Question

I am using JPA for persistence layer. Have a simple table EventCategory

@Entity
@Table(uniqueConstraints = @UniqueConstraint(columnNames = { "CATEGORY" }))
public class EventCategory {

    @Id
    @GeneratedValue(strategy = GenerationType.AUTO)
    private Long categoryId;

    @NotNull
    private String category;

    @OneToMany(mappedBy = "category", cascade = CascadeType.ALL)
    private List<Event> events;

    // getters and setter

}

I am trying to get all rows by

public List<EventCategory> getAllCategories() {     
    final String query = "SELECT c from EventCategory c";       
    TypedQuery<EventCategory> query1 = em.createQuery(query, EventCategory.class);
    final List<EventCategory> category = query1.getResultList();
    return category;
}

But some how I am getting null pointer exception. By running sql query from command prompt I see required result.

Exception stack

02:51:52,726 ERROR [org.apache.catalina.core.ContainerBase.[jboss.web].[default-host].[/OSU-eTicket-EJB-Servlet].[jsp]] (http-localhost-127.0.0.1-8080-1) Servlet.service() for servlet jsp threw exception: java.lang.NullPointerException
at com.cse769.EJB.Service.EventCategoryService.getAllCategories(EventCategoryService.java:45) [OSU-eTicket-EJB-Session-Entity.jar:]
at com.CSE769.servlet.CategoryCreateServlet.getlist(CategoryCreateServlet.java:38) [classes:]
at org.apache.jsp.events_jsp._jspService(events_jsp.java:137)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70) [jbossweb-7.0.13.Final.jar:]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.0.Final.jar:1.0.0.Final]
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:369) [jbossweb-7.0.13.Final.jar:]
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:326) [jbossweb-7.0.13.Final.jar:]
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:253) [jbossweb-7.0.13.Final.jar:]
at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.0.Final.jar:1.0.0.Final]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:329) [jbossweb-7.0.13.Final.jar:]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:248) [jbossweb-7.0.13.Final.jar:]
at org.jboss.weld.servlet.ConversationPropagationFilter.doFilter(ConversationPropagationFilter.java:62) [weld-core-1.1.5.AS71.Final.jar:2012-02-10 15:31]
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:280) [jbossweb-7.0.13.Final.jar:]
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:248) [jbossweb-7.0.13.Final.jar:]
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275) [jbossweb-7.0.13.Final.jar:]
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161) [jbossweb-7.0.13.Final.jar:]
at org.jboss.as.jpa.interceptor.WebNonTxEmCloserValve.invoke(WebNonTxEmCloserValve.java:50) [jboss-as-jpa-7.1.1.Final.jar:7.1.1.Final]
at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:153) [jboss-as-web-7.1.1.Final.jar:7.1.1.Final]
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:155) [jbossweb-7.0.13.Final.jar:]
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) [jbossweb-7.0.13.Final.jar:]
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) [jbossweb-7.0.13.Final.jar:]
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:368) [jbossweb-7.0.13.Final.jar:]
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:877) [jbossweb-7.0.13.Final.jar:]
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:671) [jbossweb-7.0.13.Final.jar:]
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:930) [jbossweb-7.0.13.Final.jar:]
at java.lang.Thread.run(Thread.java:662) [rt.jar:1.6.0_30]

get all rows works for other tables. Not sure why it is failing here. Am I doing any silly mistake?

---

Entity manager code

@PersistenceContext(unitName = "examples-769-EJB")
EntityManager em;

Answer 1

If the code that you have put of getAllCategories() is right, then the only posibility is that the entity manager (em) in getAllCategories() is null. You’ll see it if you debug or put a message before creating the query.