NullPointerexception in getting session - spring-mvc

Question

I am getting the following exception.Its due to the line
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$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)
My dao class is as follows.
package com.mkyong.common.dao;
import org.hibernate.SessionFactory;
import org.hibernate.Session;
import com.mkyong.common.model.User;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Repository;
public class UserDao {
private SessionFactory session;
public void setSessionFactory(SessionFactory session){
if(session == null){
throw new IllegalStateException();
}
this.session=session;
}
public int saveUser(User user) {
Session ss=session.getCurrentSession();
System.out.println(user.getUserName());
System.out.println(user.getPassword());
//Session ss=session.getCurrentSession();
ss.save(user);
return 1;
}
}
My config file is as follows:
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:mvc="http://www.springframework.org/schema/mvc" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd
http://www.springframework.org/schema/mvc
http://www.springframework.org/schema/mvc/spring-mvc-3.0.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">
<context:property-placeholder location="classpath:jdbc.properties" />
<context:component-scan base-package="com.mkyong.common.controller" />
<context:annotation-config/>
<mvc:annotation-driven />
<bean id="dataSource"
class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="${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

Your session is null.You are using getCurrentSession on null .So you are getting NullpointeException here

Answer 2

Your session is not injected in your DAO. Ensure your configuration is correct.
You can inject your session factory in two ways (choose just one)
1) Xml declaration
Here you will declare your userDAO bean in your xml configuration file this way :
<bean id="userDAO" class="com.mkyong.common.dao.UserDAO">
<property name="session" ref="SessionFactory" />
</bean>
I sometimes have issue when the id of my bean start with a Uppercase letter, so I would rename "SessionFactory" by "sessionFactory".
2) With annotations
Here, Spring will scan all packages declared with
<context:component-scan base-package="com.foo.bar" />
and look for Classes annotated with "#Repository", "#Service" or "#Component" in com.foo.bar package. So, Your class UserDAO should be annotated with "#Repository" to be found and your package must be in component-scan to be scanned.
Now Spring will detect your userDAO bean but don't see any bean to inject, so you must annotate your SessionFactory field with "#Autowired", your class must look like this :
#Repository
public class UserDao {
#Autowired
private SessionFactory session;
public void setSessionFactory(SessionFactory session){
if(session == null){
throw new IllegalStateException();
}
this.session=session;
}
...
And your configuration file look like this :
<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>