NullPointerException异常在得到会议

Question

我正在以下exception.Its由于线路

Session ss=session.getCurrentSession(); 

java.lang.NullPointerException 
    at com.mkyong.common.dao.UserDao.saveUser(UserDao.java:25) 
    at com.mkyong.common.controller.JSONController.getShopInJSON(JSONController.java:31) 
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method) 
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57) 
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43) 
    at java.lang.reflect.Method.invoke(Method.java:601) 
    at org.springframework.web.bind.annotation.support.HandlerMethodInvoker.invokeHandlerMethod(HandlerMethodInvoker.java:176) 
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.invokeHandlerMethod(AnnotationMethodHandlerAdapter.java:426) 
    at org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter.handle(AnnotationMethodHandlerAdapter.java:414) 
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:790) 
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:719) 
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:644) 
    at org.springframework.web.servlet.FrameworkServlet.doPost(FrameworkServlet.java:560) 
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:647) 
    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.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:310) 
    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)

吾道等级如下表所示。

package com.mkyong.common.dao; 
import org.hibernate.SessionFactory; 
import org.hibernate.Session; 
import com.mkyong.common.model.User; 

import org.springframework.beans.factory.annotation.Autowired; 
import org.springframework.stereotype.Repository; 

public class UserDao { 

    private SessionFactory session; 

    public void setSessionFactory(SessionFactory session){ 
     if(session == null){ 
     throw new IllegalStateException(); 
     } 
     this.session=session; 
    } 


    public int saveUser(User user) { 

     Session ss=session.getCurrentSession(); 
     System.out.println(user.getUserName()); 
     System.out.println(user.getPassword()); 
     //Session ss=session.getCurrentSession(); 
     ss.save(user); 



     return 1; 



} 


} 

我的配置文件如下：

<beans xmlns="http://www.springframework.org/schema/beans" 
    xmlns:context="http://www.springframework.org/schema/context" 
    xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
    xmlns:tx="http://www.springframework.org/schema/tx" 
    xsi:schemaLocation=" 
     http://www.springframework.org/schema/beans  
     http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
     http://www.springframework.org/schema/context 
     http://www.springframework.org/schema/context/spring-context-3.0.xsd 
     http://www.springframework.org/schema/mvc 
     http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd 
     http://www.springframework.org/schema/tx 
     http://www.springframework.org/schema/tx/spring-tx-3.0.xsd"> 
    <context:property-placeholder location="classpath:jdbc.properties" /> 
    <context:component-scan base-package="com.mkyong.common.controller" /> 
    <context:annotation-config/> 

     <mvc:annotation-driven /> 





    <bean id="dataSource" 
     class="org.springframework.jdbc.datasource.DriverManagerDataSource"> 
     <property name="driverClassName" value="${database.driver}" /> 
     <property name="url" value="${database.url}" /> 
     <property name="username" value="${database.user}" /> 
     <property name="password" value="${database.password}" /> 
    </bean> 

    <bean id="SessionFactory" 
     class="org.springframework.orm.hibernate3.annotation.AnnotationSessionFactoryBean"> 
     <property name="dataSource" ref="dataSource" /> 

     <property name="annotatedClasses"> 
      <list> 
       <value>com.mkyong.common.model.User</value> 
      </list> 
     </property> 
     <property name="hibernateProperties"> 
      <props> 
       <prop key="hibernate.dialect">${hibernate.dialect}</prop> 
       <prop key="hibernate.show_sql">${hibernate.show_sql}</prop> 
      </props> 
     </property> 
    </bean> 
    <bean id="hibernateTransactionManager" class="org.springframework.orm.hibernate3.HibernateTransactionManager"> 
     <property name="SessionFactory" ref="SessionFactory" /> 
    </bean> 


</beans> 

Answer 1

你session是null.You上null使用getCurrentSession。所以你在这里得到NullpointeException

Answer 2

你会不会在你的注入DAO。确保你的配置是正确的。

您可以通过两种方式注入你的会话工厂（只选一个）

1）XML声明 在这里，你会在你的XML配置文件中这样声明你userDAO的豆：

<bean id="userDAO" class="com.mkyong.common.dao.UserDAO"> 
    <property name="session" ref="SessionFactory" /> 
</bean> 

我有时会遇到问题，因为我的bean的id以大写字母开头，所以我会将“SessionFactory”重命名为“sessionFactory”。

2）使用注释

这里，春天将扫描具有

<context:component-scan base-package="com.foo.bar" /> 

声明的所有包和寻找在COM与 “@Repository”， “@服务” 或 “@Component” 注解的类.foo.bar包。所以，您的类UserDAO应该注明“@Repository”以便找到并且您的包必须在组件扫描中进行扫描。 现在，春天将检测userDAO的豆，但没有看到任何豆注入，所以你必须以“@Autowired”注释SessionFactory的领域，你的类必须是这样的：

@Repository 
public class UserDao { 

@Autowired 
private SessionFactory session; 

public void setSessionFactory(SessionFactory session){ 
    if(session == null){ 
    throw new IllegalStateException(); 
    } 
    this.session=session; 
} 

... 

而且你的配置文件的样子像这样：

<beans xmlns="http://www.springframework.org/schema/beans" 
xmlns:context="http://www.springframework.org/schema/context" 
xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
xmlns:tx="http://www.springframework.org/schema/tx" 
xsi:schemaLocation=" 
    http://www.springframework.org/schema/beans  
    http://www.springframework.org/schema/beans/spring-beans-3.0.xsd 
    http://www.springframework.org/schema/context 
    http://www.springframework.org/schema/context/spring-context-3.0.xsd 
    http://www.springframework.org/schema/mvc 
    http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd 
    http://www.springframework.org/schema/tx 
    http://www.springframework.org/schema/tx/spring-tx-3.0.xsd"> 
<context:property-placeholder location="classpath:jdbc.properties" /> 
<context:component-scan base-package="com.mkyong.common.controller" /> 
<context:component-scan base-package="com.mkyong.common.dao" /> 
<context:annotation-config/> 

    <mvc:annotation-driven /> 

... 

</beans>