@Autowired
private SessionFactory sessionFactory;
public void setSessionFactory(SessionFactory sessionFactory) {
this.sessionFactory = sessionFactory;
}
public List getDBValues() {
Session session = getCurrentSession();
List<Singer> singers = session.createCriteria(Singer.class).list();
return singers;
}
private org.hibernate.classic.Session getCurrentSession() {
return sessionFactory.getCurrentSession();
}
public void updateSinger(Singer singer) {
Session session = getCurrentSession();
session.update(singer);
}
public Singer getSinger(int id) {
Singer singer = null;
Session session = getCurrentSession();
singer = (Singer) session.load(Singer.class, id);
return singer;
}
public void deleteSinger(Singer singer) {
Session session = getCurrentSession();
session.delete(singer);
}
public void insertRow(Singer singer) {
Session session = getCurrentSession();
session.save(singer);
}
}
在简单的Java项目中它工作得很好。我认为sessionFactory不会 Autowiring ，但为什么呢？ 谢谢大家。
最佳答案
您不能使用@Autowired在普通 servlet 中，因为它们不受 Spring 管理。
但是，您可以使用以下技巧来手动启动 servlet 的 Autowiring :
public class ControlServlet extends HttpServlet {
@Autowired
private SingerDao singerdao;
public void init(ServletConfig cfg) {
super.init(cfg);
WebApplicationContextUtils
.getWebApplicationContext(cfg.getServletContext())
.getAutowireCapableBeanFactory()
.autowireBean(this);
}
...
}
此外，正如评论中所建议的，因为您已经拥有 Spring MVC 的 DispatcherServlet在您的设置中，也许最好实现 ControlServlet 的功能作为 Spring MVC Controller 而不是 servlet(除非您有充分的理由将其作为 servlet)。
关于java - 在Web应用程序中使用Hibernate和Spring的问题，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/5079768/