Question

我试图使用spring MVC和hibernate将表单数据保存到数据库但是当调用hibernate session.getSession.save（s）的save方法时，它返回NullPointerException。

这是我的index.jsp

的代码

<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
    <title>Welcome to Spring Web MVC project</title>
</head>

<body>
    <form action="insert.htm">
        <label>  Name:</label><input type="text" name="name"><br>
        <label> Id:</label><input type="text" name="id"><br>
        <input type="submit" value="Enter">
    </form>
</body>
</html>

这是web.xml文件

 <servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <load-on-startup>2</load-on-startup>
</servlet>
<servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>*.htm</url-pattern>
</servlet-mapping>
<session-config>
    <session-timeout>
        30
    </session-timeout>
</session-config>
<welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
</welcome-file-list>
</web-app>

我的dispatcher-servlet.xml是

<bean class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean"  id="sessionFactory">
<property name="dataSource" ref="dataSource" />
<property name="annotatedClasses">
    <list>
        <value>com.model.Student</value>
    </list>
</property>
<property name="hibernateProperties">  
<props>
        <prop key="hibernate.dialect">org.hibernate.dialect.Oracle10gDialect</prop>
        <prop key="hibernate.hbm2ddl.auto">update</prop>
</props>
</property>
</bean>
<bean id="dataSource"
    class="org.apache.commons.dbcp.BasicDataSource"
    p:driverClassName="oracle.jdbc.driver.OracleDriver"
    p:url="jdbc:oracle:thin:@localhost:1521:Xe"
    p:username="hibernate"
    p:password="hibernate"></bean>
   <bean id="hibernatetransactionManager"             class="org.springframework.orm.hibernate3.HibernateTransactionManager">
  <property name="sessionFactory" ref="sessionFactory"></property>                
   </bean>

这是我的模特班学生

package com.model;

import javax.persistence.Id;
import javax.persistence.Entity;


 @Entity
  public class Student {
  @Id    
  private int id;
  private String name;

  public int getId() {
    return id;
 }

 public void setId(int id) {
     this.id = id;
 } 

 public String getName() {
     return name;
 }

 public void setName(String name) {
     this.name = name;
 }

  }

我的控制器是

@Controller
public class MyController {

@Autowired
    private Dao d;
@RequestMapping(value="/insert.htm",method = RequestMethod.GET)
public ModelAndView insert(HttpServletRequest req,Student s)
{
   String name=req.getParameter("name");
    int id=Integer.parseInt(req.getParameter("id"));
    s.setId(id);
    s.setName(name);
   System.out.println(s.getName());
    d.save(s);
    return new ModelAndView("display","Student",s);

}

这是我的Dao

 @Repository
 public class Dao {
 @Autowired
 private SessionFactory sessionFactory;

 public int save(Student s)
   {

     /*Session s1=sf.openSession();
     s1.beginTransaction();
     int i=(Integer)s1.save(s);
     s1.getTransaction().commit();
     return i;*/
     int i=(Integer)sessionFactory.getCurrentSession().save(s);
     return i;
     }
   }

我在MyController中的d.save（s）获得的异常

SEVERE: Servlet.service() for servlet [dispatcher] in context with path [/Spring5]          
threw exception [Request processing failed; nested exception
at com.controller.MyController.insert(MyController.java:30)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at s   un.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at  org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(Ha ndlerMethodInvoker.java:176)
    at  org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:436)
    at  org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:424)
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923)
at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852)
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882)
     at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:621)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at  org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.netbeans.modules.web.monitor.server.MonitorFilter.doFilter(MonitorFilter.java:393)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.jav a:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:472)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:936)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:407)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1004)
    at  org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:312)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:722)

我打电话给春天的mvc请帮帮我。我在调用插入时遇到异常，我也使用了@Autowired ......

Answer 1

除非您发布的堆栈跟踪不准确，否则空引用是控制器中的Dao。你确定它正确连线吗？

Answer 2

NullPointerException 的原因是：既没有使用 @ModelAttribute 进行bean绑定，也没有创建

Student s = new Student();

如果您不想要 @ModelAttribute 。您您在控制器代码中的参数 Student s 之前缺少 @ModelA rrtibute 。如果对bean绑定使用 @ModelAttribute 注释，则不需要从请求中获取请求参数并填充bean。因此，请删除以下内容：

String name=req.getParameter("name");
int id=Integer.parseInt(req.getParameter("id"));
s.setId(id); /* Here you are setting a value with a reference wcich points to null */
s.setName(name); /* Here you are setting a value with a reference wcich points to null */

Annotation @ModelAttribute 自动将请求参数绑定到应用它的bean的匹配属性。

@Controller
public class MyController {

    @Autowired(required = true) 
    private Dao d;
    @RequestMapping(value="/insert.htm",method = RequestMethod.GET)
    public ModelAndView insert(HttpServletRequest req,@ModelAttribute Student s)
    {
        System.out.println(s.getName());
        d.save(s);
        return new ModelAndView("display","Student",s);

    }

编辑：您已使用 @Repository 注释了Dao类。它将创建一个名为 dao 的单例对象。如果您想要除此之外的任何其他名称，请使用

@Repository(value ="d") 
 public class Dao{

}

现在你可以像正在做的那样自动装配 d 实例

@Autowired (required = true) 
private Dao d;

在您的情况下，自动装配的Dao实例为null，因为spring无法自动装配名为 d 的bean。因此，您在null引用上调用save方法。

Answer 3

@Rahul，你在Get Method中绑定数据，但实际上你不应该在GET方法中这样做当您处理表单时，您应始终使用POST方法我认为它可能会对你有所帮助： - ）

@RequestMapping(value="/insert.htm",method = RequestMethod.POST)
    public ModelAndView insert(HttpServletRequest req,@ModelAttribute Student s)
    {
        System.out.println(s.getName());
        d.save(s);
        return new ModelAndView("display","Student",s);

    }

在spring mvc中获取java.lang.NullPointerException

3 个答案: