this.getSession throws NullPointerException?!

[liren]

Hi friends

I use spring with HibernateDaoSupport class. When I run the following code:

public class UserDAOImpl extends HibernateDaoSupport implements UserDAO {
.....................................................................................................
...............................................................................
public User createUser(User user, UserDetail detail) {
User hasuser = (User) this.getHibernateTemplate()
					.createQuery(
							this.getSession&#40;&#41;,  <----- NullPointerException here
							"from User u where u.userName='"
									+ user.getUserName&#40;&#41; + "'"&#41;.uniqueResult&#40;&#41;;
&#125;
.................................................................................................

Tomcat throws Exception:

root cause 

java.lang.NullPointerException
	org.springframework.orm.hibernate.support.HibernateDaoSupport.getSession(HibernateDaoSupport.java:141)
	lyo.hotmail.site.service.UserDAOImpl.createUser(UserDAOImpl.java:41)
	lyo.hotmail.site.action.RegisteAction.registeUser(RegisteAction.java:51)
	sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
	sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
	sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
	java.lang.reflect.Method.invoke(Method.java:324)
	org.apache.struts.actions.DispatchAction.dispatchMethod(DispatchAction.java:280)
	org.apache.struts.actions.DispatchAction.execute(DispatchAction.java:216)
	org.apache.struts.action.RequestProcessor.processActionPerform(RequestProcessor.java:484)
	org.apache.struts.action.RequestProcessor.process(RequestProcessor.java:274)
	org.apache.struts.action.ActionServlet.process(ActionServlet.java:1482)
	org.apache.struts.action.ActionServlet.doPost(ActionServlet.java:525)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:709)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:802)
	lyo.hotmail.site.util.HiberFilter.doFilter(HiberFilter.java:46)


note The full stack trace of the root cause is available in the Apache Tomcat/5.0.29 logs.

My config file is the following :

<beans>
<bean id="MyDataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
        <!-- results in a setDriverClassName&#40;String&#41; call -->
        <property name="driverClassName">
            <value>com.mysql.jdbc.Driver</value>
        </property>
        <property name="url">
            <value>jdbc&#58;mysql&#58;//127.0.0.1&#58;3306/Hibernate?useUnicode=true&amp;characterEncoding=gb2312</value>
        </property>
        <property name="username">
            <value>root</value>
        </property>
		<property name="password">
            <value>root</value>
        </property>
		<property name="defaultAutoCommit"> 
            <value>false</value> 
        </property>
    </bean>
	<!--
<bean id="MyJNDIDataSource" class="org.springframework.jndi.JndiObjectFactoryBean">
  <property name="jndiName">
    <value>jdbc/mysql</value>
  </property>
</bean>
-->
<bean id="MySessionFactory" class="org.springframework.orm.hibernate.LocalSessionFactoryBean">
   <property name="mappingResources">
      <list>
        <value>lyo/hotmail/site/bean/Article.hbm.xml</value>
        <value>lyo/hotmail/site/bean/Forum.hbm.xml</value>
        <value>lyo/hotmail/site/bean/Message.hbm.xml</value>
        <value>lyo/hotmail/site/bean/User.hbm.xml</value>
        <value>lyo/hotmail/site/bean/UserDetail.hbm.xml</value>
      </list>
   </property>
   <property name="hibernateProperties">
      <props>
        <prop key="hibernate.dialect">net.sf.hibernate.dialect.MySQLDialect</prop>
        <prop key="hibernate.query.substitutions">true=1 false=0</prop>
        <prop key="hibernate.show_sql">true</prop>
        <prop key="hibernate.use_outer_join">false</prop>
      </props>
   </property>
   <property name="dataSource"><ref bean="MyDataSource"/></property>
</bean>
<bean id="fproxy" class="lyo.hotmail.site.util.ForumProxy">
   <property name="fdao">
      <ref bean="formDao"/>
   </property>
</bean>
<bean id="viewSpringForumController" class="lyo.hotmail.site.action.ViewForumcontroller">
<property name="forumProxy">
     <ref bean="fproxy"/>
</property>
   </bean>
   <bean id="rewriteURLController" class="lyo.hotmail.site.action.DispatchForumController">
<property name="fdao">
      <ref bean="formDao"/>
   </property>
   </bean>
<bean id="postArticleController" class="lyo.hotmail.site.action.PostArticleController">
<property name="fdao">
      <ref bean="formDao"/>
   </property>
</bean>
<bean id="viewDetailController" class="lyo.hotmail.site.action.viewDetailController">
<property name="forumProxy">
     <ref bean="fproxy"/>
</property>
</bean>
    <bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
        <property name="mappings">
            <props>
                <prop key="/oldForum.spring">viewSpringForumController</prop>
				<prop key="/viewForum.spring">viewSpringForumController</prop>
				<prop key="/detail.spring">viewDetailController</prop>
				<prop key="/newPost.spring">rewriteURLController</prop>
				<prop key="/post.spring">postArticleController</prop>
            </props>
        </property>
   
    </bean>

<bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="viewClass"><value>org.springframework.web.servlet.view.JstlView</value></property>
        <property name="prefix"><value>/WEB-INF/forum/</value></property>
        <property name="suffix"><value>.jsp</value></property>
    </bean>
<bean id="formDao" class="lyo.hotmail.site.service.ForumDAOImpl">
   <property name="sessionFactory">
      <ref bean="MySessionFactory"/>
   </property>
   <property name="udao">
      <ref bean="userDao"/>
   </property>
</bean> 
 <bean id="userDao" class="lyo.hotmail.site.service.UserDAOImpl">
   <property name="sessionFactory">
      <ref bean="MySessionFactory"/>
   </property>
</bean> 
</beans>

Why "this.getSession()" throws NullPointerException?! Help!

[Rod Johnson]

From the Javadoc for HibernateDaoSupport.getSession():

Get a Hibernate Session, either from the current transaction or a new one. The latter is only allowed if the "allowCreate" setting of this bean's HibernateTemplate is true.
Either rely on a thread-bound Session (via HibernateInterceptor), or use it in combination with closeSessionIfNecessary.

It seems you don't have a Session in scope, so it's null.

[tentacle]

public class UserDAOImpl extends HibernateDaoSupport implements UserDAO {
.....................................................................................................
...............................................................................
public User createUser(User user, UserDetail detail) {
User hasuser = (User) this.getHibernateTemplate()
               .createQuery(
                     this.getSession&#40;&#41;,  <----- NullPointerException here
                     "from User u where u.userName='"
                           + user.getUserName&#40;&#41; + "'"&#41;.uniqueResult&#40;&#41;;
&#125;
.................................................................................................

I'm going to rewrite your code to show you how I would deal with this:

public User createUser(User user, UserDetail detail) {
User hasuser = (User) this.getHibernateTemplate()
               .execute(
                   new HibernateCallback() {
                       public Object doInHibernate(Session session) throws HibernateException {
                            return createQuery&#40;session,  /* <----- __NO__ NullPointerException here */
                                "from User u where u.userName='" +
                                user.getUserName&#40;&#41; +
                                "'"&#41;.uniqueResult&#40;&#41;;
                       &#125;
                   &#125;
               &#41;;
&#125;

I use the callback mechanism offered by HibernateTemplate. HibernateTemplate provides a Hibernate session, you - the developer - don't have to worry about opening the session or closing it or doing something when an exception occurs. This is approach is superior to getting the Hibernate session yourself.

[liren]

Thank you . It works well. I should use HibernateCallback if I want to use session myself. It really is a good taste